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  • 301.
    Green, Torbjörn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    PIV in Practice2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Experimental fluid mechanics has for a long time been used to visualize flow phenomenonqualitatively. Traditionally, visualization has been done with dye or tracer particle dueto their ability to follow the flow pattern well. One of the early pioneers in experimentalfluid mechanics was Ludwig Prandtl who used mica particles in water flumes to accuratelydescribe the flow around wing profiles. Due to Prandtl’s results in the early 20thcentury, some of the most important theories in aviation were founded. By combiningPrandtl’s attempt to trace particles, and contemporary laser and computer technologiesa quantitative non-intrusive whole field technique, so called Particle Image Velocimetry(PIV), has been developed. The PIV technique has through the advances in computerscience the recent decades, been improved significantly and has also grown in popularityamong the scientific- and technological community.This thesis describes implementation of PIV in several diverse research areas frommacro- to micro scale. First, it is described how PIV is used as a pure measurementtechnique to understand complex flow phenomena. The technique is demonstrated on asmall U-shaped channel designed to facilitate salmonoid like fishes upstream migrationto their spawning grounds. Second, PIV is used as a validation tool for ComputationalFluid Dynamics, CFD. In the current situation, CFD is undergoing a generation shiftfrom Reynolds Averaged Numerical Simulation, RANS, to Large Eddy Simulations, LES.This is for instance motivated by energy production units which has many applicationswith high turbulence and temperature fluctuations. Hence it is desirable to be able toestimate the impact on thermal loads on the materials inside the plant (e.g. the pipewalls). An LES approach is superior to applying to RANS since the large eddies areresolved. However, LES is still not mature enough to be used without validation incritical applications. Therefore, PIV has been used to create a validation database fora generic T-junction. Finally, a description of how PIV technique can be adopted tostudy the flow of complex fluids in small geometries by means of microscopy, is given andapplied on lubrication grease flow in labyrinth seals which have been used in bearingsand other lubricated applications since the 1940’s. The intention with labyrinth seals isto lubricate the bearing and prevent contamination from entering the rolling elements.Although it is widely applied, little is known about the actual function and mechanismof labyrinth seals. To learn more about the flow and particle migration within a sealgeometry, a new method to visualize and quantify grease flow within a labyrinth seal hasbeen developed based upon micro-PIV.

  • 302.
    Green, Torbjörn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Baart, Pieter
    Westerberg, Lars-Göran
    Lundström, Staffan
    Höglund, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Lugt, Piet
    Li, Jinxia
    A new method to visualize grease flow in a double restriction seal using microparticle image velocimetry2011Ingår i: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 54, s. 784-792Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new method to visualize and quantify grease flow in between two sealing lips or, in general, a double restriction seal is presented. Two setups were designed to mimic different types of seals; that is, a radial and an axial shaft seal. The flow of the grease inside and in between the sealing restrictions was measured using microparticle image velocimetry. The results show that grease flow due to a pressure difference mainly takes place close to the rotating shaft surface with an exponentially decaying velocity profile in the radial direction. Consequently, contaminants may be captured in the stationary grease at the outer radius, which explains the sealing function of the grease.

  • 303.
    Green, Torbjörn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Baart, Pieter
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Höglund, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Lugt, Piet
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Li, Jinxia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Visualisering och kvantifiering av fettströmning i lagertätningar med µPIV2011Konferensbidrag (Övrigt vetenskapligt)
  • 304. Green, Torbjörn
    et al.
    Lindmark, Elianne
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gustavsson, Håkan
    Flow characterization of an attraction channel as entrance to fishways2011Ingår i: Rivers Research and Applications: an international journal devoted to river research and management, ISSN 1535-1459, E-ISSN 1535-1467, Vol. 27, nr 10, s. 1290-1297Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The flow field inside and downstream of an open channel placed near the surface of a free flow (such as the tail water of a turbine) is characterized in detail. The channel cross-section is U-shaped and in the downstream end is placed a ramp on the bottom which accelerates the flow passing through the channel. This flow is intended to catch the attention of fish and improve their entrance to fishways, which has also been successfully demonstrated in field tests.

  • 305.
    Green, Torbjörn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Odemark, Y.
    Vattenfall Research & Development.
    Angele, K.
    Vattenfall Research & Development.
    Westin, J.
    Vattenfall Research & Development.
    Alavyoon, F.
    Forsmarks kraftgrupp AB.
    Lundström, Staffan
    Termisk utmattning av T-koppling: en jämförelse mellan LES och PIV2009Ingår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 107-Konferensbidrag (Övrigt vetenskapligt)
  • 306.
    Green, Torbjörn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wassvik, Elianne
    Lundström, Staffan
    Gustavsson, Håkan
    Helfältsmätning av strömning genom lockvattenanordning2007Ingår i: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, s. 117-Konferensbidrag (Övrigt vetenskapligt)
  • 307.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    A pulsed TV holography system for the study of transients in experimental mechanics2000Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    An all-electronic system for pulsed holographic interferometry called pulsed TV holography is developed. This is a whole-field non-contacting optical measurement method suitable for studies of transient events like wave propagation in solids and fluids. Chemical wet processing of holographic film and optical reconstruction of holograms are no longer needed. The technique was first developed using a double pulsed ruby laser as light source. The holograms are recorded directly on a CCD-detector. Quantitative data of changes in optical path length, caused either by a deformation of a solid object or a change in refractive index in a fluid, are calculated directly in a computer. The system for pulsed TV holography has recently been further developed by the purchase of a new pulsed laser (twin cavity, injection seeded pulsed Nd:YAG) and a CCD camera (PCO Sensicam) with higher spatial resolution and dynamic range. In the survey of this thesis the increased versatility compared to a ruby laser based system is discussed. During the development of the pulsed TV holography system a number of experiments in mechanics and acoustics have been accomplished. Bending waves in impacted plates propagating at a speed of about 2000 m/s are easily “frozen” due to the short duration laser pulses (<30 ns). These waves act as supersonic travelling acoustic sources and generate sound waves in the surrounding air. For the first time, transient sound fields from impacted plates have been visualised and measured using pulsed holographic interferometry. In another experiment, we have demonstrated that the pulsed TV holography system is feasible in combination with tomography. By recording a three-dimensional acoustic pressure field from a number of viewing directions followed by a tomographic reconstruction, the pressure in any point can be calculated. Finally, a method to restore fringes lost by large bulk motions is proposed. This technique may become very attractive in the study of vibrations (preferable transient) on moving or rotating objects. In conclusion, pulsed TV holography is proved to be a fast and reliable method to quantitatively study transients in mechanics and acoustics. The technique has a great potential in experimental mechanics in the future.

