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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.

Abstract The effect of the cone tip-diameter on the flow field and performance of cyclone separator was investigated computationally and via mathematical models. Three cyclones with different cone tip diameters were studied using large eddy simulation (LES). The cyclone flow field pattern has been simulated and analyzed with the aid of velocity components and static pressure contour plots. In addition the cyclone collection efficiency based on one-way discrete phase modeling has been investigated. The results obtained demonstrate that LES is a suitable approach for modeling the effect of cyclone dimensions on the flow field and performance. The cone tip-diameter has an insignificant effect on the collection efficiency (the cut-off diameter) and the pressure drop. The simulation results agree well with the published experimental results and the mathematical models trend.