Secondary Instability of Boundary Layers
Secondary Instability of Boundary Layers
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DOI：
10.1146/annurev.fl.20.010188.002415
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发表时间：
1988
影响因子：
27.7
通讯作者：
T. Herbert
中科院分区：
文献类型：
--
作者：
T. Herbert
粘性边界层中从层流到湍流的转变问题具有重要的实用价值。层流边界层流动的低摩擦系数对那些为飞机等高速飞行器布置发动机或支付燃料的人非常有吸引力。然而，流体性质的低混合，如化学成分、热量或动量，对于设计这些发动机或应对在不利压力梯度下分离的危险的其他人来说可能是无法容忍的；他们可能显然更喜欢湍流状态的流动。因此，如果不能控制，至少预测所考虑的流动是层流还是湍流是非常可取的。然而，几十年的紧张研究所做的巨大努力并没有起到什么作用(Reshotko 1976)。经验EN标准仍然是工程实践中的标准工具，尽管众所周知，它忽略了转变物理学的基本成分，因此如果超出支持数据库的使用，可能会有危险的误导。数值模拟在充分详细地再现转变过程方面获得了可靠性，从而提取了实验室实验无法获得的信息。然而，边界层的流动周期性和时间增长的固有假设，加上初始条件的不确定性，阻碍了在实践中预测过渡。因此，理论在确定过渡过程的内在机制和结构以及解释其他难以理解的观察结果方面仍然占有重要地位。在过去的十年里，稳定性理论取得了一些重要的进展，速度或慢或快，这取决于读者的判断。
The problem of transition from laminar to turbulent flow in viscous bound ary layers is of great practical interest. The low skin-friction coefficient of laminar boundary-layer flow is very attractive to those who lay out the engines or pay the fuel for high-speed vehicles such as airplanes. However, the low mixing of fluid properties such as chemical species, heat, or momen tum may be intolerable for others who design these engines or cope with the danger of separation in adverse pressure gradients; they may clearly prefer a turbulent state of the flow. Therefore, it would be highly desirable to at least predict, if not to control, whether the flow under consideration is laminar or turbulent. The tremendous efforts of decades of intense research, however, have been to little avail (Reshotko 1976). The empirical en-criterion is still the standard tool in engineering practice, although it is known to ignore essential ingredients of the physics of transition and therefore may dangerously mislead if used beyond the supporting data base. Numerical transition simulations have gained reliability in repro ducing the transition process in sufficient detail to extract information unobtainable from laboratory experiments. However, the inherent assumptions of stream wise periodicity and temporal growth of the bound ary layer, in addition to the uncertainty of initial conditions, prevent predicting transition in practice. Hence, theory still holds an important place in identifying inherent mechanisms and structures of the transition process and in explaining otherwise unintelligible observations. The past decade saw some important progress in stability theory, slow or fast, depending on the reader's judgment ..