Application of Particle Image Velocimetry in Acoustic and Aeroacoustic Experiments

Different applications of the Particle Image Velocimetry (PIV) in the field of acoustics and aeroacoustics are presented. This includes the investigation of cavity resonance and the calibration of a p-u probe, which is used for acoustic intensity measurements. For the later case velocity fluctuations down to the range of micrometers are resolved with a frequency resolution of 20 kHz. Additionally, applications of the causality correlation technique by means of simultaneous PIV and microphone measurements will be shown. The method is used for the identification of flow structures that are involved in the generation mechanism of aeroacoustic noise sources. Correlation results for the aeroacoustic investigation of a high lift device will be shown in detail, illustrating how the coherence in the flow topology influences such correlation results. The ambiguity of the proposed method will be discussed, focusing on the analyses of the temporal and spatial evolution of the coefficient matrix along trajectories of vortices emanating from the slat cusp. By taking into account the travel time of these vortices together with the sound travel time, sound generating flow structures can be clearly identified.