  • 308.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Bending wave propagation in rotating objects measured by pulsed TV holography2002Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 41, nr 34, s. 7237-7240Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transient bending waves in a rotating hard disk is measured by means of pulsed TV holography. The speckle motion in the detector plane caused by the rotation is compensated for in the interference phase evaluation. The technique is all electronic and needs no image derotator

  • 309.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Four-pulse interferometric recordings of transient events by pulsed TV holography2003Ingår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 40, nr 5-6, s. 517-528Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With traditional double-pulsed holographic interferometry or pulsed TV holography, the experiment usually has to be repeated to allow the recording of a time sequence of interferograms of the event. With the proposed technique a sequence of four interferograms of a solitary transient event is measured. A twin oscillator, injection-seeded, pulsed Nd:YAG laser is incorporated into a pulsed TV holography set-up. With orthogonal polarisation and double pulsing of each of the two channels of the laser, four pulses are recorded on two separate CCD-frames. Four interferograms of a laser-impacted plate obtained from the same experiment, show how the bending waves develop and propagate in the plate.

  • 310.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Pulsed TV holography combined with digital speckle photography restores lost interference phase2001Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 40, nr 14, s. 2304-2309Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The measuring of situations with optical measuring methods is difficult when a deformation field must be determined while it is superposed to comparatively large rotating or translating object motion. Interferometric methods such as pulsed TV holography might be suitable to measure the small transient deformation, but the often-large bulk motion makes the phase information disappear. However, by a combination of digital speckle photography (DSP) (also called digital image correlation) with pulsed TV holography, such measuring problems can be mastered. A method to calculate the bulk in-plane motion by DSP from the usual pulsed TV holography recordings and then to use this information to restore the interference phase is proposed. This technique may be attractive in the study of transient vibrations overlaid on rotating or translating motions.

  • 311.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Structured surfaces and turbulence1987Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 312.
    Gren, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Kassfeldt, Elisabet
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Feasibility of using digital speckle correlation in the study of seal contacts2009Ingår i: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 21, nr 4, s. 123-134Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents studies of the contact between a soft rubber specimen and glass counterface using the Digital Speckle Correlation method, which provides information of displacements and structural similarities between recorded images. The setup is designed with a real contact and changes in the contact can be varied. Microscopic images using laser light illumination for different displacements are recorded and correlated. The results show that the contact area can be identified both for dry and lubricated contacts. The method can be applied on different geometries, surface roughness and lubricants. Influences of scars and contaminations, e.g. wear particles, may also be analysed.

  • 313.
    Gren, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Olsson, Robin
    Aeronautical Research Institute of Sweden.
    Deformation during impact on an orthotropic composite plate1990Ingår i: Hologram interferometry and speckle metrology : proceedings ; 25. anniversary edition, Society for Experimental Mechanics , 1990Konferensbidrag (Refereegranskat)
  • 314.
    Gren, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Schedin, Staffan
    Luleå tekniska universitet.
    Transient wave fields in mechanics and acuostics recorded by pulsed TV holography1998Ingår i: Experimental mechanics: advances in design, testing and analysis, Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 1998Konferensbidrag (Refereegranskat)
  • 315.
    Gren, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Schedin, Staffan
    Luleå tekniska universitet.
    Xide, Li
    Department of Modern Mechanics and Engineering, University of Science and Technology of China.
    Tomographic reconstruction of transient acoustic fields recorded by pulsed TV holography1998Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 37, nr 5, s. 834-840Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pulsed TV holography together with CT reconstruction were used to measure the three-dimensional distribution of transient acoustic fields in air. Holograms from several directions were directly recorded onto a CCD detector. From the recorded holograms, phase maps were quantitatively evaluated

  • 316.
    Gren, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Tatar, Kourosh
    Granström, Jan
    Molin, Nils-Erik
    Jansson, E.V.
    Department of Speech, Music and Hearing, Royal Institute of Technology (KTH).
    Laser vibrometry measurements of vibration and sound fields of a bowed violin2006Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 17, nr 4, s. 635-644Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Laser vibrometry measurements on a bowed violin are performed. A rotating disc apparatus, acting as a violin bow, is developed. It produces a continuous, long, repeatable, multi-frequency sound from the instrument that imitates the real bow-string interaction for a 'very long bow'. What mainly differs is that the back and forward motion of the real bow is replaced by the rotating motion with constant velocity of the disc and constant bowing force (bowing pressure). This procedure is repeatable. It is long lasting and allows laser vibrometry techniques to be used, which measure forced vibrations by bowing at all excited frequencies simultaneously. A chain of interacting parts of the played violin is studied: the string, the bridge and the plates as well as the emitted sound field. A description of the mechanics and the sound production of the bowed violin is given, i.e. the production chain from the bowed string to the produced tone

