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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
Åpne denne publikasjonen i ny fane eller vindu >>Computation of two- and three-dimensional water hammer flows
2019 (engelsk)Inngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 57, nr 3, s. 386-404Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
Taylor & Francis, 2019
Emneord
Ball valve modelling, fluid dynamics, laminar flow, three-dimensional numerical simulation, turbulent flow, two-dimensional numerical simulation, water hammer
HSV kategori
Forskningsprogram
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-70075 (URN)10.1080/00221686.2018.1459892 (DOI)000465125300009 ()
Merknad

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

Tilgjengelig fra: 2018-07-05 Laget: 2018-07-05 Sist oppdatert: 2019-05-03bibliografisk kontrollert
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.
Åpne denne publikasjonen i ny fane eller vindu >>Development of the pressure-time method as a relative method
2019 (engelsk)Inngår i: IOP Conference Series: Earth and Environment, Institute of Physics (IOP), 2019, Vol. 240, artikkel-id 022003Konferansepaper, Publicerat paper (Fagfellevurdert)
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.

sted, utgiver, år, opplag, sider
Institute of Physics (IOP), 2019
HSV kategori
Forskningsprogram
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-70966 (URN)10.1088/1755-1315/240/2/022003 (DOI)2-s2.0-85063917267 (Scopus ID)
Konferanse
29th IAHR Symposium on Hydraulic Machinery and Systems 17-21 September, 2018, Kyoto, Japan
Tilgjengelig fra: 2018-09-25 Laget: 2018-09-25 Sist oppdatert: 2019-05-03bibliografisk kontrollert
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.
Åpne denne publikasjonen i ny fane eller vindu >>Evaluation of transient effects in the pressure-time method
2019 (engelsk)Inngår i: Flow Measurement and Instrumentation, ISSN 0955-5986, E-ISSN 1873-6998, Vol. 68, artikkel-id 101581Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
Elsevier, 2019
Emneord
Pressure-time method, Flow rate measurement, Transient flow, CFD, Experiments
HSV kategori
Forskningsprogram
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-71997 (URN)10.1016/j.flowmeasinst.2019.101581 (DOI)000483649300016 ()
Merknad

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

Tilgjengelig fra: 2018-12-11 Laget: 2018-12-11 Sist oppdatert: 2019-09-24bibliografisk kontrollert
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.
Åpne denne publikasjonen i ny fane eller vindu >>Experimental Investigation of a High Head Francis Turbine Model During Shutdown Operation
2019 (engelsk)Inngår i: IOP Conference Series: Earth and Environment, Institute of Physics (IOP), 2019, Vol. 240, artikkel-id 022028Konferansepaper, Publicerat paper (Fagfellevurdert)
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.  

sted, utgiver, år, opplag, sider
Institute of Physics (IOP), 2019
HSV kategori
Forskningsprogram
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-70969 (URN)10.1088/1755-1315/240/2/022028 (DOI)2-s2.0-85063871783 (Scopus ID)
Konferanse
29th IAHR Symposium on Hydraulic Machinery and Systems, Kyoto, Japan, 17-21 September, 2018
Tilgjengelig fra: 2018-09-25 Laget: 2018-09-25 Sist oppdatert: 2019-05-03bibliografisk kontrollert
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.
Åpne denne publikasjonen i ny fane eller vindu >>Fluid added polar inertia and damping for the torsional vibration of a Kaplan turbine model runner considering multiple perturbations
2019 (engelsk)Inngår i: IOP Conference Series: Earth and Environmental Science, Institute of Physics (IOP), 2019, Vol. 240, artikkel-id 062007Konferansepaper, Publicerat paper (Fagfellevurdert)
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.

sted, utgiver, år, opplag, sider
Institute of Physics (IOP), 2019
HSV kategori
Forskningsprogram
Strömningslära; Datorstödd maskinkonstruktion
Identifikatorer
urn:nbn:se:ltu:diva-72503 (URN)10.1088/1755-1315/240/6/062007 (DOI)2-s2.0-85063961671 (Scopus ID)
Konferanse
29th IAHR Symposium on Hydraulic Machinery and Systems, 17-21 September 2018, Kyoto, Japan.
Tilgjengelig fra: 2019-01-09 Laget: 2019-01-09 Sist oppdatert: 2019-06-26bibliografisk kontrollert
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.
Åpne denne publikasjonen i ny fane eller vindu >>Formation of Rotating Vortex Rope in the Francis-99 Draft Tube
2019 (engelsk)Inngår i: IOP Conference Series: Earth and Environment, Institute of Physics (IOP), 2019, Vol. 240, artikkel-id 022017Konferansepaper, Publicerat paper (Fagfellevurdert)
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.

sted, utgiver, år, opplag, sider
Institute of Physics (IOP), 2019
HSV kategori
Forskningsprogram
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-70968 (URN)10.1088/1755-1315/240/2/022017 (DOI)2-s2.0-85063905433 (Scopus ID)
Konferanse
29th IAHR Symposium on Hydraulic Machinery and Systems, Kyoto, Japan, 17-21 September, 2018
Tilgjengelig fra: 2018-09-25 Laget: 2018-09-25 Sist oppdatert: 2019-05-03bibliografisk kontrollert
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.
Åpne denne publikasjonen i ny fane eller vindu >>Improved frictional modeling for the pressure-time method
2019 (engelsk)Inngår i: Flow Measurement and Instrumentation, ISSN 0955-5986, E-ISSN 1873-6998, Vol. 69, artikkel-id 101604Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
Elsevier, 2019
Emneord
Pressure-time method, Transient friction modeling, Pipe flow
HSV kategori
Forskningsprogram
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-75599 (URN)10.1016/j.flowmeasinst.2019.101604 (DOI)2-s2.0-85070506497 (Scopus ID)
Merknad

