Numerical investigation of wingtip vortices of coflow jet active flow control wings

This paper investigates the wingtip vortices and their feeding shear-layer interactions for a 3D Co-Flow Jet (CFJ) wing and a baseline wing at cruise conditions at an aspect ratio of 10. The wings are based on a NACA 6421 airfoil, with the CFJ airfoil containing injection and suction slots for active flow control. A momentum coefficient C_µ of 0.03 is used at the cruise condition at α = 5^◦ based on the optimum aerodynamic efficiency found in a previous study. The total pressure of the injection slot is fixed at this value for the entire angle of attack sweep from α = −1^◦ to α = 26^◦ . The simulations employ the validated in house FASIP CFD code, utilizing a 3D RANS solver with Spalart-Allmaras (S-A) turbulence model, 3rd order WENO scheme for the inviscid fluxes, and 2nd order central differencing for the viscous terms. The maximum aerodynamic efficiency occurs at an AoA of 2^◦, across which the vortex core axial velocity remains mostly wake-like in the near wake region. However, the axial velocity in the vortex core edge increases with jet-like axial velocity when the AoA is at 5^◦ . At the high AoA of 12^◦, the core axial velocity has a strong jet in the near wake region. With the tip vortex growing in size while propagating downstream, an adverse pressure gradient is created as predicted by Batchelor’s model. At this point the axial velocity decreases to a wake-like profile. This phenomenon is observed for both the CFJ and baseline wings. The CFJ wing expectedly produces more lift than its baseline counterparts at the same angle of attack. This results in a smaller wake-momentum deficit at lower angles of attack, and a stronger jet-like axial velocity profile at higher angles of attack. The vortex core axial velocity profile and vortex tangential velocity profiles are linked. When greater axial velocity is observed in the core region, higher the tangential velocity is also observed. The overall strength of the tip vortex is greater for the CFJ wing, compared to the baseline wing at the same angle of attack. The free-shear layer roll-up is also examined and indicates a corresponding increase in absolute magnitude for the CFJ when compared to the baseline wing.