Direct numerical simulation of vortex-induced instability for a zero-pressure-gradient boundary layer.
Direct numerical simulation of vortex-induced instability for a zero-pressure-gradient boundary layer.
复制标题
零压力梯度边界层涡旋引起的不稳定性的直接数值模拟。
作者：
A. Sengupta;V. K. Suman;T. Sengupta
本文利用控制计算结果定量地探讨了自由流涡激引起的涡致不稳定性。首先，将计算结果与Lim等人的实验结果进行比较[Exp. fluid, 37, 47 (2004)10.1007/s00348-004-0783-5]，以验证三维（3D）计算的正确性。然后，使用研究不可压缩流的非线性和时空可接受性和不稳定性的方法来解释计算结果。在这里，零压力梯度（ZPG）边界层受到在固定高度以恒定速度运动的恒定强度涡旋的扰动，如引用的实验所示。在实验中，涡旋是由一个平移旋转的圆柱产生的，其物理参数是绝对控制的。平移涡的符号由平移圆柱的旋转方向确定。采用高精度的计算方法求解了不同平移速度和符号下的三维Navier-Stokes方程（NSE）。用不可压缩流的非线性扰动熵输运方程（DETE）来解释涡旋诱导的不稳定性。这个方程是精确的，并且解释了由NSE控制的不稳定性。在Sengupta等人的研究中，DETE方法已经成功地用于解释二维（2D）涡致不稳定性。[j] .流体力学与工程学报，2011,32 (5):589 - 589 .]除了量化涡致不稳定性外，另一个主要目标是展示扰动如何从最初的2D阶段演变到3D阶段。虽然平动涡的标志对产生响应场很重要，但我们还强调了自由流涡平动速度和强度的增加对整体不稳定性造成的明显差异。这些解释了通过平衡流的不稳定性产生小规模漩涡的原因，即使激励只是二维的。在某些情况下，这会导致3D旁路转换。我们还展示了一个具有弯曲速度剖面的强非定常分离的案例，但扰动流基本上仍然是二维的，这可以称为旁路过渡。
Vortex-induced instability caused by a free-stream vortical excitation is explored here quantitatively with the help of controlled computational results. First, the computed results are compared with experimental results in Lim et al. [Exp. Fluids 37, 47 (2004)10.1007/s00348-004-0783-5] for the purpose of validation of the three-dimensional (3D) computations. Thereafter, the computed results are explained using methods developed to study nonlinear and spatiotemporal aspects of receptivity and instability for incompressible flows. Here a zero-pressure-gradient (ZPG) boundary layer is perturbed by a constant strength vortex traveling at a fixed height, moving with constant speed, as in the cited experiment. The vortex is created by a translating and rotating circular cylinder in the experiment, with absolute control of the physical parameters. The sign of the translating vortex is fixed by the direction of rotation of the translating cylinder. A high accuracy computing method is employed to solve the 3D Navier-Stokes equation (NSE) for different translation speeds and signs of the free-stream vortex. A nonlinear disturbance enstrophy transport equation (DETE) for incompressible flows is used to explain the vortex-induced instability. This equation is exact and explains the instabilities, as governed by the NSE. The DETE approach has been successfully developed to explain two-dimensional (2D) vortex-induced instability in Sengupta et al. [Phys. Fluids 30, 054106 (2018)10.1063/1.5029560], to trace the linear and nonlinear stages of disturbance growth. Apart from quantification of vortex-induced instability, another major goal is to show how the disturbance evolves from an initial 2D to a 3D stage. While the sign of the translating vortex is important in creating the response field, we additionally highlight the distinct differences caused by increased translation speed and strength of the free-stream vortex on the overall instability. These explain creation of small-scale vortices via the instability of an equilibrium flow, even though the excitation is 2D only. For some cases, this causes 3D bypass transition. We also show a case which demonstrates strong unsteady separation with inflectional velocity profiles, yet the disturbance flow remains essentially 2D, which can be termed a bypass transition.
离散和连续边界层模式的相互作用引起转变
DOI：
10.1016/j.ijheatfluidflow.2008.12.008
发表时间：
2009
影响因子：
2.6
作者：
Durbin P
通讯作者：
Durbin P