Abstract
KEYWORDS:
Aerodynamic characteristics, underbody geometry, CFD
ABSTRACT:
The aerodynamic characteristics of a vehicle have a significant role on its dynamics performances, fuel consumption, level of produced noise etc. In this sense the automotive engineers design vehicle having some very elaborated exterior shape, the main scope being the reduction of drag. But, in many cases, the geometry of
underbody was neglected from this point of view.
Mathematically, the drag that an air stream exerts on a vehicle is the integral, over all
surfaces exposed to the stream, of the local streamwise component of the normal (pressure) and tangential (skin friction) forces.
In this way, direct evaluation of the contribution on total drag of an element of the
vehicle (mirrors, wheels, driving axles a.o.) requires knowledge of the detailed stress
distributions over all element surfaces, also for entire vehicle. To obtain this experimentally is very difficult, except for simple shapes, even in a research sense. However, direct evaluations of components of have been made in selected regions of a vehicle body. This is feasible operation in the regions where the pressure distribution
is reasonably uniform, for example in the regions where the flow is fully separated: engine bonnet, windscreen and other continuously uniform surfaces.
Generally, direct evaluation of force components is not practical for bodies with the complex geometries e.g. road vehicle, especially on underbody side. Detailed stress distributions are the specific output CCFD (computational fluid dynamics). Adequately validated computational codes can contribute greatly to a better understanding of road vehicle aerodynamics.
In this paper, using a prototype of terrain vehicle as example, are studied the contribution of the underbody geometry on total drag using the facilities offered by a professional CFD code. These can provide solutions for the optimization of the body of vehicles, even in a very early design stage, the aerodynamic design process being
accelerated.