Research On Flow Characteristics Of Spiral Flow In A Reducing Pipe Under Rotation Condition

Spiral flow in a reducing pipe under the rotating condition is a kind of complex turbulent problem,which has coupled effect of circumferential rotation and flow direction shear.This flow has both characteristics of spiral flow and forced rotation flow in axially rotating pipe.It contains complex physical mechanism of the turbulence,which has important application background in engineering area,such as wall motion in the application of the turbulent flow drag reduction,and application of hydrocyclone in downhole oil-water separation and the offshore platform.However,because of the lack of research on complex wall motion turbulence at present,improvement of related equipment performance is restricted.The research on the mechanism of related scientific becomes extremely urgent.Aiming at this turbulence problem,National Natural Science Foundation of China“Research on Flow Characteristics of Spiral Flow in Reducing Pipe under Rotation Condition "(No.11172061)is carried out,and this paper is a part of the research.Based on the analysis of the two kinds of typical turbulence,flow in traditional hydrocyclone and axially rotating pipe,this paper predicts the flow characteristics of spiral flow in the reducing pipe under rotating condition.Tensor invariant theory is used to analyze traditional Reynolds stress model,and the inherent defect under pure rotation turbulence is found.Aiming at damping Reynolds stress anisotropic tensor,a second order nonlinear correction term of rotation rate tensor to pressure strain correlation is built.According to spiral flow characteristics of the reducing pipe,nonlinear correction term of strain rate tensor is built in the same form.So the application of correction model is expanded to the flow studied in this paper.correction model is added to quadratic pressure-strain model(SSG)to build correction model applied to spiral flow in the reducing pipe under rotating condition.Based on reducing pipe of major separation part in double-cone hydrocyclone,geometric model of the reducing pipe under rotating condition is built by reasonable simplification.Based on finite volume method,using Reynolds-Averaged Navier-Stokes(RANS)and Reynolds stress model(RSM)including corrected pressure strain correlation,spiral flow of single phase fluid in the reducing pipe is calculated under different rotating speed and different flux.Characteristics of time-average macro flow field and fluctuating flow field of spiral flow under rotation are studied in depth.The influence of variation in rotating speed and flux on flow parameters such as mean velocity,velocity gradient,pressure drop,turbulent kinetic energy,Reynolds stress and Reynolds stress transport are analyzed.According to characteristics of the reducing ripe under rotating condition,experimental facility for LDV measurement is built.Two-dimensional flow field at big and small cone part of the reducing pipe is measured by LDV for the frirst time.Distribution of tangential velocity and axial velocity under different rotating speed and different flux are obtained.The measured results are compared with numerical simulation results.The comparison results verify the reasonability of nonlinear correction model.Above all,aiming at the complex turbulence characteristics of spiral flow in a reducing pipe under rotating condition,the study is carried out in this paper.The results can provide theoretical basis for the application of related equipment in rotating condition,and can also provide reference value and basis of research on this kind of wall coupling complex rotating turbulence.