Stability Improvement Of A Turbocharger Centrifugal Compressor By Tip Leakage Control

Turbochargers are widely used in the automotive industry in order to improve the performance of the engine by means of feeding high pressure inlet air into the cylinders.However,the centrifugal compressors used in turbo chargers have their limitations(i.e.Surge/stall line).Different flows generate instabilities in the flow field of the centrifugal compressor;among these,tip leakage flow is of great importance.The occurrence of surge/stall in a centrifugal compressor and the role of the tip clearance flow on the occurring instabilities in the centrifugal compressor is investigated in this study.A computational method is used in order to study the flow field in the centrifugal compressor in order to gain a better understanding of the surge/stall mechanism.It is found that at near surge/stall condition,the tip leakage flow at leading edge deflects more upstream,as the deflection gets more severe spillage happens which finally leads to the instability of the compressor.Once a thorough understanding of the surge/stall mechanism in the compressor and the role of tip clearance flow in the instabilities is achieved,a ring air jet injection is used in order to eliminate the instabilities and extend the stable flow range of the compressor.Using air jet injection,the stable flow range of the compressor was successfully increased with little drop in the efficiency of the compressor.The effect of different air jet injection parameters such as mass flow,yaw angle,injection angle,slot width and slot distance on the compressor flow field is studied and an optimum design for the air jet injection is developed.Further investigation of the compressor with optimum air jet injection configuration shows that the at near surge/stall conditions,the tip leakage at leading edge is still under control,manifesting a much smaller spillage in comparison with the datum compressor without air jet injection.The dominant factor for the instability of the compressor with injection is found to be the leading edge separation rather than the tip leakage.The effect of the injection on the compressor performance is also investigated in different rotational speeds and the results illustrate that the as the rotational speed decreases the air jet injection becomes a more viable choice for stabilizing the centrifugal compressor flow field.