Numerical Study On The Heat Transfer Characteristics Of High Speed Train Brake Disc

The brake disc works normally and the braking effect is stable,which is one of the guarantees for the safe operation of train.A large amount of heat energy will be generated in the emergency braking process of high-speed trains.The brake disc is subjected to a huge thermal load,thus its temperature rises rapidly.The convective heat transfer coefficient of the brake disc surface will affect the heat dissipation of the brake disc in the braking process.If the brake disc temperature is too high,it will be prone to brake failure,thermal recession and local high temperature,and even generate thermal cracks,which will eventually lead to brake disc fracture,seriously affecting the safe operation of the train.Therefore,the study of heat transfer performance and temperature field in the braking process of the brake disc is of great significance to the structural design and life evaluation of the brake disc.In this paper,the braking process of the brake disc of high-speed train with an initial speed of 250km/h is studied.According to the braking principle of the brake disc and the basic theory of thermal analysis,a three-dimensional solid model is established.The heat transfer characteristics and temperature field of the brake disc during braking were calculated and analyzed by numerical simulation method.And verified the simulation results of the convection heat transfer coefficient.The conclusions obtained are as follows:1.In the process of emergency braking,the air flow around the brake disc belongs to turbulent flow,and the air around and inside the brake disc forms a complex vortex structure.2.The convection heat transfer coefficients corresponding to each surface at different braking moments are different,and the distribution of corresponding heat transfer coefficients on different surfaces is also different.The average convective heat transfer coefficient on the surface of the brake disc decreases with increasing braking time.The distribution of convection heat transfer coefficient on the surface of the brake disc is uneven and has no obvious regularity.From the outer surface of the entire brake disc,the convective heat transfer coefficient of the outer circumferential surface is larger.At the beginning of braking,the convective heat transfer coefficient of the friction surface and the outer circumferential surface in the windward area is greater than the convective heat transfer coefficient of the leeward area,and at the end of braking,the convection heat transfer coefficient of the friction surface of the brake disc and the outer circumferential surface leeward area It is larger than the windward area;from the surface of the internal channel of the brake disc,the convection heat transfer coefficient on the surface of the fin is large.At the beginning of braking,the convective heat transfer coefficient of the friction surface and the outer circumferential surface in the windward zone is greater than that in the leeward zone.At the end of braking,the convective heat transfer coefficients of the internal disc surface of the brake disc and the surface of the radiating rib are larger in the leeward area than in the windward area.3.The maximum temperature of the brake disc at any moment during the braking process appears on the friction surface,and its value shows a trend of increasing first and then decreasing.The minimum temperature of the brake disc at any moment appears at the axle and the connection between the brake disc and the axle;from the outer surface of the brake disc,its temperature increases first and then decreases with the increase of the braking time.Trends,the rate of temperature increase from fast to slow.At the beginning of braking,the temperature of the brake disc surface continues to rise.After the temperature of the friction surface reaches the maximum temperature,the temperature gradually decreases;the friction surface has a large temperature gradient in the radial direction.As the braking time increases,the highest temperature position on the friction surface always appears on the outside;from the brake disc From the surface of the internal channel,the temperature gradually increases with the increase of braking time.At the beginning of braking,the temperature increases slowly,and the temperature of the internal channel surface of the brake disc continues to rise throughout the braking process.The temperature around the junction of the brake disc cooling ribs and the inner channel disc surface is relatively low.4.The change trend of the temperature of the nodes at different radii of the friction surface of the brake disc with time is roughly the same.The radial temperature at any time decreases with the decrease of the friction radius,and the temperature curve increases in a zigzag manner.The temperature changes of the nodes at different thicknesses along the axial direction of the outer surface of the brake disc are roughly the same with time.The axial temperature at any time decreases as the distance from the node to the friction surface increases,and the temperature curve also gradually increases in a zigzag shape.At the end of the dynamic period,the temperature of each node tends to be approximately the same.