ADVANCED STUDY OF SECONDARY FLOWSTRUCTURES IN A HIGHLY LOADED COMPRESSOR CASCADE

Abstract

The current paper deals with a detailed experimental and numerical investigation of the secondary flow structures in the corner region between blade and endwall in a highly loaded compressor cascade, with the objective to provide extensive validation data and performing a first comparison with numerical results. The used cascade has been designed and optimized specifically for use at low Reynolds number conditions, as can be found at high altitudes. The study was divided into an experimental and a numerical part. The experimental part of the investigation was performed in the transonic cascade wind tunnel of DLR in Cologne at a Mach number of 0.6 and Reynolds number of 9.0x105. Wake measurements with a 5-hole probe at four distances behind the cascade trailing edge were carried out, in order to obtain measurement data of the loss distribution, comparable to the numerical results. Furthermore, oil streak patterns on the endwall and blade surface were conducted. Additionally, tomographic PIV (tomo-PIV) and conventional stereo PIV (SPIV) are utilized, in order to assess the quality of CFD prediction of the flow structure in the corner region. The numerical investigation of the cascade flow was performed by means of the turbomachinery CFD code TRACE, which is an in-house developed code of the DLR Institute of Propulsion Technology. The focus was on the detailed description of the secondary flow close to the corner region and on the determination of the loss distribution in the wake behind the cascade. Furthermore, the influence of the boundary layer transition on the cascade flow was considered by the usage of a transition model. In the paper a detailed comparison between the experimental and the nurmerical results is given. It is shown, that the experimental extension of the corner separation on the cascade surfaces and the development of the loss distribution behind the cascade is well reflected by the CFD results, but there are differences in the loss intensity