Research On Friction Brake Heat Production-dissipation Mechanism And Structural Optimization Of Ventilated Disc Brake

Disc brakes are an important part of the braking system for high-speed trains.The brake disc generates a lot of heat due to friction during braking.It is subject to the joint action of the surrounding high-speed fluid and internal high temperature,causing a large temperature gradient and internal thermal stress.The braking efficiency of brake discs and the safety performance of train operation are seriously affected.This paper investigates the disc braking mechanism by means of a fluid-solid-thermal multi-physical field coupling method.On this basis,the ventilated brake disc heat production and heat dissipation model was developed.The temperature and stress field of different heat dissipation surfaces of the disk were analyzed.And the response surface optimization method was adopted to optimize the geometric parameters of the heat sink rib structure.Ventilated brake discs capable of rapid heat dissipation are obtained.The main studies are as follows:(1)The basic theories of fluid dynamics and heat transfer were referenced.Considering the limitations of the vehicle chassis,the width of the vehicle body and the ground on the external flow field size when the train was running,the fluid-solid coupling model of the ventilated brake disc for high-speed trains was established.The flow and pressure field distribution around the brake disc during braking was analyzed.The variation laws of velocity field,pressure field and average convective heat transfer coefficient of different heat dissipation surfaces of ventilated brake discs are obtained.(2)The interaction of high-speed flow field,rapid temperature change and structural characteristics of the disc was considered.For the complex process of heat generation and heat dissipation during friction braking of ventilated disc brakes on high-speed trains,a fluid-solid thermal coupling analysis method was proposed.According to this method,considering the joint influence of brake disc heat conduction,heat convection and heat radiation,the brake disc heat production-heat dissipation model was established.Based on the functional transformation relationship,the loading equation for the frictional heat source was derived.The expression for the total energy dissipated is obtained according to the different forms of heat dissipation on the brake disc cooling surface.In turn,the method of calculating the energy conversion of heat-producing and heat-shedding simultaneous ventilated brake discs is obtained.(3)The heat production-heat dissipation simultaneity energy conversion calculation method was referenced.The flow fields of different heat dissipation surface velocities from the results of fluid-solid coupling analysis were used as input.And the frictional heat source obtained by derivation was used as input.Different forms of convective heat transfer on the brake disc cooling surface were considered.Ventilated brake disc fluid-solid-thermal coupling model for a single high-speed train at 250km/h under full load conditions was developed.Finite element model accuracy verified by high-speed train braking tests.The temperature and stress distribution trends of different heat dissipation surfaces of ventilated brake discs under high-speed heavy load conditions were studied.Temperature and stress variation patterns are obtained for different node locations along the radial and axial directions.And the variation law of the total energy generated and dissipated by the braking process with the braking time is obtained.(4)Response surface optimization design method was adopted.The design variables were the number of heat sink structures,thickness,and alignment angle.Response value was the maximum temperature of the surface of the heat sink.The experimental protocol was designed.And the obtained response models were evaluated.The optimization objective was to minimize the surface temperature of the heat sink bar.The design variables were the structural geometric parameters.The penalty function method was used to obtain the optimal geometric parameter solutions.The optimized geometric model was reconstructed.And it was simulated numerically.The surface temperature of the optimized heat sink structure is reduced by 16%.When the heat generation is the same.The ventilated disc structure with better heat dissipation performance is obtained.The above research work provides feasible ideas for the study of the thermodynamic performance of disc brakes under the coupling of multiple physical fields.At the same time,it has certain guiding significance for improving the heat dissipation performance of high-speed train brake discs.