Chin et al. / Malaysian Journal of Fundamental and Applied Sciences Vol. 15, No. 3 (2019) 389-393 389 Yaw angle effect on the aerodynamic performance of hatchback vehicle fitted with wing spoiler Kwang-Yhee Chin a , See-Yuan Cheng a, b, * , Shuhaimi Mansor c a Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia b Centre for Advanced Research on Energy, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia c Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia * Corresponding author: cheng@utem.edu.my Article history Received 27 February 2019 Revised 28 March 2019 Accepted 21 May 2019 Published Online 25 June 2019 Abstract Research on spoiler available to date was mainly done to optimize the performance of spoiler in non- zero yaw condition. However, the effect of spoiler is most needed during cornering to ensure the stability of the vehicle. Therefore, this study aims to inspect the effect of yaw angles change on the aerodynamic performance of the NACA 0018 wing spoiler and the subsequent influence on the flow characteristics of the hatchback vehicle. Computational Fluid Dynamics (CFD) has been applied to model the flow. Comparison between numerically obtained results and experimental data was done to validate the CFD method. The findings show that both the drag coefficient, Cd, and lift coefficient, Cl have increased with increasing yaw angle. However, the spoiler has performed in favor of reducing the Cd and Cl even with increasing yaw angle. The averaged proportion contributions from the spoiler to the overall Cd and Cl are 2.7% and 4.1%, respectively. The other body parts that have contributed to the Cd and Cl reductions were the base and slant, and the roof. Keywords: Yaw angle, spoiler, aerodynamics © 2019 Penerbit UTM Press. All rights reserved INTRODUCTION During cornering, a vehicle needs sufficient frictional forces in between its tires and the road surface to develop sufficient centripetal force to pass the curve without slip. The frictional forces are directly proportional to the downward forces exerted on the vehicle. In principle, the downward forces depend on the weight of the vehicle and the downward component of the aerodynamic force. Although, it may seem intuitive to increase the weight of the vehicle to enhance the frictional force, but this will not improve the performance of the vehicle during cornering due to the fact that the additional weight will produce additional inertia for which the vehicle will need to overcome. Besides, a heavier vehicle will result in higher fuel consumption rate, which is a disadvantage for both economic and environmental considerations. Therefore, the only viable solution would be to rely on aerodynamic effects. The aerodynamic effects can be obtained by properly installing the aerodynamic devices on the vehicle. One of the common aerodynamic devices is known as spoiler. In general, there are two types of spoilers, front and rear spoilers. A front spoiler is attached to the bumper while a rear spoiler is usually attached to the trailing edge of the roof for hatchback vehicles. The function of a rear spoiler is, as the name implies, to ‘spoil’ the smooth airflow passing over a vehicle in order to alter its aerodynamic characteristics, such as to reduce drag and increase downforce. Spoilers of various kinds had been widely researched (S. Cheng & S. Mansor, 2017), S. Y. Cheng and S. Mansor (2017), Hu and Wong (2011), Mitra (2010), and Kieffer, Moujaes, and Armbya (2006). To date, numerous studies concerning the optimization of the performance of wing spoilers have been reported in the literature. For example, Tsai, Fu, Tai, Huang, and Leong (2009) have studied the effect of various rear spoiler designs which were of aerofoil profiles on the aerodynamic characteristics of a simplified car model. It shows a reduction in lift. Besides, the study of Kim, Chen, and Shulze (2006) shows that by using a spoiler on a minivan, the lift force can be reduced by 100% when the minivan is driving at a speed of 108km/h. Moreover, the studies conducted by Daryakenari, Abdullah, Zulkifli, Sundararajan, and Sood (2013) and Kodali and Bezavada (2012) have also shown the similar lift reduction tendency produced by the spoilers. Although the studies on optimizing the performance of wing-type spoilers are not uncommon, but most of them are limited to zero degree yaw condition (i.e. simulating a vehicle driving in a straight path). However, during cornering, the effect of spoilers in enhancing the downforce is most needed to ensure drive stability and safety through the curve. Therefore, to address the issue, the main objective of the present study is to investigate the aerodynamic performance of the wing spoiler in yawing conditions. The paper is organized as follows: the chosen hatchback vehicle model is first introduced together with the features of the spoiler. In addition, the convention of yaw condition is briefly explained. Section II documents the CFD settings and validation of the numerical method. In Section III, the results obtained are being reported and discussed. The paper ends with the conclusion in Section IV. METHODOLOGY Hatchback model and spoiler configuration In this study, the Ahmed body, a reference road vehicle model introduced by Ahmed, Ramm, and Faltin (1984) is adopted for simulating the hatchback-type vehicle. The 35° slant angle of the upper rear section of the model is chosen which is typical for most hatchback vehicles. The Ahmed body fitted with a rear-roof NACA 0018 wing spoiler with 5° angle of attack is shown in Fig. 1. The chord length of the wing RESEARCH ARTICLE