EXPERIMENTAL STUDY OF FULLY DEVELOPED TURBULENT PIPE FLOW
充分发展圆管湍流的实验研究

In the paper, DPIV technique and quantitative flow visualization are adopted to study fully developed turbulent pipe flow. The measured results from DPIV are in good agreement with those of direct numerical simulation. Based on the experimental data bank, some dynamic characteristics of turbulent pipe flow arid their roles in turbulence production are analyzed, including ejection and sweeping. The measurements show that sweeping dominates the production of turbulence in the near-wall region of pipe and ejection is overwhelming in the region far from wall. Furthermore from the data bank it is found that there are spikes in the region near the wall whose streamwise length is about 50 friction scales, apparently less than that of the usual streamwise structures, such as streamwise vortex and streak. According to the statistics, the strength of the negative spike which always goes with high speed fluid is higher than that of positive one. The conditional statistics are studied in the paper on the base of the velocity distribution in the coherent structures. The conditional mean velocity is smaller than ensemble average of fully developed turbulent pipe flow while the higher moments of fluctuation velocity is greater. Consequently, ejection is dominant in the bursting events of near-wall flow visualization. Furthermore, the study of velocity fluctuating field in the structure shows that the rollup pattern results from a vortex, in addition there is one vortex below the rollup interface of the visualized structure.