ABSTRACT

We performed large-eddy simulations of the flow over an aerofoil to understand the effects of leading-edge roughness designed to mimic ice accretion. The roughness elements protrude outside the boundary layer, which, near the leading edge, is very thin; thus, the configuration does not represent a classical rough-wall boundary layer, but rather the flow over macroscopic obstacles. A grid convergence study is conducted and results are validated by comparison to numerical and experimental studies in the literature. The main effect of the obstacles is to accelerate transition to turbulence. Significant variations in structure generation are observed for different roughness shapes. The three-dimensionality of the irregularities has a strong impact on the flow: it creates alternating regions of high-speed (‘peaks’) and low-speed (‘valleys’) regions, a phenomenon termed ‘channelling’. The valley regions resemble a decelerating boundary layer: they exhibit considerable wake and higher levels of Reynolds stresses. The peak regions, on the other hand, are more similar to an accelerating one. Implications of the channelling phenomenon on turbulence modelling are discussed.

摘要

我们对机翼上的流动进行了大涡模拟，以了解旨在模拟积冰的前缘粗糙度的影响。粗糙度元素突出到边界层之外，边界层在前缘附近非常薄；因此，该配置不代表经典的粗糙壁边界层，而是代表越过宏观障碍物的流动。进行了网格收敛研究，并通过与文献中的数值和实验研究进行比较来验证结果。障碍物的主要作用是加速向湍流的过渡。对于不同的粗糙度形状，观察到结构生成的显着变化。不规则的三维度对流动有很强的影响：它创造了高速（“峰值”）和低速（“谷”）区域的交替区域，一种称为“通灵”的现象。山谷区域类似于一个减速的边界层：它们表现出相当大的尾流和更高水平的雷诺应力。另一方面，峰值区域更类似于加速区域。讨论了通道现象对湍流建模的影响。