On the Aerodynamics of Rear of Vehicle Model with Active Control by Blowing: Computational and Experimental Analysis Rustan Tarakka 1 *, Nasaruddin Salam 1 , Andi Amijoyo Mochtar 1 , Wawan Rauf 2 , Muhammad Ihsan 3 1 Department of Mechanical Engineering, Hasanuddin University, Gowa, Indonesia; Email:{nassalam.unhas@yahoo.co.id}{andijoyo@unhas.ac.id} 2 Department of Mechanical Engineering, Gorontalo University, Gorontalo, Indonesia; Email: {wawanrauf241193@yahoo.com } 3 Department of Civil Engineering, Sekolah Tinggi Teknik Baramuli, Pinrang, Indonesia; Email: {muhammadihsan@alumni.ait.asia} *Correspondence: rustan_tarakka@yahoo.com Abstract—Aerodynamics related to the generation of drag due to flow separations that occurs at rear parts of vehicles is an important consideration in vehicle design. It includes flow separation, wake formation, and pressures, which, in this paper, are focused on the ones exerted on the model’s rear wall. The pressure reductions could differ significantly between vehicles’ front and rear walls. This pressure difference can generate a phenomenon of backward pull and an increase in drags. The effort to minimize backflow as well as to cater increasing pressure on vehicles’ rear wall can be achieved by applying active control, including attached blowing apparatus. The paper presents the analysis of the effect on the application of blowing active control on the aerodynamics on rear part of vehicles, which is represented by a modified Ahmed body, reversed in flow direction and altered dimensions. The research was conducted using a validated numerical simulation method with laboratory experiments at an upstream air speed of 16.7 m/s and blowing velocities of 0.5 m/s, 1.0 m/s, and 1.5 m/s. The results showed that the application of blowing active control was capable to reduce aerodynamic drag, with the highest decrease achieved in the model with a ratio of velocity UBL3/U0=0.09 of 12.187% for the computational method and 11.556% for the experimental one. Keywords—aerodynamic drag, blowing active control, vehicle model I. INTRODUCTION Aerodynamics related to the generation of drag due to flow separations at rear parts of vehicles is an important consideration in vehicle design. The magnitude of the aerodynamic drag force, works in contrast to the relative motion of a moving object, undergone by vehicles will affect vehicles’ energy consumption and stability [1, 2]. This opposing movement usually occurs between the fluid and the surface of a solid object [3]. One approximation on amount of fuel consumption to overcome these adverse Manuscript received September 10, 2022; revised October 4, 2022; accepted November 30, 2022. aerodynamic drag is about 50-60% [4]. Reduction of the aerodynamic drag by as small as 15% will contribute to 5- 7% fuel consumption savings [5]. The aerodynamic drag on a vehicle is closely related to the flow characteristics and the pressure distribution at the rear part, which are also influenced by flow separations occurring at the upper rear part [6]. The design of this part is then very important in the effort of reducing aerodynamic drag [7]. The flow separation is expected to cause backflow and decrease pressure field in the onset area of the separation. The rate of the flow separation tends to increase the extent of the wake area positively and, at the same time, reduce the pressure on the rear wall region. This results in notable differences in the pressure exerted at both front and rear parts, triggering the backward pull phenomenon [8]. The process of minimizing negative pressure, and the intensity, at the rear area of vehicles could decrease the aerodynamic drag [4]. Flow engineering is a method used to minimize backflow and, at the same time, increase pressures exerted on the rear parts. As a results, it positively impacts delaying separation and reducing the re-circulation zone. Furthermore, flow engineering is realized by the application of active controls, such as blowing, with a combination with other forms of control, either active or passive [7], [9], [10]. An investigation carried out on the effect of continuous blowing on the interface of vehicles’ roof and rear window was published by Mestiri et al. Based on an experiment performed on steady blowing at 25° tangent to the surface of the slanted rear window of an Ahmed model, it was proven that tangential steady blowing produced the separated area on the rear window as well as disturbed the appearance of the counter-rotating longitudinal vortex at the end side. Furthermore, the direct flow control was considered effective in the re-circulation area at the upper part of the rear window [11]. 84 International Journal of Mechanical Engineering and Robotics Research Vol. 12, No. 2, March 2023 © 2023 Int. J. Mech. Eng. Rob. Res doi: 10.18178/ijmerr.12.2.84-90