Interaction between different kind of cars and study of its aerodynamic drag

Abstract

. Technically, it is the study of the relative movement between all kind of fluis, not limited to air or gases, and a solid but in general it is the branch of Fluid dynamics which studies the motion of air when it interacts with a solid object such a sphere, a wing or a car in our case. Anything that moves through air reacts to aerodynamics from for example a bike to a thing such a big rocket. Automotive aerodynamics is the study of the aerodynamics of road vehicles and its main goals are reducing drag and wind noise and also preventing undesired lift forces which could cause instability. For some race vehicles it may be important also to produce a downforce to improve traction. The reduction of drag is a constant in history as the resistance to air is the principal one when the car is from medium to high velocities. For that reason, a good aerodynamic design allow the car to reach higher velocities with the same engine or, more important in a general way, increase the vehicle’s fuel efficience which is the same that reducing the fuel consumption. Understanding the motion of air around an object enables as result the calculation of forces and moments acting on the object by the pressure field around the object. Usually they are calculated asumming the flow field as a continuum one which is characterized by a flow velocity, density, temperature and pressure. These properties may be measured from the general equations for the conservation of mass, momentum and energy in air flows, which is the analytic method used in aerodynamics, but because of the high difficult of these complex equations is not possible the complete resolution and some assumptions are needed and some phenomena as turbulence and viscosity are not taken into account, which lead us to an approximated solution. 5 The alternative is an experimental procedure using a wind tunnel and a car which simulates the situation of the road. However, the construction of a system like a wind tunnel is very expensive and usually the method works with scaled models. The two main factors for the drag are the frontal área of the vehicle and the drag coefficient which is a dimensionless value that denotes how much resistance a vehicle has to the movement through air because of its form. An aerodynamic study has been performed in the wind tunnel of the university “La Sapienza di Roma” with two scaled cars that have been studied when they are closed enough to each other for generating an aerodynamic suction tunnel between them in order to reduce the drag when they are closed enough.