Numerical investigation of inlet distortion on the stall inception of a radial compressor

In this paper unsteady CFD computations are used to study the stability and the rotating stall inception of a transonic radial compressor, considering two different configurations influencing the inlet flow. The prediction of the surge and stall limit for a centrifugal compressor is a key parameter for operating such machines, and hence requires attention already in the early design phase. Moreover, the operating margin can be dramatically influenced by non-uniform inlet conditions due to for example bended pipes mounted close to the inlet, as found more often today due to space limitation and optimization. In this case, it is not trivial to understand how the performance of the machine will be affected. The influence on the stability limit of an elbow installed in front of the compressor inlet is analyzed in this paper by means of unsteady RANS simulations: results for two different configurations, with elbow and with straight inlet placed in front of the compressor, are compared. All simulations are done modeling the whole annulus of the radial machine, using high performance computing, in order to accurately take into account the non-periodic phenomena leading to stall inception. Moreover, mechanisms leading to flow separation for unstable solutions are studied, pointing out how they are influenced by the unsteady interactions of the tip leakage vortices with the main flow and by the distorted flow from the inlet elbow.