ENHANCEMENT OF AERODYNAMIC PERFORMANCE OF A FORMULA-1 RACE CAR USING ADD-ON DEVICES B. N. Devaiah 1, S. Umesh 2

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1 ENHANCEMENT OF AERODYNAMIC PERFORMANCE OF A FORMULA-1 RACE CAR USING ADD-ON DEVICES B. N. Devaiah 1, S. Umesh 2 1- M. Sc. [Engg.] Student, 2- Asst. Professor Automotive and Aeronautical Engineering Department, M. S. Ramaiah School of Advanced Studies, Bangalore 58. Abstract Aerodynamics plays a very important role in motorsports. Car manufacturers around the world have been fascinated and influenced by the various aerodynamic improvements that are used in racing. There has been a constant effort on their side to incorporate these changes to road vehicles not just as an aesthetic design feature but also since they believe that these features can contribute to improving fuel economy and vehicle handling. One of the main areas of concern in racing is to balance aerodynamic forces and to streamline the air flow across the body towards improving stability and handling characteristics, especially, while cornering. At present, formula racing cars are regulated by stringent FIA norms, there is a constraint for the dimensions of the vehicle used, engine capacity, power output and emission. It is difficult to obtain the optimum aerodynamic performance with the existing racing car. There is a need for improvement in the aerodynamic performance of these race cars by using add-on devices locally with different configurations to streamline and channelize the airflow besides reducing aerodynamic forces and providing stability that improves cornering and handling characteristics. In this project work, an attempt has been made to improve the aerodynamic performance of F1 race car by using various add-on devices with different configurations through steady state CFD simulations. Initially, steady state external air flow simulation on the baseline model F-1 car without add-on devices has been carried out to obtain air flow pattern around and for aerodynamic forces using FLUENT solver. A detailed survey on different add-on devices used for racing applications has been made and geometric models of some add-on devices like front wing, bargeboard, nose wing, rear wheel scallops, roof spoiler and rear wing with best possible configurations were created and attached to the baseline model. Steady state CFD simulation on the modified F1 race car with add-on devices has been carried out for different speeds. Aerodynamic performances like lift force, drag force and their co-efficients are evaluated for different configurations of add-on devices for different speeds From parametric CFD simulations on F-1 car attached with add-on devices, there is a considerable amount of drag and lift force reduction besides streamlining the airflow across the car. The best possible configuration for all add-on devices, i.e. front and rear wings, nose wing, barge board, roof spoiler and wheel scallops, are derived from CFD simulations. The combination of all these add-on devices with the most appropriate configurations is suggested to incorporate for F1 race car to improve aerodynamic performance.. Key Words: F-1 Car, Steady State Aerodynamic Analysis, Wings, Add-on Devices, Drag Reduction 1. INTRODUCTION A Formula-1 car has many add-on devices that aim at reducing the lift and drag forces on the car and there-by reducing the lap times. But, the lift and drag forces are inversely proportional to each other. Often one tends to ignore the fact that the combination of the right configuration of all the add-on devices is what contributes to the reduced lap times and not just the design of the individual add-on devices. For example, the lift reduction achieved by an add-on device, say the front wing, comes at the cost of higher area being exposed the air leading to an increase in the drag force, but, the additional downforce is essential for F1 cars as the high speed requires huge amount of traction to improve its stability, especially at corners to allow high cornering speed. In race cars, especially the open wheel types like the ones used in Formula-1, the add-on devices play a major role in the lap timings and ultimately is the difference between the best and the rest. The design of these add-on devices is also not a simple task with the constraints imposed by the regulations and also the practical constraints. The configuration of the add-on devices is as important as the design itself, if not more. In order to maintain desirable handling qualities, the fore-aft location of the aerodynamic centre of pressure (CP) is very important. Typically the centre of pressure needs to be located within a certain distance forward or behind the car centre of gravity. The add-on devices used in the F-1 car model and their functions have been explained in detail in section 2 of this paper. The rear wing is a crucial component for the performance of a Formula 1 race car. These devices contribute to approximately a third of the car s total down force, while only weighing about 7 kg [7]. Figure 2.1 shows a rear wing with the airfoil profiles. Usually the rear wing is comprised of two sets of aerofoils connected to each other by the wing endplates. The upper aerofoil, usually consisting of three elements, provides the most downforce. The lower aerofoil, usually consisting of two elements, is smaller and SASTECH Journal 72 Volume 12, Issue 1, April 2013

