Abstract
KEYWORDS: Aerodynamic loads, ground effect, Venturi effect, virtual environment, numerical methods
ABSTRACT:
As aerodynamic phenomenon, the ground effect represents the effect of the air between a moving vehicle and a thick boundary. It is results in a change of the aerodynamic behaviour and depending of vehicle has various ways of acting. Concerning the aviation's point of view, two phenomena are involved when a wing approaches the ground. Ground effect is one name for both effects which is sometimes confusing. These two phenomena are referred to as span influence and chord influence ground effect. The former results in a reduction of induced drag and the latter in an increase of lift. Regarding the influence of the cord, ground effect not always increases the lift. It is possible under certain conditions that lift is reduced when an airfoil approaches the ground. In the case when the bottom of the foil is convex and
the angle of incidence is low, a Venturi tunnel is created between the wing and the ground and the high-speed low-pressure air sucks the airfoil down. This Venturi-type ground effect is used by the high-speed cars, which have the under-body designed especially to make this effect. Some researcher are using the term of ground effect
when they are mentioning the relative motion between the road and vehicles when these are experimental evaluated in wind tunnels, a sense more adequate in my opinion, too. This is also called ground simulation.
There are various possibilities for representing of road in the wind tunnels and relative motion between this and vehicle, two of these being: the mirror method using an image model of the tested one and using a flat surface (moving belt), with or without rotations of the wheels. Last mentioned is, till now, the only technique, at least in principle, is capable of matching all the on-road properties, including the boundary layer. However, practical realisation of this is far from trivial, mainly because of the finite belt dimensions, which affect the quality of the boundary layer. All the limitations of wind
tunnels have led to CFD analyses, which have been successfully applied to study the aerodynamics in recent years. The primary reason of using numerical methods is that they can generate information before a testable model even exists. Also, simulation of relative motion between vehicle and road (including wheels' rotations) are
comparatively easy to accommodate. On the other hand, once the equations of mathematical model have been solved, there is much more information available than from a routine experiment.
The goal of this paper is to present the concepts of ground effect according with the type of studied vehicle, aeroplanes or motorcars. In addition are presented, comparatively, the results obtained in order to modelling this phenomenon in a virtual environment for an airfoil (with the aid of the numerical methods) using the techniques, previously mentioned.