Experimental and Numerical Study of Heat Transfer at the Underbody of a Production Car

The optimization of the flow field around new vehicle concepts is driven by aerodynamic and thermal demands. Even though aerodynamics and thermodynamics interact, the corresponding design processes are still decoupled. Objective of this study is to include a thermal model into the aerodynamic design process. Thus, thermal concepts can be evaluated at a considerably earlier design stage of new vehicles, resulting in earlier market entry. In a first step, an incompressible CFD code is extended with a passive scalar transport equation for temperature. The next step also accounts for buoyancy effects. The simulated development of the thermal boundary layer is validated on a hot flat plate without pressure gradient. Subsequently, the solvers are validated for a heated block with ground clearance: The flow pattern in the wake and integral heat transfer coefficients are compared to wind tunnel simulations. The main section of this report covers the validation on a full-scale production car. A specially developed heated electronic component dummy mounted to the underbody of the car introduces heat into the flow field. Again the soundness of the underlying methodology is appraised by comparing the CFD simulations to wind tunnel experiments. Attention is paid to lift and drag coefficients as well as to flow and temperature patterns around the car and the heated dummy at the underbody. With the new method, concepts can be thermally investigated in early product stages, leading to a reduced time to market.