THE INTERACTION BETWEEN INLET GUIDE VANES AND THE IMPELLER RECIRCULATING FLOW IN A CENTRIFUGAL COMPRESSOR AND THE RESULTING IMPACT ON FLOW RANGE

This paper studies the interaction between the Inlet Guide Vane (IGV) and the typical recirculation flow that occurs close to surge in a turbocharger compressor to analyse its influence on compressor performance the potential to improve the surge margin. The CFD method was first validated by experimental data, then a series of simulations were conducted to study the lengths of various part-span IGVs and also the streamwise distance between the IGV and the impeller. The results showed that, when extensive recirculating flow was generated, the IGV no longer worked in a conventional way to guide the inflow in the tip region, but instead guided the recirculation flow ejected from the impeller inducer. A three-dimensional interaction occurred at the trailing edge of the IGV where the recirculation flow turned downwards along the span of the vane and caused blockage and swirling flow below the bottom of the part span IGV. All the cases with IGVs had a similar peak efficiency to the baseline compressor but produced different impacts on the mass flow rates at the near surge point and the choke point. The IGV with shortest length placed the three-dimensional recirculating flow at a higher span-wise position. The blockage and the pre-swirl were thereby generated closer to the shroud and produced a different flow field at the impeller inlet. Based on the numerical surge criteria, the shortest IGV was found to improve stability at the near surge point compared to the full-span IGV, with no reduction of the mass flow rate at the choke point to give 25% more flow range. The surge margin was mainly increased because of the improved pressure recovery in the diffuser due to the blockage being distributed in the higher-span region of the impeller inflow. The beneficial impact of the three-dimensional interaction on the flow range was found to be associated with the distance between the impeller and the IGV. Both the short and the full-span IGVs achieved less improvement of surge margin when the IGV was placed further upstream of the impeller, showing that the interaction between the reverse flow and the IGV was a beneficial flow feature for overall performance.