声场中的粒子振速是评价空气声场特性的一个重要参量。在平面波声场中，通过获取激光多普勒测速仪对不同声压级声场中散射粒子产生的光电信号，采用光子自相关法对原始多普勒信号进行处理，粒子的速度量值根据相关函数的时间特征值得出...声场中的粒子振速是评价空气声场特性的一个重要参量。在平面波声场中，通过获取激光多普勒测速仪对不同声压级声场中散射粒子产生的光电信号，采用光子自相关法对原始多普勒信号进行处理，粒子的速度量值根据相关函数的时间特征值得出，并与传声器测量声压值计算的粒子振速值进行比较。在原有自相关算法的基础上，利用样条插值法来估计相关周期，减小原有信号频偏与多普勒频率之比并非整数倍的引入的差异。实验结果表明，光子相关法能够获得声场中的粒子振速，与传声器测量值吻合较好，当振速较大时，插值法有利于减小测量偏差。在96-110 dB 的声压量值范围内，光子相关法与传声器测量值之间的振速偏差优于0.7 dB。展开更多
In this paper the results of an experimental investigation, finalized to analyze the effect of roughness elements on the Oscillatory Boundary Layer （OBL）, were presented and discussed. These experiments can be usefu...In this paper the results of an experimental investigation, finalized to analyze the effect of roughness elements on the Oscillatory Boundary Layer （OBL）, were presented and discussed. These experiments can be useful for the characterization of the complex hydrodynamic mechanisms in coastal environment, where the bottom boundary layer is very often subject to momentum exchange processes due to the presence of macro-structures on the bottom able to strongly influence and modify its own structure. In this investigation, experiments were performed in an oscillating water tunnel, covering a range of frequencies to from 0.646 up to 2.319 rad.s^-1. The roughness elements were modelled by mean of a matrix of stiff cylinders arranged on the bottom of the tunnel and two densities of cylinders were considered, corresponding to low and high density respectively. Velocity measurements were obtained by 2C DPIV （2 Component Digital Particle Image Velocimetry） technique. A detailed visualization of the flow through adjacent cylinders, including scalar velocity maps and streamlines are presented. Furthermore phase-averaged velocity distributions are here provided. Moreover, root-mean-squared velocities are considered and an empirical relation between （1） the root-mean-squared velocities and the distance from the bottom; （2） the velocity attenuation coefficient and the Reynolds number is obtained for both the considered configurations.展开更多
Particle Imaging Velocimetry （PIV） is utilized to investigate the flow structures of an oscillating cylinder attached to a flexible tail. At the same oscillation frequency and amplitude, the mean streamwise velocity...Particle Imaging Velocimetry （PIV） is utilized to investigate the flow structures of an oscillating cylinder attached to a flexible tail. At the same oscillation frequency and amplitude, the mean streamwise velocity along the wake central-line and the mean vertical velocity around the trailing edge of the flexible tail can be greatly increased with the tail length. Meanwhile, the longer the flexible tail is, the larger its deformation is. In order to study the influence of flexible tail length on the wake pattern of the experimental model, the relationships between the swirling strength Aci of vortex structure near the tail end and the velocity of tail trailing edge have been revealed. Moreover, the convection tracks and the Aci of vortex cores for different flexible tails are discussed.展开更多
文摘声场中的粒子振速是评价空气声场特性的一个重要参量。在平面波声场中，通过获取激光多普勒测速仪对不同声压级声场中散射粒子产生的光电信号，采用光子自相关法对原始多普勒信号进行处理，粒子的速度量值根据相关函数的时间特征值得出，并与传声器测量声压值计算的粒子振速值进行比较。在原有自相关算法的基础上，利用样条插值法来估计相关周期，减小原有信号频偏与多普勒频率之比并非整数倍的引入的差异。实验结果表明，光子相关法能够获得声场中的粒子振速，与传声器测量值吻合较好，当振速较大时，插值法有利于减小测量偏差。在96-110 dB 的声压量值范围内，光子相关法与传声器测量值之间的振速偏差优于0.7 dB。
文摘In this paper the results of an experimental investigation, finalized to analyze the effect of roughness elements on the Oscillatory Boundary Layer （OBL）, were presented and discussed. These experiments can be useful for the characterization of the complex hydrodynamic mechanisms in coastal environment, where the bottom boundary layer is very often subject to momentum exchange processes due to the presence of macro-structures on the bottom able to strongly influence and modify its own structure. In this investigation, experiments were performed in an oscillating water tunnel, covering a range of frequencies to from 0.646 up to 2.319 rad.s^-1. The roughness elements were modelled by mean of a matrix of stiff cylinders arranged on the bottom of the tunnel and two densities of cylinders were considered, corresponding to low and high density respectively. Velocity measurements were obtained by 2C DPIV （2 Component Digital Particle Image Velocimetry） technique. A detailed visualization of the flow through adjacent cylinders, including scalar velocity maps and streamlines are presented. Furthermore phase-averaged velocity distributions are here provided. Moreover, root-mean-squared velocities are considered and an empirical relation between （1） the root-mean-squared velocities and the distance from the bottom; （2） the velocity attenuation coefficient and the Reynolds number is obtained for both the considered configurations.
基金supported by the National Natural Science Foundation of China (Grant No. 10832001)the Innovation Foundation of BUAA for PhD Graduates
文摘Particle Imaging Velocimetry （PIV） is utilized to investigate the flow structures of an oscillating cylinder attached to a flexible tail. At the same oscillation frequency and amplitude, the mean streamwise velocity along the wake central-line and the mean vertical velocity around the trailing edge of the flexible tail can be greatly increased with the tail length. Meanwhile, the longer the flexible tail is, the larger its deformation is. In order to study the influence of flexible tail length on the wake pattern of the experimental model, the relationships between the swirling strength Aci of vortex structure near the tail end and the velocity of tail trailing edge have been revealed. Moreover, the convection tracks and the Aci of vortex cores for different flexible tails are discussed.
