Study On Near Wall Coherent Structure And Drag Reduction Performance Of Helical Flow In A Circular Tube

More and more application of helical flow in the field of petroleum pipe at present,at home and abroad on the flow velocity of more changes in pipe flow field,the turbulence reduction of the helical flow is less studied,and the friction resistance of turbulent flow is the important factor of the helical flow attenuation.The core problem is the turbulent drag reduction by controlling the coherent structure to effectively reduce the wall friction.The helical flow near the wall of the coherent structure of the pipe,the analysis of coherent structure formation and evolution,and study the Reynolds number effects of vibration conditions such as helical flow near the wall of the pipe resistance.In this paper,helical pipe flow as the research object,considering the complexity of the near wall region of the flow field by large eddy simulation(LES)method,adopt Top-hat filter function flow field filtering,application of small scale vortex turbulent kinetic energy transport subgrid model(KET),the near wall region by completely solving model of coherent structure.The application of Q criterion method to identify the helical pipe flow in the near wall region,analysis of near wall belt,vorticity contours,the formation mechanism of streamwise vortex and Hairpin Vortex,pulsation of solution of Reynolds stress distribution in the region near the wall and wall shear stress.According to the static wall surface analysis results,to develop simulation programs,respectively,from the three aspects of the Reynolds number,vibration frequency and vibration velocity of helical flow in the near wall region flow field analysis of circular pipe,the mean velocity profile,velocity RMS,RMS ripple vorticity,Reynolds stress analysis and stress reduction effect the wall friction resistance and so on.According to the flow characteristics of helical flow in circular pipe construction of PIV experimental device,and the results were compared with the large eddy simulation results,to verify the numerical simulation,proved the correctness of the model and calculation method of numerical calculation,numerical simulation calculation method of the spiral flow tube that is reasonable.The results of this paper are the preliminary study on the coherent structure and wall drag reduction in the near wall region of the helical flow,which can provide a theoretical guidance for the subsequent control of the drag reduction of the wall.