International Journal of Automotive Technology, Vol. 20, No. 4, pp. 763777 (2019) DOI 10.1007/s1223901900721 Copyright © 2019 KSAE/ 10912 pISSN 12299138/ eISSN 19763832 763 EFFECTS OF WHEEL CONFIGURATION ON THE FLOW FIELD AND THE DRAG COEFFICIENT OF A PASSENGER VEHICLE Michael Donald Peter Bolzon 1)* , Simone Sebben 1) and Alexander Broniewicz 2) 1) Vehicle Engineering and Autonomous Systems, Chalmers University of Technology, Gothenburg 412 58, Sweden 2) Environment & Fluid Dynamics Center, Volvo Cars, Volvo Jakobs Väg 418 78, Sweden (Received 9 August 2018; Revised 4 December 2018; Accepted 10 January 2019) ABSTRACTThe effects of wheel rotation, rim coverage area, fan spokes, spoke sharpness, and tread pattern on the flow field and drag coefficient of a passenger vehicle were investigated. Force measurements and wake surveys were taken on a 1/ 5 th scale passenger vehicle at a Reynolds number of 2.0 × 10 6 . The wake surveys were conducted at three planes. Vorticity, total pressure coefficient, and local drag coefficient plots are presented. Wheel rotation reduced the drag coefficient of all of the wheel configurations tested, which generally agrees with literature. Wheel rotation reduced the front wheel’s jetting vortex’s drag while increasing the drag from the center of the front wheel to the upper rim track. Reducing the rim coverage area increased the drag coefficient. This increase was attributed to an increased jetting vortex drag and a change in flow separation around the front wheel. The fan spoke rim performed the worst, regardless of rotation. Rounding the spoke edges reduced the drag coefficient of a rotating wheel. The tread pattern slightly reduced the shoulder vortex vorticity and slightly increased the separation around the front wheel. KEY WORDS : Rotating wheels, Rim aerodynamics, Wake surveying, Jetting vortex NOMENCLATURE u : velocity in x-direction, m/s v : velocity in y-direction, m/s w : velocity in z-direction, m/s y : Y-direction z : Z-direction C DL : local drag coefficient C Pt : total pressure coefficient P S : static pressure, pa V : resultant velocity, m/s : freestream velocity, m/s  : density, kg/m 3  : vorticity, 1/s 1. INTRODUCTION Wheels account for approximately 25 % of the total drag coefficient of a passenger vehicle (Schnepf et al., 2015). Furthermore, above approximately 70 kph, more than 50 % of the vehicle’s power is used in overcoming the vehicle’s drag (Hucho, 1998; Barnard, 2001). As such, with regulations becoming increasingly strict (Council of European Union, 2014) and consumer demands rising, reducing the drag of passenger vehicles (and hence increasing its efficiency) is important. 1.1. Literature Review A sizable body of literature exists detailing various aerodynamic principles of wheels, both when the wheel is stationary and when it is rotating. One of the most pertinent examples is the effects of wheel rotation; when the flow passes over a stationary wheel, a stagnation point is created on the front of the wheel. It is generally accepted that two relatively large vortices are created at the base of the wheel (termed ‘jetting vortices’), and two at the top of the wheel (termed ‘top vortices’) (Mercker et al., 1991; Croner et al., 2013; Huminic and Huminic, 2017). Two more vortices are created around the shoulder of the tyre. However, when a wheel rotates, the stagnation point moves upwards, the jetting vortices reduce in size and the top vortices increase in size (Mercker et al., 1991; Wäschle et al., 2004). Furthermore, wheel rotation also affects the vehicle’s general wake (Elofsson and Bannister, 2002). Studies have shown that the effects of front wheel rotation are varied, and the front wheel drag can either decrease or increase, depending on the setup (Wickern and Lindener, 2000; Elofsson and Bannister, 2002; Koitrand and Rehnberg, 2013). In addition, the interaction between local and global effects induced by front wheel rotation is complex; one study surmised, through wind tunnel measurements, that front wheel rotation reduced the drag coefficient by 10 counts, but drag coefficient increases in non-local locations resulted in a minor change to the vehicle’s overall drag coefficient (Elofsson and Bannister, 2002). Some limitations to the studies on wheel rotation are that they V  *Corresponding author. e-mail: michael.bolzon@chalmes.se