Distinct Wing-in-Ground Effect of Airfoil in Proximity to Water Waves

The present study numerically explores the distinct aerodynamic characteristics of an airfoil flying in proximity to water waves. The water wave is treated by both two-phase-flow wavy water and rigid moving wavy ground, with a specific goal to clarify whether the water wave can be substituted by rigid wavy ground. Results show that for large ground clearance (h/c & GE;0.4), the aerodynamic forces and flow structures of the near-field airfoil are basically dominated by the passage shape between airfoil and wave surface where the wavy water can be replaced by means of using wavy ground. However, it is different for small ground clearance that the airfoil-induced airflow has a strong relative speed to the water flow and subsequently creates a strong shear force on the forthcoming wave to eject water spray from wave crest. The spray has a sufficient influence on the flow topology and consequently leads to a distinct aerodynamic behavior. Particularly, the strong upstream shear on the wave resulted from the stagnation region at a positive angle of attack induces upwind spray, which can be elevated to hit onto the airfoil with larger density and momentum than airflow causing extraordinarily high pressure on the lower surface as well as unstable aerodynamic forces.