  • 317.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Direct resonance of nonaxisymmetric disturbances in pipe flow1989Ingår i: Studies in applied mathematics (Cambridge), ISSN 0022-2526, E-ISSN 1467-9590, Vol. 80, nr 2, s. 95-108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    On considère un mécanisme qui peut conduire à la croissance algébrique, suivie d'une décroissance exponentielle de petites perturbations non axisymétriques dans un écoulement en conduite. Le mécanisme est interprété comme une résonance directe entre les perturbations de pression et de vitesse d'écoulement. Résolution numérique des problèmes de valeur propre pour les modes de pression et de vitesse. Influence du nombre de Reynolds

  • 318.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Energy growth of three-dimensional disturbances in plane Poiseuille flow1991Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 224, s. 241-60Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The development of a small three-dimensional disturbance in plane Poiseuille flow is considered. Its kinetic energy is expressed in terms of the velocity and vorticity components normal to the wall. The normal vorticity develops according to the mechanism of vortex stretching and is described by an inhomogeneous equation, where the spanwise variation of the normal velocity acts as forcing. To study specifically the effect of the forcing, the initial normal vorticity is set to zero and the energy density in the wavenumber plane, induced by the normal velocity, is determined. In particular, the response from individual (and damped) Orr-Sommerfeld modes is calculated, on the basis of a formal solution to the initial-value problem. The relevant timescale for the development of the perturbation is identified as a viscous one. Even so, the induced energy density can greatly exceed that associated with the initial normal velocity, before decay sets in.

  • 319.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Excitation of direct resonances in plane Poiseuille flow1986Ingår i: Studies in applied mathematics (Cambridge), ISSN 0022-2526, E-ISSN 1467-9590, Vol. 75, nr 3, s. 227-248Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The direct resonance mechanism between vertical vorticity and vertical velocity is studied for plane Poiseuille flow. The resonance term, obtained from the initial-value problem, has been determined numerically for various initial disturbances. The amplitude, in wave-number space, is found to decay with time for all resonances. Because of its appearance in the Laplace-transform plane as a double pole, we show that a resonance term will have an initial amplitude which grows with Reynolds number, thus indicating that resonances will dominate the initial development of a disturbance at large Reynolds number.

  • 320.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Non-linear wave interactions from transient growth in plane-parallel shear flows2009Ingår i: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 28, nr 3, s. 420-429Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Based on the normal velocity-normal vorticity (v - η) formulation for the development of 3D disturbances in plane-parallel shear flows, the non-linear terms in the governing equations are derived as convolution integrals of the Fourier-transformed variables. They are grouped in three categories: v - v, v - η and η - η terms, and are expressed in a simple geometric form using the modulus of the two wave-vectors (k′ and k″) appearing in the convolution integrals, and their intervening angle (χ). The non-linear terms in the v-equation involving η are all weighted by sin χ (or sin2 χ). This confirms the known result that non-linear regeneration of normal velocity, necessary for a sustained driving of 3D disturbances, is not possible for stream-wise elongated structures (α = 0), only. It is therefore suggested how transiently amplified η can interact with decaying 2D waves to activate (oblique) waves which may be less damped than the 2D wave. This is shown to be possible for Blasius flow. In the η-equation, non-linear effects are possible for elongated structures resulting in shorter spanwise scales appearing at a shorter time-scale than the (linear) transient growth. A numerical example shows the details of this process in plane Poiseuille flow. From an inspection of the y-dependency (wall-normal direction) of the non-linear terms it is suggested that higher y-derivatives may give rise to non-linear effects in the inviscid development of perturbations. Also, a result for the y-symmetry of the non-linear terms is derived, applicable to plane Poiseuille flow.

  • 321.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Parameter study of direct resonance in water table flow1984Rapport (Övrigt vetenskapligt)
  • 322.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Resonant growth of three-dimensional disturbances in plane Poiseuille flow1981Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 112, s. 253-264Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A linear mechanism for growth of three-dimensional perturbations on plane Poiseuille flow is investigated. The mechanism, resonant forcing of vertical vorticity waves by Tollmien-Schlichting waves, leads to an algebraic growth for small times. Eventually, viscous damping becomes dominant and the disturbance decays. The resonance occurs only at discrete points in the wave-number space. Nine resonances have been investigated. For these, the phase velocities range from 0.67 to 0.81 of the center-line velocity. The lowest Reynolds number for which the resonance can occur is 25. The strongest resonance appears only above a Reynolds number of 341. Also, two cases of degeneracy in the Orr-Sommerfeld dispersion relationship have been found.$

  • 323.
    Gustavsson, Håkan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Shanthini, Rajaratnam
    Luleå tekniska universitet.
    Degeneracies and direct resonances in water-table flow1990Ingår i: Studies in applied mathematics (Cambridge), ISSN 0022-2526, E-ISSN 1467-9590, Vol. 83, nr 1, s. 61-89Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Degeneracies of the Orr-Sommerfeld eigenmodes and direct resonances between the Orr-Sommerfeld eigenmodes and vorticity eigenmodes are studied in water-table flow. The sensitivity of the characteristics of these algebraic mechanisms to flow parameters, such as the Reynolds number (R), the slope of the table $(\theta)$, and the material parameter $(\gamma)$, are investigated. It is found that the mechanisms become operative at subtransitional R, and their damping rates decrease with increasing R. When the mean flow profile is slightly distorted from the ultimate parabolic profile, the characteristics of the direct resonances show remarkable variations. Also, some of the algebraic mechanisms in water-table flow are shown to have the same characteristics and modal structures as some of those in plane Poiseuille flow.

