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Åkerstedt, H. O. (2019). Transport and Deposition of Large Aspect Ratio Prolate and Oblate Spheroidal Nanoparticles in Cross Flow. Processes, 7(12), Article ID 886.
Open this publication in new window or tab >>Transport and Deposition of Large Aspect Ratio Prolate and Oblate Spheroidal Nanoparticles in Cross Flow
2019 (English)In: Processes, ISSN 2227-9717, Vol. 7, no 12, article id 886Article in journal (Refereed) Published
Abstract [en]

The objective of this paper was to study the transport and deposition of non-spherical oblate and prolate shaped particles for the flow in a tube with a radial suction velocity field, with an application to experiments related to composite manufacturing. The transport of the non-spherical particles is governed by a convective diffusion equation for the probability density function, also called the Fokker–Planck equation, which is a function of the position and orientation angles. The flow is governed by the Stokes equation with an additional radial flow field. The concentration of particles is assumed to be dilute. In the solution of the Fokker–Planck equation, an expansion for small rotational Peclet numbers and large translational Peclet numbers is considered. The solution can be divided into an outer region and two boundary layer regions. The outer boundary layer region is governed by an angle-averaged convective-diffusion equation. The solution in the innermost boundary layer region is a diffusion equation including the radial variation and the orientation angles. Analytical deposition rates are calculated as a function of position along the tube axis. The contribution from the innermost boundary layer called steric- interception deposition is found to be very small. Higher order curvature and suction effects are found to increase deposition. The results are compared with results using a Lagrangian tracking method of the same flow configuration. When compared, the deposition rates are of the same order of magnitude, but the analytical results show a larger variation for different particle sizes. The results are also compared with numerical results, using the angle averaged convective-diffusion equation. The agreement between numerical and analytical results is good.

Place, publisher, year, edition, pages
Basel: MDPI, 2019
Keywords
transport, deposition, non-spherical particles, Stokes flow, cross flow, boundary layers, composite manufacturing
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-76979 (URN)10.3390/pr7120886 (DOI)
Note

Validerad;2019;Nivå 2;2019-12-06 (johcin)

Available from: 2019-11-29 Created: 2019-11-29 Last updated: 2019-12-06Bibliographically approved
Åkerstedt, H. O., Eller, S. & Lundström, S. T. (2017). Numerical Investigation of Turbulent Flow through Rectangular and Biconvex Shaped Trash Racks. Engineering, 9(5), 412-426, Article ID 76642.
Open this publication in new window or tab >>Numerical Investigation of Turbulent Flow through Rectangular and Biconvex Shaped Trash Racks
2017 (English)In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 9, no 5, p. 412-426, article id 76642Article in journal (Refereed) Published
Abstract [en]

Turbulent flow through a trash rack of bars of rectangular and biconvex shapes is considered. A trash rack is composed of an array of bars fitted into a hydro-electric power station to prevent debris and fish to enter the waterway towards the turbine. The work is directed towards modeling a large number of bars for which the flow turn out to have a periodic structure. It is here shown that this case can be simplified with the flow past a single bar together with periodic boundary conditions. Using this approach the head loss is derived for different angles of attack α and blockages P for two shapes of the rack, a rectangular bar and an aerodynamically shaped biconvex bar. It is found that overall loss of the biconvex bars is in general about 15% of the loss for the rectangular case for small angles of attack. For large angle of attack this difference diminishes. Of interest for the biconvex bars is also a local minimum in the head loss for angles approximately greater than 20˚ and for a blockage P around 0.35. This combination of parameters gives a low loss together with an efficient barrier for debris and fishes.

