EXPERIMENTAL AND ANALYTICAL INVESTIGATION OF THE EFFECT OF BODY KIT USED WITH SALOON CARS IN BRUNEI DARUSSALAM M.G., Yazdani, H. Ullah, T. Aderis and R. Zainulariffin, Faculty of Engineering, Institut Teknologi Brunei, Jalan Tungku Link, BE 1410, Brunei Darussalam E-mail: Gholam.yazdani@itb.edu.bn, hamid.ullah@itb.edu.bn, pg.aderis@live.com, zainul0989@hotmail.com. Key Words: Car Aerodynamics, Wind Tunnel, Flow Visualization, Body Kits, Power Loss. Abstract The purpose of this paper is to study the effect of the aerodynamic forces on saloon car with and without the body kit. Two cars were selected for this project namely Nissan 350z and Mazda RX-8. Body kits of the manufacturer s standard specification are used for the analysis. The aerodynamic analysis is made using wind tunnel equipment and also flow visualization is made to see the air flow profiles. From the experimental measurement, the stability of the car with and without body kit is discussed. Using Microsoft Excel, the functional relationship between drag coefficient (C d ) at zero degree angle of attack (α) and Reynolds number (Re) is determined. Using the above functional relationship, the C d at other Re is found. Using above C d and appropriate equation, energy loss due to drag and energy loss due to rolling resistance is found and discussed. Flow visualization is done to offer explanation for the results obtained from wind tunnel experiment. I. Introduction Background A body kit is a special car part generally used to modify the exterior of a car. Most body kits include side skirts, front and rear bumpers (fenders), spoilers and occasionally front and rear side guards. Body kits are purchased and installed to the car body for the purpose of enhancing both the exterior appearance as well as performance. A body kit can affect car performance in various ways. For example, ground skirt kit is capable of improving aerodynamics to a car, as well as reduces the lift under the car which helps the chance of losing control of the car when driving at higher speed. As early as 1960s, race car designers, inventors and mechanics conducted various tests and experiments with the automobile s design, shape and closeness to the ground through the use of body kits. Today, there is a wide variety of body kits available in the market. Any alteration in the shape of body of a car will radically affect the drag, lift, and side forces of the car when it is moving in the air. In Brunei Darussalam, drivers use body kits on their cars, without knowing its aerodynamic effect on the car. The paper presents the aerodynamic effect of using a body kit on acar. Two types of saloon cars namely Nissan 350z and Mazda RX-8fitted with body kit are considered in the paper. 2. Literature Review Yazdani et.al 1] conducted some experimental study to compare the aerodynamic forces acting on Subaru WRX STi version IV (SPC) with a recommended World Rally Championship (WRC) and a non-recommended GT Wing Type-A (GTA) spoilers. The experiment was conducted with the following combination: SPC, SPC+WRC (REC), and SPC+GTA (NRE). The above experiments were conducted at a Reynolds Number (R) range of 2.19 x 10 4 to 10.94 x10 4 and an angle of attack (α) of 0 to 20. The lift coefficient (C l ), drag coefficient (C d ) and side force coefficient (C s ) are computed from the measured data. From the data analysis, it was found that, for REC C l decreased in almost all the investigated ranges of α and R. The maximum decrease in C l is about 40% (at α = 20 ). On the other hand for NRE, C l increases for almost all the investigated ranges of α and R. The maximum increase of C l is about 177%. At, 2.19 x 10 4 R 6.57 x 10 4, there is little or no change in the value of C d for REC and SPC in the investigated ranges of α. It was found that value of C s for REC is less than that of NRE in the investigated range of α and R. Koike et. al, [2] tested bump-shaped vortex generators at the roof end of a sedan to reduce drag. Their paper presents the optimization result, the effect of vortex generators in the flow field and the mechanism by which these effects take place. The behaviour of different add-on parts to a basic car model has been studied experimentally [3]. Experiments were conducted with different add-on parts, like rear end spoiler and front end spoiler in order to find out how these add-on parts influence the drag and lift coefficients of a basic car model. The experiment was conducted in Jadavpur University low turbulence subsonic closed circuit wind tunnel at different Reynolds number. The results from the experiment indicated that the addition of different add-on parts like front end spoiler and rear end spoiler to a basic car model reduces the lift coefficient to a considerable amount while the drag coefficient is reduced by a small amount. It was concluded that the addition of these add-on parts increases the aerodynamic
