Analysis of Coflow Jet Flow Control for an Airfoil Using Large-Eddy Simulations

Large-eddy simulations (LESs) were performed using a high-order scheme to explore multiple aspects of coflow jet (CFJ) active flow control for a modified NACA 6421 airfoil. This study examined changes in flow due to the presence of an inactive jet, elucidation of the startup process, and performance of the CFJ at various angles of attack and jet momentum coefficients. When the baseline airfoil was modified to include an inactive CFJ, time-mean lift and drag increased by 13% and 284%, respectively. The CFJ startup process generated a large vortex that rapidly increased lift and drag during the first characteristic time. Over the next nine characteristic times, both forces slowly rose as the flow reached a steady state. Lift increased faster for a fixed jet momentum coefficient than for the baseline airfoil as the angles of attack increased. At each angle, minimal variations were present in the lift coefficient; however, the drag coefficient varied by 21–36%. At a fixed angle of attack, the CFJ was explored for multiple steady jet momentum coefficients and for an unsteady case with a 50% duty cycle. The steady CFJ generated thrust as the jet momentum coefficient increased. The unsteady case generated similar lift and slightly more thrust than a steady jet with a momentum coefficient half its magnitude.