Numerical Study of the Effect of Freestream Turbulence on by-pass Transition in a Boundary Layer☆
Numerical Study of the Effect of Freestream Turbulence on by-pass Transition in a Boundary Layer☆
复制标题
自由流湍流对边界层旁路转变影响的数值研究☆
DOI：
10.1016/j.egypro.2014.01.062
复制
发表时间：
2014
期刊：
影响因子：
--
通讯作者：
P. Palma
中科院分区：
文献类型：
--
作者：
S. Cherubini;J. Robinet;P. Palma
我们使用直接的数值模拟中存在的自由流湍流具有不同的值的强度，T-U，和积分长度尺度，L，以确定哪种结构中涉及的路径过渡的边界层流。其主要目的是确定在何种条件下的过渡路径涉及类似的结构的线性或非线性的最优扰动。对于高值的T u和L，我们观察到一个大振幅的过渡路径，其特征在于本地化的旋涡结构和补丁的高和低动量波动。这样的情况下，发现相关性以及与L和发夹结构的时间演变的非线性最优扰动，而，对于较低的Tu和L，一个更大的相关性被发现相对于线性最优扰动。这表明，一个大振幅的过渡路径的存在，不同于一个特征的细长条纹经历二次不稳定性。为了区分两个过渡方案，一个简单的参数连接到流向本地化的高，低动量区。最后，一个准确的法律来预测过渡的位置，同时考虑到Tu和L，有效的过渡方案。
We use direct numerical simulations in the presence of free-stream turbulence having different values of intensity, T u, and integral length scale, L, in order to determine which kind of structures are involved in the path to transition of a boundary-layer flow. The main aim is to determine under which conditions the path to transition involves structures similar to the linear or non-linear optimal perturbations. For high values of T u and L, we observe a large-amplitude path to transition characterized by localized vortical structures and patches of high- and low-momentum fluctuations. Such a scenario is found to correlate well with the L and hairpin structures resulting from the time evolution of non-linear optimal perturbations, whereas, for lower T u and L, a larger correlation is found with respect to linear optimal disturbances. This indicates that a large-amplitude path to transition exists, different from the one characterized by elongated streaks undergoing secondary instability. To distinguish between the two transition scenarios, a simple parameter linked to the streamwise localisation of high- and low-momentum zones is introduced. Finally, an accurate law to predict the transition location is provided, taking into account both T u and L, valid for both the transition scenarios.
影响因子：
3.7
作者：
Matsubara, M;Alfredsson, PH
通讯作者：
Alfredsson, PH