Numerical Simulation of Discrete Co-Flow Jets NACA-6415 Airfoil

Abstract

This paper numerically simulates Co-Flow Jet (CFJ) airfoils using discrete injection jets, which is motivated by the hypothesis that a discrete CFJ (DCFJ) airfoil will generate both streamwise and spanwise vortex structures to achieve more effective turbulent mixing than an open slot CFJ airfoil. An effective open-slot CFJ momentum coefficient Cμ is defined for DCFJs. A NACA-6415 airfoil is used as baseline.Two sets of CFD models for open-slot CFJ and DCFJ NACA-6415 wings are used, one simulating the actual rectangular test section in wind tunnel, the other using the far field conditions. All the DCFJ airfoil models are simulated at the experimental flow conditions of freestream Mach number of 0.029, Reynolds number of 2.05E5 at a range of angles of attack (AoA) from 0deg to 35deg. The numerical simulations employ the intensively validated in-house CFD code FASIP, which utilizes a 3-D 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. This initial study shows that, at a given Cμ, the DCFJ provides extra lift enhancement and drag reduction compared with open slot CFJ airfoil. The DCFJ airfoil can achieve up to a 250% increase of maximum lift, and simultaneously generates a tremendous thrust. The stall angle of attack is also significantly increased. The vortex structure near discrete injection slots are visualized. The numerical simulation confirms the previous experimentation result that the performance improvement brought by DCFJ are at the cost of high energy expenditure compared with the open slot CFJ airfoil. The lift coefficients versus AoA and power coefficients from CFD simulation are in good agreement with the previous wind tunnel experiment.