Optical measurement and visualization of transonic airflow in a compressor blade cascade

The paper deals with optical measurements of transonic flow past a five-blade compressor blade cascade. The middle blade of this cascade can be set to different incidence angles simulating its torsional deformation. Classical optical methods (shadowgraphy, monochrome and color schlieren) were applied to visualize flow field in the inlet part of the cascade and compared to results obtained using a recent fiber based spatial carrier digital interferometric setup. Measurements were done at inlet Mach number 1.09 and pressure ratio 1.32 with the middle blade set at 0 degrees and 3 degrees incidence offset. Results of individual techniques are analyzed and their utility is assessed. Shock wave configuration is best revealed by shadowgraphy, which is the least demanding method, whereas most information is provided by the digital interferometry. It is proved that the current interferometric setup is well applicable even when inexpensive acrylic glass optical windows are used. Thus, the method can be readily used for aerodynamic investigations where modifications of sidewalls are required.