Browsing by Author "Roberts, L."

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    Aerodynamic characteristics of a wing-and-flap configuration in ground effect and yaw
    (IMechE, 2015-08-11) Roberts, L.; Correia, J.; Finnis, Mark V.; Knowles, Kevin
    The influence of the yaw angle on a model representative of a monoposto racing car’s 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 while cornering. Because of the need for downforce in corners rather than on a straight, it is standard practice to test a racing car at various orientations of yaw, pitch and roll quasi-statically. Wind tunnel testing with a 50%-scale model at a unit Reynolds number of 1.69 × 106 was used to investigate the forces and the surface flow structures. The results were then used to validate simulations with the three-equation k–kL–ω transitional turbulence model to observe the surface pressures and the wake structures. It was found that a change in the surface pressure 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 the drag of the wing; all these were amplified as the yaw angle was increased or the ground clearance reduced. The fundamental aerodynamic flow features of a racing car’s front wing operating at yaw are established.
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    Forcing boundary-layer transition on an inverted airfoil in ground effect and at varying incidence
    (AIAA, 2016-06-17) Roberts, L.; Finnis, Mark V.; Knowles, Kevin; Lawson, Nicholas J.
    The influence of the laminar boundary-layer state on a wing operating in ground effect at Re = 6 × 10 has been investigated using experiments with a model that provides two-dimensional flow and computations with a panel-method code. The effect 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, flow visualisation and hot-film anemometry, and off-surface characteristics with LDA 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 effect 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 deficit. The importance of considering laminar phenomena for wings operating in ground effect has been shown