Journal of Engineering Research and Studies. Review Article

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1 Review Article AERODYNAMIC PERFORMANCE ASSESSMENT OF SEDAN AND HATCHBACK CAR BY EXPERIMENTAL METHOD AND SIMULATION BY COMPUTATIONAL FLUID DYNAMICS- A REVIEW Bhagirath zala 1, Dr. Pravin P.Rathod 2, Prof. Sorathiya Arvind S. 3 Address for Correspondence 1. PG Student 2 Professor 3 Professor Mechanical Engineering Department, Government Engineering College Bhuj, Bhuj (Kutch) ABSTRACT The paper will describe comparative assessment of aerodynamic performance of two different popular hatchback and sedan car model by two distinct experimental strategies of aerodynamic predictions by conventional wind tunnel approach and its subsequent validation with advanced computational procedures, carried out on two popular model of sedan and hatchback car model. the experimental investigations will be performed on an open circuit suction type wind tunnel having a 30 cm x 30 cm x 100 cm test section, on a geometrically similar, reduced scale (1:20) aluminium car models, while the three dimensional computational analysis was carried out using with the help of software tools like ANSYS-CFX to simulate the flow of air around the automobiles and results like drag force, lift force, pressure and velocity distribution, wake region, turbulence kinetic energy etc will investigated for aerodynamic analysis. KEYWORDS Aerodynamics, CFD, wind tunnels, hatchback & sedan. I INTRODUCTION Airflow over a vehicle determines the drag forces, which in turn affects the car s performance and efficiency. I will design the testing equipment to measure both the vertical and horizontal components of air resistance on a model car. Downforce, the vertical component, is simply negative lift. When a car goes faster and faster the weight of the car changes due to air resistance. Depending on the direction (upward or downward) this is called either lift or downforce, respectively. I will also measure the horizontal component, the drag of the model cars. Drag is the amount of force that the air is pushing on the car at a certain speed. In other words, it is the amount of resistance the air imposes on the car in a horizontal direction. For a vehicle to maintain its speed it must overcome friction. The most important source of friction at high speeds is air resistance. If air resistance can be minimized, the car will be more efficient because less energy is lost to friction. Today, with increasing energy costs, efficiency is finally receiving the attention it deserves. If a car can cut through the air with little resistance, it will get better gas mileage. The automotive industry is accordingly devoting more attention and resources to the aerodynamics of their vehicles. i will hopefully be able to apply the skills that I learn modifying and testing the wind tunnel to my work later in life. However, comprehensible knowledge of lift and drag characteristics for automotive, is of great interest for future designs of the racer & car designer. The latter has been the general motivation for this investigation. A more elaborate description of the two approaches is given in the following. A. Wind Tunnel Experiments Lift and drag coefficients are to be determined experimentally on a test model at 33 m/s in a wind tunnel. The lift and drag coefficients are to be determined by strain gauge measurements. In order to measure the surface pressure variation in a longitudinal section of the geometry, a line of pressure transducers are fitted to the model structure. The test model will be reduced to a generic shape by neglecting wheels, wings, etc to solate the performance from any other aerodynamic influences. Measurement data uncertainty is evaluated before presenting the final results. The results of the Experiment will serve as a method of validation of the CFD analysis. Experimental setup Wind tunnel B. CFD Analysis CFD analysis of the test model in a wind tunnel provides results within lift and drag coefficients and pressure distributions Here the comparison of approximated models of MARUTI ESTEEM and TATA-INDICA with a scale of 1:20 have been simulated for air flow around the car and results like drag force, lift force, pressure and velocity distribution, wake region, turbulence kinetic energy etc have been investigated for aerodynamic analysis. For this as illustrated in the previous chapters both the model is simulated in ANSYS-CFX 10.0 with following data. Both the model is simulated for

2 velocity of 33m/s. The conditions like boundary conditions, domains etc are imposed as in methodology. Mass flow rate will be changing as change in the speed of the car and change in the cross section means model of the car. Pressure distribution on Sedan car surface Pressure distribution on Hatchback car surface II REVIEWS Number of research papers and studies has been conducted on various car model by various experimental method and using technique called computational fluid dynamic. Number of reviews have been taken and analysed below to complete the present study. Manan desai, S.A chaniwala, H.J nagarserth[1] in their study on Experimental and Computational Aerodynamic Investigations of a Car describes comparative assessment of two distinct experimental strategies of aerodynamic predictions by conventional wind tunnel approach and its subsequent validation with advanced computational procedures, carried out as a part of design process of a small hybrid car proposed to be named as ADRENe. The experimental investigations were performed on an open circuit suction type wind tunnel having a 30cm x 30cm x 100cm test section, on