Origins and Structure of Spike-Type Rotating Stall

Abstract

In this paper we describe the structures that produce a spike-type route to rotating stall and explain the physical mechanism for their formation. The descriptions and explanations are based on numerical simulations, complemented and corroborated by experiments. It is found that spikes are caused by a loss of pressure rise capability in the rotor tip region, due to flow separation resulting from high incidence. The separation gives rise to shedding of vorticity from the leading edge and the consequent formation of vortices that span between the suction surface and the casing. As seen in the rotor frame of reference, near the casing the vortex convects toward the pressure surface of the adjacent blade. The approach of the vortex to the adjacent blade triggers a separation on that blade so the structure propagates. The above sequence of events constitutes a spike. The simulations show shed vortices over a range of tip clearances including zero. The implication is that they are not part of the tip clearance vortex, in accord with recent experimental findings. Evidence is presented for the existence of these vortex structures immediately prior to spike-type stall and, more strongly, for their causal connection with spike-type stall inception. Data from several compressors are shown to reproduce the pressure and velocity signature of the spike-type stall inception seen in the simulations.

Computational fluid dynamics simulations of blade damage effect on the performance of a transonic axial compressor near stall

“…The interface between the streamwise inflow and with tip clearance flow is aligned with the leading edge plane. This is consistent with the explanation [24] and also recently confirmed by Weichert et al [25] and Pullan et al [26]. The similarity predicted in this study is due to the design of this rotor, some blades encounter higher incidence beyond the critical value near the tip region which leads to separations from the suction side.…”

“…[ 26], who predicted a radial vortex starting from the blade's leading edge at the suction side which could be due to the different compressor blade design used in their analysis where the blades have lower hub to tip ratio and thus rotor blades have much less twist near the tip than Rotor 37. are not shown here to avoid repetition. it showed that the non-rotating stall cell was caused by the damaged blade because the flow was always diverted by the damage feature at the leading edge.…”

Observations on Rotating Instabilities and Spike Type Stall Inception in a High-Speed Multistage Compressor

“…Recent numerical and experimental works converge towards explaining the typical increase and decrease in wall pressure by a vortex structure forming at the leading edge of the rotor blade and spanning to the casing ("tornado vortex"). Inoue et al [3] identified this numerically at first, and recent numerical and experimental works by Pullan et al [4] support those results. In high-speed compressors, the spike type structure evolves very quickly (a few rotor revolutions) into a rotating stall cell.…”

“…At 100% shaft speed, the typical increase and decrease related to a spike type perturbation are found [4]. The increase and decrease of the static pressure extend each over four rotor blade passing instances (not detailed here).…”

Observations of the Growth and Decay of Stall Cells during Stall and Surge in an Axial Compressor

“…At approximately revolution 0, a single stall cell or spike begins to form and rotate around the annulus. A static pressure rise occurs upstream of the blade row similar to Pullan et al [18], which extends over the span of multiple blade passages. Initially, the trailing edge of the stall cell rotates at a rate of 0.71N and slows down in the laboratory frame as the stall cell increased in circumferential size.…”