2 provides some downforce. However, the lower aerofoil creates a low-pressure region just below the wing to help the diffuser create more downforce below the car. The rear wing is varied from track to track because of the trade-off between downforce and drag. More wing angle increases the downforce and produces more drag, thus reducing the cars top speed. So when racing on tracks with long straights and few turns, it is better to adjust the wings to have small angles. On the other hand, when racing on tracks with many turns and few straights, it is better to adjust the wings to have large angles. Splitting the aerofoil into separate elements as shown in Figure 1 is one way to overcome the flow separation caused by adverse pressure gradients. Multiple wings are used to gain more downforce in the rear wing. Two wings will produce more downforce than one wing, but not twice as much. Figure shows the relationship between the number of airfoils with both the lift coefficient and the lift/drag ratio. The lift coefficient increases and lift/drag (L/D) ratio decreases when increasing the number of aerofoils. The position of the wings relative to each other is important. If they are too close together, the resultant forces will be in opposite directions and thus cancel each other. Fig. 1 Cascaded wing with aerofoil profile Rear wing endplates are designed with form and function in mind. Because of their form they provide a convenient and sturdy way of mounting wings. The aerodynamic function of these endplates is to prevent air spillage around the wing tips and thus they delay the development of strongly concentrated trailing vortices. Trailing vortex or induced drag is the dominating drag on rear wings. An additional goal of the rear endplates is to help reduce the influence of upflow from the wheels. Figure 2 shows a rear wing endplate. Fig. 2 Endplate design The front wing of an F1 car has a lot of constraints too like the rear wing and other parts. It is required to have a neutral central section. This section must be at least 50 cm in length and cannot induce any amount of downforce, hence the name neutral central section. There is freedom though in the number of cascades and the flexibility of the wings, i.e., the regulations do not specify or limit the number of cascades and its flexibility. It is found that the stability of a car, while slipstreaming, improves when the wings are flexible. Also, the closer the wings are to the ground, the more is the downforce that it produces, since it make use of the ground effect of the car. But, the regulations specify the minimum ground clearance of the car at standstill position which cannot be compromised on. Hence, flexible wings are added which, due to its flexibility, moves down during cornering which induces a higher downforce on the car and improves its handling and stability. Aerodynamic performance enhancement is a very important part of the strategy of any race car team and is a subject of great interest. Many researchers have studied the means to enhance the aerodynamic performance and also the effect these changes have on the overall performance of the car employing analytical and experimental methods. Noah J McKay and Ashok Gopalarathnam [1] conducted an analytical study to determine the effects of wing aerodynamics on the performance of race cars and its effect on lap times on different kinds of tracks. Different airfoil shapes were considered for the design and were analyzed during cornering, straight line braking and straight line acceleration conditions. These shapes were tried for single and dual wing configurations. The results showed the importance of maintaining a proper lift to drag ratio and that the front wing downforce had to balance the rear wing downforce for optimal results. Joseph Katz and Darwin Garcia [4] conducted a study on an open-wheel type, 1/4th scale model of an Indy car to analyse the aerodynamic components of the add-on devices. The testing has been done at low speeds in a wind tunnel using the elevated ground plane method. The aerodynamic loads were measured by a six component balance to maintain accuracy. It is concluded that the two wings and the vortex generators generated the maximum downforce and the major contributors of drag are the wheels and wings. SASTECH Journal 73 Volume 12, Issue 1, April 2013

