Simulation Study On The Windage Loss Of Turbomachinery Rotor In Carbon Dioxide Working Fluid

In this study,for the medium-pressure carbon dioxide working fluid,computational fluid dynamics(CFD)simulation methods were used to analyze the effects of physical properties,geometrical parameters,and axial flow on flow fields and the windage loss.For the windage loss,this research conducted extensive investigations.The Reynolds stress model was selected for simulation calculation.The simulation values were compared with the Bilgen-Boulos windage loss relationship and experimental values to verify the simulation method for the windage loss.According to the simulation results,under constant physical conditions without axial flow,the windage loss decreases with the increase of temperature of the working fluid,and increases with the increase of pressure and the rotation speed of the rotor.In the above cases,Bilgen&Boulos windage loss relationship can provide accurate predictions.But when the chamber width exceeds the prediction range,the prediction accuracy decreases.The surface roughness and axial flow make the windage loss significantly increase.However,the above factors are not considered in the Bilgen&Boulos relationship.For the above two cases,based on the simulation results,this research proposed correction coefficient relationships to modify the Bilgen&Boulos windage relationship.The calculation values of the relationship were compared with the simulation values to verify the accuracy of the relationship.The relative error does not exceed ±10%.In the study,the viscous heating process was also introduced to simulate the temperature change in the chamber caused by the windage loss.The research simulation results showed that the windage loss will cause the working fluid temperature increases linearly in the axial direction.The temperature difference between inlet and outlet decreases with the increase of axial flow velocity.The stress analysis of these conditions showed that the deformation due to the windage loss is gradually increased in the axial direction and uniformly distributed in the radial direction.The stress value of the rotor is less than the allowable shear stress of the rotor material,so it can operate safely under medium pressure carbon dioxide working fluid.This study can provide a reference for windage loss prediction of turbomachinery operating under medium pressure carbon dioxide working fluid.