a geometrically similar, reduced scale (1:15) clay model, while the three dimensional computational analysis was carried out using Gambit as the pre processing software and Fluent as the solver and post processor. A good agreement between performance values obtained independently by two experimental methods, suggests their reliability and suitability for further experimentation purposes. The comparison with computational approach shows that the computed drag forces and pressure distributions agree well with the experimental values over the entire range of air velocities, however, the agreement with the data for drag coefficient varies, which appears to suggest a higher degree of dependency on the grid quality and elements selection. Two experimental approaches for the investigation of external aerodynamics of a small car ADRENe were presented. Agreement between values predicted by both methodologies confirms their reliability and recommends them for further experimentation. The drag co efficient (CD) evaluated for proposed exterior profile of ADRENe, comes out to be of the order of 0.4, which is sufficiently acceptable for the said purpose of effective fuel savings. However, verification and further optimization of these wind tunnel estimations are strongly recommended. Experimental investigations were further validated computationally. Unlike wind tunnel tests, the computational procedure adopted, due to the benefit of advanced computer configurations with high speed processing capabilities, could rapidly generate data for the entire flow field around the car, providing significant insight into the basic flow features, made the evaluation process faster and cost effective. Philippe Planquart[2] in his work on integration of CFD and Experimental Results at VKI in Low- Speed Aerodynamic Design Presented Three examples of recent investigations combining CFD analysis and wind tunnel tests at the von Karman Institute for Fluid Dynamics (VKI) are presented to illustrate the integration process between experimental tests and numerical results. For each project, the requirements and the methodology were different but the final goal was to obtain an optimized aerodynamic design. The first project presented is dealing with a fluid-structure interaction problem. The second project concerns the aerodynamic design of a new Belgian polar base station for Antarctica and the last project concerns the design of an ultrastreamlined land vehicle for the next Solar World Challenge. Using three different examples of low-speed aerodynamic design, combining wind tunnel experiments and CFD computation, he has shown how integration of both methods can lead to a better aerodynamic design. For each project, the requirements and the methodology were different, but the final goal was to obtain an optimized aerodynamic design. He believes that the best integration is obtained when the scientists performing the wind tunnel tests and the CFD people are integrated in a global team knowing the final objective of the project and able to have a critical view on the results gained using each method. Communication between wind tunnel specialists and CFD specialists is therefore crucial throughout the study. The three examples have also shown that wind tunnel tests are still a very useful tool necessary for aerodynamic design. Daniel favier[3] in his work on The Role of Wind Tunnel Experiments in CFD validation concluded that integrating the use of experiments and CFD will be one of the major challenges to perform an efficient cross fertilization between the two approaches. Future challenges and requirements for experiments

3 and CFD will include the successful numerical simulations of available experimental databases and the complete validation of relevant and detailed experiments, especially for unsteady flow phenomena on complex 3D geometries. In this context, the respective roles of experiments and CFD thus appear as synergistic and complementary in the dialectic process. This strategy of integration is an emerging trend and must be strongly encouraged and developed for the maturation of the CFD approach. The dual role of mutually guiding and stimulating the advances and benefits of each approach will lead us to improve the global knowledge on fluid flow physics. Chainani. A, Perera[4]. N in his work on CFD Investigation of Airflow on a Model Radio Control Race Car contributed that The modern day design of vehicles, especially in theracing industry involve a great deal of air flow study. This study shows that drag force adversely affects the forward motion of the car and that there is a difference in the pressure between the air flowing above and below the car. This produces forces along the vertical axis. Aerodynamic forces acting on a car greatly reduces its efficiency. If the car is redesigned to optimise these forces it could produce better results. This paper discusses various techniques that have been used to redesign and optimise the aerodynamics of a model radio control race car. This investigation has demonstrated that there is a significant change in the coefficients of lift and drag of the model race car when a more streamlined body design is adopted. The results obtained show a 40.49% reduction in drag coefficient with a loss of 24% in the down force. This further verifies previous research indicating that a body having an inverted tear-drop shape generates a lower drag force than one with a conventional shape. The findings of this investigation also confirm previous research detailing that bob-tailing the rear end of the car reduces the recirculation region behind the car. This