Toward Ultra-High Cruise Lift Coefficient Using Flapped Coflow Jet Airfoil
Jaehyoung Jeon, Yan Ren, Gecheng Zha
Abstract
View Video Presentation: https://doi.org/10.2514/6.2023-1008.vid Differing from the maximum lift coefficient for takeoff/landing, the cruise lift coefficient must have high aerodynamic efficiency and sufficient stall margin. Conventional 2D subsonic airfoil has the typical cruise lift coefficient CL in the range of 0.4 to 0.6. This study introduces a 2D flapped CoFlow jet(FCFJ) airfoil to achieve a cruise lift coefficient about one order of magnitude higher to CL of 4 with a constraint that the 2D aerodynamic efficiency should be about 50, similar to the CL/CD level of the baseline airfoil with no flow control. The regular CFJ airfoil applies the injection very close to leading edge at about 2-4%Chord location. The FCFJ airfoil has a long flap(60%C) with the CFJ applied inside the flap as a part of the airfoil. The research is based on validated CFD simulation, which employs a 2D RANS solver with Shear-Stress-Transport(SST) turbulence model, a third-order WENO scheme for the inviscid fluxes, second-order central differencing for the viscous terms. The regular CFJ airfoil and FCFJ airfoil are created from the baseline NACA 6421 airfoil. For a CFJ airfoil to be used at cruise conditions with high aerodynamic efficiency of CL/(CD + Pc), both the drag and power coefficient, CD and Pc, must be low. Applying CFJ on the flap appears to be the desired configuration to substantially increase lift coefficient and maintain very low CD and Pc. This is benefited from the feature that applying CFJ at the region of adverse pressure gradient is the most effective and efficient. Increasing cruise lift coefficient to such a high level would bring many advantages such as reduced aircraft size/weight, increased payload, high transportation productivity, high altitude flight, and possible fixed-wing VTOL air vehicles in thin Martian atmosphere. In this study, we are able to achieve CL of 4.17, CL/CD of 263.5, and (CL/CD)c of 48, through parametric studies on flap deflection angle, slot size, and jet momentum coefficient. The final configuration has a flap deflection angle β of 35◦, the injection slot size of 0.4%C, and the jet momentum Cμ of 0.1. This 2D numerical study indicates that a cruise lift coefficient about one order of magnitude higher than conventional level is possible.