A study was conducted on a GA(W)-1 wing in order to investigate the effect of testing inverted wings in ground effect at low Reynolds numbers. The wing was tested at a range of ground clearances and Reynolds numbers and results showed that the wing's performance was dependent on both these parameters. Surface flow-visualisation and numerical simulation results highlighted the existence of a laminar separation bubble on the wing's suction surface. The results also indicated that both the bubble's length and the onset of separation were sensitive to ground clearance and Reynolds number. Attempts were made to minimise the wing's Reynolds number dependency by using transition strips on the suction surface. The transition strip results highlighted the influence that a laminar separation bubble has on the overall performance of the wing and how its presence alters the force enhancement and reduction mechanisms on an inverted wing in ground effect.

The influence of yaw on a model representative of a monoposto racing car front wing and nose section operating in close proximity to the ground is discussed. The yawed condition is representative of a car operating in a crosswind or with side-slip whilst cornering. Due to the need for downforce in corners rather than on a straight it is standard practice to test a racing car at varying orientations of yaw, pitch and roll quasi-statically. Wind tunnel testing with a 50% scale model at a chord-based Reynolds number of 1.69 x 10 6 /m was used to investigate forces and surface flow structures. The results were then used to validate simulations with the 3-equation k-kL-ω transitional turbulence model to observe surface pressures and wake structures. It was found that a change of surface pressures caused asymmetric loading of the wing, the strengthening or inhibiting of vortices depending on their rotational sense, and an overall reduction in both the downforce and drag of the wing; all of which were amplified as yaw angle was increased or ground clearance reduced. The fundamental aerodynamic flow features of a racing car front wing operating at yaw are established.

The transition from a laminar to turbulent boundary layer on a wing operating at low Reynolds numbers can have a large effect on its aerodynamic performance. For a wing operating in ground effect, where very low pressures and large pressure gradients are common, the effect is even greater. A study was conducted into the effect of forcing boundary-layer transition on the suction surface of an inverted GA(W)-1 section single-element wing in ground effect, which is representative of a racing-car front wing. Transition to a turbulent boundary layer was forced at varying chordwise locations and compared to the free-transition case using experimental and computational methods. Forcing transition caused the laminar-separation bubble, which was the unforced transition mechanism, to be eliminated in all cases and trailing-edge separation to occur instead. The aerodynamic forces produced by the wing with trailing-edge separation were shown to be dependent on trip location. As the trip was moved upstream the separation point also moved upstream, this led to an increase in drag and reduction in downforce. In addition to significant changes to the pressure field around the wing, turbulent energy in the wake was considerably reduced by forcing transition. The differences between free- and forced-transition wings were shown to be significant, highlighting the importance of modeling transition for ground-effect wings. Additionally, it has been shown that while it is possible to reproduce the force coefficient of a higher Reynolds-number case by forcing the boundary layer to a turbulent state, the flow features, both on-surface and off-surface, are not recreated.

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The inuence of the laminar boundary-layer state on a wing operating in ground eect has been investigated using experiments with a model that provides twodimensional ow. The eect of a boundary-layer trip placed at varying distances from the leading edge was observed at various incidences in terms of on-surface characteristics, including pressure measurements, ow visualisation and hot-lm anemometry, and o-surface characteristics with velocity surveys below and behind the wing. The act of forcing transition led to downforce being reduced and drag increased, moreover it altered almost all aspects of the wing's aerodynamic characteristics, with the eect becoming greater as the trip was placed closer to the leading edge. These aspects include the replacement of a laminar separation bubble with trailing-edge separation, a thicker boundary layer, and a thicker wake with greater velocity decit. The importance of considering laminar phenomena for wings operating in ground eect has been shown. Nomenclature c Wing chord length, m C D Drag coecient C F Friction coecient

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