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Saemi, S., Raisee, M., Cervantes, M. J. & Nourbakhsh, A. (2019). Computation of two- and three-dimensional water hammer flows. Journal of Hydraulic Research, 57(3), 386-404
Open this publication in new window or tab >>Computation of two- and three-dimensional water hammer flows
2019 (English)In: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 57, no 3, p. 386-404Article in journal (Refereed) Published
Abstract [en]

This paper investigates water hammer flows using two- and three-dimensional (2D and 3D) numerical simulations. The unsteady Reynolds-averaged Navier–Stokes (URANS) equations in conjunction with the k–ω SST turbulence model are employed for the computations. The valve modelling approach is used for 3D simulations, with superior agreement with the experiments. Similar predictions are obtained by 2D simulations and the flow rate reduction curve obtained from the 3D computations. The asymmetric flow patterns induced by the valve are confined within approximately one pipe diameter upstream of the valve. The contributions of inertia and pressure gradient terms are dominant at the instance of pressure wave passage, leading to abrupt changes in the fluid flow parameters. However, the effects of inertia and viscous shear stress terms are significant after the pressure wave passage, resulting in the flow tendency to approach a new steady condition. The viscous and turbulent dissipations are dominant close to and away from the wall, respectively.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
Ball valve modelling, fluid dynamics, laminar flow, three-dimensional numerical simulation, turbulent flow, two-dimensional numerical simulation, water hammer
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-70075 (URN)10.1080/00221686.2018.1459892 (DOI)000465125300009 ()
Note

Validerad;2019;Nivå 2;2019-04-23 (oliekm)

Available from: 2018-07-05 Created: 2018-07-05 Last updated: 2019-05-03Bibliographically approved
Jonsson, P., Dunca, G. & Cervantes, M. (2019). Development of the pressure-time method as a relative method. In: IOP Conference Series: Earth and Environment. Paper presented at 29th IAHR Symposium on Hydraulic Machinery and Systems 17-21 September, 2018, Kyoto, Japan. Institute of Physics (IOP), 240, Article ID 022003.
Open this publication in new window or tab >>Development of the pressure-time method as a relative method
2019 (English)In: IOP Conference Series: Earth and Environment, Institute of Physics (IOP), 2019, Vol. 240, article id 022003Conference paper, Published paper (Refereed)
Abstract [en]

The pressure-time method is an absolute method commonly used for flow rate measurements in hydropower plants. The method determines the flow rate by measuring the differential pressure and estimating the losses between two sections in the penstock during a closure of the guide vanes. The method has limitations according to the IEC41 standard, which make it difficult to use at low head hydropower plants. The relative method called Winter-Kennedy is usually used on low head machines to determine the step-up efficiency between the old and refurbished runner. However, due to differences of the flow field in the spiral casing induce by both runners, the Winter Kennedy method might not allow estimate the flow rate similarly and thus the correct step-up efficiency. In cases where the absolute pressure-time method cannot be used because of waterway geometry limitations, the method might be used as a relative method by measuring the pressure difference between the free surface and a section in the penstock or even a point in the spiral casing without knowing the exact geometry, i.e., pipe factor. Such measurements may be simple to perform as most of the spiral casings have pressure taps for Winter-Kennedy measurements. Furthermore, the viscous losses do not need to be accurately determined if they are handled similarly before and after the refurbishment. The pressure-time method may thus become an alternative to the Winter-Kennedy method. The present paper consists in the experimental analysis of the pressure-time method accuracy used as a relative method. The experiments are performed on Porjus U9, a Kaplan prototype turbine operated under a head of 55 m generating 10 MW at full load. The flow rate is evaluated based on pressure-time measurements with different friction models and considering or not the compressibility effect. The accuracy of the flow rate evaluation method is compared using an 8-path transit-time flow rate measurement device as reference.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2019
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-70966 (URN)10.1088/1755-1315/240/2/022003 (DOI)2-s2.0-85063917267 (Scopus ID)
Conference
29th IAHR Symposium on Hydraulic Machinery and Systems 17-21 September, 2018, Kyoto, Japan
Available from: 2018-09-25 Created: 2018-09-25 Last updated: 2019-05-03Bibliographically approved
Saemi, S., Sundström, J., Cervantes, M. & Raisee, M. (2019). Evaluation of transient effects in the pressure-time method. Flow Measurement and Instrumentation, 68, Article ID 101581.
Open this publication in new window or tab >>Evaluation of transient effects in the pressure-time method
2019 (English)In: Flow Measurement and Instrumentation, ISSN 0955-5986, E-ISSN 1873-6998, Vol. 68, article id 101581Article in journal (Refereed) Published
Abstract [en]

