Agelin-Chaab, MartinIbrahim, Mohamed2018-07-192022-03-292018-07-192022-03-292018-04-01https://hdl.handle.net/10155/929At highway speeds, up to 65 % of the total energy used by large trucks is for overcoming aerodynamic drag. The underbody region of a tractor-trailer is responsible for up to 30 % of the aerodynamic drag on tractor-trailers, which is the highest drag created by any region on the vehicle. In this study, a novel concept of an active underbody drag reduction device is developed and investigated. The device was evaluated and optimized using computational fluid dynamics (CFD) techniques. It successfully decreased the drag coefficient of the tractor-trailer model by 4.1 %. Additionally, the device eliminated the underbody recirculation region and reduced the negative adverse pressure in the wake. A novel mechanism is also developed to allow for the active deployment of the device to mitigate some operational issues such as roadway protrusions, parasitic drag at low speeds, snow and dirt accumulation.enCFDAerodynamicsTractor-trailerUnderbody deviceDrag reductionThesis