  • 324.
    Gustavsson, Håkan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wallin, Stefan
    Luleå tekniska universitet.
    Effect of three-dimensional surface elements on boundary layer flow1990Ingår i: Structure of turbulence and drag reduction: Proceedings of the IUTAM Symposium / [ed] Albert Gyr, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 1990, s. 399-406Konferensbidrag (Refereegranskat)
    Abstract [en]

    The perturbation velocity field induced by a three-dimensional surface distortion in a boundary layer flow is considered. For small amplitudes, the kinetic energy is shown to be composed of two factors: one associated with the surface structure and the other with the velocity profile. Level curves of the profile factor, in the (alpha, beta) wavenumber plane, are ridge-like and approach the beta-axis as the Reynolds number increases. Thus, in the inviscid limit, the kinetic energy is confined to structures infinitely extended in the streamwise direction. For a certain class of surface structures, also the level curves for the kinetic energy have been determined. It is shown how a spanwise modulation and an aspect ratio of the surface distortion change the position of the level curves and the amplitudes.

  • 325.
    Gustavsson, Håkan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Nordlund, Erling
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Forsling, Willis
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Öhlander, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Forssberg, Eric
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Norrländsk vattenkraft och gruvnäring: två svenska välståndsbyggare2009Ingår i: Thule: Kungl. Skytteanska samfundets årsbok 2009, Umeå: Kungl. Skytteanska samfundet , 2009, s. 331-345Kapitel i bok, del av antologi (Övrig (populärvetenskap, debatt, mm))
  • 326.
    Gustavsson, Håkan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ögren, Jan-Erik
    Luleå tekniska universitet.
    Observations of turbulent spots on a water table1982Rapport (Övrigt vetenskapligt)
  • 327.
    Göktepe, Burak
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Hazim, Ammar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Cold flow experiments in an entrained flow gasification reactor with a swirl-stabilized pulverized biofuel burner2016Ingår i: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 85, s. 267-277Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Short particle residence time in entrained flow gasifiers demands the use of pulverized fuel particles to promote mass and heat transfer, resulting high fuel conversion rate. The pulverized biomass particles have a wide range of aspect ratios which can exhibit different dispersion behavior than that of spherical particles in hot product gas flows. This results in spatial and temporal variations in temperature distribution, the composition and the concentration of syngas and soot yield. One way to control the particle dispersion is to impart a swirling motion to the carrier gas phase. This paper investigates the dispersion behavior of biomass fuel particles in swirling flows. A two-phase particle image velocimetry technique was applied to simultaneously measure particle and gas phase velocities in turbulent isothermal flows. Post-processed PIV images showed that a poly-dispersed behavior of biomass particles with a range of particle size of 112-160 μm imposed a significant impact on the air flow pattern, causing air flow decelerated in a region of high particle concentration. Moreover, the velocity field, obtained from individually tracked biomass particles showed that the swirling motion of the carrier air flow gives arise a rapid spreading of the particles

  • 328.
    Göktepe, Burak
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Umeki, Kentaro
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Hazim, Ammar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Soot reduction in an entrained flow gasifier of biomass by active dispersion of fuel particles2017Ingår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 201, s. 111-117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Soot is an undesired by-product of entrained flow biomass gasification since it has a detrimental effect on operation of the gasifier, e.g. clogging of flow passages and system components and reduction of efficiency. This study investigated how active flow manipulation by adding synthetic jet (i.e. oscillating flow through orifice) in feeding line affects dispersion of fuel particles and soot formation. Pine sawdust was gasified at the conditions similar to pulverized burner flame, where a flat flame of methane-air sub-stoichiometric mixture supported ignition of fuel particles. A synthetic jet flow was supplied by an actuator assembly and was directed perpendicular to a vertical tube leading to the center of the flat flame burner through which pine sawdust with a size range of 63–112 μm were fed into a reactor. Quartz filter sampling and the laser extinction methods were employed to measure total soot yield and soot volume fraction, respectively. The synthetic jet actuator modulated the dispersion of the pine sawdust and broke up particle aggregates in both hot and cold gas flows through generation of large scale vortex structures in the flow. The soot yield significantly reduced from 1.52 wt.% to 0.3 wt.% when synthetic jet actuator was applied. The results indicated that the current method suppressed inception of young soot particles. The method has high potential because soot can be reduced without changing major operation parameters.

  • 329.
    Hadi Jafari, Pantea
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Wingren, Anders
    Meva Energy AB, Hisings Backa.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Effect of process parameters on the performance of an air-blown entrained flow cyclone gasifier2019Ingår i: International Journal of Sustainable Energy, ISSN 1478-6451, E-ISSN 1478-646XArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    Entrained flow gasification of biomass in a cyclone reactor combined by a gas engine has been applied in Nordic countries as one of the preferred methods for generating combined heat and power in small scales. The purpose of the current study was to optimise the gasification plant efficiency and understanding the influence of operating conditions. The experiments were carried out in a 2.4 MW(th) commercial gasification power plant. The gasifier was operated in optimum at a rather low lambda around 0.27 and a temperature of 950°C. The lower heating value of the clean product gas at this lambda was 5.95 MJ/Nm3. The experimental results also were compared with the predicted values from thermodynamic equilibrium calculations by Factsage 7.0. The performance of five different types of biofuels including torrefied spruce, peat, rice husk, bark and stemwood were assessed and compared with each other using thermodynamic equilibrium and available experimental data.

