CFD ANALYSIS OF HATCHBACK CAR WITH VORTEX GENERATORS

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1 Vels Journal Of Mechanical Enginee Vol-, Issue-, July 05 CFD ANALYSIS OF HATCHBACK CAR WITH VORTEX GENERATORS S.Ezhil Muthalvan *, A.Arulmurugu PG Scholar, Department of Mechanical Engineering, Anna University, Coimbatore. TamilNadu, India, Teaching Fellow, Department of Mechanical Engineering, Anna University, Coimbatore. TamilNadu, India. Abstract: Aerodynamics is a study of the effects of air when in movement. The vehicle aerodynamics have become critical since have become conscious about its importance. This study has been motivated on the optimization of the aerodynamics with worth of some external tools. The split-up of flow near the vehicle s rear end due to Aerodynamic drag. To delay flow split-up, Delta shaped vortex generators () are experienced for application at the front wind shield of a hatchback car, frequently used on aircrafts to prevent flow split-up. The effects depends up on the shape of the vortex generators, which are on the vehicle roof will be optimized. The CAD ling is done by Solid Works and all the analysis and variations have been carried out computationally in the CFD software ANSYS Fluent. Keywords: Hatchback car, Delta shaped Vortex Generators (), Computational analysis, Aerodynamic drag I.INTRODUCTION The study of aerodynamics includes the drag force that compete against the motion of a car, this have huge contribution in the consumption of fuel. The of drag is different from car to car; hence manufacturers assign big proportion of their care to aerodynamics. There are numerous regions in the car that contributes in increasing the drag ; in this study they all have been come across. A number of aerodynamic tools are realised in the market today to decline the impact and weaken those areas. In this study a sum of devices have been designed and analyzed for reducing the drag force. The achievement of considerable down force is also beneficial when driving at high speeds. Some devices have been designed for attaining that. The down force enhances the traction of the car hence giving stability. The down force is very important when determining the performance of a car, since the presence of this allows to corner at high speed. In parts where the body transitions at a rate of more than 0, vortex generators, Diffusers and other devices can be applied to "Trip the Airflow". The idea is that areas like the transition in the middle of the roof and rear window on the regular car creates a large vortex, which effectively take hold of the car and try to hold it back as it tries to slip-up through the air. If the air that creates the vortex can be "tripped" before it vegetation the back of the car, it will make lesser vortices, which will have a slighter effect on the complete aerodynamics of the vehicle. Vortex generators and front bonnet channel are applied to contribute in dropping the drag while ground clearance, diffuser and rear wing for growing the negative lift force. At the first drag has been considered followed by the negative lift. By using CFD it is easily to validate pressure on the centre line of the car, it is possible to find where the low pressure exits and what is the drag created in the. II.COMPUTER AIDED MODEL A Hatchback car has been designed for the analysis. The of the car has been designed using CAD software, Solid Works, provided image of the is shown in Fig.. Fig. image of

2 III.CFD SETUP Area is a requirement for external flows analysis. It is a box occupied with fluid and has boundaries. These boundaries are given settings and the fluid is given a motion. The exact result from CFD though is difficult but least error can be attained with an appropriate size of domain. In view of this the suitab. Size used for this type of analysis is established pictorially in Fig.. IV.ANALYSIS OF BASIC MODEL The first methodology to the detail study and analysis of the basic. To read the flow and meet the regions in charge for high drag is the main drive of this step. The analysis of the basic shape largesse the value of drag as 0.40 and the lift as The of lift attained gives an idea about the behaviour of car at the speed of 0 m/sec. The air applies the force on to the car that lifts the car of the ground back up unsteadiness rather than pushing it into the ground. Primarily the drag has been targeted to be abridged. The images below show the flow of air around the car and further shows the detailed analysis of the regions firming up the drag. Fig.. Pictorial illustration of domain size The height and the width of the domain were chosen times the Length (L). On the other hand the boundary condition for the flow is also a key factor. Boundary conditions used for this analysis are established in Table.. Tab.. Boundary conditions Velocity inlet Sides and top Road 0 m/sec Symmetric walls Wall Once the simulation was attained forces acting in the horizontal and vertical direction were computed. The horizontal axis and the vertical axis present drag and lift respectively. The reported for the individuals are shown in Tab.. Tab.. s for basic Drag 0.40 Lift Fig.. Pressure contours across car The front of a car deteriorates the air hence upturns the pressure; this causes the good ratio of high pressure region. At the inclined front windscreen due to swift high angle the pressure also appears to be increasing to the level of yellow region that is reflect as high pressure as well. Diagonally the windscreen at the top the velocity raises again causing decrease in pressure. Finally at the rear declining angle the pressure rises due to flow separation taking place. In order to reduce the drag these in elevation regions are to be considered. The air below the vehicle is of elevated pressure compared with the air above it. For presenting the negative lift force that plays a vigorous role in stability, the low pressure region has to be created beneath the car body. The positive sign for the drag demonstrates the force in an opposite direction to the movement of the car whereas for the lift presents the vertically upward acting force. Fig. 4. Velocity stream around the car

