Drag Reduction Of Off-path Resistance Of Pipeline And Its Flow Pressure Fluctuation Characteristics

When the fluid flows in the pipeline network,there will be resistance and energy consumption.The flow resistance in the pipe can be divided into along-process resistance and non-process resistance according to its characteristics,and the non-along-process resistance is mainly local resistance.Scholars at home and abroad have more and tend to be perfect in the literature on the research and output of the resistance along the path,while the research on the resistance along the path is relatively less,especially in how to reduce the local resistance and the corresponding flow characteristics.Supported by the National Natural Science Foundation of China,this thesis studies how to reduce the local resistance caused by the sudden change of the pipeline cross-section and the reduced pressure pulsation characteristics.Rings with different inner diameters are placed to control the flow before and after the sudden change of the pipeline,so as to achieve the purpose of changing the local resistance,so as to find the conditions and pressure pulsation characteristics of reducing the non-travel resistance.At the same time,since the overall drag reduction effect of surfactant drag reducing agent is much worse than that of straight long pipe in the complex pipeline flow with a large proportion of non-passage resistance,this thesis selects clean water and additive solution as the test fluid.In this thesis,the variation of local resistance with Reynolds number is tested by using the sudden shrinkage water flow with the sudden shrinkage ratio of 2:1 and 5:1.It is found that for the sudden shrinkage tube(D20:D10)flow,when the Reynolds number is less than 30000,the local resistance coefficient As the Reynolds number increases,it gradually decreases,and after 30000,it basically no longer changes with the Reynolds number,and is stable around 0.3;while in the pipeline sudden contraction(D50:D10)flow,the local resistance coefficient is basically stable after the Reynolds number 35000 around 0.425.In the sudden shrinkage water flow with a sudden shrinkage ratio of2:1,it is found that the local resistance of the ring with an inner diameter of 12.5mm at a distance of 5mm from the sudden shrinkage interface is reduced by 60～70% compared with that without the ring.The optimal drag reduction condition of the ring in the sudden shrinking water flow.However,in the sudden contraction flow of the aqueous solution with added surfactant,the corresponding maximum local resistance drag reduction rate is 40～50%.The maximum local resistance drag reduction rate after the ring was placed in the clear water flow with a sudden expansion ratio of 1:2 was 30%,while the maximum local resistance drag reduction rate in the sudden expansion adding surfactant flow was 25%.In reducing the local resistance flow generated by the sudden change of the pipeline,the resistance reduction rate is negatively correlated with the maximum pressure pulsation.The higher the resistance reduction rate,the smaller the corresponding maximum pressure pulsation;The pressure pulsation measured between different pressure measuring points changes slowly and the pressure pulsation trend between the points is different when there is no loop;in the sudden expansion pipe flow,the maximum pressure pulsation is closer to the sudden change interface in the condition with higher drag reduction rate.The research conclusions of this thesis have both economic and scientific significance for improving the overall drag reduction effect of drag reducers in the pipeline network and for influencing the local resistance structure by controlling the non-along resistance flow.