Experimental Investigation And Numerical Simulation Of Turbulent Pipe Flow And The Tripping Effects

The turbulent flow in a circular pipe is one of the most primary flow in the theoretical research and application. The research on it is an old but renewable subject, which may not only deepen the understanding of many fundamental flow phenomena and the responsible mechanism for turbulence, improve the turbulence model, but also optimise its application in engineering. The goal of this paper is to study fully developed turbulent pipe flow. With the aid of the tripping annulus at the inlet, based on the experimental investigation and numerical simulation, detailed researches on a few basic rules in pipe flow have been performed, such as mean velocity profile, relative intensity of turbulence, the log-law, von Karman's constant and reattachment length, thus filling some gaps in the research work of predecessors and obtaining a far-reaching understanding.The main aspects of the research work are as following:1. An apparatus of pipe flow was built with D = 112mm and D = 67.8mm in theReynolds number range from 2000 to 3.6 x 105. With the different tripping annulus at the inlet, a new method of the distance definition from the wall was used to measure 35 mean velocity profiles on seven sections in the pipe length x/D = 125.2. A new coefficient of Prandtl's relation was obtained from the experimental data. Compared with three conventional relations of friction factor, the range of Reynolds number was extended. According to the integral equations of pipe flow, the relationship between the friction factor and the log-law was approached, as well as the effects of low Reynolds number on the relation of friction factor.3. Based on the wall equation and k-?model, the variable C?and the variable lmwere used to improve the numerical simulation of pipe flow with the tripping annulus at the inlet. The numerical results under different methods, especially the simulation of recirculation region and reattachment length were carefully checked and compared. It indicated that the "variable Cî–²" model could effectively increase the dissipationnear the wall and, more over improve the simulation of the reattachment length to close to the experimental results.4. In accordance with different tripping annulus at the inlet, the numerical simulations of the reattachment length were performed with the "variable Cî–²" model. In therange of experimental Reynolds number, the tripping effect on the reattachment length was developed in the figure. The dependence of the reattachment length on Reynolds number was also analysed in the different status of pipe flow.5. The method to determine von Karman's constant with the integral equations was reviewed. The variation of von Karman's constant in the overlap region was also analysed. A new conclusion was driven, that von Karman's constant is a function of Reynolds number or Karman number in the overlap region.6. The existence of a log-law in the centreline velocity profile and the variation of the turbulence intensity in the centreline were discussed in detail. The anisotropy invariant map was also introduced briefly. The effect of the distance away from the wall and the Reynolds number on the turbulence structure in a pipe flow was also analysed.7. The effects of tripping annulus on a pipe flow and a channel flow were compared and analysed. It indicated that the effect on both flow are mostly identical. In case of high Reynolds number, the turbulence intensity of centreline drifted off its stable course in the sections, where the flow was in the transition. The effects of the different tripping size were not alike, 20% tripping annulus was the best size for a pipe flow to obtain fully developed turbulence in the experiment.8. The factors on the turbulent entrance length were analysed, based on the variable Recr, a new empirical formula was developed for the turbulent entrance length in a pipe flow.