Experimental and numerical studies for a dynamical coherent structure of the skewed turbulent boundary layer on a rotating cylinder

本研究的目的是了解湍流边界层的动力学相干结构。在轴向流动的旋转圆柱体上，有扭曲的速度分布。这是一个基本的三维模型。紊流壁层，应视为包含体力和额外应变率的复杂紊流。今年，根据前一年获得的瞬时时间序列数据，利用VITA技术和四象限方法研究了爆破现象和湍流相干结构。VITA分析的结果表明，波动速度信号的幅度减小，间歇时间缩短，爆破现象的检测频率降低。四象限方法的结果表明，近壁面区域的扫描事件的贡献相对大于平板边界层的贡献。对圆柱平面内局部平均速度方向的波动速度分量和垂直于该平面的波动速度分量分别进行了连续和离散小波变换。连续小波变换的结果承认小波谱峰的存在是固有现象。离散小波变换结果表明，脉动速度的某些分量存在高能谱。由高能系数重组的速度分量表现出明显的差异。负相关。利用方位方向上两个位置的时间序列数据，得到了速度波动的两点时空相关和交叉谱。然后，利用两点空间相关得到横向谱。结果表明，在旋转圆筒周围存在大规模的螺旋涡。作为数值分析的第一步，进行了考虑轴对称边界条件的层流分析，以及基于k-ε模型和代数湍流模型的湍流分析。紊流分析结果表明，对平均流场和波动流场进行充分的预测是困难的。目前，我们正在开发一个低雷诺数的DNS代码，并在信道流中进行验证。少

The objective of the present study is to understand a dynamical coherent structure of a turbulent boundary layer. which has skewed velocity profiles, on a rotating cylinder in an axial flow. This is one of the basic models of a three-dimensional. turbulent wall layer, which should be treated as a complicated turbulent flow containing body force and extra strain rate.This year, the bursting phenomena and the turbulent coherent structure were investigated using VITA technique and four-quadrant method according to the instantaneous time series data obtained the previous year. The results of the VITA analysis exhibit a decrease in amplitude of the fluctuating velocity signal, reduction of the intermittent period and a decrease in the detected frequency of the bursting phenomena. The results of the four-quadrant method exhibit that the contributions of a sweep event in the near wall region become relatively larger than those of the flat plate boundary layer. Continuous and discrete wavelet … More transform were also performed to the fluctuating velocity components in the local mean velocity direction within the cylindrical plane, and to the velocity components perpendicular to that plane. The results of the continuous wavelet transform recognized the existence of the peak of wavelet spectra as inherent phenomena. The results of discrete wavelet transform exhibit that there are high-energy spectra in some components of the fluctuating velocity. The velocity components recomposed by high-energy coefficient exhibit distinct. negative correlation.Two-point space-time correlation and cross-spectra of velocity fluctuations were obtained from time series data at two positions in the azimuthal direction. Then, lateral spectra were obtained from two-point space correlations. The results suggest the existence of large scale helical eddies surrounding the rotating cylinder.As a first step of numerical analysis, laminar flow analysis considering axisymmetric boundary condition, and turbulent flow analysis based on a k-ε model and algebraic turbulence model, were conducted. The results of turbulent flow analysis show that it is difficult to predict sufficiently both the mean and fluctuating flow filed. At present, we are developing a DNS code for low Reynolds number and verifying it in a channel flow. Less