Research On Turbulent Drag Reduction Characteristics Over Profiled Travelling Wave Surface Of Pipes

With the increasing energy shortage seriously,Energy conservation and consumption reduction have become an important issue of concern to the country.As the pipeline transportation,it is necessary to overcome the frictional resistance of the wall to do work,and the frictional resistance work accounts for more than 70%of the total pipeline transportation consumption.Pipeline transportation,as the main means of oil and gas transportation,has important influence on the energy consumption of the world.Scientists have discovered that the non-smooth surface structure of plants and animals can reduce the frictional resistance of fluids.With more analyzing the microstructure of dolphins,sharks and lotus leaf surfaces,a series of non-smooth surface drag reduction structures were imitated.These structures exhibit superior drag reduction performance compared to traditional smooth surfaces,and non-smooth surface drag reduction studies show great research prospects.Based on previous theoretical research background,It is represented by the profiled structure formed by the airflow driving the ripples on the surface.A cycloidal structure with a large aspect ratio,is obtained by simplifying abstract extraction.With the depending on the three-dimensional CAD software to complete the design of structure,based on the actual flow of the pipeline to establish a CFD numerical simulation model.Comparing with the theoretical calculation,the numerical simulation relative error was less than 0.5%.According to the actual conditions,the simulated experiments with three flow rates set,to complete the simulation of different structural dimension models.In order to study the drag reduction performance under different structure,orthogonal analysis was used for experimental analysis.The order of depth,the width and depth ratio(the ratio of width to depth),and eccentricity ratio(the ratio of eccentricity to width),which is the order of the factors that influence the total resistance with the size factor of traveling wave elements.With the analysis of range and variance,it can be concluded that depth and breadth ratio play a decisive role in drag reduction performance.In the case of a flow rate of 15 m/s,the optimal drag reduction dimension is 0.4 mm depth,width to depth ratio 20,and eccentricity ratio 0.25 to obtain the best drag reduction rate of 5.52%.In order to further exploring about the drag reduction mechanism of profiled travelling wave surface structures,the wall boundary layer on the profiled travelling wave surface is significantly increased compared with the smooth surface by analyzing flow field.On the same wall surface height,the profiled travelling wave surface flow speed is less than the smooth surface,the low velocity fluid stays in the trough have become the buffer layer,lowering the velocity gradient near the wall surface,and this is the reason that the frictional resistance is reduced to achieve drag reduction effect.Considering the situation about actual process and demands,the influence of the traveling wave surface roughness on the drag reduction effect need be further studied.The profiled travelling wave surfaces which have different size roughness are compared with the smooth surface of the same rough grade.With the higher of the absolute roughness height,the bigger drag of the profiled traveling wave surface and the smooth surface.However,the resistance growth rate of the profiled traveling wave surface is lower than that of the smooth surface,and the drag reduction rate is improved to some extent.Set different shape protrusions at the bottom of the valley to explore the effect of ash fouling on the drag reduction performance of the profiled traveling wave surface.The profiled traveling wave surfaces caused by the valley bottom bumps will change the drag reduction characteristics of the original structure,and the surface pressure difference resistance and friction resistance will be improved and higher than the smooth surface.In the medium pressure environment of pipeline gas transportation,the profiled traveling wave surfaces designed in this paper has excellent drag reduction performance compared with smooth surface,and has a wide range of application,which has certain engineering application value.