Stabilisation of subcritical bypass transition in the leading-edge boundary layer by suction
Stabilisation of subcritical bypass transition in the leading-edge boundary layer by suction
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DOI：
10.1080/14685248.2014.933226
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发表时间：
2014-01-01
影响因子：
1.9
通讯作者：
Kleiser, Leonhard
中科院分区：
文献类型：
--
作者：
John, Michael O.;Obrist, Dominik;Kleiser, Leonhard
本文通过直接数值模拟（DNS）研究了后掠Hiemenz边界层的亚临界空间转捩。一对稳定的同向旋转的旋涡位于附着线被强制作为一个主要的干扰，导致条纹是稳定的。一个小的二次，随时间变化的扰动与这些条纹相互作用，使不稳定和崩溃的湍流可能会发生。不稳定性只发生在一定的二次扰动频率带。当雷诺数Re = 100时，二次不稳定性增长率为正，而线性临界雷诺数Re = Re-crit，Re- lin约为583。吸力对初生条纹形成和二次生长速率的影响是解耦的。对于不同吸力的条纹，其振幅通过调节雷诺数保持恒定，吸力被证明增加二次不稳定性的增长率。壁面抽吸的稳定影响仅在于减小条纹幅度。取决于雷诺数和抽吸强度，破裂可能局部发生，并可能沿远场流线沿着对流，或全局发生，并覆盖下游方向的广泛区域。
This work investigates the subcritical spatial transition in the swept Hiemenz boundary layer by means of direct numerical simulations (DNS). A pair of steady co-rotating vortices located at the attachment line is enforced as a primary disturbance leading to streaks which are stable. A small secondary, time-dependent disturbance interacts with these streaks such that instability and breakdown to turbulence may occur. The instability only occurs for a certain band of secondary disturbance frequencies. Positive secondary instability growth rates could be observed for Reynolds numbers as low as Re = 100, whereas the linear critical Reynolds number is Re-crit,Re- lin approximate to 583.Uniform wall suction is shown to stabilise this transition mechanism, analogously to results from linear stability theory. The effects of suction on the formation of primary streaks and on the secondary growth rate are decoupled. For streaks of different suction whose amplitude is held constant by adjusting the Reynolds number, the suction is shown to increase the growth rate of the secondary instability. The stabilising influence of wall suction consists in decreasing the streak amplitude only.Depending on the Reynolds number and the suction strength, breakdown may either occur locally and may be convected along the far-field streamlines, or occur globally and cover broad regions in the downstream direction.