An Explanation for Flow Features of Spike-Type Stall Inception in an Axial Compressor Rotor

Abstract

The unsteady behavior and three-dimensional flow structure of spike-type stall inception in an axial compressor rotor were investigated by experimental and numerical analyses. Previous studies revealed that the test compressor falls into a mild stall after emergence of a spike, in which multiple stall cells, each consisting of a tornado-like vortex, are rotating. However, the flow mechanism from the spike onset to the mild stall remains unexplained. The purpose of this study is to describe the flow mechanism of a spike stall inception in a compressor. In order to capture the transient phenomena of spike-type stall inception experimentally, an instantaneous casing pressure field measurement technique was developed, in which 30 pressure transducers measure an instantaneous casing pressure distribution inside the passage for one blade pitch at a rate of 25 samplings per blade passing period. This technique was applied to obtain the unsteady and transient pressure fields on the casing wall during the inception process of the spike stall. In addition, the details of the three-dimensional flow structure at the spike stall inception were analyzed by a numerical approach using the detached-eddy simulation (DES). The instantaneous casing pressure field measurement results at the stall inception show that a low-pressure region starts traveling near the leading edge in the circumferential direction just after the spiky wave was detected in the casing wall pressure trace measured near the rotor leading edge. The DES results reveal the vortical flow structure behind the low-pressure region on the casing wall at the stall inception, showing that the lowpressure region is caused by a tornado-like separation vortex resulting from a leadingedge separation near the rotor tip. A leading-edge separation occurs near the tip at the onset of the spike stall and grows to form the tornado-like vortex connecting the blade suction surface and the casing wall. The casing-side leg of the tornado-like vortex generating the low-pressure region circumferentially moves around the leading-edge line. When the vortex grows large enough to interact with the leading edge of the next blade, the leading-edge separation begins to propagate, and then the compressor falls into a stall with decreasing performance.

Experimental Study of Surge and Rotating Stall Occurring in High-speed Multistage Axial Compressor

“…In Ref. [6], the same result can be drawn with circumferential located pressures of spike-type stall precursors. In Ref.…”

Inception mechanism and suppression of rotating stall in an axial-flow fan

“…Vo et al [5] suggested two criteria necessary for spike-type stall-inception. Yamada et al [6] also suggested that leading edge separation and a tornado-like separation vortex mainly influenced the spike-type stall inception. März et al [4] found that the rotating instability was induced by the interaction between the incoming flow, the reversed tip-leakage flow, and the end wall backflow from the trailing edge of the rotor blade.…”

Stall inception and control in a transonic fan, part A: Rotating stall inception

“…In the experimental and numerical work of Yamada et al [22], the low-pressure region near the casing wall during stall inception was concluded to be caused by a tornado-like separation vortex resulting from a leading-edge separation from the suction surface at the rotor tip.…”