3 Behaviour of air streams shows the incidence of a huge flow separation region behind the car. Vortices are created because of pressure differences of the air escaping top of a car and the under the car. The flow separation and the fabrication of vortices at the rear of the car also rises the drag hence has to be accounted. The obtained results are in accordance with results by Ahmed, H (). V. MATHEMATICAL CALCULATION of drag The drag force is the factor of the resultant force parallel and opposite to the flow. The drag (CD) is obtained experimentally through the vehicle geometry or form, and it allows the results do not depend on the real dimensions of the vehicle. The CD represents the relation between drag force and the force of the relative fluid, being expressed by the Equation (). This equation is used by Gopal(9) to calculate the of drag The calculated value and the analysed values are approximately equal. VI.DESIGNING OF VORTEX GENERATORS There are different shapes of vortex generator, delta shape vortex generator are most effective hence are used. The efficiency of the vortex generators depends on the design, height, length and thickness. There is a relationship between length and height (l/h). Vortex generator is most effective at l/h= and it is selected. But the thickness is a variable by varying the thickness what happened to the drag and lift is presented in this paper. The below Fig 5 shows the CAD s of vortex generators. () Model The drag of a car at the design conditions of atm, 5 C, and 0m/s. The height and width of the car are.407 m and.68 m, respectively. If the horizontal force acting on the car is measured to be 5 N. The density of air at atm and 5 C is ρ=.64kg/m. ( ) Model of lift The lift force is the component of the resultant force perpendicular and opposite to the flow. The lift (CL) is obtained experimentally through the vehicle geometry or form, and it allows the results do not depend on the real dimensions of the vehicle. The CL represents the relation between lift force and the force of the relative fluid, being expressed by the Equation (). This equation is used by Gopal(9) to calculate the of lift The drag of a car at the design conditions of atm, 5 C, and 0m/s. The height and width of the car are.407 m and.68 m, respectively. If the vertical force acting on the car is measured to be 45 N. The density of air at atm and 5 C is ρ=.64kg/m. () Model Fig. 5. Design of vortex generator Tab.. Dimension of Vortex Generator vortex Length Height Thickness generator Model 5 mm.5 mm 5 mm Model 5 mm.5 mm 0 mm Model 5 mm.5 mm 5 mm VII.RESULTS The results for each alteration are presented in this section. The previous change that resulted in evident improvement was comprised in the. Further tool were analysed on that ( )

4 The vortex generators by an exchange of momentum between upstream and downstream of the flow reduce the high pressure region at the rear wind screen; can be observed by comparing Fig 6. Fig. 6. Pressure contours across car with Vortex Generator The vortex generator in addition reducing the drag also creates a drag because of its presence. The efficiency of the vortex generator is the measure of proportion between the drag generated to drag reduced by the generators. In the design shown in Fig. 5 the total drag is be reducing by an excessive hence they are considered to be performing well. Fig. 7. Velocity stream around the car with Vortex Generator The analysis of car with of thickness 0mm presents the value of drag as and the lift as The of lift obtained gives an idea about the behavior of car at the speed of 0 m/sec. The analysis of car with of thickness 5mm presents the value of drag as 0.77 and the lift as The of lift obtained gives an idea about the behavior of car at the speed of 0 m/sec. The results obtained with the device are presented in Tab. 4 Tab. 4. Results obtained from vortex generators at velocity 0 m/sec. Drag Lift out Total drag and lift Different Vortex Generator Thickness of drag of lift Fig 8. Total drag and lift s versus various position at velocity 0 m/sec. Fig 8 shows the variation of of drag and lift values for different thickness values at varying free stream velocities along the longitudinal centre plane of the scale. It is clearly evident from the figure that the value of C d and C l decreases due to the addition of. This can be attributed due to the avoidance of flow separation with the help of. For instance at a velocity of 0 m/s the of drag and of lift is reduced by a maximum of when with thickness 5 is used when compared to the values obtained without. However the value of C d and C l decreases with increase in thickness of. The vortex generators by an exchange of momentum between upstream and downstream of the flow reduce the high pressure region at the rear wind screen; can be observed by comparing Fig 9. Fig. 9. Pressure contours across car with Vortex Generator The vortex generator in addition reducing the drag also creates a drag because of its presence. The efficiency of the vortex generator is the measure of proportion between the drag generated to drag reduced by the generators. In the design shown in Fig. 5 the total drag is be reducing by an excessive hence they are considered to be performing well. 4

