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An experimental investigation into the use of a bistable winglet to enhance the lift characteristics of a wing transitioning from lower to higher subsonic flow speeds is presented in this paper. The concept centers around the use of a specifically designed composite winglet, manufactured with an unsymmetric layup, which, when increasingly loaded, snaps between two stable states. Initially, during low-speed operation, the winglet is fixed in one stable state that is specifically designed to be cambered, thus enhancing the lift capability of the wing. At higher dynamic pressures, the winglet snaps to a configuration more intuitive and conventional to current winglet design. Results presented in this paper show the concept to be viable at enhancing the lift produced by a swept wing as aerodynamic loading increases before snap-through. During snap-through, however, the absence of any method of controlling the snap-through process generated significant dynamic loading that was transmitted, unhindered, throughout the entire test rig.c tip = root and tip chords, m h = winglet height S = wing area, m 2 V = freestream velocity, m s 1 = angle of attack, deg = cant angle, measured as dihedral angle relative to wing plane, deg = sweep angle, deg Subscripts bs = before snap max = maximum min = minimum rms = root mean square tip = tip spanwise location wl = winglet

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Unsteady flow around deployed landing gears is a significant contributor to aircraft noise on approach. The far-field sound is largely determined by the fluctuating pressures on the gear surface, quantities which have yet to be fully characterized even for simplified representations. The current work reports axle-and wheel-surface data from a comprehensive set of measurements on a generic, two-wheel, landing-gear model. The results show the expected high levels of unsteadiness on areas exposed to large-scale separated flow, of which some (wheel rear surfaces and forward edges) can be identified from steady data, but others (wheel faces adjacent to axle wakes, flow impingements on sidewalls) cannot. The forward-edge values for the current, untripped, configuration are markedly greater than previously reported measurements with artificial transition fixing. Spectral analysis highlights a further category of potentially important contributions that are not easily detected in overall RMS values: high-frequency unsteadiness associated with turbulent attached, or attaching, flows. A key implication of these results is the need for accurate representation of the true, full-scale, boundary-layer state in computations and model-scale testing. Nomenclature C p = pressure coefficient

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Minimising the aerodynamic drag of commercial vehicles is important economically and ecologically. This work demonstrates the effective use of lobed-mixing geometries, traditionally used to enhance flow mixing, as a viable, passive flow control method for reducing base pressure drag of boat-tailed ground vehicles. Experiments were performed on a 1/24 th-scale Heavy Goods Vehicle representative model at a Reynolds number of 2.3 × 10 5 with force and hot-wire anemometry measurements used to quantify drag and wake characteristics. Tests on a baseline (no boat-tail), an unaltered boat-tail, and lobed-mixing configurations with varying pitch and height were compared. Overall, the baseline and unaltered boat-tail exhibited good correlation to previous results. This provided confidence in the methodology adopted. Results using lobed mixers showed up to a 10.2% drag reduction with the added vorticity produced acting to fundamentally shift the nature of the wake. This is manifested principally through the generation of counter-rotating vortical structures which enhance crosswise flow entrainment into the base wake. This action is observed to limit flow entrainment towards the ground leading to a higher wake and a characteristic 'waist'. Enhanced mixing is also demonstrated. Overall, results suggest the suitability of lobed mixers as an effective means for drag reduction of boat-tailed ground vehicles.

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