Centrifugal compressors for turbochargers are affected by pressure pulsations, generated by the engine valvetrain. It results in a hysteresis loop on a compressor performance map, and the time-averaged performance deviates from the one in constant pressure condition. Since regulations of greenhouse gas emissions are tightening, achieving higher turbocharger efficiency in real-operating conditions is essential. Therefore, understanding of loss mechanisms in pulsating pressure conditions is crucial.

A high number of studies far have contributed to revealing the effects of pulsation on compressor performance. However, numerical investigations of unsteady flow structure in a volute are still lacking, and there are only some validated examples by measurement.

This paper presents a comprehensive experimental and numerical study that sheds light on the pulsating flow field in the volute. An instantaneous and time-averaged pressure signal inside a volute has been captured by measurement. A numerical simulation with Unsteady Reynolds Averaged Navier-Stokes equations has been carried out. Pressure distributions from the simulated results has shown good consistency with experimental results.

Leading off from the validated simulation results, the instantaneous velocity distribution and energy loss profile have been obtained. It can be seen that the flow direction is switched around the volute tongue when the volume flow rate reaches the maximum value. This phenomenon leads to different flow patterns depending on whether the flow rate increases or decreases. When the volume flow rate turns to decrease from the maximum value, the switched flow direction leads a leak flow from the tongue to the volute exit. The total pressure of this flow significantly decreases when it passes the tongue, and it finally appears as the low-energy fluid at the volute exit. It causes a notable blockage, and consequently leads to an additional friction loss. Due to these effects, the energy loss of volute increases from the steady flow condition.

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