5 Fig. 0. Velocity stream around the car with Vortex Generator The analysis of car with of thickness 0mm presents the value of drag as 0.64 and the lift as The of lift obtained gives an idea about the behavior of car at the speed of 0 m/sec. The analysis of car with of thickness 5mm presents the value of drag as and the lift as The of lift obtained gives an idea about the behavior of car at the speed of 0 m/sec. The results obtained with the device are presented in Tab. 5 Drag Lift out can be attributed due to the avoidance of flow separation with the help of. For instance at a velocity of 0 m/s the of drag and of lift is reduced by a maximum of when with thickness 5 is used when compared to the values obtained without. However the value of C d and C l decreases with increase in thickness of. The vortex generators by an exchange of momentum between upstream and downstream of the flow reduce the high pressure region at the rear wind screen; can be observed by comparing Fig. Fig.. Pressure contours across car with Vortex Generator The vortex generator in addition reducing the drag also creates a drag because of its presence. The efficiency of the vortex generator is the measure of proportion between the drag generated to drag reduced by the generators. In the design shown in Fig. 5 the total drag is be reducing by an excessive hence they are considered to be performing well. Tab. 5. Results obtained from vortex generators at velocity 0 m/sec. Total drag and lift Fig. Total drag and lift s versus various position at velocity 0 m/sec. Fig shows the variation of of drag and lift values for different thickness values at varying free stream velocities along the longitudinal centre plane of the scale. It is clearly evident from the figure that the value of C d and C l decreases due to the addition of. This 5 Coefficien t of drag Coefficien t of lift Different Vortex Generator Thickness Fig.. Velocity stream around the car with Vortex Generator The analysis of car with of thickness 0mm presents the value of drag as 0.74 and the lift as The of lift obtained gives an idea about the behavior of car at the speed of 40 m/sec. The analysis of car with of thickness 5mm presents the value of drag as 0.74and the lift as 0.6. The of lift obtained gives an idea about the behavior of car at the speed of 40 m/sec. The results obtained with the device are presented in Tab. 6 5

6 Drag Lift out Tab. 6. Results obtained from vortex generators at velocity 40 m/sec. Total drag and lift Different Vortex Generator Thickness of drag of lift Fig 4. Total drag and lift s versus various position at velocity 40 m/sec. Fig 4 shows the variation of of drag and lift values for different thickness values at varying free stream velocities along the longitudinal centre plane of the scale. It is clearly evident from the figure that the value of C d and C l decreases due to the addition of. This can be attributed due to the avoidance of flow separation with the help of. For instance at a velocity of 40 m/s the of drag and of lift is reduced by a maximum of when with thickness 5 is used when compared to the values obtained without. However the value of C d and C l decreases with increase in thickness of. VIII.CONCLUSION Efficient aerodynamics results in the enhancement of many factors required with the motion of a car such as fuel consumption and the performance. the decrement in the drag the fuel consumption can be enhanced as there would be less opposing force acting on the car. As far as the performance is worried the induction of down force is the prime factor of the performance. When car would be stuck solider into the ground it would result in better performance. The drag and lift reduces directly with increase in thickness of vortex generator. As a result of the verifications, it is confirmed that s create stream wise vortices, the vortices mix higher and lower layers of boundary layer and the mixture causes the flow separation point to shift downstream, consequently separation region is narrowed. From this, we could predict that s cause the pressure of the vehicle s entire rear surface to increase therefore decreasing drag, REFERENCES []Masaru Koike; Tsunehisa Nagayoshi and Naoki Hamamoto. Research on Aerodynamic Drag Reduction by Vortex Generators, technical papers (004) [] Ahmed, H And Chacko, S, Computational Optimization Of Vehicle Aerodynamics, Daaam International (0) []J. Katz, Race-Car Aerodynamics, Robert Bentley Inc., Cambridge, Massachusetts (006) [4]Debojyoti Mitra, Design Optimization of Ground Clearance of Domestic Cars, International Journal of Engineering Science and Technology (00) [5]Md. Rasedul Islam, Md. Amzad Hossain, Mohammad Mashud, Md. Tanvir Ibny Gias, Drag Reduction of a Car by Using Vortex Generator International Journal of Scientific & Engineering Research, (0) [6]Jean-Luc Aider, Jean-Franc ois Beaudoin, Jose Eduardo Wesfreid, Drag and lift reduction of a D bluff-body using active vortex generators, Research Article (00) [7]K.Sai Sujith, G.Ravindra Reddy, Cfd Analysis Of Sedan Car Vortex Generators, International Journal of Mechanical Engineering applications Research (0) [8]Bhagirath Zala, Dr. Pravin P.Rathod, Prof. Sorathiya Arvind S. Aerodynamic Performance Assessment Of Sedan And Hatchback Car By Experimental Method And Simulation By Computational Fluid Dynamicsa Review, Journal of Engineering Research and Studies (0) [9]Gopal P And Senthilkumar T. Aerodynamic Drag Reduction In A Passenger Vehicle Using Vortex Generator Varying Yaw Angles, ARPN Journal of Engineering and Applied Sciences (0) [0]Simon Watkins, Gioacchino Vino The Effect Of Vehicle Spacing On The Aerodynamics Of A Representative Car Shape, Journal of Wind Engineering and Industrial Aerodynamics (008) 6