Wavelet analysis of vortical structures in turbomachinery applied to PIV data

Abstract

In this paper the unsteady flow field of a highly loaded turbine rotor blade at different transonic Mach numbers by means of Particle Image Velocimetry (PIV) is investigated. The experiments are performed using the linear cascade wind tunnel at DLR Goettingen at isentropic exit Mach numbers 0.7, 0.9, and 1.1. The process of vortex shedding at the trailing edge of the blade and its proceeding downstream in the wake area is analyzed using a wavelet based vortex identification algorithm. The wavelet algorithm automatically detects vortices and extracts e.g. their position, their vorticity, and their convection velocity. This procedure enables a statistical analysis on the basis of numerous PIV recordings. The vortex production, the downstream transport and the vortex decay are observed successfully. The Strouhal number and the shedding frequency are directly derived from the vortex position and confirm previous investigations. The PIV combined with a wavelet based analysis constitutes a remarkable insight to time dependent flow structures.