3-D Transonic Flow in a Compressor Cascade With Shock-Induced Corner Stall

Abstract

An experimental and numerical study of the transonic flow through a linear compressor cascade with endwalls was conducted. The cascade with a low aspect ratio of 1.34 was tested at an inlet Mach number of 1.09 and a Reynolds number of 1.9×106. Detailed flow visualizations on the surfaces and five-hole probe measurements inside the blading and in the wake region showed clearly a three-dimensional boundary layer separation on the blade surface and the sidewall, and a severe corner stall induced by a strong 3-D shock system at blade passage entrance. The experimental data have been used to validate and improve the 3-D Navier-Stokes code TRACE. Results showed an excellent resolution of the complex flow field. Surface pressure distributions on the entire blade surface and the endwalls, flow angle and total pressure contours within the blade passage and the wake are compared with the experimental results. An analysis of the secondary flow of this highly staggered cascade did not show the classical corner vortex. Instead, a severe flow deviation and partly reverse flow near the walls is seen. The flow solver helped to identify a weak ring vortex that originates from the passage sidewall. Surface oil flow pictures on the blade contour and the sidewall are in qualitatively good agreement to numerical surface streaklines. A considerable improvement of the numerical results could be achieved by a gradual grid refinement, especially in the corner region and by successive code development.

Corner effect and separation in transonic channel flows

“…Two possible mechanisms for how corner flows affect the centreline are proposed: Firstly, large corner flow separations may cause a large three-dimensional bifurcation of the shock wave structure that spans a significant proportion of the wind tunnel and has an effect on the amount of pressure smearing experienced by the tunnel wall boundary layers. This is in agreement with the findings of previous authors such as Weber et al (2002) and Handa, Masuda & Matsuo (2005), who observed that the 3-D (bifurcated) shock structure produced in a confined transonic SBLI increased the amount of pressure smearing near the corners. Secondly, corner flow separations may act as an effective blockage to the core flow in the tunnel and (depending on their size and relative positions) could decelerate the (supersonic) pre-shock flow and/or re-accelerate the (subsonic) post-shock flow, both of which would act to smear the adverse pressure gradient imposed by the normal shock wave.…”

The evolution of the flow topologies of 3D separations in the stator passage of an axial compressor stage

“…12). This three-dimensional flow structure for corner separation was first derived by Schulz et al [5] and has been proved by other researchers by numerical simulations [3,7,13,26]. The appearance of the limiting streamlines for the type B flow can be seen in Fig.…”

“…In the experiments conducted by Schulz et al [5], they did not observe this type of flow. However, according to the numerical simulation results given by Hah and Loellbach [7] and Weber et al [26], the corner separation of flow type C may occur when the back pressure decreases below a certain value. Thus to say, the flow topology of the corner separation may appear as flow type B or C, depending on the compressor operating condition and the flow interactions inside the flow passage.…”

Evaluation of RANS turbulence models in simulating the corner separation of a high-speed compressor cascade

“…CFD application to a highspeed compressor cascade is more difficult because of the more severe corner separations and fully developed flow unsteadiness. Even so, studies on high-speed compressor cascades have greatly benefited from the robust RANS methods (Chen et al, 2014;Gmelin, Thiele, & Liesner, 2011;Hergt, Meyer, & Engel, 2013;Hergt, Meyer, Liesner, & Nicke, 2011;Weber, Schreiber, Fuchs, & Steinert, 2002). The turbulence models applied in the previous highspeed compressor cascade studies were carefully selected eddy viscosity models, which can easily diverge.…”