考虑波浪形底面影响的边界层风场大涡模拟

Large-eddy simulation of fully developed turbulent flow over a wavy surface

为了研究强风作用下海面上的平均风剖面,采用大涡模拟方法对带有余弦波形状底面、自由滑移顶面的渠道流进行了模拟,波幅、波高比2a/λ为0.1,基于平均速度Ub和渠道高度的雷诺数Reb为6760。统计结果表明,波浪形下表面对上方风场分布有着显著的影响,y/H=0.3(y+≈200)是内区、外区的分界线,内区受壁面影响显著,外区受壁面影响较小。流动的分离点位于x/λ=0.14,而再附点位于x/λ=0.65。展向速度脉动峰值出现在上坡处,且超过竖向脉动。表面压力要比表面摩擦力大一个数量级,是阻力的主要来源。随着波幅的增大,回流区面积增大,速度峰值和展向脉动峰值也会增大,展向脉动峰值甚至会超过流向脉动峰值。

Large eddy simulation（LES）is used to study flow over a sinusoidal bottom wall,with ampli-tude-wavelength ratio 2a/λ=0.1 and bulk velocity based Reynolds number Reb =6760.Different from a con-ventional flat channel,flow over a wavy lower surface is affected by the bottom wall in terms of form drag, leading to the change of both mean and instantaneous fields.Wall bounded flow turns into a separation flow with the increasing of Reynolds number,changing the way in which momentum flux transports and mixes. Statistical properties,transient flow fields as well as surface drag are studied.Averaged fields and turbulent structures are different from those of a flat channel.Distribution and shape of streamwise vortex are closely related to the configuration of the lower surface.Comparison of averaged fields with 2a/λ=0.2 shows the dependence of flow characteristics on the wave steepness.