Influence of Short Rear End tapers on the Base Pressure of a Simplified Vehicle.

Abstract

Author, co-author (Do NOT enter this information. It will be pulled from participant tab in MyTechZone)Affiliation (Do NOT enter this information. It will be pulled from participant tab in MyTechZone) AbstractThis paper looks into the effect on base pressure of applying a high aspect ratio chamfer to all edges of a simplified squareback model (the Windsor model). The effects are investigated using force and moment measurements along with surface pressure measurements on the slanted surface and vertical base. The work forms part of a larger study to develop understanding of the mechanisms that influence overall base pressure and hence the resulting aerodynamic drag.A short slant (approx. 4% of model length) was applied to the trailing edges of the simplified vehicle model, representing the small rear end optimisation typical of many real vehicle geometries. Two experiments were performed: the first applied a chamfer at varying angles to the top and bottom edges; the second test looked at the same chamfer angle applied to the sides of the model geometry while the top and bottom angle remained square. The changes in drag are discussed and explained in the context of the base pressures and area weighted pressure coefficients.

Influence of Short Rear End Tapers on the Unsteady Base Pressure of a Simplified Ground Vehicle

“…The experiment was carried out with the Windsor Model, already used by Littlewood and Passmore [10] and Perry et al [11]. The model has an overall lengthL of 1044 mm, a width H of 389 mm and a height H of 289 mm.…”

“…The model was manufactured by using polyurethane machinable slabs and has multiple rear inserts to allow the testing of the different rear slant angles considered in the present work. As in [11], all the tapers have a length of 45 mm. Slant angles of 0°, 6°, 12°, 16°, 20° were considered both for the horizontal and vertical trailing edges, together with two different rear sections in order to allow the fitting of the horizontal and vertical tapers (as shown in Figure 1).…”

“…Slant angles of 0°, 6°, 12°, 16°, 20° were considered both for the horizontal and vertical trailing edges, together with two different rear sections in order to allow the fitting of the horizontal and vertical tapers (as shown in Figure 1). These values were chosen since they are representative of aerodynamic behavior of the slanted surface, which is characterized by the presence of a suction region close to the taper leading edge whose extension increases with the chamfer angle until a critical angle is reached (Perry et al in [11]). Beyond this, the flow fully separates from the tapered surface, increasing the pressure acting on the surface itself.…”

“…For values of the slant angle greater than 12°, however, this suction force was found to outweigh the base drag growth, yielding an increase of the overall drag. Most recently, Perry et al [11] investigated the effects produced by similar slants applied to both the two horizontal trailing edges and to the side trialing edges of a similar model. In the first case it was noticed that, applying the top and bottom tapers asynchronously, the interactions between the upwash and the downwash had a large effect on the base pressure distribution and the minimum drag value was achieved with a 16° top edge taper and a 6° bottom edge taper in place.…”

A Parametric Study of Automotive Rear End Geometries on Rear Soiling

“…Roof slant angle variations were selected for the study because they are commonly employed as a drag reduction method [11]. The work reported contains a thorough description of the experimental and numerical methods and analysis of the results.…”