Abstract
The effect of mixing andd diffusion of turbulence upon the accuracy of the flow velocity measurement by means of the cross-correlation technique is discussed in this paper. The transport process of a random fluctuation of physical properties in turbulent flow is treated in the domain of frequency by assuming that the process is described by the diffusion equation, and the difference beween the delay time of this process and the distance/velocity lag is estimated. It is shown that the diffusion effect causes the delay time at the peak position of the cross-correlation function to be shorter than the distance/velocity lag, and that it is fully possible to keep the measurement error due to this cause within 0.5% by properly selecting the dimension and the disposition of the detectors.
The other source of the static error is due to the inequality of the dynamic characteristics of the two detectors. This error can be reduced by utilizing the high frequency component of the signals.
The theoretical considerations are compared with experimental results on an air pipe flow with velocity fluctuations.