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

Tilgjengelig fra: 2019-08-20 Laget: 2019-08-20 Sist oppdatert: 2019-08-20bibliografisk kontrollert
Sundström, J., Saemi, S., Raisee, M. & Cervantes, M. (2019). Improved frictional modelling for the pressure-time method. Flow measurement and instrumentation
Åpne denne publikasjonen i ny fane eller vindu >>Improved frictional modelling for the pressure-time method
2019 (engelsk)Inngår i: Flow measurement and instrumentationArtikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
Elsevier, 2019
HSV kategori
Forskningsprogram
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-71998 (URN)
Tilgjengelig fra: 2018-12-11 Laget: 2018-12-11 Sist oppdatert: 2019-04-16
Iovanel, R. G., Bucur, D. M., Dunca, G. & Cervantes, M. (2019). Numerical analysis of a Kaplan turbine model during transient operation. 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 022046.
Åpne denne publikasjonen i ny fane eller vindu >>Numerical analysis of a Kaplan turbine model during transient operation
2019 (engelsk)Inngår i: IOP Conference Series: Earth and Environmental Science, Institute of Physics (IOP), 2019, Vol. 240, artikkel-id 022046Konferansepaper, Publicerat paper (Fagfellevurdert)
Abstract [en]

Hydropower plants are currently being intensively employed for electrical grid regulation. As a consequence, the frequency of start/stops and load variations is considerably increasing, leading to the operation of hydraulic turbines under improper conditions. During the last years, studies have focused on Francis turbines. The present paper aims to investigate a Kaplan turbine model. The flow through the turbine is modelled during transient operation, from the best efficiency point to a part load operating point, using a moving mesh for the guide vane displacement. The simulations are validated against experimental velocity profiles. A time step sensitivity analysis is performed in order to determine the optimum discretization time. The possibility of using large time steps is explored. The numerically simulated unsteady pressure pulsations on the runner blades are analysed. The influence of the inlet boundary conditions on the accuracy of numerical simulations is studied. The results show that a linear flow rate variation defined during the guide vane closure leads to an overestimation of the turbine head compared to the experimental value due to an overestimation of losses. The second type of boundary conditions, a constant total pressure, results in an underestimation of the flow rate compared to the experimental value due again to an overestimation of the losses.

sted, utgiver, år, opplag, sider
Institute of Physics (IOP), 2019
HSV kategori
Forskningsprogram
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-73589 (URN)10.1088/1755-1315/240/2/022046 (DOI)2-s2.0-85063861550 (Scopus ID)
Konferanse
29th IAHR Symposium on Hydraulic Machinery and Systems 17–21 September 2018, Kyoto, Japan
Tilgjengelig fra: 2019-04-11 Laget: 2019-04-11 Sist oppdatert: 2019-05-03bibliografisk kontrollert
Maddahian, R., Cervantes, M. & Bucur, D. M. (2019). Numerical investigation of entrapped air pockets on pressure surges and flow structure in a pipe. Journal of Hydraulic Research
Åpne denne publikasjonen i ny fane eller vindu >>Numerical investigation of entrapped air pockets on pressure surges and flow structure in a pipe
2019 (engelsk)Inngår i: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079Artikkel i tidsskrift (Fagfellevurdert) Epub ahead of print
Abstract [en]

This research presents a numerical investigation of two-phase flow during the expulsion of entrapped air in a non-confined pipe. A modified version of the volume of fluid (VOF) approach is employed considering the effect of compressibility in the liquid. A modification is introduced to the original approach relating the density changes in the liquid to the pressure changes using the fluid bulk modulus. The bulk modulus is also modified to consider the pipe elasticity, the air bubble entrainment and the two-phase flow regime in a pipe. Fluid–structure interaction (FSI) code is developed and used to calculate the motion of the downstream orifice wall during the impact of the water column on the pipe end wall. The numerical results of the pressure variation agree well with experimental data. The two-phase flow structure and physics behind the pressure waves are investigated. The numerical results show that to capture the amplitude and time interval of the pressure surges, the effect of FSI should be considered during the expulsion of the entrapped air. Additionally, the effects of initial air pocket size, supply pressure and orifice size on the pressure increase are investigated. The developed VOF-FSI approach can be employed as a numerical tool to investigate the transient flow during pipe filling.

sted, utgiver, år, opplag, sider
Taylor & Francis, 2019
Emneord
Computational fluid dynamics, entrapped air pocket, fluid–structure interaction, pressure surge, volume of fluid (VOF)
HSV kategori
Forskningsprogram
Strömningslära
Identifikatorer
urn:nbn:se:ltu:diva-74904 (URN)10.1080/00221686.2019.1579112 (DOI)000470385600001 ()2-s2.0-85065166801 (Scopus ID)
Tilgjengelig fra: 2019-06-24 Laget: 2019-06-24 Sist oppdatert: 2019-06-25
Organisasjoner
Identifikatorer
ORCID-id: ORCID iD iconorcid.org/0000-0001-7599-0895