Feasibility study on seeding and imaging on a transonic cascade

The goal of this feasibility study is to assess an existing flow facility, namely a transonic compressor cascade, for possible application of advanced particle image velocimetry (PIV) methods within the current project as part of Task 5.3. Modifications to the facility are recommended and partially already implemented to enable the future application of these techniques there, in particular tomographic PIV and long distance microscopic PIV. The report first introduces the Transonic Cascade Windtunnel (TGK) facility in the context of a recent planar PIV setup and then describes the latest improvements both of a seeding injection device as well as a new purging concept for the light-sheet probe used in the facility. These improvements were essential in enabling successful measurements using conventional PIV (2C-PIV) but will be of direct use for future applications of advanced methods. Within the described 2C-PIV campaign the transonic flow around the leading edge of a highly loaded transonic cascade at M1=1.28 was measured. Exemplary instantaneous and averaged velocity data of this campaign are presented to illustrate the quality improvement in consequence of various modifications. The available measurement data also allow an analysis of the imaging conditions in the presence of strong density gradients within the TCW facility. Furthermore a detailed vibration analysis was carried out in order to examine the spatial and temporal stability of the cascade and the windtunnel (TCW) prior to the high-speed high-resolution PIV measurements. Finally, first suggestions for possible viewing geometries for tomographic PIV are in an effort to find a suitable configuration which maximizes the field of view with respect to a sufficient range of viewing angles