3 Michael S Selig and Mark D Maughmert [5] suggested a method for the selection of the different parameters of an airfoil like the airfoil maximum thickness ratio, pitching moment, part of the ve1oclty distribution, or boundary-layer development. A hybrid-inverse airfoil design technique has been developed by coupling a potential-flow, multipoint inverse airfoil design method with a direct boundary-layer analysis method. Ashok Gopalarathnam et al [6] conducted a study on the design of high lift airfoils for low aspect ratio wings with endplates that are extensively used in rear wings of race cars. The induced effects of this setup and the optimum angle of attack is determined. A parametric study is conducted on the airfoils to study the effects of the constraints due to the regulations. Magnus O Johansson and Joseph Katz [8] conducted a series of experiments on sprint car model in a small scale wind tunnel to test the effect that the wings can have on the downforce and cornering ability. They conducted parametric studies by considering different airfoil profiles and concluded that the center of pressure can be varied by adjusting the front wing configuration and the modified airfoil shapes resulted in greater downforce and cornering ability. Car Specifications The car chosen is the Ferrari F2003 GA and its specs are as shown in the table below. Table 1. Engine specs Configuration Ferrari Type 052 Location Construction Mid-engine, rear wheel drive, longitudinally mounted Aluminum alloy block and head Height Front track width Rear track width Wheel base Overall length 959 mm 1470mm 1405 mm 3100mm 4545mm 2. MODELLING, DISCRETIZATION AND ANALYSIS Geometric modeling of the Ferrari F2003-GA was done using the software tool CATIA V5. Fluid domain discretization was done in ICEM CFD, which was used as a pre-processor. Steady state external aerodynamic analysis has been carried out for the three models of the car, namely, (i) baseline model, (ii) baseline model with the front and rear wings attached, (iii) final car model with all add-on devices attached, at five different speeds of 150 kmph, 200 kmph, 250 kmph, 300 kmph and 350 kmph in FLUENT V6 which was used as a solver and post-processor. The geometric model of the F1 car is first cleaned up. The geometry is simplified by closing or filling the tyre treads. This is done in order to ensure that the discretization or meshing of the model does not fail at the treads because of it shape and minute size. Figure 3 shows the geometric model of the baseline car in isometric view. It can be seen from the figure that the baseline car does not have any addon devices. This model is analyzed just to check how the car behaves at high speeds without the influence of any add-on devices. Displacement Valve Aspiration 2,997cc, V10 4 valves per cylinder, DOHC Naturally Aspirated Fuel feed Table 2. Dimensions of the car Weight Length Width Magnetti Marelli Fuel Injection 600 kg 4545 mm 1796 mm Fig. 3 Geometric model of the baseline car The next step is to attach the front and rear wings to the baseline car. The baseline model with the wings attached (Figure 4.3) is again analysed for five different speeds of 150, 200, 250, 300, 350 kmph to study the amount of downforce and drag force on the car with just the wings attached and to find how much of an improvement it is from the initial baseline model without any add-on devices. The final step in modelling is to design the add-on devices. The different add-on devices that are designed are: SASTECH Journal 74 Volume 12, Issue 1, April 2013

4 Modified Front Wing: The front wings are responsible for up to 30% - 40% of the downforce generated in an F1 race car. The front wing in the original design does not have end plates and deflectors on it. This results in the air directly coming in contact with the front wheels which contribute to the drag. Hence, the base plate is designed such that the trailing edges of the plate help in streamlining the flow of the under-body air away from front wheels as shown in figure 4. The deflectors also have the same function of streamlining the air around the front wheels on the upperbody side. As its name suggests, it just deflects the air away from the tyre such that the streamlines get re-attached with the flow along the car body as soon as it passes the tyres. moments on the front and rear ends of the car and to streamline the flow of air above and below the upper control arm of the double wishbone suspension assembly. The figure 6 shows the designed nose wing and its location on the nose. Fig. 4 Modified front wing with the base plate and the deflector Bargeboard: It is a piece of bodywork mounted vertically between the front wheels and the start of the sidepods to help smooth the airflow around the sides of the car. The bargeboard in the car is located just behind the suspension control arms. It helps in streamlining the flow around the car body thus helping in reducing aerodynamic drag on the car. The air after passing through the front wings, come in contact with the suspension control arms and the flow-lines become haphazard. The main function of the bargeboard is to streamline this haphazard flow around the body of the car such that it