摘要:
在雷诺数为7200的圆柱尾流中对眼镜蛇探针与热线的测量结果进行了详细对比,主要包括:时均速度、雷诺应力、概率密度函数、自相关函数和能谱等。从对比结果可以发现眼镜蛇探针数据的拒绝率随湍流度增大而增大,但在本实验中其对时均测量结果无明显影响。尽管眼镜蛇探针数据有效率在95%以上,但相对于热线其明显高估了雷诺应力。尤其是主雷诺剪切应力u*v*,眼镜蛇探针与热线测量结果的差异要显著大于两者在雷诺正应力上的测量差异。由于无法反映高频随机脉动的影响,眼镜蛇探针所测信号自相关系数的周期性明显强于热线。眼镜蛇探针对速度u和v的响应存在区别,使得两者能谱在惯性子区内有显著差异,不能像热线一样反映出惯性子区内小尺度湍流的各向同性。
Abstract:
The performance of cobra probe and hotwire is compared in a circular cylinder wake at the Reynolds number of 7200,including time-averaged velocity,Reynolds stresses,probability density functions,auto-correlation coefficients and spectra.Based on the experimental results,it is found that the rejection rate of cobra probe increases with turbulence intensity.However,its effect on the time-averaged results is negligibly small.Although the acceptability rate of cobra probe is higher than 95%,it over estimates the Reynolds stresses compared to hotwire.Particu-larly,for the main Reynolds shear stress u*v*,the difference of measurements between cobra probe and hotwire is significantly larger than those for the Reynolds normal stresses.Since cobra probe can not capture high frequency fluctuation,the auto-correlation coefficients of velocities present stronger periodicity relative to that of hotwire.The responses of cobra probe are different for u and v,resulting in significant difference in their spectra in the inertial sub-range,and thus it can not reveal the local isotropy of small scale turbulence in the inertial sub-range.
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