Place, publisher, year, edition, pages
Scientific Research Publishing, 2017
National Category
Engineering and Technology Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-65457 (URN)10.4236/eng.2017.95024 (DOI)
Note

Validerad;2017;Nivå 1;2017-09-05 (rokbeg)

Available from: 2017-09-02 Created: 2017-09-02 Last updated: 2018-05-04Bibliographically approved
Holmstedt, E., Åkerstedt, H., Lundström, S. & Högberg, S. (2016). Modeling Transport and Deposition Efficiency of Oblate and Prolate Nano- and Micro-particles in a Virtual Model of the Human Airway (ed.). Journal of Fluids Engineering - Trancactions of The ASME, 138(8), Article ID 81203.
Open this publication in new window or tab >>Modeling Transport and Deposition Efficiency of Oblate and Prolate Nano- and Micro-particles in a Virtual Model of the Human Airway
2016 (English)In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 138, no 8, article id 81203Article in journal (Refereed) Published
Abstract [en]

A model for the motion and deposition of oblate and prolate spheroids in the nano- and microscale was developed. The aim was to mimic the environment of the human lung, but the model is general and can be applied for different flows and geometries for small nonspherical particle Stokes and Reynolds numbers. A study of the motion and orientation of a single oblate and prolate particle has been done yielding that Brownian motion disturbs the Jeffery orbits for small particles. Prolate microparticles still display distinguishable orbits while oblate particles of the same size do not. A statistical study was done comparing the deposition efficiencies of oblate and prolate spheroids of different size and aspect ratio observing that smaller particles have higher deposition rate for lower aspect ratio while larger particles have higher deposition rates for large aspect ratio.

National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-11039 (URN)10.1115/1.4032934 (DOI)000379589700009 ()2-s2.0-84973508328 (Scopus ID)9f112cec-8570-4373-955e-d6f548e3c363 (Local ID)9f112cec-8570-4373-955e-d6f548e3c363 (Archive number)9f112cec-8570-4373-955e-d6f548e3c363 (OAI)
Note

Validerad; 2016; Nivå 2; 20160816 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Jansson, I. & Åkerstedt, H. (2015). The dynamics of cylinder in a confined swirling flow with constant vorticity (ed.). Paper presented at . European journal of mechanics. B, Fluids, 54, 98-104
Open this publication in new window or tab >>The dynamics of cylinder in a confined swirling flow with constant vorticity
2015 (English)In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 54, p. 98-104Article in journal (Refereed) Published
Abstract [en]

In this work, we present a rigid body dynamics model that accounts for phenomena earlier studied both within hydrodynamic stability theory and the area of fluid-induced vibrations. The model captures the transverse dynamics of a rigid cylinder in a confined swirling flow. We show that a linear inviscid stability analysis of the whole system with respect to two-dimensional disturbances could be decomposed intoa solution governing rotational disturbances with homogeneous boundary conditions and a solution governing irrotational disturbances with inhomogeneous boundary conditions. This implies that the continuous stable spectrum of rotational disturbances is unchanged by the supposition of a free boundary. Moreover, the time-dependence of irrotational disturbances is governed by the disturbance of the rigid cylinder. Consequently, a rigid body dynamics model suffices to determine the time evolutionof irrotational disturbances. The model is based on the definition of a merged homogeneous state in which the solid mass of the rigid cylinder equals the displaced fluid mass and the flow is in solid body rotation. A departure from this merged homogeneous state yields an imbalance of the fictitious Coriolis and centrifugal force of the rigid cylinder and the counterbalancing motion-induced fluid forces. Thisimbalance makes the fluid flow support propagation of waves and may render a concentric position of the body unstable. A non-uniform distribution of the angular velocity delays the onset of instability so that the rigid cylinder can maintain a concentric position even though it is denser than the fluid.