The pressure-time is a method for measuring the flow rate in closed conduits and is typically used in hydropower applications. The scope of the present paper is to examine the flow physics in the pressure-time method using experimental measurements and two-dimensional numerical simulations. The Unsteady Reynolds-averaged Navier–Stokes (URANS) equations and the low-Re k-ω SST turbulence model are employed for the simulations. The contributions of inertia, pressure gradient, viscous and turbulent shear stresses are investigated in the flow during a pressure-time measurement. It is shown that away from the wall and at the first times, the turbulent shear stress balances with the pressure gradient. By increasing the time, the inertia effect becomes dominant and balances with the pressure gradient and turbulent shear stress. Close to the wall, both viscous and turbulent shear stresses are the dominant terms which are decreasing by increasing the time. It is also shown that the prediction of the friction losses can be improved by modeling the dependence of the friction factor on the dimensionless parameter instead of the Reynolds number.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Pressure-time method, Flow rate measurement, Transient flow, CFD, Experiments
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-71997 (URN)10.1016/j.flowmeasinst.2019.101581 (DOI)000483649300016 ()
Note

Validerad;2019;Nivå 2;2019-07-08 (johcin)

Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2019-09-24Bibliographically approved
Soltani Dehkharqani, A., Engström, F., Aidanpää, J.-O. & Cervantes, M. (2019). Experimental Investigation of a 10 MW Prototype Kaplan Turbine during Start-Up Operation. Energies, 12(23), Article ID 4852.
Open this publication in new window or tab >>Experimental Investigation of a 10 MW Prototype Kaplan Turbine during Start-Up Operation
2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 23, article id 4852Article in journal (Refereed) Published
Abstract [en]

An increase in the start/stop cycles of hydraulic turbines due to the penetration of intermittent renewable energy sources is important. Hydraulic instabilities that occur in hydraulic turbines during start/stops may cause structural issues in the turbine components. High-stress fluctuations on the runner blades are expected during start-ups due to the unsteady pressure loading on the runner blades. This paper presents experiments performed on a 10 MW prototype Kaplan turbine at the Porjus Hydropower Center during a start-up cycle. Synchronized unsteady pressure and strain measurements on a runner blade and axial, bending (in two directions) and torsion strain measurements on the shaft were performed. In addition, the general parameters of the turbine (e.g., rotational speed, guide vane opening and runner blade angle) were acquired. Low-frequency fluctuations (0–15 Hz) were observed in the pressure data on the runner blade after opening the guide vanes from the completely closed position. A higher strain value was observed on the strain gauges installed on the runner blade near the hub (200–500 μm/m ) compared to the ones near the shroud at the leading and trailing edge. The strain fluctuation level on the shaft decreased after loading the generator by further opening the guide vanes. Higher fluctuations were observed in the torsion strain compared to axial and bending strain. In addition, the torsion strain peak-to-peak value reached 12 times its corresponding value at 61% guide vane opening.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
prototype Kaplan turbine, start-up, pressure measurement, strain measurement, axial strain, bending strain, torsion strain
National Category
Fluid Mechanics and Acoustics Other Mechanical Engineering
Research subject
Fluid Mechanics; Computer Aided Design
Identifiers
urn:nbn:se:ltu:diva-77053 (URN)10.3390/en12234582 (DOI)
Note

Validerad;2020;Nivå 2;2020-01-03 (johcin)

