Numerical Study On Influence Of Tip Clearance Parameters On Aerodynamic Performance Of Unshroud Centrifugal Impeller

Centrifugal compressor is a kind of turbomachinery widely used in turbochargers and turbine engines for the advantage of high efficiency,high velocity and wide operating range.As one of the main working parts in centrifugal compressor,the aerodynamic performance of centrifugal impeller decides the efficiency of centrifugal compressor.With advantages of high pressure ratio and circumference velocity,centrifugal impeller,especially unshroud impeller,has been the focus of research.However,the tip clearance will lead to the interaction of tip leakage flow with secondary flow and boundary layer flow,and finally result in leakage flow loss.To understand the internal flow field in impeller and the tip clearance effects on the aerodynamic performance,simulation method is applied to analysis impeller performance parameters such as efficiency,pressure ratio,,tip leakage,static pressure and entropy production of different impellers with varied tip clearance.By numerical simulation and analysis of impeller with different blade loading distribution,it is found that the location of blade loading does not affect the impeller efficiency and the pressure ratio of shrouded impeller;For unshrouded impeller,the influence of tip clearance on impeller aerodynamic performance is related to the distribution of blade loading,when it locates in the forward of impeller,the performance is affected by the change of tip clearance at low level.By comparing impeller with constant tip clearance with impeller whose tip clearance changes along the streamwise,it is found that tip clearance besides trilling edge makes more contribution to performance of impeller,it means that little tip clearance carries little flow loss.By numerical simulation and analysis of impeller with different lean angles,it is found that lean angle has little influence on impeller performance in boss design and low flow condition.The lean angle has a major effect on the latter half flow channel of impeller,no matter the lean angel increases or decreases,the decline rate of tip leakage and blade loading will let down.The total tip leakage increases when lean angle decreases,vise versa.In high flow condition,change the lean angle will improve the flow condition beside trilling edge and improve impeller performance.