Mass-Flow Reduction Strategies of Co-Flow Jets on Finite Wings

Large Eddy Simulations (LES) were performed using a high-order scheme to explore steady, pulsed, and discrete sweeping co-flow jet (CFJ) active flow control strategies for a modified finite NACA 6421 wing. The main purpose of this work was to determine if unsteady and spanwise-segmented CFJ flow control techniques using significantly less mass flow could generate similar performance as a steady, spanwise-continuous jet case. The simulations were performed at a chord-based Reynolds number of 200,000, freestream Mach number of 0.1, and an angle-of-attack of 12 degrees. The jet momentum coefficient was 0.109 for the steady jet which led to a 24% increase in lift over the baseline NACA 6421 airfoil. Using the same total pressure and temperature for the pulsed and sweeping injection slot approaches led to a jet momentum coefficient of 0.019 and 0.01, respectively. The pulsed case had significant flow separation and 15% less lift than the baseline NACA wing. The sweeping jet case had fully attached flow and an 8% increase in lift using only one-tenth the jet momentum of the steady CFJ case. The marginal performance increase of the CFJ flow control was driven in part by the small aspect ratio used in the LES which led to a lower effective angle of attack. For the current configuration, losses and only minimal gains were achieved with low mass flow pulsed and sweeping jet flow control, respectively, which may define a lower limit of effectiveness for future co-flow jet research.