Control of Secondary Flow in a High Loaded Compressor Stage by Means of a Groove Structure on the Sidewalls

Abstract

A large component of the total pressure loss in a compressor stage is caused by secondary flow effects, such as separation between the wall and vane i.e., a corner separation. An experimental investigation in a highly loaded compressor cascade was performed to minimize the corner separation induced losses using a grooved surface on the side walls under cross flow conditions. The experiments were performed with the aim of controlling flow separation and secondary flows, in order to minimize losses in the compressor stage. Transverse grooves on the side wall of the cascade were employed as a passive means of flow control. The grooves were located at the side walls of the cascade in-between two vanes. The flow control device hampers the secondary flow on the side walls of the cascade in such a way, that the corner separation on the vane is less pronounced. This results in a 9.8% total pressure-loss reduction and a 2° increase of the cascade deflection angle in vicinity of the sidewalls. The experiments were carried out at the peak efficiency (design point) of the cascade in order to optimize the design of the grooves. The research was carried out experimentally with a compressor cascade at a high-speed test facility at DLR in Berlin. The cascade consisted of five vanes with NACA 65 K 48 profiles. The experiments were accomplished at Reynolds numbers up to Re = 0.56 x 10 6 (based on 40 mm chord) and Mach numbers up to M = 0.67. To understand the flow physics of the underlying mechanism of the transverse grooves, additional experiments at lower Reynolds numbers in low speed wind tunnels as well as in an oil channel were performed.