Application of Stereoscopic and Tomographic PIV in a Transonic Cascade

Abstract

The contribution demonstrates the applicability of volumetric PIV in a highly loaded compressor cascade at Ma_1 = 0.60. Under these operation conditions the secondary flow structures in the cascade are dominated by a passage vortex located at the base of the blade and near the suction side. The application of volume resolving thick-sheet PIV (or tomo-PIV) near the trailing edge of the cascades blades is intended to demonstrate the techniques potential of instantaneously resolving secondary flow structures within the separation region of the cascade and its ability to derive three dimensional statistical data of fluctuations of velocity in the turbulent flow region. The report describes various aspects of the adaption of the tomographic PIV setup to the restricted access on the cascade wind tunnel. A four camera setup is was used to resolve a measuring volume of 36x24x4 mm^3 from which a total of 54x74x13 vectors at a spacing of 0.64 mm in x (chord-wise direction) and a spacing of 0.32 mm in y and z could be recovered. The stability of the camera setup is documented by evaluating the image shifts of stationary features due to vibrations of the wind tunnel. Three dimensional reconstruction of the imaged particle volume is achieved with the maximum entropy reconstruction technique (MENT) and validated against a conventional MLOS-SMART reconstruction. The reconstruction quality of experimental data is documented by plots of the reconstructed intensity along volume depth. The extraction of the three-dimensional displacement field relies on multi-resolution, 3-D correlation processing with iterative volume deformation. The recovered three-dimensional velocity fields are compared at selected planes with (thin-sheet) stereo PIV data.