further reduces the drag force acting on the car. Furthermore it was also determined that varying the angle of the front grille has an affect on the down force acting on the car. Prof p.r sonawane, prof. S.p sekhawat, prof k.k rajput [5] in their studies on aerodynamic analysis of car body for minimum fuel consumption From their experiment & result analysis it is very clear that the fuel consumption can be significantly reduced by appropriate change in slant angle for the car body. Fuel consumption is directly dependent on the drag force resistance acting over the car body. The drag force depends on the vortices shed generated at the back of the car body which causes separation and produces less pressure areas at the back of the car body as a result the body is resisted by the air moving over the car body. The drag is directly dependent on the slant angle of the body. The larger the slant angle more pressure difference of the front and back surfaces generates more drag but less slant angle allows more surface of the body to be in contact with the fluid and more skin friction is resulted. In this paper the simulation was performed for different slant angles and concluded that with change in slant angle of the car body from 30 degree to 20 degree there is a reduction of 8 % in drag force this will lead to 1.5 to 5.0 % of decrease in fuel consumption. Masaru koike,tsunehisa nagayoshi, Naoki hamamoto[6] in their work on research on aerodynamic drag reduction by vortex generators contributed that One of the main causes of aerodynamic drag for sedan vehicles is the separation of flow near the vehicle s rear end. To delay flow separation, bump-shaped vortex generators are tested for application to the roof end of a sedan. Commonly used on aircraft to prevent flow separation, vortex generators themselves create drag, but they also reduce drag by preventing flow separation at downstream. The overall effect of vortex generators can be calculated by totalling the positive and negative effects. Since this effect depends on the shape and size of vortex generators, those on the vehicle roof are optimized. This paper presents the optimization result, the effect of vortex generators in the flow field and the mechanism by which these effects take place. In their study factors contributing to the effect of VGs were verified by conducting measurement of total pressure, velocity distribution and CFD. As a result of the verifications, it is confirmed that VGs 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 VGs cause the pressure of the vehicle s entire rear surface to increase therefore decreasing drag, also the velocity around the rear spoiler to increase, and the lift to decrease. The deltawing-shaped VG, which demonstrated high effectiveness in this research, is planned for commercialization as an accessory for sedans after slight modifications to the shape with respect to design, legal conformance and practicality. Debojit mitra in his studies on effect of relative wind on notch back car with add on parts studied behaviour of different add-on parts to a basic car model has been experimentally.experiments were conducted with different add-on parts, like rear end spoiler & 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 done 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 like rear-end spoiler etc increases the aerodynamic stability of a basic car model and hence they can be used in real life which will be an added advantage. With this design the air flows over the rear

4 roof edge and follows the contour of the downward sloping rear screen for a short distance before separating from it ; however, the downwash of the airstreams causes it to re-attach itself to the body near the rear end extended boot lid. Thus the base wake area will virtually be the vertical rear boot and light panel; however, standing vortices will be generated on each side of the body just in board on the top surface of the boot lid and will then be projected in the form of trailing conical vortices well beyond the rear end of the boot. Vortices will also be created along transverse rear screen to boot lid junction and across the rear of the panel light. Drag Coefficient and Lift Coefficient for a Notchback car model with and without add-on parts was calculated. They indicate that the drag coefficient almost remains unaffected with the addition of rearend spoiler. While the addition of front spoiler increases the drag coefficient, the addition of both the rear end and front spoilers also increases the drag coefficient significantly. However, it is seen that the addition of rear end spoiler considerably reduces the lift coefficient. Front spoilers also reduces the lift coefficient but not as that of rear end spoilers. The addition of both the spoilers brings down the lift coefficient to a large extent. The addition of rear end spoiler increases the pressure in the rear part of the vehicle, while the addition of front spoiler increases the pressure on the upper surface of the vehicle. As there is a air dam in front of the vehicle a low pressure region is created underside, and with the increased pressure on the upper surface of the vehicle, gives rise to a increment in negative lift. Hugo G. Castro, Rodrigo R. Paz, Mario A. Storti, Victorio E. Sonzogni, Jorge O[8].in their studies on Experimental and numerical studies of the aerodynamic behaviour of simplified road vehicle presented the first preliminary results of the experimental and numerical determination of pressure coefficients and aerodynamic forces on bluff bodies exposed to a turbulent flow. Experimental and numerical analysis of the