re-attaches to flow through the rear wing which is critical in generating downforce. The design is such that flow of air happens on both the inner and outer edges of the bargeboard and this ensures there is no flow separation. Figure 5 shows the bargeboard design. Fig. 5 Design and position of bargeboard Nose wing: The nose wing has an inverted negative lift airfoil shape and is modelled using the NACA 6 series coordinates. It is placed just before the suspension arms assembly of the front wheel on the front nose of the car. Its main purpose is to maintain the balance of aerodynamic Fig. 6 Nose wing Roof spoiler: It is a wing that is placed just above the driver cockpit and its main purpose is to provide downforce by streamlining and re-directing the air towards the rear spoiler. The front and the rear parts of an F1 car has wings that generate the required amount of downforce, but the middle part also must have a sufficient amount of downforce to balance the overall aerodynamic moments on the car. The basic idea is to keep the centre of pressure as close to the centre of gravity (CG) of the car to provide maximum stability during operation. Figure 7 shows the roof spoiler designed of the car. Fig. 7 Roof spoiler Rear Wheel Scallops: The rear wheel scallops positioned just in front of the rear wheels serve the purpose of streamlining the air coming from the bargeboard and the front wings towards the rear wing and away from the rear tyres. This helps in generating downforce and also reduces the drag force on the car. The rear wheel scallops are designed such that the stream of air passes on both its faces and re-directs it away from the rear tyres thereby reducing the drag force and helps in knocking off a few crucial milliseconds off the lap times! Figure 8 shows the rear wheel scallops. SASTECH Journal 75 Volume 12, Issue 1, April 2013

5 Fig. 8 Rear wheel scallops Rear wing: The two main parts of the rear wings are the cascading wing profiles and the end plates. The rear wings produce downforce towrds the rear end of the car. Most of the contours on the car are designed such that they streamline the air into the rear wings so as to induce the largest amount of downforce. Another important part of the rear wing is the beam wing. It is the lowest wing section and is very strictly regulated by crash test regulations. It is also quite heavy sine it supports the whole wing and some cars use it as a part of the chassis also. Fig. 11 Discretized model of car with all add-on devices 3 DISCUSSION OF RESULTS AND VALIDATION The results from the steady state analysis carried out on the three models of the F-1 car are discussed in this chapter. The performance and the aerodynamic forces and their coefficients are analysed by simulating at five different speeds of 150, 200, 250, 300 and 350 kmph for all the three models. 3.1 Solver settings and parameters The solver settings set in FLUENT software for the simulation is as shown in the table 3 Table 3. Solver settings Solver type velocity flow viscosity model 3d- pressure based absolute steady Turbulent (K-epsilon) Fig. 9 Rear wing Figure 9 shows the model of the F1 car after all the designed add-on devices have been attached. The other settings that have to be specified for the simulation are the boundary conditions. Table 5.2 gives the boundary conditions set in Fluent software for the analysis. Table 4. Boundary Conditions Fig. 10 Model with all add-on devices Figure 10 shows the discretized model of the car with all add-on devices and the different mesh sizes adopted in order to save computational time, without compromising on the accuracy of the results. Parts Car body Add-on devices Wheels Domain bottom wall Domain top, left and right walls Domain Inlet Domain outlet Boundary Conditions Stationary wall, no slip Stationary wall, no slip Rotational wall with specified angular velocity Translational wall with specified velocity Stationary wall, with specified shear condition Velocity Inlet Pressure outlet SASTECH Journal 76 Volume 12, Issue 1, April 2013

6 3.2 Results The baseline model of the F1 car is simulated and the results are as tabulated in table 5. Table 5. Comparison of aerodynamic forces at different speeds for baseline model car body and regions of low velocity just behind the car (wake region), which is considerably large. Baseline Model Car Speed Drag Force Cd Lift Force Cl Fig. 14 Contours of pressure and velocity Fig. 12 Variation of drag force (N) v/s speed (kmph) Fig. 15 Pathlines seen from the side view showing streamlines along the body The model of the F1 car with all the add-on devices that have been designed, like, the bargeboard, nose wing, front wing modifications, roof spoiler, rear wheel scallops and the rear wing are attached is analysed and simulated and the results are as tabulated in Table 6. Table 6. Comparison of aerodynamic forces at different speeds model with all add-on devices Car Speed Model with all add-on devices Drag Force (N) Cd Downforc e (N) Cl Fig. 13 Variation of down force (N) v/s speed (kmph) Figure 13 shows the contours of pressure distribution and velocity distribution along the center plane in x- direction. High pressure points can be observed at the nose tip, the front wheel, the body of the car and the area behind the cockpit. The velocity plot shows stagnation points on the Both the drag and lift forces are increasing with increase in speed. The variation in the drag and lift forces with speed is almost linear as shown in figure 5.17 and 5.18 respectively. SASTECH Journal 77 Volume 12, Issue 1, April 2013