  • 330.
    Hamedi, Naser
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Modelling of Flexible Fibres in Viscous Fluid Flow2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    The current study relates to the development of a multiphase model of flexible fibre suspensions. An understanding of the rheology and dynamics of the deformation of such suspension is desirable in order to be able to fully disclose the flow behaviour from very low to very high shear rates. We present an approach for numerically simulating the dynamics of flexible fibres employing a particle-level method. This is performed by investigating the fibre dynamics against several orbit classes - i.e. rigid, springy, flexible and complex rotation of the fibres [1-3] enabling the model to have all degrees of freedom (translation, rotation, bending and twisting). The three-dimensional Navier-Stokes equations which describes the fluid motion are employed while the fibrous phase of the fluid is modeled as chains of fiber segments interacting with the fluid through viscous- and drag forces. The simulations are performed using OpenFOAM and the numerical outcomes are validated against experimental data.The purpose of the modelling framework applied in this work is to enable the numerical model to be extended to a 4-way coupling model, capturing shear thinning, shear thickening and the yield stress properties of a fibrous fluid suspension.

  • 331.
    Hamedi, Naser
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    On the deformation of fibrous suspensions2019Ingår i: Transactions of the Nordic Rheology Society, Nordic Rheology Society , 2019, Vol. 27Konferensbidrag (Refereegranskat)
    Abstract [en]

    An understanding of the rheology and dynamics of the deformation of fibrous suspension as a multiphase fluid is important in order to be able to fully disclose the flow behaviour from very low to very high shear rates. In this study, a flexible fibre model has been implemented in an open source Computational Fluid Dynamics code. The three-dimensional Navier-Stokes equations which describe the fluid motion are employed while the fibrous phase of the fluid is modeled as chains of fiber segments interacting with the fluid through viscous- and drag forces. The aim of this study is to investigate the fibre dynamics against several orbit classes - i.e. rigid, springy, flexible and complex rotation of the fibres1-3 enabling the model to have all degrees of freedom - translation, rotation, bending and twisting. The simulations are performed using the OpenFOAM open source software.

  • 332.
    Hamedi, Naser
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Westerberg, Lars-Göran
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    On the Interaction of Side-By-Side Circular Cylinders in Viscoplastic Fluids2019Ingår i: Fluids, ISSN 2311-5521, Vol. 4, nr 2, artikel-id 93Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the static interaction of a train of three cylinders in a Bingham fluid is studiednumerically using Computational Fluid Dynamics. The variation of drag forces for the cylinders inseveral configurations is investigated. Positions of the particles in relation to the reference particleare recognized by the separation distance between the cylinders. A steady state field is considered,with Bingham numbers between 5 and 150. Several separation distances (d) were considered, such that2.0D d 6.0D where D is the cylinder diameter. The Reynolds number was chosen in the range of5 Re 40. In particular, the eect of the separation distance, Reynolds number and Bingham numberon the shape and size of the unyielded regions was investigated. The functional dependence of thisregion and the drag coecient is explored. The present results reveal the significant influence of thegap between the cylinders on the drag force and the shape of the unyielded regions surrounding thecylinders. It was found that there are several configurations in which the drag forces over the first andthe third cylinders are almost equal depending on variation of the Bi, Re and the separation distance.

  • 333.
    Hammargren, Kristoffer
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Aerodynamics Modeling of Sounding Rockets: A Computational Fluid Dynamics Study2018Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 334.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Rheological Properties of Cement-Based Grouts Determined by Different Techniques2014Ingår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 6, nr 5, s. 217-229Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rheological properties of cement-based grouts containing talc or palygorskite were investigated for optimizing fluidity and quick strengthening at injection. The fluidity controls the ability of grout to penetrate fractures and can be determined by pipe flow tests, Marsh funnel tests, mini-slump cone tests and rheometer tests. The grouts were 1) Talc for fluidity and strength by reacting with cement, 2) Palygorskite (attapulgite) for early gelation by being thixotropic, and 3) Powdered quartz for chemical integrity. The freshly prepared grouts behaved as Bingham fluids with viscosities from 0.151 to 0.464 Pas and yield stresses 5.2 Pa to 36.7 Pa. Statistical analysis of the flow test data converted Marsh flow time into viscosity. The pipe flow tests gave 26.5% higher values than the viscometer for grout with Portland cement and talc, and about 13.7% lower than the viscometer data for the grout with low-pH cement and talc. The big Marsh funnel gave valuesdiffering by 5.2% - 5.3% from those of the viscometer for grout with talc and Portland, and Merit 5000 cements. For grout with palygorskite the viscosity was at least twice that of the other grouts. Grout fluidity was positively affected by talc and negatively by palygorskite and early cement hydration

  • 335.
    Hazim, Ammar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Non-Spherical Particle Interaction in Duct and Jet Flow2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Wood waste is the most popular biomass recourse for many nations. Burned wood can, direct or indirect, release one of the greenhouse gases, carbon dioxide. The process can still be seen as a renewable source of energy since replanting of the trees and crops are consuming nearly the same amount of carbon dioxide through photosynthesis. Thermal gasification is one of the efficient methods to utilize energy from wood waste. Products from the component of concern can be used for direct energy production like in boilers and gas turbines or indirectly via dimethyl ether (DME), for instance. The physics of gasification is complex and several issues can influence the process. There is a lack of knowledge of several phenomena, some of which are related to solid-gas flow in the gasifier and in the premixed feeding pipelines. One such area is mechanisms related to turbulence modulation in the presence of spherical and non-spherical particles and how much the flow can disturb the motion of the particles. This is studied in the present thesis and the motion of the particles in different flow field is disclosed. At the moment there is no agreement in the scientific community on a single dimensionless number that can safely describe the influence of spherical particles in turbulent flow. For non-spherical particles additional levels of freedom are introduced and the dependence on drag and lift from the orientation of the particles as a function of Reynolds number adds to the complexity.Based on a literature review a fundamental experimental study is carried out in simple flow field geometry, a 2D duct flow. The aim is to reveal the influence of spherical glass particle on the turbulent flow field in the core and near wall flows. Additional studies with wood particles gave more information about how real biomass particles affect the turbulence as compared to spherical ones. Next the instantaneous distribution of biomass particles was studied experimentally. It is known that this distribution significantly influences the soot formation in a gasifier. Two different techniques of flow control were studied, swirling flow and synthetic jet flow. Particles shape and inertia and the strength of vortices and vortices interaction in coaxial jets and swirling jet flow were studied and yielded a high influence on the preferential concentration of particles as well as on the root mean square values for velocity in coaxial jets flow. The synthetic jet add momentum to the flow without disturbing the mass loading ratio and result in higher dispersion of the particles away from the centreline of the jet.