Available from: 2019-12-03 Created: 2019-12-03 Last updated: 2020-01-03Bibliographically approved
Goyal, R., Gandhi, B. & Cervantes, M. (2019). Experimental Investigation of a High Head Francis Turbine Model During Shutdown Operation. In: IOP Conference Series: Earth and Environment. Paper presented at 29th IAHR Symposium on Hydraulic Machinery and Systems, Kyoto, Japan, 17-21 September, 2018. Institute of Physics (IOP), 240, Article ID 022028.
Open this publication in new window or tab >>Experimental Investigation of a High Head Francis Turbine Model During Shutdown Operation
2019 (English)In: IOP Conference Series: Earth and Environment, Institute of Physics (IOP), 2019, Vol. 240, article id 022028Conference paper, Published paper (Refereed)
Abstract [en]

Increased penetration of intermittent energy resources disturbs the power grid network. The frequency band of the power grid is normally controlled by automatic opening and closing of the guide vanes of hydraulic turbines. This has increased the number of shutdown cycles as compared to the defined ones for the normal operation of turbines. Turbine shutdown induced a significantly higher level of pressure fluctuations and unsteadiness in the flow field, decreasing its expected life. This paper presents experiments performed on a high head model Francis turbine during shutdown. The pressure and 2D Particle Image Velocimetry (PIV) measurements were performed to investigate the pressure fluctuations and flow instabilities in the turbine. The pressure sensors were mounted in the draft tube cone and vaneless space to measure the instantaneous pressure fluctuations. In the present study, the initial high load operating condition was considered to perform the turbine shutdown. The data were logged at the sampling frequency of 40 Hz and 5 kHz for PIV and pressure measurements, respectively. Time-resolved velocity and pressure data are presented in this paper to show the pressure fluctuations and causes of generation of unsteady flow in the draft tube.  

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2019
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-70969 (URN)10.1088/1755-1315/240/2/022028 (DOI)2-s2.0-85063871783 (Scopus ID)
Conference
29th IAHR Symposium on Hydraulic Machinery and Systems, Kyoto, Japan, 17-21 September, 2018
Available from: 2018-09-25 Created: 2018-09-25 Last updated: 2019-05-03Bibliographically approved
Soltani Dehkharqani, A., Aidanpää, J.-O., Engström, F. & Cervantes, M. (2019). Fluid added polar inertia and damping for the torsional vibration of a Kaplan turbine model runner considering multiple perturbations. In: IOP Conference Series: Earth and Environmental Science. Paper presented at 29th IAHR Symposium on Hydraulic Machinery and Systems, 17-21 September 2018, Kyoto, Japan.. Institute of Physics (IOP), 240, Article ID 062007.
Open this publication in new window or tab >>Fluid added polar inertia and damping for the torsional vibration of a Kaplan turbine model runner considering multiple perturbations
2019 (English)In: IOP Conference Series: Earth and Environmental Science, Institute of Physics (IOP), 2019, Vol. 240, article id 062007Conference paper, Published paper (Refereed)
Abstract [en]

