Investigation of vortical flow over bluff bodies with base cavities

Shu-Cheng Pan; Jin-Sheng Cai

摘要

Based on our previous research about drag reduction in term of the base cavity length using two dimensional simulations,this paper describes a numerical study of a bluff body of which the number of base cavities is successively increased and the cavity geometries are also modified to assume different shapes.Here we attempt to find an effective configuration to reduce the drag by increasing the number of base cavities.The numerical simulations examining varied number of base cavities reveal the presence of different strength of vortices in the wake zone which is the reason why the drag coefficients are distinctly different for different cases.In the case with double and triple rectangular cavities,we use the pressure contours snapshots at successive time instants to describe the wake evolution.We further investigate the effect of variable base cavity shapes for a constant cavity length at an identical time instant.A total of two different geometries of base cavities are discussed here:the rectangular and the sinusoidal cavities with sharp and rounded trailing edges,respectively.The numerical results reveal that the former is an effective drag reduction configuration which can produce a significant base pressure recovery corresponding to the strength of the vortices shown in the pressure contour figures.While the latter shows no obvious reduction in drag coefficient and a similar intensity of vortex in the wake zone compared with the unmodified case.Reductions in drag are observed for all the investigated cavity configurations,and additionally it is found that the magnitude of the reduction bears a direct relationship with the number of the cavities up to a certain minimum value.

机译：基于我们先前使用二维模拟对基腔长度进行减阻的研究，本文描述了一种钝体的数值研究，该基体的数量不断增加，并且对腔体的几何形状进行了修改以假定不同在此我们试图找到一种有效的构型，以通过增加基本型腔的数量来减少阻力。数值模拟检查了不同数量的基本型腔，发现在尾流区存在不同强度的涡流，这就是阻力的原因对于不同的情况，系数明显不同。在具有两个和三个矩形腔的情况下，我们使用连续时间瞬间的压力轮廓快照来描述尾流演变。我们进一步研究了可变基腔形状对于恒定腔长度的影响。在同一时刻，总共讨论了两种不同的基本型腔几何形状：数值结果表明，前者是一种有效的减阻结构，可产生与压力等值线图中所示涡旋强度相对应的显着基本压力恢复率。与未修改的情况相比，后者在尾流区没有显示出明显的阻力系数减小和相似的涡流强度。在所有研究的腔结构中都观察到阻力减小，并且还发现减小幅度具有与腔的数量（到一定最小值）的直接关系。

Investigation of vortical flow over bluff bodies with base cavities

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