Unsteady Predictions of Mixing Enhancement with Steady and Pulsed Control Jets

Unsteady Reynolds-averaged Navier-Stokes predictions are reported for a single round jet at high Reynolds number and high subsonic Mach number (Re = 10(6), M = 0.9) excited by steady and pulsed control jets. Comparison has been made with experimental validation data to assess the ability of k-epsilon-based unsteady Reynolds-averaged Navier-Stokes modeling for predicting control-jet-driven flow control of near-field jet mixing and potential core-length reduction. The well-known overprediction of the clean (unexcited) core length with this level of turbulence closure remains, but taking this into account, the relative effect of control jets on core-length reduction was predicted remarkably well. For example, steady control jets and pulsed control jets in symmetric/antisymmetric modes indicated a core-length reduction (relative to the unexcited case) of 43/45/60% in predictions, compared to 48/40/51% in measurements. Comparison of radial profiles showed that unsteady Reynolds-averaged Navier-Stokes modeling was also able to predict the three-dimensional near-field behavior induced by control jets throughout the jet cross section. The vortex structures produced in the pulsed-control-jet predictions were compared. Symmetric and antisymmetric modes produced different vortex structures; these caused different levels of enhanced mixing in the two azimuthal modes and explained the better performance of antisymmetric pulsing.