flow over the Ahmed body with a 35_ rear slanted angle were performed. Ahmed body was chosen as a standard reference given that it was numerically and experimentally studied in an exhaustive way. Comparing both, results from the experimental tests made in this work and the other experimental reference as well as the provided by the computational simulation presents some appreciable differences. Mean drag force in the experimental tests (Cd mean = 0:40) presents a high value when comparing with the obtained by Ahmed et al. (1984) (Cd mean = 0:257) while the numerical obtained value had a difference lower than a 9% (Cd mean = 0:28). Is important to note that both values corresponds to the model with the four stilts whereas in the work of Ahmed et al. (1984) the total drag has been corrected for tare drag of stilts. To account for this, a numerical simulation of the model with the stilts was performed. Nevertheless, experimental values were still higher. it can be shown that pressure measured in the wind tunnel on the rear slanted plane are almost in agreement with those of (Lienhart and Becker, 2003) in spite of the low Reynolds number (in our case is of 1:7 _ 106) while for the rear base of the model significantly exceeds the reported values. This result explains the differences in the drag forces. In the experimental tests, the flow is accelerated in the lower zone of the rear base possibly due to a mass of air entering into the test section in the drag balance hole by suction. Improvement of the experimental equipment is a work currently in progress. III CONCLUSION Two experimental approaches for the investigation of external aerodynamics of different car models were presented by different authors, Agreement between values predicted by both methodologies confirms their reliability and recommends them for further experimentation.. However, verification and further optimization of these wind tunnel estimations are strongly recommended. Experimental investigations were further validated computationally. Unlike wind tunnel tests, the computational procedure adopted, due to the benefit of advanced computer configurations with high speed processing capabilities, could rapidly generate data for the entire flow field around the car, providing significant insight into the basic flow features, made the evaluation process faster and cost effective. combining wind tunnel experiments and CFD computation, he has shown how integration of both methods can lead to a better aerodynamic design. For each project, the requirements and the methodology were different, but the final goal was to obtain an optimized aerodynamic design. authors believes that the best integration is obtained when the scientists performing the wind tunnel tests and the CFD people are integrated in a global team knowing the final objective of the project and able to have a critical view on the results gained using each method. Communication between wind tunnel specialists and CFD specialists is therefore crucial throughout the study. REFERENCES 1. Manan desai, S.A chaniwala,h.j nagarserth[1] Experimental and Computational Aerodynamic Investigations of a Car ISSN: Issue 4, Volume 3, October Philippe Planquart integration of CFD and Experimental Results at VKI in Low- Speed Aerodynamic Design 3rd International Symposium on Integrating CFD and Experiments in Aerodynamics June 2007 U.S. Air Force Academy, CO, USA. 3. Daniel favier The Role of Wind Tunnel Experiments in CFD validation Institute of Movement Sciences, University of M editerran ee, Marseille, France. 4. Chainani. A, Perera. N CFD Investigation of Airflow on a Model Radio Control Race Car Proceedings of the World Congress on Engineering 2008 Vol II WCE 2008, July 2-4, 2008, London, U.K. 5. Prof.p.rsonawane,prof.s.p.sekhawat,profk.k.rajput aerodynamic analysis of car body for minimum fuel consumption journal of information knowledge and research in mechanical engineering ISSN X NOV 10 TO OCT 11 VOLUME 01, ISSUE Masaru koike, Tsunehisa nagayoshi, Naoki hamamoto research on aerodynamic drag reduction by vortex generators mitshibishi motors technical paper review 2004 no-16.

5 7. Debojyoti Mitra Effect of Relative Wind on Notch Back Car with Add-On Parts in International Journal of Engineering Science and Technology Vol. 2(4), 2010, Hugo G. Castro, Rodrigo R. Paz, Mario A. Storti, Victorio E. Sonzogni, Jorge O. experimantal and numerical studies of the aerodynamic behavoir of simplified road vehicle. 9. W. Kieffer, S. Moujaes, N. Armbya CFD study of section.characteristics of Formula Mazda race car wings March F. Muyl, Laurent Dumas, Vincent Herbert Hybrid method for aerodynamic shape optimization, June G.de Vahl Davis and C. Fletcher, Computational Fluid Dynamics. 11. Amsterdam : Elsevier Science Publishers B.V., 1988, pp Hiroshi China, Masahiro Yoshida, Morihiro Takada, Kunio Nakagawa, Air flow control around the cabin of a convertible car July AJ Scibor - Rylski, Road Vehicle Aeerodynamics London: Pentech. Ressl, 1975, ch Masaru Koike, Tsunehisa Nagayoshi, Naoki hamamoto, Research on. Aerodynamic Drag Reduction by Vortex Generators. 15. Appupillai Baskaran and Ahmed Kashef, Investigation of air flow around buildings using computational fluid dynamics techniques, Heller, A. Der neue Kraftwagen von Dr. Ing Rumpler, Eppinger,A. Tropfenwagen-AnwendungderFlugzueg Aerodynamik, Rumpler, E. Das Auto im Luftstrom, W. Kieffer, S. Moujaes, N. Armbya CFD study of section. characteristics of Formula Mazda race car wings March Morelli, A. Aerodynamic actions on an automobile Stapleford, W. R. and Carr. Aerodynamic characteristics of exposed. rotating wheels 1970.