二维湍流外力尺度影响的格子Boltzmann方法研究

该文基于格子Boltzmann方法,研究系统外力尺度kmax/kf对二维湍流的能谱和统计行为的影响。考虑了两种系统外力(高斯力和Kolmogorov力)和三种外力尺度max/fk k。在不存在线性摩擦力情况下,验证了描述二阶涡量结构函数与能谱关系的Benzi理论。研究表明:当外力尺度kmax/kf逐渐增大时,Kolmogorov外力情况下的二阶涡量结构函数与能谱之间的关系逐渐符合Benzi理论。在存在线性摩擦力情况下,出现能谱双能级。随着外力尺度kmax/kf逐渐增大,Kolmogorov外力情况下的直接惯性区能谱逐渐接近Kraichnann理论。在两种系统外力情况下涡量场和速度场的概率分布函数(PDF)具有指数尾迹,与Falkovich和Lebedev理论预测的结果一致。PDF随着kmax/kf增加有更大的峰度(Kurtosis),这意味着在直接级联惯性区具有更强的间歇性。     

Energy dissipation statistics along the Lagrangian trajectories in three-dimensional turbulent flows

Energy dissipation rate is relevant in the turbulent phenomenology theory, such as the classical Kolmogorov 1941 and1962 refined similarity hypothesis. However, it is extremely difficult to retrieve experimentally or numerically. In this paper, the full energy dissipation, its proxy and the pseudo-energy dissipation rate along the Lagrangian trajectories in the three-dimensional turbulent flows are examined by using a state-of-art high resolution direct numerical simulation database with a Reynolds number Re_λ= 400. It is found that the energy dissipation proxy ε~P is more correlated with the full energy dissipation rate ε. The corresponding correlation coefficient p between the velocity gradient and ε shows a Gaussian distribution. Furthermore, the coarse-grained dissipation rate is considered. The cross correlation p is found to be increased with the increasing of the scale τ.Finally, the hierarchical structure is extracted for the full energy dissipation rate, its proxy and the pseudo one.The results show a power-law behavior in the inertial range10≤τ/τ_η≤100. The experimental scaling exponent of the full energy dissipation rate is found to be h_L=0.69, agrees very well with the one found for the Eulerian velocity. The experimental values for ε~P and ε~S are around h_L=0.78, implying a more intermittent Lagrangian turbulence. Therefore, the intermittency parameter provided by ε~P and ε~s will be biased.     

雷诺数对近壁面圆柱绕流和壁湍流相互作用结构特性的影响

该文采用流动显示和PIV对近壁面放置圆柱的流场进行了精细测量,重点研究了不同雷诺数下近壁区圆柱绕流与壁湍流的相互作用规律、尺度演化规律及标度律特性.当雷诺数从10 600降至4 800时,波数能量级串标度行为呈现从-5/3至-1变化规律.而联合概率密度分析发现随雷诺数的下降,大尺度结构出现的概率降低,而雷诺数在5 60...