Investigation of Passage Flow Features in a Transonic Compressor Rotor With Casing Treatments

Abstract

An experimental investigation on casing treatments in a one-stage transonic compressor is presented. The reference case consists of a radially staggered blisk and six circumferential grooves. Speedlines show that this axisymmetric treatment already provided a substantial increase in operating range with relatively small losses in efficiency. Since the onset of rotating stall in tip-critical high-speed compressors is always linked to the tip-leakage flow and the build-up of blockage within the blade passage. High-resolution measurement techniques have been employed to investigate the corresponding effects. Results with Particle Image Velocimetry show that the interaction between the tip leakage vortex and the shock front cause a blockage area. When throttled further, the blockage increases. The shock structure changes similar to the phenomena of vortex breakdown described by different researchers in the past, but a stagnation point is not present. Before reaching the stability limit, the interface line between the incoming flow and the blocked area moves towards the inlet plane of the rotor indicating spike-type stall inception. Wall pressure measurements confirmed this theory for the smooth wall, but with circumferential grooves applied, a part span stall cell develops prior to the stability limit. In order to assess the performance of circumferential grooves, two additional configurations are presented. The corresponding measurements addressed the questions whether circumferential grooves also provide an operating range extension when applied to an optimized rotor design with higher initial stall margin. Therefore, an identical casing treatment is applied to a forward swept rotor. The second question is, how circumferential grooves perform in direct comparison to a non-axisymmetric endwall structure. Axial slots have been applied to the radially staggered rotor. While the stall margin exceeds all other configurations, detrimential effects in efficiency are observed. A detailed anaylsis of probe data shows the changes of the radial profile at the rotor outlet which allows recommendations for more efficient CT designs. Parameters allowing to evaluate the CT influence are presented.

Stall inception and warning in a single-stage transonic axial compressor with axial skewed slot casing treatment

“…Lim [15] showed that an axial skewed slot had the limitation of stall margin improvement when used in a subsonic axial compressor that exhibited modal-type stall inception. A study by Müller et al [16] showed that although the inception of a typical spike-type stall occurred in the smooth casing of a single-stage transonic axial compressor, a part-span stall gradually developed into a full-span stall when circumferential grooves were employed. Their results also show that the mode-type phenomenon did not take place before the stall occurrence.…”

Study of Convective Flow Effects in Endwall Casing Treatments in Transonic Compressor Rotors

“…Many studies to investigate casing treatments in compressors have been reported (Moore et al [1971], Prince et al [1974], Paulon and Dehoudt [1982], Smith and Cumpsty [1985], Fujita and Takata [1985], Lee and Greitzer [1990], Crook et al [1993], Hall et al [1996], Rabe and Hah [2002], Shabbir and Adamczyk [2004], Chen et al [2010], and Mueller et al [2011]). Paulon and Dehoudt [1982] conducted a theoretical investigation of the effects of circumferential-groove casing treatments.…”

“…Mueller et al [2007] investigated various circumferential grooves applied to the rotor in a single-stage transonic compressor. Particle Imaging Velocimetry (PIV) was applied to measure the detailed steady flow field near and inside circumferential grooves in an axial transonic compressor stage by Mueller et al [2011].…”

Toward Optimum Configuration of Circumferential Groove Casing Treatment in Transonic Compressor Rotors

“…A variety of casing treatments have been applied to extend the operating range of various compressors (Smith and Cumpsty [1985], Lee and Greitzer [1990], Moore et al [1971], Prince et al [1974], Fujita and Takata [1985], Paulon and Dehoudt [1982], Van de Wyer et al [2010], Chen et al [2010], and Mueller et al [2011]). Most previous experimental studies indicate that casing treatments, which are more effective in delaying stall, tend to induce additional aerodynamic loss at peak efficiency conditions.…”

“…Most of the previous studies were aimed at obtaining changes in the overall compressor performance data. Mueller et al [2011] applied Particle Imaging Velocimetry (PIV) to measure detailed steady flow field near and inside circumferential grooves in an axial transonic compressor stage.…”