Turbocharger has experienced a prompt expansion in vehicle industry in recent years, because it enables downsizing of internal combustion engines (ICEs) so as to cutting down CO2 emissions. Turbocharger turbine efficiency is vital for the performance and emission of ICEs. Conventionally, turbines are designed and optimized under steady and uniform inflow conditions, but they are always fed with pulsating and swirling inflow on ICEs. Understanding turbine behaviors under enginelike unsteady swirling inflow conditions is significant to improve turbine on-engine performance.

The purpose of the present study is to examine and compare the unsteady and steady swirling inflow effect on turbocharger turbine performance. The investigation reveals that the turbine suffers substantial efficiency reductions under swirling inflow conditions, no matter under unsteady or steady state, and the efficiency reductions are related with the intensity of inlet swirls. The unsteady and steady swirling inflow leads to reductions in both the absolute and relative flow angles. The swirling inflow results in different effect on turbine performance under unsteady state from steady state. Time lags exist between the unsteady swirling inflow affect the turbine performance. Besides, unsteady swirling inflow effect lead to fluctuations of turbine performance parameters, which discloses a coupled effect of the unsteady and swirling inflow. The unsteady effect and the swirling inflow effect do not simply superpose with each other, but have complicated interactions with each other. Both pulsating and swirling inflow can lead to circumferential flow distortions at rotor inlet by themselves, and when turbine is fed with both pulsatile and swirling inflow together the circumferential flow distortion would be result of their synergetic effect.

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