Experimental study of velocity distributions in the transition region of pipes

The accuracy of an ultrasonic flowmeter meaurement depends on the profile-linear average velocity. But this velocity in the transition region is not available at the present. In this article, the velocity in the transition region in pipes is studied by experimental methods. The Particle Image Velocimetry (PIV) is used to measure the flow field in the transition region in pipes, and the measured results from PIV are in good agreement with the Westerwell's experimental data. Based on the experimental data of PIV, the curves of the profile-linear average velocity in the transition region against the Reynolds number in the range from 2 000 to 20 000 are obtained, and it is shown that the coefficient k is constant when the Reynolds number is in the range of 2 000–2 400 and 6 000–20 000, and the coefficient k is increasing when the Reynolds number is in the range of 2 400–6 000. The results of this article can be used to improve the measurement accuracy of the ultrasonic flowmeters and as a theoretical basis for the research on the transition flow.