Investigation of Flow Field at the Inlet of a Turbocharger Compressor Using Digital Particle Image Velocimetry

The flow field at the inlet of a turbocharger compressor has been studied through stereoscopic particle image velocimetry (SPIV) experiments under different operating conditions. It is found that the flow field is quite uniform at high mass flow rates; but as the mass flow rate is reduced, flow reversal from the impeller is observed as an annular ring at the periphery of the inlet duct. The inception of flow reversal is observed to occur in the mid-flow operating region, near peak efficiency, and corresponds to an incidence angle of about 15.5 deg at the inducer blade tips at all tested speeds. This reversed flow region is marked with high tangential velocity and rapid fluctuations. It grows in strength with reducing mass flow rate and imparts some of its angular momentum to the forward flow due to mixing. The penetration depth of the reversed flow upstream from the inducer plane is found to increase quadratically with decreasing flow rate.