Abstract
This paper numerically studies the spanwise distribution of Co-Flow Jet (CFJ) for a straight wing at freestream Mach number of 0.30, C-mu=0.03 and 0.06 at angles of attack (AOA) of 5 degrees and 14 degrees. Five configurations with different CFJ distributions along the wing span with an aspect ratio (AR) of 10 are investigated. Among these configurations, CFJ-covered suction surface area varies from 38.5% to 90% of the wing span in continuous or discrete distribution along the span. The numerical simulations employ the validated in-house CFD code FASIP, which utilizes 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 study shows that, due to the existence of vortex near the tip, CFJ in this region does not provide as large lift enhancement as in near-root places in the span, and an area including as large as 20% of wing span can thus be freed from CFJ device to satisfy requirements from weight or structural considerations. Also with the help of tip vortices, under normal working condition at a small angle of attack of 5 degrees, with 61.5% of suction surface area free from coflow jet, the CFJ lift enhancement effect can decrease for a slighter 49.8%.
Meanwhile, with constant C-mu, the performance of wings mounted with discrete CFJ is penalized with the increasing size of gaps between the discrete jets. Narrow gaps between injection and suction slots of parallel CFJ sets only lead to minor penalty at small AoAs. Still, to optimize the lift performance at large AoAs, these gaps are expected to be minimized or eliminated. There is an exception that at stall condition with not enough C-mu to eliminate the separation, which is abnormal, a "concentrated" C-mu distribution method can maintain some lift enhancement, but generally speaking, when the CFJ is discretized, the larger angle of attack has more performance penalty.