Abstract
KEYWORDS:
Aerodynamic loads, Venturi effect, underbody drag of vehicle, dimensionless characteristic indicators
ABSTRACT:
The aerodynamic performances of the air- or ground vehicles are characterised using specific coefficients, dimensionless a.g. drag coefficient, lift coefficient a.o. They are
representing similitude criteria between equivalent shape body and can be computed
analytically with some very complex procedures only if the geometry can be described exactly mathematically. This situation is specific especially for the aeronautical structures, as wings, empenagges, propeller blade etc. In this sense aerodynamic theories concerning aeronautical structure split the global aerodynamic load in components, for a better description of produced phenomena. For example the drag coefficient of an airplane wing is representing the sum of the two components, where
first one refers to the wing profile drag and the second one to induced drag (due to finite span of wing). This is very useful especially when are required specific methods for improving of aerodynamic behaviour e.g. using of winglets for the decreeing of the induced drag.
Due to very complex shape of a vehicle body, drag coefficient, that is critical for vehicle's aerodynamic behaviour, is evaluated only experimental, mainly in wind tunnel. In this paper, the authors are proposing a splitting up of global drag force in some major components, and also a theoretical method for evaluating of one of them, respectively of the underbody drag.
The analytically emphasizing of the main factors which having importance on the aerodynamic behaviour of vehicles can have as result specific solutions for improving of the performances of the cars, even in a very early design stage. In this sense, some aerodynamic efficiency factors are proposed, regarding the flow rate in the relative motion under the vehicle, the inferior component of the drag load, and the corresponding coefficient of drag load.
The study is illustrated by means of a numerical exemplification. The analytical emphases of the constructive, exploiting, random etc influence factors may lead to optimising steps with respect to the aerodynamics of vehicles.