stability of a basic car model and hence they can be used in real life situations as an added advantage. An assessment of the role of fluid dynamic resistance and aerodynamic drag and the relationship to energy use in the United States is presented [4]. Existing data indicates that 16% of the total energy consumed in the United States is used to overcome aerodynamic drag in transportation systems. Application of existing pressure drag reduction technologies to all ground vehicles within the United States will reduce yearly energy cost by 20 billion dollars. Three simple, low cost aerodynamic drag reduction devices have been developed for application to the trailer of a tractortrailer truck [5]. The three devices have undergone extensive operational testing where they have amassed over 85,000 miles of use. These technologies have shown a combined fuel savings of 10% at an average speed of 47.5 mph. This improvement in fuel economy correlates to an equivalent drag reduction of approximately 30% with a corresponding drag coefficient of 0.45. Observations and anecdotal evidence from the test activity have shown that the addition of these devices to the trailers has no negative impact on either the operational utility of the trailers or the maintenance procedures and requirements. A numerical study [6] with two different types of simulations was made, one for the flow around a simplified high speed passenger car with a rear-spoiler and the other for the flow without a rear-spoiler. The standard k-s model was selected to numerically simulate the external flow field of the simplified Camry model with or without a rear-spoiler. Through an analysis of the simulation results, a new rear spoiler was designed which shows a mild reduction of the vehicle aerodynamics drag. This leads to less vehicle fuel consumption on the road. 3. Methodology Two types of cars, Nissan 350z and Mazda RX-8, were selected. The scaled down models of the cars selected for the purpose were 1:32 for Nissan 350z and 1:24 for Mazda RX- 8.The cars were tested with and without the body kits for knowing the aerodynamic effect of using body kits on these cars. Body kits having specifications available in Brunei Darussalam were used for the cars. All the experimental measurements were performed in a subsonic wind tunnel. The functional relationship between drag coefficient (C d ) at zero degree angle of attack (α) and Reynolds number (Re) is determined using Microsoft Excel. Using this functional relationship, the C d against another Re was determined. Using this C d and appropriate equation, power loss (due to drag) and power loss (due to rolling resistance) were found and discussed. Flow visualization was performed to provide explanation for the results obtained from the wind tunnel experimentation. 4. Results and discussions Drag Coefficients Fig. 1.Coefficient of Drag against Angle of Attack for different Reynolds number for Nissan 350z without body kit Fig. 2. Coefficient of Drag against Angle of Attack for different Reynolds number for Nissan 350z with body kit Generally, the C d increases as α increases for all Re except for Nissan 350z with body kit (Fig. 2). Without the body kit for Nissan 350z and Mazda RX-8, the coefficient of drag (C d ) for all Re lies around 0.25 to 0.3 (Fig.1) and 0.29 to 0.31(fig. 3) respectively for all ranges of α. For Nissan 350z at lower Re, which is below 23 x 10 5, there is a sudden decrease of C d at α = 5 0 and increase back at α = 10 0. Overall, C d increases as α increases. For Nissan 350z, with body kit, C d remains constant between 0.350to 0.29,at all ranges of Re and α (Fig. 1-2). Fig. 3.Coefficient of Drag against Angle of Attack for different Reynolds number for Mazda RX-8 without body kit
