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 separation at the leading edge due to 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 computed structure of the spike is shown to be consistent with rotor leading edge pressure measurements from the casing of several compressors: the centre of the vortex is responsible for a pressure drop and the partially blocked passages associated with leading edge separations produce a pressure rise. The simulations show leading edge separation and shed vortices over a range of tip clearances including zero. The implication, in accord with recent experimental findings, is that they are not part of the tip clearance vortex. Although the computations always show high incidence to be the cause of the spike, the conditions that give rise to this incidence (e.g., blockage from a corner separation or the tip leakage jet from the adjacent blade) do depend on the details of the compressor.

Physics of Prestall Propagating Disturbances in Axial Compressors and Their Potential as a Stall Warning Indicator

“…However, in contrast to the findings of Pullan et al (2015) [20], the localised disturbance does not evolve into a stall cell after a few rotor revolutions. In the presented case, discrete vortex structures remain unchanged when the through-flow is constant-they represent indeed a kind of flow non-uniformity but they are not responsible for flow separation or part span stall.…”

“…Rotation of the vortex tube is indicated by white and black arrows. In general, the coherent flow topology strongly resembles a classical spike formation known from spike stall inception mechanisms [20]. A similar flow topology was also addressed by Inoue et al (2001) [21] who described the occurrence of short length-scale stall cells when the compressor is operating in a mild stall condition.…”

PIV measurements of the transient flow structure in the tip region of a transonic compressor near stability limit

“…When impinging on the leading edge, the vortex causes significant variations in Once the described pattern has established, it is self-sustaining and travels around the circumference, as depicted in Figure 12. This agrees with the system described by Inoue et al (2000), and was recently documented by Pullan et al (2015) for a subsonic compressor. The measurements cannot be used to determine whether the tip leakage vortex is part of the shed radial vortices or remains attached to the blade.…”

“…The vortices may be the initiator of a spike (Camp and Day, 1998), i.e., a short-length scale disturbance with high circumferential velocity (>70% rotor speed depending on the setup), developing into a rotating stall cell. The shape of the structures is described as a tornado-like vortex, with one end attached to the rotor blade and the other bound to the casing and traveling towards the adjacent blade (Inoue et al, 2000;Pullan et al, 2015).…”

Numerical Investigation for the Impact of Single Groove on the Stall Margin Improvement and the Unsteadiness of Tip Leakage Flow in a Counter-Rotating Axial Flow Compressor

“…Up to now, much effort has been made to reveal the nature of TLF and researchers have made noteworthy progress on the potential relation between the stall inception and the unsteady phenomena in the tip region [3][4][5][6][7][8][9][10][11][12]. It has been found that the TLF could become unsteady at high loading operating conditions and the tip leakage vortex plays an important role in the stall inception process.…”