Experimental Investigation of Turbine Wake Flow by Interferometrically Triggered PIV and LDV Measurements

The process of vortex shedding had been investigated in a a linear turbine blade cascade by non-invasive optical measurement techniques. The experiments were carried out in the wake behind a linear arrangement of turbine profiles (VKI-1) with a chord length of 58 mm at an isentropic exit Mach number of 0.7 and a Reynolds number of 9.75×10⁵. Shedding frequency was approx. 18.2 kHz. Density fluctuations in the vortex street were measured by guiding the beam of a Laser Vibrometer (LV) through the turbine blade cascade behind the trailing edge and a frequency analysis was performed. These interferometrically detected density fluctuations had then been used to trigger two-dimensional velocity measurements by Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) in the turbine wake flow, by means of an analog filter. This resulted in phase resolved measurements of the flow field during vortex shedding at this high frequency. Results of these velocity measurements within the wake flow are presented with a decomposition of the velocity into mean, periodic and turbulent components performed.