Effect of inclined transverse jets on trailing-edge noise generation

Abstract

In this work, the effect of multiple transverse jets on the turbulent boundary layer developing over a flat plate is experimentally investigated for aeroacoustic purposes. A single line of jet nozzles with different spanwise spacings is located parallel to the trailing-edge of the plate, at approximately 30 jet diameters upstream of the trailing-edge. The axes of the jet nozzles have an inclination of 15° with respect to the streamwise direction. Two values of the jet velocity ratio (r = ujet/u∞) are considered, r = 1 and r = 2. The simultaneous measurement of streamwise velocity and surface pressure fluctuations is performed with hot-wire anemometry and flush-mounted microphones, respectively. The mean velocity profiles show that the low inclination angle of the multiple jets prevents the formation of adverse pressure gradients, and therefore, the multiple jets injection does not lead to flow separation, at least at the range of downstream locations under investigation. From the velocity measurements, the jets merge downstream of the jet nozzles and form a layer of jet fluid characterized by a low energy content. The estimates of the far-field noise show that jets injection at a velocity ratio of r = 1 leads to noise attenuation over the whole range of frequencies under analysis. At a velocity ratio of r = 2, jets injection enables to gain a larger noise reduction than at r = 1 at low frequencies, but the estimated far-field noise is expected to increase at high frequencies.