Cl Fig. 4.Coefficient of Drag against Angle of Attack for different Reynolds number for Mazda RX-8 with body kit Overall, C d for the car with the body kit is higher than the car without the body kit (Fig. 1-4). Fig. 7. Coefficient of Liftagainst Angle of Attack for different Reynolds number for Mazda RX-8 without body kit Lift Coefficients Fig. 5.Coefficient of Lift against Angle of Attack for different Reynolds number for Nissan 350z without body kit Fig. 8.Coefficient of Lift against Angle of Attack for different Reynolds number for Mazda RX-8 with body kit 0-0.05 0 2 4 6 8 10-0.1-0.15-0.2-0.25 Angle of Attack α Fig. 6.Coefficient of Lift against Angle of Attack for different Reynolds number for Nissan 350z with body kit For Nissan 350z without the body kit, the C l for all Re lies around -0.045 to -0.055 at α = 0 0 to 5 0. (Fig.5)It is seen that C l increases as α increase. For the above car with the body kit, the C l lies around -0.15 to -0.23 for all Re and α. In general, C L increases as α increase (Fig. 6) Fig. 9.Side Force Coefficient against Angle of Attack for different Reynolds number for Nissan 350z without body kit For Mazda RX-8 without the body kit, the C l lies around -0.2 to -0.1 for all Re and α. The trend shows that the C l decreases as α increases for all Re (Fig. 7).For the above car with the body kit, the C l lies around 0.02 to - 0.04 for all Re and α values. The trend of C l is approximately constant for all Re and α values (Fig. 8).Overall, it is seen that C L decreases with the addition of body kit for Nissan 350z whereas it increases in case of Mazda RX-8 (Fig 5-8). Side Force Coefficient For both the car with and without the body kit, it is observed that Cs increases with the increase of α for all the investigated ranges of Re. Generally, the C s of the cars is increased by 50% when it is installed with the body kit for all the investigated ranges of Re and α (Fig.9-12).
Power Loss Fig. 10.Side Force Coefficient against Angle of Attack for different Reynolds number for Nissan 350z with body kit Fig.13. Percentage of Energy Loss against Velocity for Nissan 350z without body kit Fig. 14.Percentage of Energy Loss against Velocity for Nissan 350z with body kit Fig. 11. Side Force Coefficient against Angle of Attack for different Reynolds number for Mazda RX-8 without body kit Fig. 15. Percentage of Energy Loss against Velocity for Mazda RX- 8 without body kit Fig. 12 Side Force Coefficient against Angle of Attack for different Reynolds number for Mazda RX-8 with body kit
Plate 3.Nissan 350z at Angle of Attack 10 0 Fig. 16. Percentage of Energy Loss against Velocity for Mazda RX-8 with body kit For Both the models, there is a sharp increase in loss of energy due to drag when the car is fitted with the body kit. The body kit is shown to have a little or no effect on energy loss due to rolling resistance(fig. 13-16).This increase in energy loss due to drag is about two times for any speed for the car with the body kit compared to without the body kit(fig. 13-16). This means that the body kit has an adverse effect on fuel consumption due to drag. Flow Visualization Plate 1.Nissan 350z at Angle of Attack 0 0 Flow visualization experiment was conducted using model car Nissan 350z without and with the body kit for angle of attack (α) 0 0, 5 0 and 10 0 at Reynolds number (Re) of 4 x 10 5. Pictures were taken during the experiments for analysis. From the wind tunnel experiment, it was found that the drag for the car with the body kit is more than the drag of the car without the body kit for all ranges of investigated α and Re. From flow visualization experiment, the wake region is larger for the car with the body kit compared to without the body kit for all α (Plates 1-6). This shows that there is more pressure difference between the front and the back pressure of the car with the body kit resulting in more drag force created. For the car without the body kit, it is shown in the wind tunnel experiment when Re is below 23 x 10 5, the C d decreases at α = 5 0 and increases back at α = 10 0 as shown in figure 1. This behaviour is proved in the flow visualization experiment (Plate 2).The wake region at α = 5 0 is smaller compared to that at α = 0 0. Smaller wake region means smaller pressure difference thus lower drag force. At α = 10 0, the wake region becomes larger which means higher drag force (Plate 3). For the car with the body kit, it is shown in the wind tunnel experiment that the trend of C d remains the same for all α as shown in figure 2. This is proven in flow visualization experiment as the size of the wake regions remains the same for all α. Same wake region size means same pressure difference thus same drag force; the C d is constant. From wind tunnel experiment, the lift is found to be higher for the car without the body kit than the car with the body kit. For the flow visualization it is seen that due to deflection from a body kit of car spoiler, there might be a formation of positive pressure which can lead to a lower lift.thisis supported by the wind tunnel experiment. Plate 2.Nissan 350z at Angle of Attack 5 0 Plate 4.Mazda RX-8 at Angle of Attack 0 0
