IDDES Analysis of Flapped Coflow Jet Airfoil at Low Reynolds Numbers

This paper investigates the flow physics of a flapped coflow jet (FCFJ) airfoil designed to achieve ultra-high cruise lift coefficients (CL) at low Reynolds number conditions of the Martian atmosphere.The study aims to develop a fundamental understanding of how coflow jet active flow control achieves attached flow at low Reynolds number conditions, which is crucial for future Mars exploration missions that require efficient aerial vehicles. Computational fluid dynamics (CFD) simulations are conducted using a validated 3D Navier-Stokes solver incorporating the Improved Delayed Detached Eddy Simulation (IDDES) turbulence model, a fifth-order WENO scheme for inviscid fluxes, and second-order central differencing for viscous terms. The flow conditions are at Mach number of 0.17 and Reynolds number of 56,300 with a momentum coefficient Cμ of 0.25. Results demonstrate that 2D RANS and 3D IDDES predictions exhibit similar lump performance parameters, but the IDDES reveals more detailed flow structures. Detailed component analysis using the turbulent wall jet momentum equation reveals distinct flow attachment mechanisms across the airfoil. Near the leading edge, the flow is primarily laminar and is driven by a favorable pressure gradient for flow attachment. In the injection region, the high-momentum jet introduces significant streamwise inertia force term, which becomes the critical factor for energizing the boundary layer and promoting mixing with the main flow. As the flow moves over the flap, turbulent diffusion emerges as the primary mechanism for mixing and maintaining flow attachment against the adverse pressure gradient, with streamwise inertia force remaining a key contributor. Finally, in the vicinity of the suction slot, the strong favorable pressure gradient generated by the micro-compressor actuator becomes the dominant force, effectively suppressing separation. The insights gained into the low Reynolds number flow physics and attachment mechanisms provide a robust foundation for the design of future Martian aerial vehicles.