Geometric Parameter Effects on Lift Enhancement of a Circulation-Control Airfoil for Aerodynamically Alleviated Marine Vehicles Under Fixed Ground Effect

Circulation control is an efficient active flow control technique that enhances aerodynamic lift by injecting a tangential jet near the trailing edge, altering the circulation around the airfoil. This study investigates the influence of three key geometric parameters—Coanda surface radius, slot height, and jet angle—on the aerodynamic performance of a NACA4309-based circulation-control airfoil (NACA4309-CCA) operating under a fixed ground clearance (hg/c = 0.14), representative of high-speed aerodynamically alleviated marine vehicles. Numerical simulations are performed using the Reynolds-averaged Navier–Stokes equations with the SST k-ω turbulence model. The results show that increasing r/c enhances lift up to a limit (r/c ≈ 0.017), beyond which flow separation occurs, reducing lift. For a fixed momentum coefficient (=0.01), an optimal h/c = 0.0007 balances jet momentum and mass flow, yielding the highest lift. The jet angle study reveals that the maximum lift (CL = 2.684) is achieved at θ ≈ 10°, but θ = 0° (CL = 2.581) is recommended for practical implementation due to simpler geometry and stable attachment, with only a 3.84% loss in lift relative to the maximum. The findings provide comparative numerical trends for the design of circulation-control systems on aerodynamically alleviated marine vehicles under the investigated conditions.