INVESTIGATION OF THE MEAN-FLOW SCALING AND TRIPPING EFFECT ON FULLY DEVELOPED TURBULENT PIPE FLOW

摘要

Fully developed turbulence measurements in pipe flow were made in the Reynolds number range from 10 X 10~3 to 350 X 10~3 with hot-wire anemometer and a Pilot tube. Comparisons were made with the experimental results of previous researchers. The mean velocity profile and the turbulent intensity in the experiments indicate that for the mean velocity profile, in the fully developed turbulent pipe flow, von Karman's constant κ is a function of the Reynolds number, i. e. κ increases slowly with the Reynolds number. For turbulent pipe flow, the outer limit depends on whether the Kdrmdn number R~+ is greater or less than 850 in the centerline velocity profile: a log law exists for 850 < R~+< 1750 in the experiment, and von Karman' s constant κ is shown to be 0. 408. Under the effects of the test trip at the inlet, fully developed turbulence was obtained in pipe flow at lower Reynolds number when the entrance length (x/D) was larger than 40. In the experiment it was also found that turbulence quantities in pipe flow remain independent of the upstream conditions when the trip blockage ratio is higher than 20%, and the comparison with channel water flow was also performed.