No abstract

An investigation of a cambered, double-element, high-lift wing operating in ground effect was performed. The effect of ground proximity and ap setting was quanti ed in terms of aerodynamic performance and off-surface ow eld characteristics. From that, it was found that the ow is three-dimensional toward the wing tip with the main element generating most of the downforce but retains quasi-two-dimensional features near the center of the wing. However, at large heights the downforce increases asymptotically with a reduction in height. Then there is either a plateau, in the case of a low ap angle, or a reduction in downforce, in the case of a large ap angle. The downforce then increases again until it reaches a maximum and then reduces with decreasing height above the ground. The maximum downforce is dictated by gains in downforce from lower surface suction increases and losses in downforce caused by upper surface pressure and lower surface suction losses, with a reduction in height. For the high ap angle there is a sharp reduction just beyond the maximum, mainly because of the boundary layer separating, and a resultant loss of circulation on the main element.

No abstract

Unsteady Reynolds-averaged Navier-Stokes (URANS) simulations and detached-eddy simulations (DES) were performed of flow around a circular cylinder placed near and parallel to a moving ground, on which substantially no boundary layer developed to interfere with the cylinder. The results were compared with experiments previously reported by the authors to examine how accurately the URANS and DES can predict the cessation of von Ka´rma´n-type vortex shedding and the attendant critical drag reduction of the cylinder in ground effect. The DES, which were performed in a three-dimensional domain with spanwise periodicity imposed, correctly captured the cessation of the vortex shedding, whereas both two-and three-dimensional URANS also predicted it but at a much smaller gapto-diameter ratio compared with the experiments. The wake structures of the cylinder predicted by the DES were in good agreement with the experiments in both large-and small-gap regimes, and also in the intermediate-gap regime, where the DES captured the intermittence of the vortex shedding in the near-wake region. Based on the results obtained, further discussions are also given to the reason why the von Ka´rma´n-type vortices in the URANS solutions incorrectly 'survived' until the cylinder came much closer to the ground. r

The behaviour of four drystone masonry retaining walls of different geometry has been modelled numerically using the discrete element code UDEC, and the results have been compared with the ®eld trials carried out by Burgoyne in Ireland in 1834. By using appropriate soil and wall mass densities, strengths and stiffnesses, it was possible to reproduce in the numerical analyses the ®eld behaviour observed by Burgoyne. Reasonably close agreement was obtained between the horizontal components of earth pressures calculated in the numerical analyses and using the earth pressure coef®cients given by Caquot and Kerisel. Basal stress distributions calculated using the condition of equilibrium of the wall were also broadly consistent with those resulting from the numerical analyses. The results also con®rm both the in¯uence of the geometry of a drystone masonry retaining wall on its performance and ultimate stability, and the soundness of Burgoyne's engineering judgement in specifying his programme of ®eld tests.