7 model with all add-on devices when compared to the model with only the front and rear wings attached. Figure 18 shows the drag co-efficient variation and it follows the same pattern as the drag force. Fig. 16 Variation of drag force (N) v/s speed (kmph) Fig. 18 Graph showing variation of drag force for the different models Fig. 17 Variation of down force (N) v/s speed (kmph) 4. COMPARISON OF RESULTS The results for the three models are compared and the changes in their aerodynamic forces and co-efficients are analysed. The comparison of these values at different speeds is as shown in table In table 5.10, baseline stands for the baseline model of the car, wings only stands for the car model with the front and the rear wings attached and all addons stands for the car model with the modified front wing, rear wing, bargeboard, nose wing, rear wheel scallops and the roof spoiler attached. Table 7. Comparison of aerodynamic forces and their co-efficients of the three models at a speed of 200 kmph Drag Force (N) Cd Downforce (N) Baseline Wings only All addons Figure 17 shows the drag force variation for different models. It can be seen that the drag force is least on the baseline model which is understandable since it has a very small frontal projected area. The drag force is less on the Cl Fig. 19 Graph showing variation of drag coefficient for the different models Fig. 20 Graph showing variation of down force for the different models The variation of downforce and its co-efficient are as shown in figure 19 and 20. It can be seen that the add-on devices have reduced the drag but, at the expense of reduced downforce. But the reduction in the lift co-efficient is very small. SASTECH Journal 78 Volume 12, Issue 1, April 2013

8 Fig. 21 Graph showing variation of lift co-efficient for the different models at 200 kmph Table 5.8 shows the lift to drag ratio for the three models. The L/D ratio gives the ratio of lift force by drag force. The variation of L/D ratio for the three models is shown in Figure The lowest L/D ratio (0.258) is for the model with all add-on devices attached. Hence it can be seen that the model of the car with the designed add-on devices attached gives the best L/D ratio and the best configuration of add-on devices is arrived at. Table 8. L/D ratio for the three models L/D Ratio Baseline model Model with wings attached Model with all add ons different configurations through steady state CFD simulations. A comparison was made with the baseline model, car with wings attached and the car with all add-on devices attached and the following points were concluded: A reduction of 10.22% and 4.75% in the drag force and drag co-efficient respectively is seen in the model with all add-on devices when compared to the baseline model. There was a reduction of 6.5% in the drag force and 5.4% reduction in the drag co-efficient in the modified model with the add-on devices when compared to the model with only the wings attached. The downforce and the lift co-efficient were seen to increase by 2 times for the model with all addon devices attached when compared to the baseline model. There was an increase of 22% and 15% in the downforce and lift co-efficient in the modified model with the add-on devices when compared to the model with only the wings attached. 6. REFERENCES [1] McKay, Noah J, The Effect of Wing Aerodynamics on Race Vehicle Performance. SAE Publications [2] Gregor Seljak, Race Car Aerodynamics. [3] 2011 FIA Regulations [4] Katz, Joseph and Garcia, Darwin, Aerodynamic Effects of Indy car components. SAE Publications [5] Selig, Michael S and Maughmert, Mark D, Generalized Multipoint Inverse Airfoil Design AIAA Journal, Vol. 30. [6] Ashok Gopalarathnam et al, Design of High Lift Airfoils For Low Aspect Ratio Wings With Endplates AIAA Journal [7] BMW Sauber F1.07 Development: Analysis & Drawings BMW Sauber F1.07 Development: Analysis & Drawings. [ONLINE] Available at: m?print=1. [8] Johansson, Magnus O and Katz, Joseph, Lateral Aerodynamics of a Generic Sprint Car Configuration SAE Publications Fig. 22 Graph showing variation of L/D ratio for the different models at 200 kmph 5. CONCLUSION In this project work, an attempt has been made to improve the aerodynamic performance of F1 race car by using various add-on devices like front wing, bargeboard, rear wing, nose wing, roof spoiler and wheel scallops with SASTECH Journal 79 Volume 12, Issue 1, April 2013