Transition of Transient Channel Flow with High Reynolds Number Ratios.
Transition of Transient Channel Flow with High Reynolds Number Ratios.
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DOI：
10.3390/e20050375
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发表时间：
2018-05-17
期刊：
影响因子：
--
通讯作者：
He S
中科院分区：
文献类型：
--
作者：
Mathur A;Seddighi M;He S
本文采用大涡模拟方法研究了高雷诺数比对槽道湍流在阶跃加速作用下的瞬态特性的影响。示出了流的响应表现出He & Seddighi（J. Fluid Mech.，第715卷，2013年，pp. 60-102和第764卷，2015年，pp. 395-427）-一个类似于边界层流旁路过渡的三级响应。随着Re比的增加，转捩的特征变得更加显著，即细长条纹变得更强更长，转捩开始时的初始湍流斑变得越来越稀疏。这些情况下的临界转捩雷诺数和转捩期雷诺数偏离He & Seddighi（2015）的趋势。高Re比的情况下，在过渡开始后不久，在流向波动剖面的瞬态响应中显示出双峰。基于λ_2准则的条件平均湍流统计表明，脉动剖面中的两个峰值是由湍流产生的活跃区和非活跃区的贡献引起的。靠近壁面的峰是由于在活动区产生“新”湍流，而远离壁面的峰是由于在非活动区的细长条纹。在低Re比的情况下，这两个区域的峰值在整个瞬态期间彼此接近，导致域平均轮廓中的单个峰值。
Large-eddy simulations of turbulent channel flow subjected to a step-like acceleration have been performed to investigate the effect of high Reynolds number ratios on the transient behaviour of turbulence. It is shown that the response of the flow exhibits the same fundamental characteristics described in He & Seddighi (J. Fluid Mech., vol. 715, 2013, pp. 60–102 and vol. 764, 2015, pp. 395–427)—a three-stage response resembling that of the bypass transition of boundary layer flows. The features of transition are seen to become more striking as the Re-ratio increases—the elongated streaks become stronger and longer, and the initial turbulent spot sites at the onset of transition become increasingly sparse. The critical Reynolds number of transition and the transition period Reynolds number for those cases are shown to deviate from the trends of He & Seddighi (2015). The high Re-ratio cases show double peaks in the transient response of streamwise fluctuation profiles shortly after the onset of transition. Conditionally-averaged turbulent statistics based on a λ_2-criterion are used to show that the two peaks in the fluctuation profiles are due to separate contributions of the active and inactive regions of turbulence generation. The peak closer to the wall is attributed to the generation of “new” turbulence in the active region, whereas the peak farther away from the wall is attributed to the elongated streaks in the inactive region. In the low Re-ratio cases, the peaks of these two regions are close to each other during the entire transient, resulting in a single peak in the domain-averaged profile.
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