Frequency analysis of turbulent compressible flows by laser vibrometry

Abstract The objective of this work was the application of laser vibrometry as a tool for non-intrusive measurement of frequency spectra in turbulent flows. A laser vibrometer system together with a signal analyser was used to obtain frequency spectra of density fluctuations across a turbulent free jet. Since laser vibrometry is based on interferometric techniques, the derived signals are path integrals along the measurement beam. Frequency spectra recorded in the rotational symmetric flow were then treated using Abel inversion in order to derive information on local density fluctuations. Results for two different flow conditions were compared to spectral data from a constant temperature anemometer and a pitot-mounted pressure sensor.