Numerical simulations of spatially developing, accelerating boundary layers
Numerical simulations of spatially developing, accelerating boundary layers
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空间发展、加速边界层的数值模拟
DOI：
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发表时间：
2013
期刊：
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通讯作者：
J. Yuan
中科院分区：
文献类型：
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作者：
U. Piomelli;J. Yuan
我们提出的直接和大涡模拟的结果进行有利的压力梯度，强大到足以导致逆转的准层流状态的流动的空间发展边界层。数值计算结果与实验数据进行了比较。流动结构的可视化显示了众所周知的稳定化条纹，在流向方向的外层涡流的重新定向，并在重新过渡区的湍流斑点的外观。瞬时可视化和湍流统计都突出了壁面法向和展向波动的显著阻尼。压力波动的快速分量似乎是这一过程的主要驱动力，有助于减少压力波动，因此，雷诺应力预算中的能量再分配项。流向应力在其预算中有一个单独的生产项起作用，它不衰减，而是保持在其上游值。壁面法线和展向波动的减少似乎是内层稳定的主要原因，通过破坏条纹的产生和随后的生长，与文献中提出的各种模型一致。外层似乎在这个过程中扮演了被动的角色。外层涡旋的拉伸和重新定向导致更有序和有组织的结构;由于发生较少的喷射，内层不会破坏这种重新组织，直到重新转变开始。
We present the results of direct and large-eddy simulations of spatially developing boundary layers subjected to favorable pressure gradient, strong enough to cause reversion of the flow towards a quasi-laminar state. The numerical results compare well with experimental data. Visualization of the flow structures shows the well-known stabilization of the streaks, the re-orientation of outer layer vortices in the streamwise direction, and the appearance of turbulent spots in the re-transition region. Both instantaneous visualizations and turbulent statistics highlight the significant damping of wall-normal and spanwise fluctuations. The fast component of the pressure fluctuations appears to be the main driver of this process, contributing to reduce pressure fluctuations and, as a consequence, the energy redistribution term in the Reynolds stress budgets. The streamwise stresses, in whose budget a separate production term plays a role, do not decay but remain frozen at their upstream value. The decrease of wall-normal and spanwise fluctuations appears to be the main cause of the inner-layer stabilization, by disrupting the generation and subsequent growth of streaks, consistent with various models of the turbulence-generation cycle proposed in the literature. The outer layer seems to play a passive role in this process. The stretching and reorientation of the outer-layer vortices results in a more orderly and organized structure; since fewer ejections occur, the inner layer does not break this re-organization, which is maintained until re-transition begins.