National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-14148 (URN)10.1016/j.euromechflu.2015.06.015 (DOI)000362614600010 ()2-s2.0-84938891501 (Scopus ID)d7bbab73-13dc-4ea6-b6ed-d546a2530091 (Local ID)d7bbab73-13dc-4ea6-b6ed-d546a2530091 (Archive number)d7bbab73-13dc-4ea6-b6ed-d546a2530091 (OAI)
Note
Validerad; 2015; Nivå 2; 20150812 (idajoh)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Åkerstedt, H. & Jansson, I. (2015). The stability of a flexibly mounted rotating cylinder in turbulent annular flow (ed.). Paper presented at . Journal of Fluids and Structures, 58, 152-172
Open this publication in new window or tab >>The stability of a flexibly mounted rotating cylinder in turbulent annular flow
2015 (English)In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 58, p. 152-172Article in journal (Refereed) Published
Abstract [en]

In this paper, we determine the inviscid linear stability with respect to two-dimensional disturbances of a fluid flow between two concentric cylinders. The inner rigid cylinder rotates with the angular velocity Ω0 and is fixed on elastic hinges at each end in the transverse direction. The outer cylinder does not rotate and is rigidly fixed. We assume that the fluid flow has an inner core that rotates as a solid body with angular velocity Ω0/2 and outside the core there are turbulent boundary layers. The velocity profile of the turbulent boundary layers satisfies the viscous Camassa−Holm equations. The perturbed fluid flow is derived from Rayleigh’s equation. The analysis yields an equation of motion of the cylinder equivalent to previous work without boundary layers and a basic flow of constant angular vorticity. The analysis is not restricted to a small gap between the cylinders. The results are compared with the results by Antunes et al. (1996), who consider a similar problem with uniform velocity profile and the limit of small gap. For ρc/ρf<1ρc/ρf<1 the results disagree in that the present analysis shows stability whereas Antunes et al. find instability. For ρc/ρf>1ρc/ρf>1 both theories predict stability and for larger values of ρc/ρfρc/ρf the agreement is good especially for small gap.

National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-12906 (URN)10.1016/j.jfluidstructs.2015.08.004 (DOI)000364248200010 ()2-s2.0-84943149440 (Scopus ID)c0d7cb7d-8780-4b17-a884-fc51ca8e51be (Local ID)c0d7cb7d-8780-4b17-a884-fc51ca8e51be (Archive number)c0d7cb7d-8780-4b17-a884-fc51ca8e51be (OAI)
Note
Validerad; 2015; Nivå 2; 20150812 (hake)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Holmstedt, E., Åkerstedt, H. O. & Lundström, T. S. (2014). Simulation of the movements and deposition rates of oblate and prolate nano- and microparticles in a virtual model of the human airways (ed.). Paper presented at European Fluid Mechanics Conference : 14/09/2014 - 18/09/2014. Paper presented at European Fluid Mechanics Conference : 14/09/2014 - 18/09/2014.
Open this publication in new window or tab >>Simulation of the movements and deposition rates of oblate and prolate nano- and microparticles in a virtual model of the human airways
2014 (English)Conference paper, Oral presentation only (Refereed)
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-30348 (URN)41f6e1f0-1bc0-439d-b98b-2757db21ddd8 (Local ID)41f6e1f0-1bc0-439d-b98b-2757db21ddd8 (Archive number)41f6e1f0-1bc0-439d-b98b-2757db21ddd8 (OAI)
Conference
European Fluid Mechanics Conference : 14/09/2014 - 18/09/2014
Note
Godkänd; 2014; 20140923 (andbra)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-28Bibliographically approved
Åkerstedt, H. O., Högberg, S. & Lundström, T. S. (2013). An asymptotic approach of Brownian deposition of nanofibres in pipe flow (ed.). Paper presented at . Theoretical and Computational Fluid Dynamics, 27(5), 561-575
Open this publication in new window or tab >>An asymptotic approach of Brownian deposition of nanofibres in pipe flow
2013 (English)In: Theoretical and Computational Fluid Dynamics, ISSN 0935-4964, E-ISSN 1432-2250, Vol. 27, no 5, p. 561-575Article in journal (Refereed) Published
Abstract [en]

