Oil Film Shear Cavitation Characteristics Between Textured Rotating Friction Pairs

The non-direct contact rotary interface uses the viscous fluid as the working medium,because the oil film friction coefficient formed is small,the rotary interface is not easy to wear and runs smoothly,so it is widely used in the fields of mechanical seal,fluid transmission and bionics.Previous studies show that micro-texture can effectively improve the friction and lubrication performance.However,the texture boundary will cause the oil film cavitation due to the pressure disturbance in the flow field,which will affect the oil film bearing capacity and transfer torque.In this paper,the oil film between textured rotating friction pairs is studied,carries out theoretical analysis and experimental verification of oil film shear cavitation,and analyzes the influence of oil film shear cavitation on oil film lubrication and transmission performance.The main contents are as follows:Based on the oil film model between smooth friction pair,oil film bearing capacity model and transfer torque model were established respectively.The analytical solutions of flow velocity and pressure are obtained based on the distribution analytic method.It was found that the circumferential flow of oil was only related to the rotation speed of the friction disk,and the radial flow was affected by the inlet pressure,centrifugal force and inertia force.At the same time,centrifugal force causes the oil film to shrink,when the inlet pressure is 0.28 MPa,the minimum friction disk speed of oil film shrinkage is 5398 rpm.In order to ensure the integrity of the oil film,the oil inlet pressure needs to be adjusted in real time.The finite difference algorithm was used to solve the flow field between the friction pairs after the texture,the oil film velocity field and the pressure field were analyzed,and the initial position of the oil film shear cavitation under the texture distribution is predicted.The results show that: the distribution of flow velocity and pressure in the non-textured region is similar to that of the smooth oil film,the flow velocity and pressure are greatly disturbed by the texture pit boundary,at low texture rate,cavitation mainly occurs in thetexture pits distributed at the outer diameter of the oil film,when the texture rate is high,the cavitation spreads to the non-texture region along the texture boundary.ANSYS CFX was used for transient calculation of oil film 3d model,and cavitation simulation was carried out for oil film of common texture types(hexahedral,cylindrical and hemispheric).The results show that: the cavitation position is basically consistent with the predicted results;cavitation develops rapidly within 0.015 s and then gradually tends to a stable state,and cavitation development is accompanied by the collapse of cavitation;Cavitation effect can reduce the low pressure and increase the oil film bearing capacity;The oil film with hexahedral texture presents the optimal lubrication and transmission performance,the bearing capacity increases by 25.8% when the texture rate is 12.917%;The velocity and direction of gas-liquid two-phase in a single texture pit are the same which verified that the oil film shear cavitation gas is a phase change from the oil.A visualization platform for cavitation experiment was designed,and a high-speed camera was used to film the cavitation form,and the transfer torque under different operating conditions is also collected.Experimental results show that the oil film without texture did not cavitate,and textured oil film did not cavitate at low rotational speed,with the increase of rotating speed,the cavitation bubbles with small structure grew into highlighted,long,narrow and circular bubbles with large structure,cavitation collapse is accompanied by cavitation development;Compared with the non-textured oil film,the cavitation is more intense at high rotating speed,and torque is reduced due to shrinkage of oil film.