URANS analysis of the effect of realistic inlet distortions on the stall inception of a centrifugal compressor

Abstract

In this paper unsteady RANS computations are used to study the inception of rotating stall in a transonic centrifugal compressor taking into account realistic installation effects on performance, as commonly found nowadays due to space limitations. To this end, the effect of an ideal uniform inlet conditions (normally found for long straight inlet) is compared with inlet distortions generated by a bent pipe installed just in front of the impeller.The numerical techniques that have to be applied to correctly represent the rotating stall are explained in detail: all simulations are done modeling the whole annulus of the radial machine, using high performance computing to represent the non-periodic phenomena leading to the stall inception. Moreover, stable boundary conditions are employed, with the aim to avoid the inception of large unphysical surge cycles.When an uniform inlet flow to the compressor is considered, the formation of 8 blockage cells rotating in the same direction of the compressor is pointed out. On the other hand, when the elbow is installed in front of the impeller, the distorted flow suppresses the formation of a rotating stall pattern.