Numerical Study Of The Cavitation Mechanism And Erosion Prediction In High-speed Gears

The high-power development of mechanical equipment requires the stability and reliability of gear transmission system under some extreme conditions such as high speed and heavy load.In high-speed gear lubrication,the oil pressure is easily changed by the high-speed motion and high-frequency vibration of two meshing surfaces,causing the appearance of cavitation bubbles.In this situation,the lubrication state could be deteriorated,increasing the erosion risk on tooth surface and reducing the transmission performance.However,the researches on the cavitation problem in gear transmission are not yet mature,and more efforts are needed.In this paper,regarding a pair of spur gears as researched objective,a novel fluid-structure coupling method combining the gear dynamic model and two-phase computational fluid model is proposed for the simulation of vibration-induced cavitation in lubricating oil flow.By this way,the temporal and spacial characteristics of cavitation vapor are studied,and the influencing factors on cavitation are discussed.In this basis,the cavitation erosion risk indicators are applied to predict the erosion region on meshing surface.First,a three dimensional finite element model is built for gear dynamic responses,which are treated as the boundary displacement conditions in the two dimensional fluid model for obtaining the transient cavitation flow features.The simulated results indicate that the cavitation vapor easily appears near teeth tips when the trapped volume opens.Because of the gear vibration,the vapor becomes fluctuating during engagement.The operating conditions,oil viscosity and gear modulus are the main factors affecting cavitation.The cavitation vapor increases in teeth meshing region when the input speed increases.The fluctuation of vapor becomes larger with the increased load torque.In addition,increasing oil viscosity can prevent the appearance of vapor in a certain extent.And the increased gear modulus can increase cavitation vapor due to the raising tangential meshing velocity.Then,a three dimensional fluid model considering the heat effect and the vapor distribution along tooth width is established for the transient non-isothermal cavitation flow during gear engagement.There is an obvious difference between the vapor distributions under light and heavy loads due to the contributions of vibration and friction heat.At light load,a large area of vapor appears on the tooth meshing surface.However,the vapor tends to gather near the tooth tip gap and contact line.With the input speed of 10000 rpm and load torque of 300 N·m,the maximum local temperature exceeds400 ℃,increasing the quantity and fluctuation of cavitation vapor significantly.Nevertheless,the effect of temperature is tiny at low speed and light load conditions.Finally,the cavitation erosion risk indicators are used for assessing the erosion risk on tooth meshing surface.For the cumulative cavitation erosion on tooth surface during engagement,the high-risk region moves from tooth root to pitch line when the input speed increases from 3000 rpm to 10000 rpm,and the degree and area of erosion are closely related with the quantity and fluctuation of cavitation vapor.During teeth engagement,vibration is the main reason for the cavitation bubble collapse.According to the numerical results,the collapse events tend to appear near the moving contact line,and the collapse intensity and frequency are the highest when contact line moves to the vicinity of pitch line.