A Numerical Aerodynamic Analysis on the Effect of Rear Underbody Diffusers on Road Cars

Abstract

The aerodynamic complexity of the underbody surfaces of conventional road vehicles is a matter of fact. Currently available literature is focused mainly on very simple Ahmed-body geometries as opposed to realistic car shapes, due to their complexity and computational cost. We attempted to understand the flow behaviour around different realistic conventional road car geometries, and we provide an extensive evaluation of the aerodynamic loads generated. The key findings of this article could potentially set a precedent and be useful within the automotive industry’s investigations on drag-reduction mechanisms or sources of downforce generation. The novelty of the work resides in the realistic approach employed for the geometries and in the investigation of barely researched aerodynamic elements, such as front diffusers, which might pave the way for further research studies. A baseline flat-underfloor design, a 7∘ venturi diffuser-equipped setup, a venturi diffuser with diagonal skirts, and the same venturi diffuser with frontal slot-diffusers are the main configurations we studied. The numerical predictions evaluated using RANS computational fluid dynamics (CFD) simulations deal with the aerodynamic coefficients. The configuration that produced the highest downforce coefficient was the one composed of the 7∘ venturi diffuser equipped with diagonal sealing skirts, achieving a CL value of −0.887, which represents an increase of around 1780% with regard to the baseline model. That achievement and the gains in higher vertical loads also entail a compromise with an increase in the overall air resistance. The performance achieved with diffusers in the generation of downforce is, as opposed to the one obtained with conventional wings, a cleaner alternative, by avoiding wake disturbances and downwash phenomena.

Parametric, response surface, and adjoint optimizations of the underbody diffuser of a generic ground vehicle

“…Since, with the usage of an underbody diffuser, although the trailing vortex region area is reduced, counter-rotating vortex cores may be closer to the rear part of the body and this limits the pressure recovery to some extent. 10 Moreover, with the usage of a curved surface on the diffuser section, the underbody exit flow is curved too, and vortex cores can be deflected with the momentum transfer of this curved underbody flow, the especially lower part of the rear. Nevertheless, the curved surface tends to have minor scaled bubbles formed starting around the underbody diffuser inlet and upper recirculation has more unstable features.…”

“…4 On the other hand, if this angle is too high, there will be flow separations and the stall issue, that is increase in drag force, similar to that of airfoils. 5,[8][9][10] In this sense, in the research and improvement studies of vehicle aerodynamics conducted for many years, the Ahmed body, which has dimensions similar to a ground vehicle, has been the subject of research. According to the information of the authors of this article, the idea of creating a relatively simpler vehicle model arose with the experimental work done by Morel in 1978.…”

“…Accordingly, if the diffuser angle is too low, the pressure recovery potential of the diffuser may remain low 4 . On the other hand, if this angle is too high, there will be flow separations and the stall issue, that is increase in drag force, similar to that of airfoils 5,8–10 …”

Energy Consumption of the Urban Transport Fleet in UNESCO World Heritage Sites: A Case Study of Ávila (Spain)

“…This concept of energy "traditionally dissipated by the braking system" is of vital importance in this study, since it is considered energy that can be used in the case of installing a regenerative braking system. Finally, regarding the aerodynamic drag of the vehicle, it is necessary to consider that a vehicle moving in a fluid (air) experiences a force that resists its forward motion [47,54,55]. This force is called aerodynamic drag (F wind ) (Phase II, Figure 2) and is developed in the following expression:…”

Shape Optimization with a Flattening-Based Morphing Method

“…The shapes of engineering objects are significant design factors that affect their functionality, particularly their aerodynamic aspects. For example, engineers have developed the shapes of ground vehicles for many years to reduce aerodynamic drag and increase fuel efficiency [1][2][3][4][5]. They have also attempted to reduce wind noise and increase the driving stability at high-speed operating conditions via the modification of a vehicle's body shape [6][7][8][9].…”