  • 336.
    Hazim, Ammar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Göktepe, Burak
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Umeki, Kentaro
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gebart, Rikard
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Active fuel particles dispersion by synthetic jet in an entrained flow gasifier of biomass: Cold flow2016Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 302, s. 275-282Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pulverized fuel (PF) burners play a key role for the performance of PF fired gasification and combustion plants, by minimizing pollutant emission, fuel consumption and hence fuel costs. However, fuel diversity in power generation plants imposes limitations on the performance of existing PF burners, especially when burning solid fuel particles with poor flowability like biomass sawdust. In the present study, a vertically downward laminar flow was laden with biomass particles at different particle mass loading ratios, ranging from 0.47 to 2.67. The particle laden flow was forced by a synthetic jet actuator over a range of forcing amplitudes, 0.35–1.1 kPa. Pulverized pine particles with a sieve size range of 63–112 μm were used as biomass feedstock. Two-phase particle image velocimetry was applied to measure the velocity of the particles and air flow at the same time. The results showed that the synthetic jet had a large influence on the flow fields of both air and powdered pine particles, via a convective effect induced by vortex rings that propagate in the flow direction. The particle velocity, particle dispersion and hence inter-particle distance increased with increasing forcing amplitude. Moreover, particles accumulated within a specific region of the flow, based on their size. The effect on particle dispersion was more pronounced in the forced flows with low mass loading ratios

  • 337.
    Hazim, Ammar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, Gunnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Influence of Inertial Particles on Turbulence Characteristics in Outer and Near Wall Flow as Revealed with High Resolution PIV2016Ingår i: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 138, nr 9, artikel-id FE-15-1428Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A fully developed turbulent particle-gas flow in a rectangular horizontalchannel 100 × 10 × 4000 mm3 is disclosed with high spatial resolution2D Particle Image Velocimetry. The objective is to increase the knowledge ofthe mechanisms behind alterations in turbulent characteristics when adding twosets of relatively large solid spherical particles with mean diameters of 525and 755 μm and particle size distributions of 450 - 600 and 710 - 800 μm,respectively. Reynolds numbers are 4000 and 5600 and relatively high volumefraction of 5.4 × 10-4 and 8.0 × 10-4 are tested. Both thenear wall turbulent boundary layer flow and outer core flow are considered. Resultsshow that the carrier phase turbulent intensities increase with volume fractionof the inertial particles. The overall mean flowvelocity is affected when adding the particles but only to a minor extent. Nearthe wall, averaged velocity decreases while fluctuating velocity componentsincrease when particles are added to the flow. Quadrant analysis shows theimportance of sweep near the wall and ejection events in the region defined byy+ > 20. In conclusion, high inertia particles can enhanceturbulence even at relatively low Particle Reynolds number < 90. In the nearbottom wall region particles tend to be a source of instability reflected asenhancement in rms values of the normal velocity component.

  • 338.
    Hazim, Ammar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, Gunnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Turbulent modulation in particulate flow: A review of critical variables2015Ingår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 7, nr 10, s. 597-609, artikel-id 8102444Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A review of the main mechanisms influencing turbulent modulation in the presence of spherical and non-spherical particles is presented. The review demonstrates the need for more numerical and experimental work with higher accuracy than obtained so far and the need to resolve the flow near the surface of particles with the aim to re-evaluate the quantitative effect of different parameters on turbulent modulation. The review reveals that non-spherical particles have more adverse effect on turbulence as compared to spherical ones, for the same ambient conditions

  • 339.
    Hazim, Ammar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Experimental study of the effect from bio-solid particles on fully developed turbulent duct flow2014Konferensbidrag (Refereegranskat)
  • 340.
    Hedlund, Jakob
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Experimental Investigation of Hydrodynamic Effects on a Vibrating Kaplan Runner2017Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    An experimental investigation of a vibrating Kaplan turbine runner was performed in order to understand the hydrodynamic effects and to obtain or confirm the mass and damping coefficients used for dimensioning at the design stage. Improved design can lead to increased efficiency and lifetime of hydropower stations. The method was based on the 90◦ phase shift between acceleration and velocity and their relationship with mass and damping respectively. The experiment examined frequencies between 1–9 Hz at displacements between 0.25–2.00 mm. Results showed a frequency dependent added mass which varied between 1.2 and 1.5 (neglecting the highest and lowest frequencies) and an added damping between 0.8 and 1.2 which became of importance at low frequencies. A mathematical interpretation of the fluid solid interactions (based on the constitutive equation for stresses in a Newtonian fluid) has been derived and connected to the obtained experimental data.

