Mixing Enhancement in Jet Exhaust Using Fluidic Actuators: Direct Numerical Simulations

Direct numerical simulation was used to study the effect of controlled forcing at the jet nozzle on downstream mixing in a Mach 0.8 jet. The jet was forced by small slot jet actuators near the nozzle lip which blew normal to the initial jet shear layer and excited a flapping mode in the jet. The actuator jets and the nozzle itself were not explicitly simulated to spare the expense of including complex geometry wall boundaries in the calculation. Instead, their effects were syntheticly included by putting ‘source’ terms into the equations. It was found that mixing could be substantially increased with relatively small amounts of forcing. The potential core length was reduced by a factor of 2 and the downstream velocity profiles became highly asymmetric. The results agree with similar but lower Mach number experiments of Parekh et al. (1990). NOMENCLATURE a Speed of sound D Jet diameter e Fluid total internal energy r Jet radial coordinate ro Jet radius StD Strouhal number = f D=U j Ta Actuator fluid temperature Tj Jet exhaust fluid temperature T∞ Ambient fluid temperature Ua Peak actuator fluid velocity U j Jet exit centerline velocity ux Axial velocity vr Radial velocity vθ Azimuthal velocity x Jet axial coordinate measured from nozzle θ Jet azimuthal coordinate ρ Fluid density ξ Scalar concentration