Modeling the Cooling Air Flow in an Electric Generator 6 th OpenFOAMworkshop Pirooz Moradnia, Håkan Nilsson PennState University, USA 2011-06-14 Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 1
Importance of cooling in generators Hydroelectric power generation: 50% of the electricity generation in Sweden Modifications to the existing units significant contributions to the total energy production Increased power output more heat generation Thetwolargesourcesofenergylossesinthegenerators: - Thermal: electric resistance in the generator coils - Ventilation: when cooling down the unit Thestatorsshouldbecooledbyairflowingthroughthestatorairchannels Axially cooled generators Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 2
Experimental test rig A small generator at Uppsala University, Sweden 4coolingchannelrows 108coolingchannelsineachrow - Some channels impossible to access Stator outer casing with 12 openings - 5 openings almost completely blocked 12poles Rotational speed: 500 rpm Innerradiusofthestator:0.365m Outerradiusofthestator:0.437m Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 3
Modelling in OpenFOAM Geometry: -Aperiodic1/12sector - Generated with blockmesh - Less air blockage than the experimental rig Boundaries: -Noin/outlet Noprescribedmassflow - Extra space for the air recirculation -Massflowgivenbythesolution Solver - OpenFOAM 1.5.x - MRFSimpleFoam(frozenrotorconcept) - LaunderSharmaKE turbulence model - Y + < 10 Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 4
Complete generator model Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 5
Stator cooling channels Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 6
Study of the flow properties Inlet flow pattern Smoke visualization vs. Steady computations Inlet velocity profiles Traverse system, total pressure tube vs. Steady computations Outlet velocity profiles Total pressure rake vs. Steady computations Volumeflow In/outlet measurements vs. Steady computations Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 7
Inlet flow pattern Smoke pen Schematic flow pattern, Experiment Unit vectors of the flow, OpenFOAM Remarks: Radially inward flow near the horizontal stator baffle Gradual growth of the axial velocity component farther from the baffle Purelyaxialvelocityclosetotherotorrings Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 8
Inlet velocity profiles Location of the inlet, Experiment & OpenFOAM Comparison of the velocity Profiles Remarks Heightoftheprofiles: -Experiment29mm(duetotheangleofattack) -OpenFOAM38mm Same behaviour in the experiments and OpenFOAM Difference in the magnitudes: - Less air blockage in OpenFOAM Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 9
Outlet velocity profiles Channel outlets, Experiment Available channels Location of the rake in the channels Outlet velocity profiles Remarks 5(outof9)channelsperrowavailableformeasurements Same behaviour in the experiments and OpenFOAM Difference in the magnitudes: - Less air blockage in OpenFOAM - Non-periodicity in the experimental rig(scattered experimental data) Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 10
Volume flow Experiment: 0.09m 3 /s OpenFOAM: 0.16m 3 /s 43% difference Less air blockage in OpenFOAM Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 11
Conclusions Non-periodicity in experiments: -Thelargestsourceoferror Less air blockage in OpenFOAM: - More qualitative comparison Flow behaviours predicted by OpenFOAM: - Close to the experimental results Better quantitative comparison: - Unsteady simulations - Exact geometrical similarity Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 12
Thank you! Acknowledgements The work has been financed by SVC(www.svc.nu): SwedishEnergyAgency,ELFORSK,SvenskaKraftnät, 1 Chalmers, LTU, KTH, UU SNIC(Swedish National Infrastructure for Computing) and C3SE(Chalmers Centre for Computational Science and Engineering) have provided the computational resources. 1 Companiesinvolved: CarlBro,E.ONVattenkraftSverige,FortumGeneration,Jämtkraft,JönköpingEnergi,Mälarenergi,SkellefteåKraft,Sollefteåforsens, Statoil Lubricants, Sweco VBB, Sweco Energuide, SweMin, Tekniska Verken i Linköping, Vattenfall Research and Development, Vattenfall Vattenkraft, VG Power, Öresundskraft, Waplans and Andritz Inepar Hydro Pirooz Moradnia, Chalmers/ Applied Mechanics/ Fluid Dynamics 13