Time resolved, near wall PIV measurements in a high Reynolds number turbulent pipe flow

Abstract

We report on near wall measurements of a turbulent pipe flow at shear Reynolds numbers up to Re = 40000 acquired in the CICLoPE facility near Bologna, Italy. With 900 mm diameter and 110m length the facility offers a well-established turbulent flow with viscous length scales ranging from y+ = 85 µm at Re = 5000 to y+ = 11 µm at Re = 40000. These length scales can be resolved with a high-speed PIV camera at image magnification near unity. For the PIV measurements the light of a high-speed, double-pulse laser is focused into an approximately 300 µm thin light sheet that is introduced radially into the pipe. The light scattered by 1 µm water-glycerol droplet seeding is observed from the side by the cameravia a 1mm thin high-aspect ratio mirror with a field of view covering 20mm in wall-normal and 5mm in stream-wise direction. Facility vibrations of up to 50 µm peak-to-peak could be accounted for with image processing thereby providing measurements with a spatial resolution at the wall unit level. Statistically converged velocity profiles could be achieved using up to 70000 samples per sequence acquired at low laser repetition rates (100 Hz). Higher sampling rates of 10 kHz provide temporally coherent data from which frequency spectra can be derived. Preliminary analysis of the data shows a well resolved inner peak that grows with increasing shear Reynolds number.