Purpose

Numerical simulations are performed for studying the vorticity dynamics of a dipole colliding with the wall in a bounded flow and the wake structure and separated flow properties past a circular cylinder at the values of Reynolds numbers.

Design/methodology/approach

The near wake statistics of separated fluid flows are investigated by using the lattice Boltzmann method (LBM) in a two-dimensional framework. A multi-block technique is applied to accurately resolve the flow characteristics by the grid refinement near the wall and preserve the stability of the numerical solution at relatively high Reynolds numbers.

Findings

The results show that the rolling-up of the boundary layer occurs due to the shear-layer instabilities near the surface which causes a boundary layer detachment from the wall and consequently leads to the formation of small-scale vortices. These shear-layer vortices shed at higher frequencies than the large-scale Strouhal vortices which result in small-scale high-frequency fluctuations in the velocity field in the very near wake. The present study also demonstrates that the efficiency of the multi-block LBM used for predicting the statistical features of flow problems is comparable with the solvers based on the Navier-Stokes equations.

Practical implications

Studying the separated flow characteristics in aerospace applications.

Originality/value

Applying a multi-block lattice Boltzmann method (LBM) for simulation of separated fluid flows at high-Reynolds numbers. Studying of the near wake statistics of unsteady separated fluid flows using the multi-block LBM. Comparison of flow characteristics obtained based on the LBM with those of reported based on the Navier-Stokes equations.

中文翻译：

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用多块格子玻尔兹曼方法研究非定常分离的流体流动

目的

进行了数值模拟，以研究偶极子在有界流和尾流结构中与壁碰撞的涡流动力学，并且在雷诺数的值下经过圆柱体的分离流特性。

设计/方法/方法

通过使用二维框架中的格子玻尔兹曼方法（LBM）研究分离的流体流的近尾流统计。应用多块技术通过壁附近的网格细化来精确地解析流动特性，并在相对较高的雷诺数下保持数值解的稳定性。

发现

结果表明，边界层的卷起是由于表面附近的剪切层不稳定性而引起的，边界层导致边界层从壁上脱离，从而导致小规模的涡旋形成。这些剪切层涡流的散布频率比大型斯特劳哈尔涡旋散发的频率高，这导致了在非常接近尾流时速度场的小规模高频波动。本研究还表明，用于预测流动问题统计特征的多块LBM的效率与基于Navier-Stokes方程的求解器相当。

实际影响

研究航空航天应用中的分离流动特性。

创意/价值

应用多块格子Boltzmann方法（LBM）模拟高雷诺数下的分离流体流动。使用多块LBM研究不稳定分离流体的近尾流统计信息。基于LBM的流动特性与基于Navier-Stokes方程报告的流动特性的比较。