  • 341.
    Hellström, Gunnar
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Parallel computing of fluid flow through porous media2007Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Fluid flow through porous media takes place in a variety of technical areas including ground water flow, flow through embankment dams, paper making, composites manufacturing, filtering, drying and sintering of iron ore pellets. When modelling these kinds of flows it is common practice to use averaging techniques rather than computing the detailed flow field in every single pore. This approach is very efficient when averaged quantities are sough for but it is not very convenient for local problems such as forces on particles within an embankment dam and drying of individual iron ore pellets. In this thesis the focus is set on the former and how such forces alter as a function of Reynolds number. Of particular interest are the effects of inertia and turbulence and when they need to be considered. For problem like this a Computational Fluid Dynamics (CFD) approach is well suited since rather complex geometries and flow conditions can be studied by using parallel computing techniques. By using this technique it is also possible to determine at which flow regimes Darcy law is applicable and thus when more elaborate descriptions of the flow like the Forchheimer equation and the Navier-Stokes equations need to be applied. In order to isolate the question above and be able to use advanced models for turbulence a neat geometry is applied being an array of quadratic packed cylinders. To start with the parallel computing capacity of the in-house cluster is scrutinized showing very promising results with up to almost full scalability. Following this study focus is set on the porous media and when inertia-effects need to be taken into account. The significance of this phenomenon turns out to be when Reynolds number is above 10. Then a study in when the flow has to be solved with a full turbulent description has been carried out with the results that as the Reynolds number increases above 100 the significance is clear. In addition a manuscript for a state of the art literature survey is appended.

  • 342.
    Hellström, Gunnar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Andersson, Anders
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Leonardsson, Kjell
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Lycksam, Henrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundqvist, Hans
    Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies.
    Simulation and experiments of entrance flow conditions to a fishway2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    When migrating fish tries to pass around man made obstacles such as hydropower dams with the aid of fish passages it is important that the migrating path is constructed in an efficient manner. By designing the entrance of the fishway in a manner that gives attractive flow conditions for migrating fish, the overall passage efficiency can be increased. In this study two alternative design solutions have been studied with numerical simulations, lab-scale experiments and in-field testing to achieve such attractive flow. Designs studied are constructions yielding a submerged jet, in order to increase the velocity of the flow at the entrance, and a half-cylinder, in order to create vortices that the fishes can utilize when continuing their journey towards their spawning grounds. A combination of the previous mentioned setups was also investigated. A first result shows that the increase in velocity decreases the residence time downstream the fishway and increases the total passage efficiency while the result from the vorticity generation is inconclusive at this point. The combination of the two designs shows similar passage efficiency as with only velocity increase although it does not show the same decrease in residence time. Improvements on the design of the vorticity generator and shape optimization of the construction generating the jet could further improve the efficiency of the fishway

  • 343. Hellström, Gunnar
    et al.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Flow through porous media at moderate Reynolds number2006Ingår i: Proceedings, 4th International Scientific Colloquium Modelling for Material Processing, 2006, s. 129-134Konferensbidrag (Refereegranskat)
    Abstract [en]

    In modelling of flow through porous media inertia-effects must sometimes be considered. This is often done by usage of the empirically derived Ergun equation that can describe the response of several porous media but does not reveal the real mechanisms for the flow. In order to increase the understanding of such flows we have therefore performed a micromechanically based study of moderate Re' flow between parallel cylinders using a Computational Fluid Dynamics approach. The simulations are carried out with quality and trust by using grid refinement techniques and securing that the iteration error is sufficiently small. Main results are that the Ergun equation fits well to simulated data up to Re' 20, that inertia-effects must be taken into account when Re' exceeds 10 and that results from stationary simulations replicate time resolved ones at least up to Re' 880.

  • 344.
    Hellström, Gunnar
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Marjavaara, Daniel
    Lundström, Staffan
    Parallel CFD simulations of an original and redesigned hydraulic turbine draft tube2007Ingår i: Advances in Engineering Software, ISSN 0965-9978, E-ISSN 1873-5339, Vol. 38, nr 5, s. 338-344Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The design of hydraulic turbine draft tubes has traditionally been based on simplified analytic methods, model and full-scale experiments. In the recent years the use of numerical methods such as computational fluid dynamics (CFD) has increased in the design process, due to the rapid escalation in computer performance. Today with parallel computer architectures, new aspects of flow can be considered. However, several problems have still to be solved before CFD can routinely be applied in product development. This paper aims to investigate the parallel performance of commercial CFD software on homogeneous computer networks, as common solutions encountered in the industry today. In addition, the efficiency improvements obtained in earlier experiments by modifying the shape of the draft tube will be considered, to deduce if the improvements can be captured with aid of CFD. Results from both the steady and the unsteady CFD simulations show that almost full scalability is obtained with the commercial CFD software CFX-5.7.1. Furthermore, no noticeable improvement in the pressure recovery factor or the flow field is noticed in the CFD simulations as compared to experiments. The discrepancy may be to the applied inlet boundary conditions and/or the turbulence model.