5. Conclusions Plate 5.Mazda RX-8 at Angle of Attack 5 0 The coefficient of drag (C d ) appears higher for a car installed with body kit compared to a car without body kit, for all the investigated range of Reynolds number (Re) and angle of attack (α). This holds true for both types of the cars investigated in this research. For Nissan 350z, the lift is lower with the body kit whereas for Mazda RX-8, it is higher with the body kit. A sharp increase appears in loss of energy due to drag for a car fitted with a body kit. The increase in loss of energy is about two times for any speed. This means that the body kit has an adverse effect on fuel consumption due to drag. It is found that increase in C s for both the cars is 50% with the body kit for almost all ranges of Re and α. This might create enough side force to topple the car with body kit if there is a significant side wind. Flow visualization reveals that the aerodynamic effect of body kit might be due to the spoiler only. This needs to be verified by doing wind tunnel experiments using spoiler only. Plate 6.Mazda RX-8 at Angle of Attack 10 0 Flow visualization experiment was conducted using model car Mazda RX-8 without and with the body kit for angle of attack (α) 0 0, 5 0 and 10 0 at Reynolds number (Re) of 40 x 10 4. Pictures were taken during the experiments for analysis. From the wind tunnel experiment, it was found that the drag for the car with the body kit is more than the drag of the car without the body kit for all ranges of investigated α and Re as shown in figure 3 and figure 4. From the flow visualization, it is seen that the wake region for the car with the body kit is larger than without body kit. This means that the back pressure of the car with the body kit is lower than the same car without the body kit. The above create a higher drag for the car with the body kit compared to that without the body kit. From the wind tunnel experiment, it is seen that the lift of the car without the body kit is less than the car with the body kit for all ranges of α and Re as shown is figure 7 and figure 8. This can be explained in the flow visualization. It is seen that the shear layers are nearer to the car with the body kit creating more suction or low pressure (Plate 4-6).As a result, it has more lift. REFERENCES [1]. Yazdani, M. G., Sumajaya, P.G. O. and Arifin, M.N. Comparison of aerodynamic forces using a recommended and a nonrecommended lift spoiler on a passenger car, 15 th International Conference on Applied Mechanics and Mechanical Engineering, Cairo, Egypt, May 28-31,pp. 1-14. 2012.. [2]. Mitra, D. Effect of Relative Wind on Notch Back Car with Add- On Parts, Int. J. of Eng. Sc. and Tech., Vol. 2(4), pp.472-476.,. 2010. [3]. Koike M., Nagayoshi T., Hamamoto N., Research on aerodynamic drag reduction by vortex Generators, Technical Review, Mitsubishi Motors, No.16,, pp 11-16, 2004. [4]. Mitra, D., Effect of Relative Wind on Notch Back Car with Add- On Parts, Int. J. of Eng. Sc. and Tech., Vol. 2(4), pp.472-476, 2010. [5]. Wood, R. M., Impact of Advanced Aerodynamic Technology on Transportation Energy Consumption, SAE 2004-01-1306, Nov. 2004. [6]. Wood, R. M., Bauer, S. X. S., Simple and Low-Cost Aerodynamic Drag Reduction Devices for Tractor-Trailer Trucks, SAE 2003-01- 3377, Nov. 2003. [7]. Hu, X., and Wong, T.T., A Numerical Study On Rear-spoiler Of Passenger Vehicle, World Academy of Science, Engineering and Technology 81, pp. 636-641, 2011. From the flow visualization, an attempt was made to find the formation length and the vortex shedding frequency. The formation length is a quantitative measure of drag force, which can be correlated with the wind tunnel measurement. The vortex shedding frequency can be used to find the fluctuation of the drag force. Unfortunately, due to low picture quality and limitation on number of frame per second of picture shots produced, both the formation length and vortex shedding frequency cannot be determined. It is recommended for further research using high quality camera.