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首页> 外文期刊>Applied optics >Measurement of spatiotemporal phase statistics in turbulent air flow using high-speed digital holographic interferometry
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Measurement of spatiotemporal phase statistics in turbulent air flow using high-speed digital holographic interferometry

机译：使用高速数字全息干涉测量法测量湍流中的时空相位统计量

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摘要

We describe a method of measuring spatiotemporal (ST) structure and covariance functions of the phase fluctuations in a collimated light beam propagated through a region of refractive index turbulence. The measurements are performed in a small wind tunnel, in which a turbulent temperature field is created using heated wires at the inlet of the test section. A collimated sheet of light is sent through the channel, and the phase fluctuations across the sheet are measured. The spatial phase structure function can be estimated from a series of images captured at an arbitrary frame rate by spatial phase unwrapping, whereas the ST structure function requires a time resolved measurement and a full three-dimensional unwrapping. The measured spatial phase structure function shows agreement with the Kolmogorov theory with a pronounced inertial subrange, which is taken as a validation of the method. Because of turbulent mixing in the boundary layers close to the walls of the channel, the flow will not obey the Taylor hypothesis of frozen turbulence. This can be clearly seen in the ST structure function calculated in a coordinate system that moves along with the bulk flow. At zero spatial separation, this function should always be zero according to the Taylor hypothesis, but due to the mixing effect there will be a growth in the structure function with increasing time difference depending on the rate of mixing.
机译：我们描述了一种测量准时光束传播通过折射率湍流区域的相位波动的时空（ST）结构和协方差函数的方法。测量是在小型风洞中进行的，在风洞中，使用加热金属丝在测试部分的入口处形成湍流温度场。准直的光片通过通道，并测量整个片的相位波动。可以从通过空间相位展开以任意帧速率捕获的一系列图像估计空间相位结构功能，而ST结构功能需要时间分辨的测量和完整的三维展开。测得的空间相结构函数与Kolmogorov理论具有明显的惯性子范围相一致，这被认为是该方法的验证。由于在靠近通道壁的边界层中发生了湍流混合，因此该流动将不服从冻结湍流的泰勒假设。这可以在随整体流量移动的坐标系中计算出的ST结构函数中清楚地看到。在空间间隔为零时，根据泰勒（Taylor）假设，该函数应始终为零，但是由于混合效应，结构函数将随着混合速度的增加而随着时间差的增加而增长。

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