Array Doppler Global Velocimeter with Laser Frequency Modulation for Turbulent Flow Analysis – Sensor Investigation and Application

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Abstract

Velocity field measurement results of a Doppler global velocimeter (DGV) using sinusoidal laser frequency modulation are presented. Contrary to conventional DGV systems, which suffer from low temporal resolutions of several seconds, the novel DGV system allows measurement rates up to 100 kHz. The high temporal resolution is afforded by using a fibre-coupled detector array, which has a higher bandwidth than conventionally applied cameras. Additionally, low uncertainties can be achieved in contrast to conventional DGV since no second reference detector unit is necessary. The optimised set-up is capable of acquiring turbulence spectra simultaneously at multiple points. The measurement data from the wake of a cylinder agrees well with comparison measurements using hot-wire anemometry and correctly yields the Kármán vortex frequency.With the novel DGV, turbulence spectra up to about 10 kHz were resolved. Further measurement results illustrate the high potential of the described technique for non-invasive, temporally resolved, imaging flow inspection e.g. in turbomachines.