  • 345.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Internal erosion in embankment dams: fluid flow through and deformation of porous media2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    För en övergripande förståelse av inre erosion i fyllnadsdammar är det viktigt att få en grundläggande förståelse av villkoren för flöde genom porösa material. Därför är det nödvändigt att belysa de detaljerade flödesförhållandena, flödesinducerade krafter som verkar inom porösa material och flödesinducerad deformering av porösa material. För att öka kunskapen om dessa flöden är "Computational Fluid Dynamics" -simuleringar ett lämpligt tillvägagångssätt att använda för att undersöka olika flöden. Dessa villkor ger upphov till olika flödesregimer allt från krypande flöde, där en formulering baserad på Darcy's lag är tillräcklig, via en region dominerad av tröghetseffekter, där en icke-linjär term måste läggas till Darcy's lag såsom är fallet i Ergun's ekvation, till den turbulenta regionen, där de fullständiga Navier - Stokes ekvationer måste lösas. Men när dessa övergångar sker är inte uppenbart, därav användandet utav CFD-simuleringar för att beräkna den skenbara permeabilitet, en friktion faktor av Blake-typ och de normala och skjuvkrafter för olika modellgeometrier. Detta inkluderar kvadratiska och hexagonala packningar av cylindrar samt sfärer. Ett resultat är att Reynoldstalet där tröghetseffekterna blir betydande, varierar med packning och porositet. För en kvadratisk packning av cylindrar inträffar detta runt ett Reynolds tal omkring 10 medan för en hexagonal packning äger den rum mellan 30 och 50 beroende på porositet. Ett annat resultat är att för kvadratisk packning med turbulenta inställningar genereras högre krafter vid höga Reynolds tal än en motsvarande laminär inställning och detta sker oavsett porositet. För hexagonal packning kan en turbulent inställning ge lägre krafter. Dessa flödesregimer har använts för att fastställa ett matematiskt uttryck för de teoretiska gränserna gällande den effektiva diametern och lämplig tryckgradient för design utav nedskalade geotekniska experiment.När det gäller deformering utav ett poröst material finns flera metoder som har potential att modellera den inre erosions processen. Ett sätt är en nätdeformationsmetod där normal och skjuvkrafter som verkar på partiklarna genererar rörelse utav det porösa materialet. Denna metod kräver att beräkningsnätet uppdateras i varje tidssteg vilket genererar ganska beräkningsintensiva simuleringar. Ett annat tillvägagångssätt är att kombinera CFD-simuleringar utav flödet i närheten av enstaka partiklar med Monte Carlosimuleringar på ett större system med partiklar. De beräknade parametrarna kombineras på det större systemet där minimering utav dissipationen ger oss ett linjärt ekvationssystem med avseende på strömfunktionen. Från strömfunktionen beräknas fördelningen av krafter på strukturen som ger upphov till en omfördelning av partiklarna, detta för att kunna förutse förändringar i permeabiliteten hos det stora systemet av partiklar. Huvudresultatet är att ju mer kompakt systemet är desto större är den möjliga relativa förändringen utav permeabilitet genom att tillämpa ett högt flöde. Om man tillämpar denna teknik på ett klassisk geotekniskt experiment, No Erosion Filter test, så indikerar resultaten att metoden beskriver huvuddragen vad gäller transport utav partiklar i ett poröst material bestående utav en zon med fint material som kopplar till en filter zon.

  • 346.
    Hellström, J. Gunnar I.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Representative volume size when modelling flow through porous structures2014Konferensbidrag (Refereegranskat)
  • 347.
    Hellström, J. Gunnar I.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Lundström, Staffan
    Mechanisms of flow-induced deformation of porous media2010Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 664, s. 220-237Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The study investigates creeping flow-induced alteration in the permeability of deformable particle systems. Low-Reynolds-number transversal flow through random arrays of aligned cylinders is considered by means of a combined methodology of directly solving the two-dimensional (2D) Stokes equations for the flow in the vicinity of two particles and minimising the dissipation rate in a system comprising thousands of particles. The results demonstrate that the more compact the system, the greater the possible relative change of permeability when a high flow rate is applied. The permeability of large random arrays always increases when increasing the flow rate, which is most apparent in compact systems with equal-sized particles. The permeability can sometimes decrease but only in structured or small systems.

  • 348.
    Hellström, J. Gunnar I.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Lundström, Staffan
    Mechanisms of fluid flow induced deformation of porous medium2009Ingår i: Proceedings of 4th ICAPM: August 10-12, 2009, Istanbul, Turkey, 2009Konferensbidrag (Refereegranskat)
  • 349.
    Hellström, J. Gunnar I.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Frishfelds, Vilnis
    Lundström, Staffan
    Mekanismer för flödesinducerad deformation av ett poröst material2009Ingår i: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, s. 103-Konferensbidrag (Övrigt vetenskapligt)
  • 350.
    Hellström, J. Gunnar I.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jonsson, Jonas
    Epsilon HighTech AB, Göteborg.
    Lundström, Staffan
    Laminar and turbulent flow through an array of cylinders2010Ingår i: Journal of Porous Media, ISSN 1091-028X, E-ISSN 1934-0508, Vol. 13, nr 12, s. 1073-1085Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    When modeling fluid flow through porous media it is necessary to know when to take inertia effects into account, as well as when to switch to a turbulent description of the flow. From an engineering point of view, the problem is often solved with the empirically derived Ergun equation or a recently upgraded version by Nemec and Levec [Chem. Eng. Sci., vol. 60, pp. 6947−6957, 2005]. The drawback with this approach is, however, that the mechanisms for the transitions between the three states of flow are not revealed and time-consuming experiments have to be performed. In order to increase knowledge of the detailed flow, numerical studies of flow through arrays of quadratically packed cylinders at a variety of Re values were carried out. One result is that the laminar and turbulent approaches used both mimic experimental results for low Re, while for higher Re only the turbulent approach resembles the empirically derived equations. The deviation from Darcy’s law for different porosities of the array can be defined by usage of Re based on the hydraulic radius and the average interstitial velocity. However, to find a common Re when turbulence need to be accounted for, another Re based solely on the averaged interstitial velocity and the diameter of the cylinders was used. It was found that at low Re the laminar and turbulent setups give practically the same velocity fields, while the turbulent dissipation at higher Re results in larger circulation zones and weaker jets.

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