'Thermal Analysis of a Car Braking System' simulation project by ahmedhussain18


#1

I created a new simulation project called 'Thermal Analysis of a Car Braking System':

This project shows the transient thermal analysis of a car braking system.


More of my public projects can be found here.


#2

In this project the thermal effect of the brake pads on a car disk was observed for a certain speed. The model of a disk brake is shown in the figure below. The red highlighted area on the front and back of the disk brakes represents the brake pads touching region.

The geometry was meshed using fully automatic tetrahedralization on SimScale platform. The mesh is shown in the figure below.

The speed and weight of the car was considered to be 30 m/s and 300 kg respectively. The coefficient of friction between ground and rubber was considered to be 0.72.

In order to stop the car in the shortest interval, the maximum friction force between tire and ground should have to be less than the maximum braking force. Therefore the maximum breaking force was calculated to be Ff = μ.m.g = (0.72)(300 kg)(9.81 m/s²) = 2119 N.

From this, the average acceleration of the car during braking comes out to be a = Ff/m = 2119 N/300 kg = 7.06 m/s². Now total time to stop the car can be calculated as t = v/a = 30 m/s/7.06 m/s² = 4.25 s. This was the total time given to this transient heat transfer simulation.

The convective heat flux of 90 W/(m² K) with 297 K (25 °C) was assumed and hence provided to all the exposed faces. To calculate the heat power i.e. heat energy generated due to pads touching the disk, kinetic energy was calculated first since the kinetic energy of the car is converted to thermal energy while braking. So U = 1/2 mv² = 1/2 (300 kg)(30 m/s)² = 135 kJ.

Heat power comes out to be P = U/t = 135 kJ/4.25 s = 31.76 kW. Since one of the front brake system was considered, we have assumed that only 60 % of the mass of car is in front, therefore P (60%) = 135 kJ . (0.6) = 19.06 kW. Applied surface heat flux on pad touching surfaces was q = 19.06 kW/0.038 m² =496.25 kW/m² (where, 0.038 m² = 2 x surface area of disk where the pad touches). The results below shows the outcome of heated disk brake temperature and flux after the car finally comes to stop.


#3

Nice Tutorial/Demonstration. But the convective heat transfer cannot be assumed to be 90 W/m2K on all surfaces without any calculation or simulation. I say this because the temperature rise in the disc depends on the convective heat transfer coefficient selected. The convective heat transfer coefficient depends on the velocity of air being blown over the disc surface and also in the holes. As the velocity of air is not same on all parts of the disc, the convective heat transfer coefficient will vary on each surface according to the blown air velocity. The story is not ended. The convective heat transfer coefficient at a given instant (time step) will also depend on the disc surface temperature until the previous time step. Combined velocity and temperature calculation in each transient time step for evaluating the heat transfer coefficient makes the simulation very complex and so cloud power should be used. Even then the boundary conditions cannot be specified in a straight forward way because flow analysis needs CFD module and heat transfer needs thermal module which are completely separate. This creates another bridging problem to interpolate results from velocity of air and brake disc temperature. Any help in finding the solution to this bridging problem ?


#4

@Inc01, Indeed you are right there. This analysis was just a test case and therefore is highly idealized. In the real world of course it would be different. Unfortunately, SimScale don’t offer so far a bridging solution here. But what SimScale right now offer is CHT (Conjugate Heat Transfer) which allows a coupled phenomena of both worlds i.e. CFD and FEA. May be you can try that some day for the similar case :wink:

Best,
Ahmed