Experimental Verification of Dimensional Analysis Results on Flow Distribution and Pressure Drop for Disc-Type Windings in OD Cooling Modes

Abstract

Oil-flow distribution in the winding has a direct impact on cooling performance. In addition, static pressure drop over the winding determines oil split among windings connected hydraulically in parallel. In this paper, experimental verifications are provided to support computational fluid dynamics (CFD) simulations for disc-type windings in oil-forced and directed (OD) cooling modes. Oil-flow distribution in and pressure drop over disc-type winding models are measured using a particle image velocimetry system and a differential pressure instrument, respectively. Dimensional analysis is adopted to analyze the relationship between flow distribution, or pressure drop, and the controlling parameters. CFD parametric sweeps of the dimensionless parameters obtained from the dimensional analysis are conducted and the CFD results are then correlated with the dimensionless parameters. The comparisons between measured results and corresponding results obtained from the correlations demonstrate constant consistency, proving the validity of both the method of dimensional analysis and the correlations. Finally, comparisons of experimental results from isothermal and nonisothermal conditions in OD cooling modes are executed, which show that the isothermal conclusions can be extended to nonisothermal cases because the effects of buoyancy force and hot-streak dynamics prove to be negligible.