Reynolds number effects on disturbances in a laminar free jet

Abstract

Several Direct Numerical Simulations (DNS) of two-dimensional free plane air jets at different Reynolds number have been carried out, in order to analyse its influence. The baseflow employed to represent the plane jet, calculated by means of MATLAB, is characterised by following Schlichting's self-similar model (1933), whose validity has been verified. Differences in Reynolds number among all the cases hinge upon a variant characteristic lengthb. This parameter in Schlichting's equations represents the width of the jet in which the axial velocity decays to a 1% of its maximum value. Modifications in this parameter have allowed to keep the maximum velocity umax constant at every case, and therefore the Mach number, so as to maintain the same compressible behaviour. Seven DNS calculations have been performed by dint of the in-house code NS3D of the Institute of Aerodynamics and Gas Dynamics (IAG) at the University of Stuttgart, Germany; from 􀀃��Reb=300􀀂�� to Reb=2500 Results in terms of axial velocity and its ˛fluctuation have been assessed with the help of Tecplot R and EAS3, with the outcome that instability generation in form of several wave packets and subsequent two-dimensional transition to non-linearity occur earlier and more intensely the greater to Reb.