An asymptotic approach is considered for the transport and deposition of nanofibres in pipe flow. Convection and Brownian diffusion are included, and Brownian diffusion is assumed to be the dominant mechanism. The fibre position and orientation are modelled with a probability density function for which the governing equation is a Fokker-Planck equation. The focus is set on dilute fibres concentrations implying that interaction between individual fibres is neglected. At the entrance of the pipe, a fully developed velocity profile is set and it is assumed that the fibres enter the pipe with a completely random orientation and position. A small parameter {Mathematical expression} is introduced, where l is the fibre half-length and a is the pipe radius. The probability density function is expanded for small {Mathematical expression} and the solution turns out to be multi-structured with three areas, consisting of one outer solution and two boundary layers. For the deposition of fibres on the wall, it is found that for parabolic flow, and for the lowest order, the deposition can be obtained with a simplified angle averaged convective-diffusion equation. It is suggested that this simplification is valid also for more complex flows like when the inflow boundary condition yields a developing velocity profile and flows within more intricate geometries than here studied. With the model fibre, deposition rates in human respiratory airways are derived. The results obtained compare relatively well with those obtained with a previously published model

National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-5180 (URN)10.1007/s00162-012-0262-1 (DOI)000322744000001 ()2-s2.0-84881480369 (Scopus ID)336a6825-c565-4dbd-a524-42e0676c665f (Local ID)336a6825-c565-4dbd-a524-42e0676c665f (Archive number)336a6825-c565-4dbd-a524-42e0676c665f (OAI)
Note
Validerad; 2013; 20110427 (stlu)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Jansson, I., Åkerstedt, H. O., Aidanpää, J.-O. & Lundström, T. S. (2012). The effect of inertia and angular momentum of a fluid annulus on lateral transversal rotor vibrations (ed.). Paper presented at . Journal of Fluids and Structures, 28, 328-342
Open this publication in new window or tab >>The effect of inertia and angular momentum of a fluid annulus on lateral transversal rotor vibrations
2012 (English)In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 28, p. 328-342Article in journal (Refereed) Published
Abstract [en]

An extensive amount of work exists on experimental and theoretical analysis of unsteady flow phenomena in hydraulic turbines. Still, resonance phenomena and self-excited vibrations of the rotor of hydropower machines are not considered as a major problem during normal operation conditions. Nevertheless, in development and research it is not sufficient to rely on earlier experience. An accurate predictive rotor model is crucial in risk assessment of rotor vibrations of hydraulic generator units. This paper discusses the effects of inertia and the rotational energy of the fluid in the turbine on lateral transversal shaft vibrations of hydraulic generator units. There is a lack of agreement among engineers upon how fluid inertia of the turbine should be included in rotor models. The rotational energy of the fluid has a potential risk of feeding self-excited vibrations. A fluid-rotor model is presented that captures the effect of inertia and angular momentum of a fluid annulus on vibrations of an inner rigid cylinder. The purpose of the model is to gain physical understanding of the phenomena at work and it is not applicable to specific turbines. The linearized equation of motion of the cylinder surrounded by a fluid annulus is solved for by one single complex equation. The constrained cylinder has two degrees of freedom in the plane perpendicular to its axis. By the assumption of irrotational cyclic flow, the fluid motion is described by a complex potential function. The motion of the cylinder is described by three parameters. Two surfaces are defined that splits the parameter space into regions with different qualitative behaviour. One surface defines the limit of stability whereas the other defines a limit when the eigenvalues have opposite signs or are both positive. The response to an external periodic rotating force is visualized by the magnitude of the inverse of the complex dynamic stiffness.

National Category
Fluid Mechanics and Acoustics Applied Mechanics
Research subject
Fluid Mechanics; Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-9972 (URN)10.1016/j.jfluidstructs.2011.10.008 (DOI)000301161800021 ()2-s2.0-84856212293 (Scopus ID)8b4de7e3-b973-42f6-a6b1-c2f60e348a63 (Local ID)8b4de7e3-b973-42f6-a6b1-c2f60e348a63 (Archive number)8b4de7e3-b973-42f6-a6b1-c2f60e348a63 (OAI)
Note
Validerad; 2012; 20111209 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Högberg, S., Åkerstedt, H. O., Holmstedt, E., Lundström, T. S. & Sandström, T. (2012). Time-dependent deposition of micro- and nanofibers in straight model airways (ed.). Paper presented at . Journal of Fluids Engineering - Trancactions of The ASME, 134(5), 051208-1
Open this publication in new window or tab >>Time-dependent deposition of micro- and nanofibers in straight model airways
Show others...
2012 (English)In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 134, no 5, p. 051208-1Article in journal (Refereed) Published
Abstract [en]

