OPTIMAL TRANSIENT GROWTH AND VERY LARGE-SCALE STRUCTURES IN ZERO-PRESSURE GRADIENT TURBULENT BOUNDARY LAYERS
OPTIMAL TRANSIENT GROWTH AND VERY LARGE-SCALE STRUCTURES IN ZERO-PRESSURE GRADIENT TURBULENT BOUNDARY LAYERS
复制标题
零压梯度湍流边界层中的最优瞬态增长和超大规模结构
DOI：
10.1615/tsfp6.190
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
S. Depardon
中科院分区：
文献类型：
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作者：
G. Pujals;C. Cossu;S. Depardon
我们对零压力梯度湍流边界层持续扰动的最优能量增长感兴趣。我们使用Monke-witz等人（2007）提出的平均流量，湍流动力学是根据del Alamo和Jim enez（2006）或Pujals等人（2009）在湍流通道流动情况下的方法，通过在扰动方程中加入涡流粘度来建模的。尽管所有考虑的湍流平均剖面都是线性稳定的，但由于算子的非正态性，它们支持瞬态能量增长。我们发现大部分的放大扰动是流向均匀的，对应于流向涡旋演变成流向条纹。与del ' Alamo和Jim ' enez（2006）的研究一致，我们发现在足够大的雷诺数下存在两个不同的最佳增长峰：一个主要的在外部单元缩放，一个次要的在壁面单元缩放。与壁单元的峰值结垢相关的最佳结构与在缓冲层中观察到的最可能的条纹相对应，并且它们的适度能量增长与雷诺数无关。与外部单元的峰缩放相关的能量增长大于内部峰的能量增长。与该主峰相关的最佳扰动存在于具有8 δ阶展向波长的非常大规模的结构中。
We are interested in the optimal energy growth of perturbations sustained by a zero pressure gradient turbulent boundary layer. We use the mean flow proposed by Monke-witz et al. (2007), the turbulence dynamics being modeled by an eddy viscosity added in the disturbance equations following the approach of del ´Alamo and Jim´enez (2006), or Pujals et al. (2009) in the turbulent channel flow case. Although all the considered turbulent mean profiles are linearly stable, they support transient energy growths due to the non-normality of the operator. We find that the most am-plified perturbations are streamwise uniform and correspond to streamwise vortices evolving into streamwise streaks. Consistently with the study of del ´Alamo and Jim´enez (2006), we find that two distinct peaks of the optimal growth exist for sufficiently large Reynolds numbers: a primary one scaling in outer units and a secondary one scaling in wall units. The optimal structures associated with the peak scaling in wall units correspond well to the most probable streaks observed in the buffer layer and their moderate energy growth is independent of the Reynolds number. The energy growth associated with the peak scaling in outer units is larger than that of the inner peak. The optimal perturbations associated with this primary peak consist in very large-scale structures with a spanwise wavelength of the order of 8 δ .