Viscous modeling of ground effect aerodynamics of airfoil and jet

Alex Earle Ockfen

Wing-in-Ground craft and aerodynamically assisted marine vehicles take advantage of increased lift and reduced drag of wing sections in ground proximity. However, at relatively low speeds or heavily loaded craft, the passive aerodynamic lift may not be sufficient to provide vehicle support. In such cases, a flap at the wing trailing-edge or properly placed jet propulsor may be implemented to augment vehicle lift. Parametric design studies are completed for several ground effect configurations gaining insight into fundamental flow patterns and optimal performance regimes with flap and/or jet components implemented. This research takes advantage of efficient and low-cost numerical methods suited for design studies. The technique consists of a two-dimensional, steady-state, incompressible, viscous, finite volume method utilizing RANS turbulence models. Grid generation and solution of the Navier-Stokes equations are completed using Fluent 6.3. Validation of solution approach is provided with experimental validation of aerodynamic forces in and out of ground effect, plane turbulent jets, planar impinging jets, and static airfoil-flap-jet configurations. The influence of flap mechanization is first studied on the NACA 4412 airfoil in ground effect. Aerodynamic forces are calculated, and the effects of attack angle, Reynolds number, ground height, and flap deflection are presented for split and plain flaps. Overall, flap use on ground-effect vehicles with small attack angles is found to be beneficial for small flap deflections up to 5% of the chord, where an enhanced aerodynamic efficiency is realized. At low speeds where flap use is insufficient, the Power-Augmented-Ram (PAR) concept implements jet support to sufficiently augment vehicle lift. A simplified aerodynamic jet propulsor model, the ducted momentum source, is developed to account for upstream jet suction and downstream jet spreading. First, beneficial obliquely impinging propulsor configurations are studied with cross flow, and are then combined with a platform-flap to simulate a PAR vehicle. Results of PAR simulations suggest that in low-speed operation, harmful jet ingestion may occur. To avoid this phenomenon, the propulsor should be placed at impingement angles less than 30° and at moderate ground distances. With increasing PAR forward speed, performance may be increased by reducing flap deflection and impingement angle.

Viscous modeling of ground effect aerodynamics of airfoil and jet

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