Scale-resolved Simulation And Analysis Of Flow Field Within Wet Clutch And It's Optimization

As an important part of connecting engine and transmission mechanism,wet clutch plays the role of controlling power transmission and cut-off.It has lots of advantages,such as long life,low failure rate,smooth engagement,fast shift response,good heat dissipation and so on.In recent years,it is widely used in various mechanical transmission systems.When the wet clutch is in the separation condition,there is a large speed difference between the friction plate and the steel plate,and the oil is viscous,which causes the friction plate to produce the drag torque under the shear effect of the oil film.The existence of the drag torque will increase the power loss of the engine,resulting in the reduction of transmission efficiency.For the wet clutch,in addition to the drag torque,the heat dissipation effect of oil on the friction plate is also an important index to measure the working performance of the wet clutch.This paper takes the wet clutch as the research object,based on CFD software,studies the simulation method of the oil film flow field between the friction plates,the drag torque,the heat dissipation performance and the optimization of the groove of the friction plate.This paper can provide some references on the numerical simulation method of the latter similar flow field and the structure design of the fluid machinery.The main research work and conclusions are as follows:1 ? In order to extract the flow field between friction plates,the original characteristics of the flow field are preserved and the shape of the flow field is ensured to not affect the accuracy of mesh generation.The sliding mesh method suitable for transient calculation is used to simulate the flow field movement between friction plates.Different from the previous researchers who considered the oil film to be divided into internal and external areas from the radial perspective,this paper also considers the oil film from the axial perspectives,which make the simulation is more suitable for the flow field characteristics of oil film.The accuracy of the mesh is high,which guarantees the accuracy of the later simulation results.2?After the simulation,the flow field results are processed and analyzed,the velocity field,pressure field,temperature field and vortex structure in the flow field are analyzed in detail,and the ability of Reynolds time average method and scale-resolved method to capture the details of the flow field in the oil film is explored.It is found that scale-resolved method can capture more detailed vortex structure in the flow field than Reynolds time average method.On the premise that the surface temperature of the friction plate is fixed,the heat transfer rate on the outlet boundary condition is taken as the index to measure the heat dissipation effect between the oil and the friction plate.Combined with the analysis of the temperature field of the flow at different rotating speeds,the influence of some factors on the cooling effect of the oil is studied.It is found that the larger the intake of the oil is,the better the heat dissipation effect of the oil on the friction plate is,but there is a trend of the heat dissipation effect which is increasing first and then decreasing with the increase of friction plate speed.It is analyzed that this is due to the decrease of oil cooling effect caused by the mixing of a large amount of air.3?Based on the analysis of the causes of the drag torque and the changing trend of the drag torque with the rotating speed,a two-phase flow model is used to simulate the process of the oil film breaking between the friction plates,which captures the dynamic process of the oil film changing from the whole oil state to the air mixed state with the time,and also analyzes the gas-liquid two-phase distribution of the oil film flow field at different rotating speeds.It is found that the proportion of gas in oil film is larger and larger with the increase of the rotating speed.Finally,the process of oil film rupture is summarized into three stages.In the first stage,the rotating speed of the friction plate is low,there is full of oil between the friction pairs,and the drag torque increases with the increasing of the rotating speed of the friction plate.In the second stage,when the specific speed is reached,the oil supply is insufficient and the oil film begins to break,but the air volume is still small.Although the increase speed of the drag torque will be affected to some extent,it is not enough to cause the drag torque to decrease.In the third stage,when the speed is greater than the speed corresponding to the peak drag torque,a large amount of air has been contacted on the friction plate surface,and the drag torque begins to decrease with the increase of the speed.4?After analyzing the flow field of oil film of the original radial groove friction plate,it is found that when the original friction plate rotates at high speed,its groove structure will lead to a pressure difference on the groove surface,which will produce a pressure difference resistance opposite to the original friction plate rotation direction and increase the value of the drag torque.According to this feature,this optimization of the groove is carried out on the basis of the original friction plate.The flow field of the optimized friction plate is simulated and compared with the original friction plate,and the results show that the drag torque of the optimized friction plate is reduced by more than four percent.