In this paper, we increase the understanding of the influence of the breathing pattern on the fate of inhaled non-spherical micro and nanoparticles and examine the accuracy of replacing the cyclic flow field with a quasi-steady flow. This is done with new analysis and numerical simulations on straight model airways using a previously developed discrete model for fiber motion. For the conditions studied, maximum deposition is obtained when fibers are released at the start of the inspiratory cycle, and minimum is received at the peak of inhalation. A quasi-steady solution generally provides a relatively good approximation to cyclic flow if an average velocity over one residence time of the particles moving with the mean fluid velocity is used. For a batch type, supply of particles deposition is favored in light activity breathing as compared to heavy breathing and the inclusion of a short pause after the inhalation results in an increased deposition in the terminal bronchiole. During zero-flow over the time of a breathing pause, spherical 10 nm particles experience considerable deposition in the distal airways, whereas only a few percent of larger and/ or fibrous nanoparticles were deposited. Hence, size and shape are crucial variables for deposition for no flow conditions. Common for all breathing parameters examined was that minimum deposition was obtained for the spherical 1 µm-particles and the fibrous 100 nm-particles. The former is expected from studies on spherical particles, and the latter is in agreement with results from a recent publication on steady inspiration.

National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-4893 (URN)10.1115/1.4006698 (DOI)000304820400008 ()2-s2.0-84862278886 (Scopus ID)2e48b609-305f-4617-b4c8-861700e18519 (Local ID)2e48b609-305f-4617-b4c8-861700e18519 (Archive number)2e48b609-305f-4617-b4c8-861700e18519 (OAI)
Note
Validerad; 2012; 20120314 (stlu)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Åkerstedt, H. O. (2011). Deposition of charged nano-particles in the human airways including effects from cartilaginous rings (ed.). Paper presented at . Natural Science, 3(10), 885-888
Open this publication in new window or tab >>Deposition of charged nano-particles in the human airways including effects from cartilaginous rings
2011 (English)In: Natural Science, ISSN 2150-4091, E-ISSN 2150-4105, Vol. 3, no 10, p. 885-888Article in journal (Refereed) Published
Abstract [en]

This paper presents a numerical study of the deposition of spherical charged nano-particles caused by convection, Brownian diffusion and electrostatics in a pipe with a cartilaginous ring structure. The model describes the deposition of charged particles in the different generations of the tracheobronchial tree of the human lung. The upper airways are characterized by a certain wall structure called cartilaginous rings which modify the particle deposition when compared to an airway with a smooth wall. The problem is defined by solving Naver-Stokes equations in combination with a convective-diffusion equation and Gauss law for electrostatics. Three non- dimensional parameters describe the problem, the Peclet number Pe = 2ūa/D , the Reynolds number Re = ūa/v and an electrostatic parameter α=α2c0q2/(4ε0κT) . Here U is the mean velocity, a the pipe radius and D the diffusion coefficient due to Brownian motion given by D=κTCu/3πμd , where Cu is the Cunningham-factor Cu=1+λ/d(2.34+1.05exp(-0.39d/λ)) Here d is the particle diameter and λ the mean free path of the air molecules. Results are provided for generations G4-G16 of the human airways. The electrostatic parameter is varied to model different concentrations and charge numbers

National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-12139 (URN)10.4236/ns.2011.310113 (DOI)b379e98c-6c59-42da-aad4-b4b95b6063e1 (Local ID)b379e98c-6c59-42da-aad4-b4b95b6063e1 (Archive number)b379e98c-6c59-42da-aad4-b4b95b6063e1 (OAI)
Note
Validerad; 2011; 20111214 (hake)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-28Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-8739-1934

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