Date of Award

8-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Mechanical Engineering

Advisor

Fadel, Georges M

Committee Member

Miller , Richard S

Committee Member

Qiao , Rui

Abstract

In recent years, there has been an increase in demand towards the improvement of car design for achieving better performance and increasing passenger comfort. Improving the design of individual components to meet the customer needs for improved vehicle performance alone is not enough. Interactions of these components with the surrounding components and their placement should also be investigated. Placement of these components in the under hood space forms a 3-Dimensional packaging problem. In the past, a multi objective optimization process was setup to determine the optimal placement of these components in the car under hood space. Three main objectives were taken into account namely, minimizing center of gravity height, maximizing vehicle maintainability and maximizing survivability in the optimization process. However, minimizing the overall under hood temperature and ensuring the temperature of heat sensitive components to be below its critical value, is not added as an objective to the optimization problem.
This study makes an assessment of the need for including the thermal objective into the optimization process and also presents an efficient way of performing CFD simulation over the under hood geometry. The under hood geometry used included radiator, engine, exhaust manifold, coolant tank, air filter, brake booster, front grille geometry and battery. These components were included as heat source, heat exchangers etc. A standard k-ɛ turbulence model with upward differencing convection scheme is used on a well refined computational mesh.
The work also describes in detail the way of accurately and effectively modeling the radiator as an ungrouped macro heat exchanger model available in Ansys FLUENT. The results obtained from the CFD simulations illustrate the importance of the under hood vehicle configuration optimization process on its thermal behavior. The temperature attained by the coolant flowing through the radiator with constant heat rejection, when placed behind the engine is very high, when compared to the temperature it attained with the radiator placed in front of the engine. The CFD analysis presented in this study is performed using Ansys FLUENT while the initial geometry preparation is done using SolidWorks.
The CFD analysis presented in this work is then used to build an approximation by my research mate, which is later tied to an optimizer based on Genetic Algorithm. Thus, including the thermal objective to the multi objective optimization problem stated above.

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