This paper reports the results from a direct numerical simulation of an initially turbulent boundary layer passing over a wall-mounted “speed bump” geometry. The speed bump, represented in the form of a Gaussian distribution profile, generates a favorable pressure gradient region over the upstream half of the geometry, followed by an adverse pressure gradient over the downstream half. The boundary layer approaching the bump undergoes strong acceleration in the favorable pressure gradient region before experiencing incipient or very weak separation within the adverse pressure gradient region. These types of flows have proved to be particularly challenging to predict using lower-fidelity simulation tools based on various turbulence modeling approaches and warrant the use of the highest fidelity simulation techniques. The present direct numerical simulation is performed using a flow solver developed exclusively for graphics processing units. Simulation results are utilized to examine the key phenomena present in the flowfield, such as relaminarization/stabilization in the strong acceleration region succeeded by retransition to turbulence near the onset of adverse pressure gradient, incipient/weak separation and development of internal layers, where the sense of streamwise pressure gradient changes at the foot, apex and tail of the bump.

本文报告了直接湍流边界层通过壁挂式“减速块”几何形状的直接数值模拟的结果。以高斯分布轮廓的形式表示的减速带在几何形状的上游一半上产生有利的压力梯度区域，随后在下游一半上产生不利的压力梯度。接近凸块的边界层在不利的压力梯度区域内出现初期或非常弱的分离之前，会在有利的压力梯度区域内经历强烈的加速。事实证明，使用基于各种湍流建模方法的低保真度仿真工具来预测这些类型的流动特别具有挑战性，并保证使用最高保真度模拟技术。当前的直接数值模拟是使用专门为图形处理单元开发的流量求解器执行的。仿真结果被用来检验流场中存在的关键现象，例如在强加速区域中的层化/稳定化，该过程通过在不利的压力梯度开始附近重新转换成湍流，内部层的初/弱分离和发展而成功实现。流的压力梯度变化在脚的底部，顶点和尾部发生变化。