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Understanding the Turbulence that Causes Jet Noise

Velocity measurements using high-repetition-rate stereoscopic PIV make it possible to observe the large scale dynamics of jet turbulence in a wind tunne, opening the way to progress in the understanding of jet noise generation. 

06 October 2011

For the first time, in the ONERA R4Ch wind-tunnel at Meudon, a series of PIV (Particle Image Velocimetry) data acquisitions was carried out at a high rate (2500 images per second), in the R4 Wind Tunnel at Meudon. With the stereoscopic installation it has been possible to measure the three components of the velocity in a plane transversal to the flow, thus allowing experimental access to the large scale dynamics of turbulence.

Large-scale axial velocity fluctuations in the jet core are represented on the cylinder. The yellow and blue structures are eddy structures of the smaller scale turbulence in th eshear layer
Large-scale axial velocity fluctuations in the jet core are represented on the cylinder. The yellow and blue structures are eddy structures of the smaller scale turbulence in th eshear layer. [ Enlarge image ]

The jet flow studied in this wind tunnel has a high Reynolds number (200,000), which means that the turbulence studied is fully developed. The measurement of velocity and charactérization of turbulence through PIV under these conditions constitutes a real achievement since these measurements are usually performed at much lower Reynolds numbers.

This work, carried out within Samuel Davoust’s PhD thesis, provides a better understanding of the dynamic interactions between the various turbulence scales. These interactions are key elements in the generation of jet noise in aeronautic engines.

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