Date of Award

Spring 5-2020

Access Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy in Mechanical Engineering

Department

Mechanical Engineering

Committee Chair

Sandra K.S. Boetcher

First Committee Member

Eduardo Divo

Second Committee Member

William Engblom

Third Committee Member

Mark Ricklick

Fourth Committee Member

Rafael Rodriguez

Abstract

Seven turbulence models were used to simulate the flow within the wheelhouse of a simplified vehicle body. The performance of each model was evaluated by comparing the aerodynamic coefficients obtained using computational fluid dynamics (CFD) to data collected from wind tunnel experiments. The performance of large eddy simulation (LES) and detached eddy simulation (DES) was largely dependent on the time step and grid size to accurately resolve turbulent eddies. The standard k-e, realizable k-e, k-w, DES, and LES all trended towards a drag coefficient which was 20% lower than the experimental value. In all numerical cases, the lift coefficient was found to be at least 60% greater than the experimental value, but was consistent with numerical studies by other authors. The standard k-w and SST k-w models provided results which were the most consistent with experimental data for the three different mesh sizes. Two types of flow modification devices were then added to the simplified vehicle model to assess drag reduction potential. Conventional wheel defectors are compared to air-jet wheel defectors on wheel drag and overall drag reduction capabilities. Two parametric studies are conducted on the Fabijanic body at a Reynolds number of 1.6x105: a study on the variation of the size and location of a conventional wheel defector, and a study on the jet speed and location of an air-jet wheel defector. Results show that wheel drag is decreased as the height of the conventional wheel defector is increased, and that the further the conventional wheel defector is from the wheelhouse, the more sensitive the wheel is to changes in drag coefficient. The air-jet wheel defector successfully decreases the wheel drag. The closer the air-jet is to the wheelhouse the less of an impact it has on wheel drag, but the greater the impact on the overall drag of the simplified body. A maximum overall drag reduction of 2.76% is achieved with a configuration which also results in a wheel drag reduction of 16%. Air-jet wheel defectors were then simulated on the DrivAer reference model -- an open source model which blends features of the Audi A4 and the BMW 3 Series. The air jets were found to be less impactful at low speeds, but at higher speeds, they were observed to reduce wheel drag and cause an overall drag reduction of up to 5.1%. Even though jet speeds as high as twice the driving speed were investigated, and caused relatively large reductions in wheel drag, a jet speed approximately 2/3 of the driving speed was observed to cause the greatest overall reduction.

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