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THE EFFECT OF SCHMIDT NUMBER ON THE MIXING IN THE WALL REGION OF AN IMPINGING JET

Johan Revstedt
Division of Fluid Mechanics, Lund Institute of Technology P.O. Box 118, S-221 00 Lund, Sweden

Laszlo Fuchs
Department of Mechanics, KTH, CICERO, SE-10044 Stockholm; Division of Fluid Mechanics Lund University Lund, 22363, Sweden

Abstract

Large Eddy Simulation of a semi-confined impinging jet at Reynolds number 10000 was performed. The impingement distance was varied between 2 and 6 nozzle diameters. The unsteady spatially filtered incompressible Navier-Stokes equations were solved together with a transport equation for the concentration of an inert additive using a multi-grid finite difference code with a staggered grid. The un-resolved scales of the flow as well as the sub-grid scale mixing were modelled implicitly through the truncation errors of the discretisation. The transport of 4 passive scalars with Schmidt numbers in the range 0.1 to 100 has been studied. The results show differences in mean concentration difference of up to 25%. As expected, that the major differences in scalar concentration occur where the velocity gradients are large, i.e. close to the nozzle and in the wall jet region.