ABSTRACT
A turbocharger when operating at low speed and high load has a limitation given by compressor, due to surge [1–8]. The surge limit of the turbocharger compressor will limit the minimum flow at which the engine can operate [1,6–8]; therefore, compressor surge margin is a significant constraint at low-end torque operating area of the engine, corresponding to full load at very low engine speed. This paper presents a novel turbo-compressor inlet shroud treatment for surge limit enhancement. This innovative shroud design aims to “accommodate” the flow when flow-separation happens by re-conducting the reverse flow back to inflow direction by means of the presence of an annular cavity in the vicinity of the compressor impeller tip. Numerical results obtained from the initial computational assessment of this concept suggest that the axial flow distortion, commonly encountered when compressor stalls, is retarded by the presence of the annular cavity, which “corrects” the flow direction, and thus retarding stall propagation when operating at low flow rates, near surge.
Furthermore, an experimental campaign was carried out at Imperial College London experimental facilities to proof the feasibility of the presented shroud treatment on a turbocharger centrifugal compressor for automotive application. Experimental results suggest that the presence of a cavity at compressor inlet facilitates the re-entering of flow reversal at compressor inlet when compared to equivalent traditional compressor shroud design.
