Instantaneous Fluctuation Velocity and Skewness Distributions Upstream of Transition Onset
Instantaneous Fluctuation Velocity and Skewness Distributions Upstream of Transition Onset
复制标题
转变开始上游的瞬时波动速度和偏度分布
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
D. McEligot
中科院分区：
文献类型：
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作者：
D. Hernon;E. Walsh;D. McEligot
本文给出了零压力梯度边界层流动在%Tu=44.2影响下，在转折开始前通过边界层厚度的流向扰动的发展。分析集中在脉动速度的最大正负两个方向上的发展，以获得对转变过程的进一步了解。在一定雷诺数范围内，峰值负脉动速度的平均位置是在y/δ和≈=0.6时在边界层上部测量的，而正峰速度的位置是在y/δ和≈=0.3时测量的。随着转折的临近，负起伏速度的扰动幅度逐渐大于正起伏速度的扰动幅度。最大正、负脉动速度的分布和扰动大小表明，转变的起始可能发生在上升到边界层上部的低速分量上。这与最近对边界层边缘附近抬升的低速条纹上的流动破裂的直接数值模拟是定性一致的。这项研究的结果还表明，通过检查与低速和高速条纹相关的流向脉动速度分量的最大正负分布(与时间平均值相比)，在确定什么结构导致湍流破裂时，获得了更多的物理洞察力。
Abstract The development of streamwise orientated disturbances through the boundary layer thickness prior to transition onset for zero-pressure gradient boundary layer flow under the influence %Tu = 4.2 is presented. The analysis concentrates on the development of the maximum positive and negative of the fluctuation velocity in order to gain further insight into the transition process. The average location of the peak negative fluctuation velocity over a range of Reynolds numbers was measured in the upper portion of the boundary layer at y / δ ≈ 0.6, whereas the location of the peak positive value was measured at y / δ ≈ 0.3. The disturbance magnitude of the negative fluctuation velocity increased beyond that of the positive as transition onset approached. The distribution and disturbance magnitude of the maximum positive and negative fluctuation velocities indicate that the initiation of transition may occur on the low-speed components of the flow that are lifted up to the upper region of the boundary layer. This is in qualitative agreement with recent direct numerical simulations on the breakdown of the flow on the lifted low-speed streaks near the boundary layer edge. The results presented in this investigation also demonstrate the increased physical insight gained by examining the distributions of the maximum positive and negative of the streamwise fluctuation velocity component associated with the low- and high-speed streaks, compared to time-averaged values, in determining what structures cause the breakdown to turbulence.