用LES模拟方背钝体尾流双峰现象
Simulation of wake bimodality behind squareback bluff-bodies using LES
摘要：
对$Re_H=33,333$上1/4比例方背Ahmed体绕流进行了大涡模拟研究。该研究包括壁解析（WRLES）和壁模化（WMLES）模拟，并调查了双峰切换的唤醒不同的水平位置之间。在1050个对流单元的无量纲时间窗内，WRLES和WMLES模拟（仅在湍流边界层的近壁区域以湍流平均的方式处理）能够捕获尾流横流方向的水平（展向）位移。平衡壁模型的形式Spalding的法律和日志法律的墙壁成功地使用。一旦这些壁模型，然而，应用到一个非常粗糙的近壁WMLES网格，其中的一部分，湍流边界层的外部区域的动态处理，在一个平均的方式，以及，大规模的水平位移尾流的方向不再检测。这表明在湍流边界层的外部区域内发现的较大尺度的流动结构负责产生触发双峰切换事件所需的临界流量。通过观察平均流结构、瞬时流特征及其相关的湍流动能（TKE）产生，可以清楚地看到，Ahmed机身头部后部的前部分离气泡通过大发夹涡的脱落产生高水平的TKE。只有在参考WRLES和（相对）精细的近壁网格WMLES模拟这些功能存在，举例说明它们在触发双峰事件的重要性。这激发了通过作用于前分离气泡来抑制尾流双峰性的研究。
英文摘要：
A large eddy simulation (LES) study of the flow around a 1/4 scale squareback Ahmed body at $Re_H=33,333$ is presented. The study consists of both wall-resolved (WRLES) and wall-modelled (WMLES) simulations, and investigates the bimodal switching of the wake between different horizontal positions. Within a non-dimensional time-window of 1050 convective flow units, both WRLES and WMLES simulations, for which only the near-wall region of the turbulent boundary layer is treated in a Reynolds-averaged sense, are able to capture horizontal (spanwise) shifts in the wake's cross-stream orientation. Equilibrium wall-models in the form of Spalding's law and the log-law of the wall are successfully used. Once these wall-models are, however, applied to a very coarse near-wall WMLES mesh, in which a portion of the turbulent boundary layer's outer region dynamics is treated in a Reynolds-averaged manner as well, large-scale horizontal shifts in the wake's orientation are no longer detected. This suggests larger-scale flow structures found within the turbulent boundary layer's outer domain are responsible for generating the critical amount of flow intermittency needed to trigger a bimodal switching event. By looking at mean flow structures, instantaneous flow features and their associated turbulent kinetic energy (TKE) production, it becomes clear that the front separation bubbles just aft of the Ahmed body nose generate high levels of TKE through the shedding of large hairpin vortices. Only in the reference WRLES and (relatively) fine near-wall mesh WMLES simulations are these features present, exemplifying their importance in triggering a bimodal event. This motivates studies on the suppression of wake bimodality by acting upon the front separation bubbles.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
