Application of Digital Particle Image Velocimetry to a turbulent pipe flow

Summary

Presented are the results of probably the first successful application of digital particle image velocimetry (DPIV) in a fully developed turbulent flow. The flow under study was a small region close to the wall (ranging from 40 < y⁺ < 90) in a smooth pipe flow, at a relatively low Reynolds number of 5,300, based on the bulk velocity and the diameter of the pipe. The advantage of DPIV in comparison with the traditional implemented PIV method is the enormous reduction in analysis time. The time needed for 1000 interrogations with the conventional PIV analysis is typically 1000 seconds, whereas for DPIV about 60 seconds are needed. This reduction in analysis time is achieved at the cost of a small reduction in accuracy. The present DPIV experiments were carried out with a simple video camera with an effective resolution of 256x512 pixels. Despite this rather poor resolution, the results demonstrate that DPIV is sufficiently accurate to yield statistically significant results. The accuracy is estimated at 0.2-0.4 u⁺, which corresponds to a measured particle image displacement of 0.1-0.2 pixel. The turbulent statistics show satisfactory agreement in comparison with data obtained with the conventional PIV method. Visual comparison of vector maps representing instantaneous fluctuating velocity fields obtained from the presen ted DPIV measurements and conventional PIV experiments previously carried out in the same facility, show that both techniques are able to capture similar flow patterns. A first investigation to detect flow structures gives promising results.