Flow separation control over a rounded ramp with spanwise alternating wall actuation
Flow separation control over a rounded ramp with spanwise alternating wall actuation
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DOI：
10.1063/1.5055948
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发表时间：
2019-01
影响因子：
4.6
通讯作者：
C. Moulinec;D. Emerson
中科院分区：
文献类型：
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作者：
C. Moulinec;D. Emerson
采用隐式大涡模拟方法研究了主动壁面激励控制下后向圆弧斜面的湍流边界层分离。这种方法被称为展向交替分布条带控制，通过交替地对展向方向上的壁面法向速度分量施加异相控制和同相控制来施加到圆形斜坡上游的平板表面上。结果，局部湍流强度交替地被抑制和增强，导致垂直剪切层的产生，这是导致大尺度流向涡的存在的原因。这些涡对抑制流动分离具有重要影响。通过流动统计分析，研究了大尺度涡与下游回流区和自由剪切层的相互作用。结果表明，与未控制的情况相比，流动分离延迟，再附着点向上游移动，平均回流区长度减少了8.49%。最佳控制的情况下，实现了窄的同相控制带。深入分析表明，流动分离的延迟是由于同相控制带激活了近壁湍流，而再附着位置的改善主要是由于大尺度流向涡的作用，本文采用隐式大涡模拟方法研究了后向流动的湍流边界层分离现象，并与实验结果进行了比较。面向圆形坡道，带有主动式墙壁驱动控制。这种方法被称为展向交替分布条带控制，通过交替地对展向方向上的壁面法向速度分量施加异相控制和同相控制来施加到圆形斜坡上游的平板表面上。结果，局部湍流强度交替地被抑制和增强，导致垂直剪切层的产生，这是导致大尺度流向涡的存在的原因。这些涡对抑制流动分离具有重要影响。通过流动统计分析，研究了大尺度涡与下游回流区和自由剪切层的相互作用。结果表明，与非控制情况相比，流动分离延迟，再附着点向上游移动，流动的稳定性得到了改善。
An implicit large-eddy simulation is carried out to study turbulent boundary-layer separation from a backward-facing rounded ramp with active wall actuation control. This method, called spanwise alternating distributed strips control, is imposed onto the flat plate surface upstream of a rounded ramp by alternatively applying out-of-phase control and in-phase control to the wall-normal velocity component in the spanwise direction. As a result, the local turbulence intensity is alternatively suppressed and enhanced, leading to the creation of vertical shear-layers, which is responsible for the presence of large-scale streamwise vortices. These vortices exert a predominant influence on the suppression of the flow separation. The interaction between the large-scale vortices and the downstream recirculation zone and free shear-layer is studied by examining flow statistics. It is found that in comparison with the non-controlled case, the flow separation is delayed, the reattachment point is shifted upstream, and the length of the mean recirculation zone is reduced up to 8.49%. The optimal control case is achieved with narrow in-phase control strips. An in-depth analysis shows that the delay of the flow separation is attributed to the activation of the near-wall turbulence by the in-phase control strips and the improvement of the reattachment location is mainly due to the large-scale streamwise vortices, which enhance the momentum transport between the main flow and separated region.An implicit large-eddy simulation is carried out to study turbulent boundary-layer separation from a backward-facing rounded ramp with active wall actuation control. This method, called spanwise alternating distributed strips control, is imposed onto the flat plate surface upstream of a rounded ramp by alternatively applying out-of-phase control and in-phase control to the wall-normal velocity component in the spanwise direction. As a result, the local turbulence intensity is alternatively suppressed and enhanced, leading to the creation of vertical shear-layers, which is responsible for the presence of large-scale streamwise vortices. These vortices exert a predominant influence on the suppression of the flow separation. The interaction between the large-scale vortices and the downstream recirculation zone and free shear-layer is studied by examining flow statistics. It is found that in comparison with the non-controlled case, the flow separation is delayed, the reattachment point is shifted upstream, an...