Structure of Reynolds Stress in the Near Wall Region of a Turbulent Pipe Flow

摘要

The structure of the Reynolds stress in the near-wall region of a fully developedturbulent pipe flow was investigated. The working fluid was glycerine, the high viscosity of which makes the viscous much larger than in water or air. The Reynolds number of the experiment, based on the diameter of the pipe, was close to 9000. The 0.285 m diameter test-section is located 25 diameters downstream of the contraction to ensure a fully developed flow. A trip ring is used to fix the location of transition at the entrance of the pipe. The test-section was built of acrylic to allow optical access for a laser Doppler velocimeter (LDV). Single-point LDV measurements as close as one wall unit from the wall were made. Agreement with previous investigations was excellent. A two component LDV and a one-component fiber-optics LDV were combined to measure the two-point velocity correlation in the wall region. Separation distances as large as 900 wall units in the streamwise direction and 64 wall units in the normal direction were investigated. The effect of velocity bias on the correlation coefficient was studied and it was found to be small in the conditions of this experiment. (kr)