【作者】 夏振炎；

【导师】 舒玮； 姜楠；

【作者基本信息】 天津大学 ， 流体力学， 2007， 博士

【摘要】 在壁湍流中引入空间展向周期分布的流向狭缝周期吹吸射流,利用局部周期吹吸扰动对壁湍流相干结构进行控制。用热线风速仪对受扰前后湍流边界层的脉动速度信号进行测量,综合采用概率统计平均、付立叶变换、条件采样、子波和子波包变换等技术对壁湍流速度信号进行分析,研究吹吸扰动对壁湍流相干结构、能谱、间歇性的影响以及壁湍流中基本流场的变化规律。提出多尺度关联的子波系数局部极值和子波系数多尺度自相关函数辨识壁湍流相干结构的方法,发现缓冲层相干结构的速度脉动较外区更剧烈,壁湍流相干结构在时空分布中呈多尺度特征;提出采用子波包提取脉动速度信号中扰动成分的方法,结果显示该方法较FFT数字滤波法更准确;运用高阶消失矩子波函数进行子波湍谱分析,可以有效减少湍谱能量泄漏,提高湍流信号谱分析的准确性。通过子波变换与VITA条件采样法等多种检测方法的比较,发现施加吹吸扰动使得缓冲层内最大含能尺度的湍流相干结构的强度明显降低,抑制了壁湍流的猝发过程,延长了平均猝发间隔,减少了猝发的数量和强度,使相干结构的条件平均波形和子波重构脉动速度波形的幅值明显降低,说明该方法是控制壁湍流相干结构的一种有效方法。通过湍谱分析,发现壁湍流惯性子区的波数范围与法向位置有关。随着法向位置靠近壁面,壁湍流惯性子区的波数范围向高波数区移动,能谱逐渐偏离均匀各向同性湍流的-5/3次幂。从提取的壁湍流相干结构脉动速度波形上看,缓冲层相干结构速度脉动较外区更剧烈。通过子波谱和最大熵谱法分析吹吸扰动对湍流能谱的影响,发现施加的低频吹吸扰动改变了壁湍流各尺度湍流相干结构的能量分布,含能最大的相干结构能量损失最多,小尺度湍流结构的能量有所增加。扰动在对数层外区的影响迅速消失,湍流能谱恢复到扰动前的状态。对加扰前后壁湍流小尺度结构的间歇性研究发现,惯性子区的标度指数比耗散区的标度指数小。缓冲层的标度指数与线性标度律偏差很大,显示出较强的奇异性,对数层及外区标度指数逐渐接近均匀各向同性湍流的状态。吹吸扰动使缓冲层内小尺度湍流结构的标度指数下降,间歇性进一步增强。更多还原

【Abstract】 The fluctuating velocity has been measured using hot wire anemometer with and without the local periodic blowing and suction disturbance coming from longitudinal thin slits periodically distributed in transverse direction of wall turbulence. The coherent structures in wall turbulence are controlled by the local sinusoidally oscillating jet flow issuing from the longitudinal thin slits. The fluctuating velocity signals have been analyzed by the comprehensive methods of probability statistics, Fourier transform, conditional sampling, wavelet and wavelet packet transform, etc in order to investigate the effects of disturbance to the coherent structures in wall turbulence. The variations of turbulence energy spectrum, intermittence and the mean flow parameters have been studied before and after blowing and suction disturbance introduced.The methods of local maximum of wavelet coefficients across related multi-scales and wavelet auto-correlation function have been put forward to detect and identify the coherent structures in wall turbulence. It is found that coherent structures in buffer layer fluctuates more actively than that in outer region of turbulent boundary layer and behaves temporally and spacially in multi-scales. Wavelet packet transform has been put forward to extract the disturbance component from the turbulent fluctuating velocity, which shows more accurate than the Fourier filter method; the wavelet function of Daubechies20 with high vanishing moments is employed to analyze turbulent spectrum so as to decrease the energy leakage of the signal effectively and improve the precision of turbulence spectrum analysis.The coherent structure detection results of wavelet transform are compared with that of VITA conditional sampling method. It is shown that blowing and suction disturbance can not only decrease the intensity of turbulent fluctuation at the most energetic scale in buffer layer and restrains the burst process in wall turbulence, but also prolong the averaged burst alternation and lessens the quantity and intensity of burst events. And then the amplitudes of conditionally averaged velocity as well as the wavelet restructured velocity are apparently decreased with the periodic blowing and suction disturbance. It can come to the conclusion that the periodic blowing and suction oscillating disturbance coming from longitudinal slit jet flow is an effective method of control wall turbulence. Through the investigation of turbulent energy spectrum, it is found that for wall turbulence, the variation of inertial wave number range is related to the vertical measurement position in turbulent boundary layer. When the measurement position is near to the wall, the inertial wave number range in wall turbulence shifts to the higher wavenumber and the spectrum gradually deviates from -5/3 exponent power, which stands for the homogeneous and isotropic turbulence. According to the velocity fluctuating waveform of coherent structures extracted from origin velocity signal, the fluctuation of coherent structure in buffer layer becomes more active than that in outer region.According to the effects of blowing and suction on turbulent energy spectrum by wavelet spectrum and maximum entropy spectrum method, it is discovered that the disturbance changes the turbulent kinetic energy distribution across scales in the near wall region, which implies that the coherent structures lose more kinetic energy and the small scale structures obtain more kinetic energy. The effect of disturbance disappears gradually when the measurement position is apart from the near wall region and the turbulent spectrum recovers to the situation without disturbance.Through investigating the intermittence of small-scale structures in wall turbulence with or without disturbance, the scaling exponent in inertial wavenumber range is lower than that in dissipative range. The scaling exponent in buffer layer extraordinarily deviates from the linear scaling law which shows intensive anomalous, whereas the scaling exponent in logarithmic region and outer region gradually approaches to the situation of homogeneous and isotropic turbulence. The blowing and suction further reduces the scaling exponent and enhances the intermittence of small scale structures in buffer layer.更多还原