沿流向微结构沟槽流场直接数值模拟

采用高阶格式对覆有V型对称沟槽表面的槽道湍流流动进行了直接数值模拟，数值方法采用有限差分法。为精确求解沟槽壁面的湍流流动，对流项的离散采用7阶WENO（Weighted Essentially Non-Oscillatory）格式；时间推进采用分数步时间推进与低耗散、低色散Runge-Kutta方法（LDDRK方法）结合的格式；黏性项的离散采用6阶中心格式。模拟的雷诺数为5 000（基于槽道高度的1/2），计算的沟槽宽度范围为13~44，沟槽斜壁与水平面夹角为60°。数值模拟结果表明，与平板相比，沿流向沟槽表面的阻力最高降低了9%。数据分析发现出现减阻效果时，沟槽减少了近壁面处顺流向涡的数目，并且减阻机理与微沟槽阻碍大尺度流向涡与沟槽壁面的直接碰撞，使沟槽表面湍流脉动得到削弱有关。

Direct numerical simulation of flow field over streamwise micro riblets

To simulate the flow over the streamwise micro riblets of symmetric V shape, this paper applies a model of channel flow where the lower wall is mounted with riblets and the upper one is flat. The finite difference method is employed as the numerical method. To accurately obtain the flow of riblets, the 7th WENO (Weighted Essentially Non-Oscillatory) scheme, the fractional-step method combined with the Low-Dissipation and Dispersion Runge-Kutta scheme (LDDRK method) and the 6th central scheme are applied to the discretization of the space, the time advancing and viscous terms. In this paper, the Reynolds number is 5 000 (based on the half width of the channel), the range of the size of the riblets is from 13 to 44 and the inclination of the slope of riblets is 60°. Simulation results illustrate that the maximum of drag reduction is 9% and indicate that in the drag-reducing cases, the riblets can prevent the large-scale streamwise vortices from interacting with the surface directly, weakening the turbulent oscillation and decreasing the number of the streamwise vortices near riblet wall.