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INVESTIGATION OF THE EFFECTS OF INITIAL TURBULENCE LEVEL ON THE FLOW FIELD PROPERTIES OF A SUBSONIC JET

Christophe Bogey
Laboratoire de Mecanique des Fluides et d'Acoustique UMR CNRS 5509, Ecole Centrale de Lyon 69134 Ecully, France

Olivier Marsden
Laboratoire de Mecanique des Fluides et d'Acoustique UMR CNRS 5509, Ecole Centrale de Lyon 69134 Ecully Cedex, France

Christophe Bailly
Laboratoire de Mecanique des Fluides et d'Acoustique UMR CNRS 5509, Ecole Centrale de Lyon 69134 Ecully, France

Abstrakt

Five round jets at Mach number 0.9 and diameter-based Reynolds number 105 originating from a pipe nozzle are computed by Large-Eddy Simulations using grids of 252 million points. In the pipe, the boundary layers are tripped, in order to obtain, at the exit section, laminar mean velocity profiles of momentum thickness equal to 1.8% of the jet radius, and peak turbulence intensities of 0, 3, 6, 9 and 12% of the jet velocity. The influence of initial turbulence on flow development is thus investigated. As the nozzle-exit turbulence level increases, the coherent structures typically found in initially laminar jets gradually disappear, which leads to shear layers spreading at lower rate with strongly reduced rms fluctuating velocities. The jets also develop farther downstream, resulting in longer potential cores.