Experimental Visualization of Unsteady Flow in a Transonic Oscillating-Blade Compressor Cascade Using High-Speed Two-Wavelength Interferometry

This study presents experimental results from high-speed interferometric measurements on a transonic compressor blade cascade, where three of the five blades were torsionally oscillated at various frequencies up to 150Hz and different inter-blade phase angles. The primary research objective is to develop and validate a non-intrusive methodology capable of quantifying unsteady flow fields surrounding aeroelastically unstable components. The resulting flow field images demonstrate the potential of the method. Unlike classical interferometric methods, the proposed approach has less stringent requirements for the optical quality of the test section windows. This advantage allows for the use of organic-glass windows, which are necessary for investigating highly loaded compressor blade cascades. Such windows are required to accommodate the suction slots used to maintain a representative Axial Velocity Density Ratio (AVDR). Unlike the classical schlieren technique, the method provides quantitative results with high spatial and temporal resolution, while the synthetic schlieren images can also be produced. The method proved suitable for measurements in the harsh environment of transonic flow through oscillating blades and is capable of capturing important unsteady flow phenomena.