This paper conducts numerical investigations for a 15% thickness Co-Flow Jet (CFJ) airfoil performance enhancement, which includes the variation of lift, drag, and energy expenditure at Mach number 0.03, 0.3, and 0.4 with jet momentum coefficient Cµ = 0.08. The angle of attack(AoA) varies from 0 • to 30 • . Two-dimensional simulation is conducted using a Reynolds-averaged Navier-Stokes (RANS) solver. A 5th order WENO scheme for the inviscid flux and a 4th order central differencing for the viscous terms are used to resolve the the Navier-Stokes equations. Turbulence is simulated with the one equation Spalart-Allmaras model.The study shows that at constant Cµ, the maximum lift coefficient is increased with the increasing Mach number due to the compressibility effect. However, at M=0.4, the airfoil stalls with slightly lower AoA due to the appearance of strong λ shock wave that interrupts the jet and trigger boundary layer separation. The drag coefficients vary less with the Mach number, but is substantially increased at Mach 0.4 when the AoA is high due to shock wave-boundary layer interaction and wave drag.The power coefficient is decreased when the Mach number is increased from 0.03 to 0.3. This is again due to the compressibility effect that generates stronger low pressure suction effect at airfoil leading edge, which makes the CFJ pumping easier and require less power. For the same reason of shock appearance at M=0.4 when the AoA is high, the power coefficient is significantly increased due to large entropy increase. Overall, the numerical simulation indicates that the CFJ airfoil is very effective to enhance lift, reduce drag, and increase stall margin with high Mach number up to 0.4 at low energy expenditure.

This paper conducts a numerical and experimental investigation of a coflow jet airfoil to quantify lift enhancement, drag reduction, and energy expenditure at a Mach number range from 0.03 to 0.4. The jet momentum coefficient is held constant at 0.08, and the angle of attack varies from 0 to 30 deg. The two-dimensional flow is simulated using a Reynolds-averaged Navier-Stokes solver with a fifth-order-weighted essentially non-oscillatory scheme for the inviscid flux and a fourth-order central differencing for the viscous terms. Turbulence is simulated with the one equation Spalart-Allmaras model. The predicted coflow jet pumping power has an excellent agreement with the experiment. At a constant Mach number, the power coefficient is decreased when the angle of attack is increased from 0 to 15 deg. When the Mach number is increased from 0.03 to 0.3, the suction effect behind the airfoil leading edge is further augmented due to the compressibility effect. This results in an increased maximum lift coefficient and reduced power coefficient at the higher Mach number because of the lower jet-injection pumping pressure required. At Mach 0.4, the lift coefficient is further improved. However as the angle of attack is increased, a λ shock wave interrupts the jet and triggers the boundary layer separation with increased drag and power coefficient. A corrected aerodynamic efficiency that includes the coflow-jet pumping power is introduced. Because of the high lift coefficient and low coflowjet power required, the coflow-jet airfoil in this study achieves a comparable peak aerodynamic efficiency to the baseline airfoil, but the lift coefficient at peak efficiency is substantially increased by 120%. This study indicates that the coflow-jet airfoil is not only able to achieve very high maximum lift coefficient, but also able to improve cruise performance at low angle of attack when the flow is benign.

This paper introduces and proves a novel automotive mirror base drag reduction method using passive jet flow control. The new concept is to open an inlet at the front part of the mirror, introduces the airflow via a converging duct, and ejects the jet surrounding the mirror surface at an angle toward the center of the mirror. The jet harnesses the energy from the free stream by jet mixing with the main flow via large coherent structures, entrains the main flow to energize the base flow, reduces the wake size and turbulence fluctuation, and ultimately significantly decreases the drag. Above phenomena are proved by wind tunnel testing with PIV and drag force measurement and CFD large eddy simulation (LES) calculation. Two jet mirrors with different inlet areas are studied. The jet mirror tunnel 1 has a smaller inlet area, and the jet mirror tunnel 2 has a 4.7 times larger inlet area. The wind tunnel testing is only done for the baseline and jet mirror tunnel 1. LES is used to study all the three mirror configurations. Both the wind tunnel testing and LES indicate that the jet mirror tunnel 1 reduces the drag by about 18% with smaller wake width. The LES indicates that the jet mirror tunnel 2 with larger inlet area further reduces the wake and achieves a drag reduction of 39%. This paper is only for proof of the concept and no design optimization is done. It is believed that there is a large room to further reduce the drag with a systematic design optimization.

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