A water turbine runner is exposed to several perturbation sources with differentfrequencies, phases, and amplitudes both at the design and off-design operations. Rotor-statorinteraction, cavitation, rotating vortex rope, and blade trailing edge vortices are examples of suchperturbations which can disturb the runner. The rotor dynamic coefficients require beingdetermined to perform a reliable dynamic analysis. Fluid added inertia, damping, and stiffnesshave previously been investigated for individual perturbation frequencies for the torsionalvibration of a Kaplan turbine model runner. However, a number of perturbation sources mostlytake place simultaneously and alter the dynamics of the runner. Soltani et al. [1] have evaluatedthe torsional added parameters for a Kaplan turbine runner using numerical simulationsconsidering single perturbation frequency. In the present work, the fluid added parameters areassessed in the presence of multiple perturbation sources. A similar methodology is used. Asingle-degree-of-freedom (SDOF) model for the dynamic model and unsteady ReynoldsaveragedNavier–Stokes approach for the flow simulations are assumed. Perturbations withdifferent frequencies are applied to the rotational speed of the runner to determine the fluid addedparameters for the torsional vibration. A number of previously investigated frequencies arechosen and their combinations are investigated. In addition, two different phase shifts areconsidered between the applied perturbations to study the effect of phase. Two more test caseswith higher perturbation amplitude are also conducted to investigate its influence on the fluidadded inertia and damping. The results are compared with the previous study and the interactionof multiple perturbations on the added parameters is investigated.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2019
National Category
Mechanical Engineering Fluid Mechanics and Acoustics Other Mechanical Engineering
Research subject
Fluid Mechanics; Computer Aided Design
Identifiers
urn:nbn:se:ltu:diva-72503 (URN)10.1088/1755-1315/240/6/062007 (DOI)2-s2.0-85063961671 (Scopus ID)
Conference
29th IAHR Symposium on Hydraulic Machinery and Systems, 17-21 September 2018, Kyoto, Japan.
Available from: 2019-01-09 Created: 2019-01-09 Last updated: 2019-11-26Bibliographically approved
Sotoudeh, N., Maddahian, R. & Cervantes, M. (2019). Formation of Rotating Vortex Rope in the Francis-99 Draft Tube. In: IOP Conference Series: Earth and Environment: . Paper presented at 29th IAHR Symposium on Hydraulic Machinery and Systems, Kyoto, Japan, 17-21 September, 2018. Institute of Physics (IOP), 240, Article ID 022017.
Open this publication in new window or tab >>Formation of Rotating Vortex Rope in the Francis-99 Draft Tube
2019 (English)In: IOP Conference Series: Earth and Environment, Institute of Physics (IOP), 2019, Vol. 240, article id 022017Conference paper, Published paper (Refereed)
Abstract [en]

The aim of this research is to understand the mechanism(s) of RVR formation duringthe changes in operating condition from the Best Efficiency Point (BEP) to Part Load (PL). AComputational Fluid Dynamic (CFD) methodology by the means of ANSYS-CFX is applied ona reduced high head Francis turbine model. The reduced model consists of one stay vane, twoguide vanes, one runner blade, one splitter and a full draft tube. Numerical simulation is firstperformed at BEP as well as PL to ensure the appropriate employment of turbulence models andboundary conditions. In the second step, the inlet boundary conditions are changed linearly fromBEP to PL in order to achieve the transient conditions inside the draft tube. The initial conditionof the second step is the converged BEP result. The transient simulation is continued until theRVR is fully developed in the draft tube at part load condition. The numerical results for BEP,PL and BEP to PL are in a good agreement with the experimental data. The effect of the RVR isconsidered from two aspects. The first one is the frequency, and the amplitude of the pressurepulsations induced by the RVR in the draft tube. The second one is the velocity field in the drafttube which is investigated over time during load rejection. Moreover, the flow structure isvisualized using the λ2 criterion. The mechanism(s) of RVR formation and damping is accuratelyinvestigated by the presented approach. Furthermore, the results provide a better understandingof the physics behind the RVR formation. The obtained results aim to design an effective RVRcontrolling approach.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2019
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-70968 (URN)10.1088/1755-1315/240/2/022017 (DOI)2-s2.0-85063905433 (Scopus ID)
Conference
29th IAHR Symposium on Hydraulic Machinery and Systems, Kyoto, Japan, 17-21 September, 2018
Available from: 2018-09-25 Created: 2018-09-25 Last updated: 2019-05-03Bibliographically approved
Sundström, J., Saemi, S., Raisee, M. & Cervantes, M. (2019). Improved frictional modeling for the pressure-time method. Flow Measurement and Instrumentation, 69, Article ID 101604.
Open this publication in new window or tab >>Improved frictional modeling for the pressure-time method
2019 (English)In: Flow Measurement and Instrumentation, ISSN 0955-5986, E-ISSN 1873-6998, Vol. 69, article id 101604Article in journal (Refereed) Published
Abstract [en]

