Session: 34-04 Endwall, Seal & Leakage Flows II

Paper Number: 78805

78805 - Flow Control Mechanism of Non-Axisymmetric Endwall in Compressor Cascades 

Non-axisymmetric endwall contouring has been proved to be an effective flow control technique in turbomachinery. However, there are different opinions on the flow control mechanism of non-axisymmetric endwall in compressors, which has significant influences on the endwall design strategy.

This paper presents both numerical and experimental results to demonstrate the effects of non-axisymmetric endwall on endwall secondary flows. Besides, the effects of non-axisymmetric endwall on radial equilibrium were analyzed to explain the static pressure redistribution mechanism. Studies were carried out using linear compressor cascades with different camber angles. Comparisons were conducted between the flat endwall and contoured endwall cascades. The contoured endwalls were designed by geometric scaling of a prior optimized endwall.

It is well known that the secondary flow control ability of non-axisymmetric endwall should be attributed to its effects on the endwall static pressure distribution. One of the issues worthy of further study is the static pressure redistribution mechanism of the non-axisymmetric endwall. Results in this paper showed that the endwall streamwise curvature rebuilds the radial pressure gradient by changing the streamline curvature term of the radial equilibrium equation. The convex endwall streamwise curvature forces nearby streamlines to become convex, resulting in additional centrifugal acceleration. In order to balance the additional centrifugal acceleration, the radial pressure gradient increases. Since the static pressure away from the endwall trends to be unaffected, the endwall static pressure decreases. Similarly, the concave endwall streamwise curvature increases the endwall static pressure. The tangential variation of the endwall streamwise curvature leads to the change of cross pressure gradient.

Another issue worthy of further study is how the non-axisymmetric endwall controls the corner separation by changing the endwall static pressure distribution. Results in this paper showed that the contoured endwall leads to a local strengthened cross pressure gradient in the rear half of the passage near suction side, thereby enhancing the local cross flow. The local enhanced cross flow prevents the corner vortex in the suction surface corner region from quickly diffusing like in the flat endwall cascades which might be responsible for the further reduction of the corner fluids kinetic energy. Besides, the corner vortex transports kinetic energy from the main flow to the corner flow, and rolls the low energy fluids downstream, suppressing the corner reverse flow.

It is concluded that the corner separation in compressor cascades can be suppressed effectively by using non-axisymmetric endwall to strengthen local cross pressure gradient. The endwall streamwise curvature distribution plays a decisive role in the endwall static pressure distribution. The parameterization of the non-axisymmetric endwall by means of the endwall streamwise curvature can be considered as a possible field for further research.

Presenting Author: Hanwen GUO Beihang University

Presenting Author Biography: Hanwen GUO received the B. Eng. degree in aircraft design and engineering from the school of aeronautic science and engineering at Beihang University in 2017 and the M. Eng. degree in aeronautic engineering from the school of energy and power engineering at Beihang University in 2020.<br/>His research interests include compressor aerodynamics and secondary flow control in turbomachinery. He is a coauthor with Xiwu LIU, Donghai JIN, Xingmin GUI and Xiaoheng LIU of the ASME paper numbered GT2018-76247.

Authors:

Hanwen GUO Beihang University
Donghai Jin Beihang University
Xiwu Liu AECC Hunan Aviation Powerplant Research Institute
Xingmin Gui Beihang University