Study of 2D Hover Performance Using Flapped Coflow Jet Airfoil at Low Reynolds Numbers

This paper conducts a trade study of a deflected slipstream system utilizing flapped coflow jet (FCFJ) airfoils for achieving optimal hover performance for fixed wing VTOL aircraft at low Reynolds number conditions in the Martian atmosphere. The deflected slipstream configuration is advantageous for vertical takeoff and landing because it avoids tilting rotors, wings, or using lift-plus-cruise configurations while enabling efficient runway-independent operations. The objective is to find the optimalFCFJ airfoil configuration that generates the required hover lift with minimal coflow jet and propeller power at low Reynolds numbers. The in-house validated 2D URANS solver with Spalart-Allmaras (SA) turbulence model, a third-order WENO scheme for inviscid fluxes, and second-order central differencing for viscous terms are used for the computational fluid dynamics simulations. The parametric study reveals a highly fairly linear relationship between propeller strength Dp and total lift coefficient, with CFJ injection size exhibiting an inverse power-law scaling with total pressure ratio following Γ ∝ Inj size(%C)−0.4. Results indicate that achieving the target lift coefficient of 72 initially requires excessively large injection slots (3.2%C) and high momentum coefficients Cμ of 30. However, a aircraft system tilting of 20deg with flap deflection β = 60 successfully achieves the target performance while reducing CFJ power coefficient by 65% and utilizing feasible injection and suction slot dimensions of 0.6%C and 1.3%C, respectively. The final configuration demonstrates that flow attachment is maintained at Cμ ≥ 3, providing critical design guidelines for efficient VTOL operations in the thin Martian atmosphere.