The pressure-time method is classified as a primary method for measuring discharge in hydraulic machinery. The uncertainty in the discharge determined using the pressure-time method is typically around ±1.5 %; however, despite dating back almost one hundred years in time, there still exists potential to reduce this uncertainty. In this paper, an improvement of the pressure-time method is suggested by implementing a novel formulation to model the frictional losses arising in the evaluation procedure. By analyzing previously obtained data from CFD, laboratory and full-scale pressure-time measurements it is shown that the new friction model improves the accuracy of the flow rate calculation by approximately 0.1–0.2% points, compared to currently utilized friction models. Despite being a small absolute improvement, the new friction model presents an important development of the pressure-time method because the relative improvement is significant.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Pressure-time method, Transient friction modeling, Pipe flow
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-75599 (URN)10.1016/j.flowmeasinst.2019.101604 (DOI)000496341600005 ()2-s2.0-85070506497 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-08-20 (svasva)

Available from: 2019-08-20 Created: 2019-08-20 Last updated: 2019-11-29Bibliographically approved
Sundström, J., Saemi, S., Raisee, M. & Cervantes, M. (2019). Improved frictional modelling for the pressure-time method. Flow measurement and instrumentation
Open this publication in new window or tab >>Improved frictional modelling for the pressure-time method
2019 (English)In: Flow measurement and instrumentationArticle in journal (Refereed) Submitted
Abstract [en]

The pressure-time method is classified as a primary method for measuring discharge in hydraulic machinery. The uncertainty in the discharge determined using the pressuretime method is typically around±1.5%; however, despite dating back almost one hundred years in time, there still exists potential to reduce this uncertainty. In this paper, an improvement of the pressure-time method is suggested by implementing a novel formulation to model the frictional losses arising in the evaluation procedure. By analyzing previously obtained data from CFD, laboratory and full-scale pressure-time measurements it is shown that the new friction model improves the accuracy of the flow rate calculation by approximately 0.1-0.2 percentage points, compared to currently utilized friction models. Despite being a small absolute improvement, the new friction model presents an important development of the pressure-time method because the relative improvement is significant.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-71998 (URN)
Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2019-04-16
Sotoudeh, N., Maddahian, R. & Cervantes, M. (2019). Investigation of Rotating Vortex Rope formation during load variation in a Francis turbine draft tube. Renewable energy
Open this publication in new window or tab >>Investigation of Rotating Vortex Rope formation during load variation in a Francis turbine draft tube
2019 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682Article in journal (Refereed) Epub ahead of print
Abstract [en]

Rotating Vortex Rope (RVR) has been a matter of focus for years due to the major effects on hydraulic turbine’s efficiency. The exact procedure of RVR formation is still vague. The present research focuses on the dynamics of the RVR formation during the load variation employing transient numerical simulations. Two different geometries including the full geometry and the reduced one, which consists of one stay vane, two guide vanes, one runner blade, one splitter blade and full draft tube, are considered. In order to capture the transient swirling flow features inside the draft tube, the Shear Stress Transport-Scale Adaptive Simulation (SST-SAS) model is utilized to approximate the turbulent stresses. The pressure results inside the draft tube agree well with the experimental measurements. Moreover, the velocity results show the central low-axial-velocity and high-tangential-velocity region in the draft tube properly. The flow structure is visualized using λ2 criterion. The dynamic of RVR and the physics behind the RVR formation are investigated during the load variation. The results indicate four flow regimes with different characteristics during RVR formation. The first flow regime is a stable swirling structure occurring at Best Efficiency Point (BEP). The second flow regime occurs at the beginning of the load variation where signs of flow instabilities appear. These instabilities are temporary and washed down by the upstream flow. Expanding the instabilities and creating the vortical structures in the draft tube are the important flow features in the third flow regime. The fourth flow regime is the presence of a developed rotating rope occurring at the Part Load (PL) condition. The flow regimes differ according to the size and shape of the stalled region during load rejection inside the draft tube cone. They also reveal that despite some shortcomings, the reduced model is reliable to simulate the RVR transient formation. The full geometry simulations could be also applicable for practical problems provided that the modified time step is slightly greater than the main blade rotational angle is used.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Hydraulic turbine, Rotating Vortex Rope, Load variation, Swirling flow, Flow instability
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-76950 (URN)10.1016/j.renene.2019.11.014 (DOI)2-s2.0-85075328751 (Scopus ID)
Available from: 2019-11-29 Created: 2019-11-29 Last updated: 2019-12-09
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ORCID iD: ORCID iD iconorcid.org/0000-0001-7599-0895

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