PIV measurement of the flow past a generic car body with wheels at LES applicable Reynolds number András Gulyás a,⇑ , Ágnes Bodor b , Tamas Regert b,1 , Imre M. Jánosi c a Department of Fluid Mechanics, Budapest University of Technology and Economics, 1111 Budapest, Bertalan L. u. 4-6, Hungary b Department of Fluid Mechanics, Budapest University of Technology and Economics, Hungary c von Karman Laboratory of Environmental Flow, Department of Physics of Complex Systems, Eotvos Lorand University, Hungary article info Article history: Available online 8 July 2013 Keywords: Ahmed body PIV Wheel Vehicle aerodynamics abstract Experiments by using 2D–2C Particle Image Velocimetry (PIV) were carried out and reported concerning the flow field past a generic car body (modified Ahmed body) which is equipped with wheels and wheel- arches. The Reynolds number was chosen to not exceed 2E+5 based on the height of the Ahmed body which makes it possible to investigate the same configuration by means of Large Eddy Simulation (LES). The wheels were rotating but the ground was stationary. The wheel-ground contact was realized by means of small rectangular openings below the wheels in the ground plane in which the wheels were immersed. The transition contour of the immersed wheels and the ground, as well as the rectangular openings below the wheels were properly sealed to prevent parasite flow and to provide well defined boundary conditions for an upcoming LES investigation. The flow field was measured in several planes with normal vectors pointing towards the directions nor- mal to the free stream. Statistical characteristics of the flow are provided and discussed. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction The aerodynamic effects of the rotating wheels on road vehicles are a topic of high importance in vehicle aerodynamics. Wheels on vehicles have high impact on both lift and drag coefficients. According to several studies (see e.g. Eloffson and Bannister, 2002; Waschle, 2007; Skea et al., 2000) the presence of wheels and wheel-arches on an aerodynamically optimized passenger car body increases drag and lift by an amount of 30% and 40%, respectively. Due to their functionality, wheels cannot have an aerodynamically favourable shape. During the last couple of decades, several publications discussed the characteristics of the flow field past isolated wheels (Fackrell et al. (1973); Mears et al., 2002; Brizzi et al., 2004), wheels in wheel-arches (Skea et al., 2000; Fabijanic, 1996; Axon et al., 1999; Cogotti, 1983) and full cars (Eloffson and Bannis- ter, 2002; Waschle, 2007) both on experimental way as well, as by Computational Fluid Dynamics (CFD). In case of wheels rotating in wheel-arches the investigated geometry was either complicated (Cogotti, 1983), not completely representing the case of a conventional car (Skea et al., 2000; Axon et al., 1999) or its details were not open for public access (Waschle, 2007; Axon et al., 1999). The intention of the present research is to provide reference data for a car model that has known, simple geometry and is equipped with four wheels rotating in their wheel-arches. The choice of the authors of this paper was made on the well known Ahmed body due to its well documented, simple geometry. The modified Ahmed body was already investigated by means of Rey- nolds-Averaged Navier-Stokes (RANS) modelling in Regert et al. (2007). The differences of the flow field characteristics between the Ahmed body and the modified Ahmed body, based on RANS modelling, were discussed in Regert et al. (2007) the RANS model- ling characteristics of such flows were investigated in detail in Reg- ert and Lajos (2007). To further improve the reliability of the computational results, the need for experimental results arose for the purpose of validation. It is well known in the research community of bluff bodies (e.g. Krajnovic ´ and Davidson, 2005a, 2005b; Schmidt and Thiele, 2002; Rodi, 1997; Craft et al., 2002) that, in spite of its excellent perfor- mance in determining the forces acting on bodies, RANS modelling fails when the structure of the flow field is to be analyzed (Krajno- vic ´ and Davidson 2005a, 2005b; Craft et al. 2002). The only reliable and affordable approach to obtain information concerning the structure of the flow field is Large Eddy Simulation (Krajnovic ´ and Davidson 2005a, 2005b). However, LES requires more and 0142-727X/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ijheatfluidflow.2013.05.012 ⇑ Corresponding author. Tel.: +36 1 463 4072; fax: +36 1 463 3464. E-mail addresses: gulyas@ara.bme.hu (A. Gulyás), agibodor@gmail.com (Á. Bodor), regert@vki.ac.be (T. Regert), janosi@lecso.elte.hu (I.M. Jánosi). 1 Present address: 72 Chaussee de Waterloo, 1640 Rhode-St-Genese, Hungary. International Journal of Heat and Fluid Flow 43 (2013) 220–232 Contents lists available at SciVerse ScienceDirect International Journal of Heat and Fluid Flow journal homepage: www.elsevier.com/locate/ijhff