Date Approved


Graduate Degree Type


Degree Program

School of Engineering

First Advisor

Dr. Wael Mokhtar

Second Advisor

Dr. Sung-Hwan Joo

Third Advisor

Dr. Shirley Fleischmann

Fourth Advisor

Brian Cavanaugh

Academic Year



Foundation air disc brakes bring Class 8 semi-trailers to a stop by converting kinetic energy into thermal energy. Recently, side skirts have been added to the underside of semi-trailers to improve fuel economy. The reduction in airflow under the trailer they create has potential to increase brake temperatures by reducing convection heat transfer. This will require an increase in conduction and radiation heat transfer to the surrounding wheel-end parts. Additional heat transfer to the surrounding parts could increase the temperatures in the hub and bearing to damaging levels.

CFD analyses were developed to model the airflow under the semi-trailer with and without side skirts to calculate the average heat transfer coefficients for the wheel-end components. Transient FEA’s were created to model the temperature distribution versus time in a disc brake wheel-end for constant drag braking scenarios. The CFD simulation was manually coupled with the FEA. Heat transfer coefficients from CFD were passed to FEA and temperature from FEA was transferred to the CFD in an iterative process.

The results have demonstrated that the methodology is capable of predicting wheel-end temperatures, dependent on convection heat transfer from the airflow around the brake. The wheels around the wheel-end assembly have the largest impact on convection heat transfer from the wheel-end. Trailer side skirts also reduce convection heat transfer, but to a lesser extent than the wheels. They have the largest impact at higher vehicle speed. The hub and bearings did not reach sufficient temperatures to cause damage during the drag braking event; however, it was determined that hub and rotor geometry can dramatically change the temperatures reached at the bearings.