CFD ANALYSIS OF AERO DYNAMIC DESIGN OF … MARUTI ALTO CAR Abdul Razzaque Ansari Department of...

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 3, March 2017, pp. 388–399 Article ID: IJMET_08_03_043 Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=3 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication Scopus Indexed

CFD ANALYSIS OF AERODYNAMIC DESIGN OF MARUTI ALTO CAR

Abdul Razzaque Ansari Department of Mechanical Engineering, Cambridge Institute of Technology, Ranchi, India

Prashant Kumar Rana

Department of Mechanical Engineering, Cambridge Institute of Technology, Ranchi, India

ABSTRACT The choice of car is often made on the basis of fuel efficiency cost and comfort.

However for general purpose fuel efficiency is the most important factor that is responsible for the overall popularity of a car of any make fuel efficiency is depend upon the performance of internal combustion engine and also on the aerodynamic design body of the car. Aerodynamic styling of car is one of the most crucial aspects of car design. In compassing task on artful integration of CAD modelling. The objective of the present study is computational fluid dynamics (CFD) analysis of a 3-D car model to find the aerodynamic design parameters. Computational Fluid Dynamics (CFD) is the numerical techniques to solve the equations of fluid flow. CFD tool is found very useful in automobile industry. 3-D solid model of a car of different make will be constructed by using pro-engineering software and the analysis was done on ansys software. The aerodynamic analysis of the design parameters of a car will be performed by using a suitable turbulence model and to find the drag coefficient and drag force of a car (Maruti, Alto etc). The result obtained from CFD analysis will be validated by field/experimental studies and the result of software analysis has agreed excellently with field experimental results. Key words: CAD, CFD, Pro-E, Ansys, Drag coefficient, Drag force

Cite this Article: Abdul Razzaque Ansari and Prashant Kumar Rana, CFD Analysis of Aerodynamic Design of Maruti Alto Car. International Journal of Mechanical Engineering and Technology, 8(3), 2017, pp. 388–399. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=3

1. INTRODUCTION CFD analysis is probability the only efficient tool in order to specific design parameters of a generic car shape. In order to achieve supplementing presently used fuel by eco friendly fuels or by enhancing current automobile design. In optimization of a car aerodynamics, more precisely the reduction of associated drag coefficient (Cd), this is mainly influenced by the exterior profile of a car, which is the major issue of the automotive research centres around the world. Average Cd values have improved impressively over the time; from 0.7 for old boxy designs of car to nearly 0.3 for the recent more streamlined ones [Desai (2008)]. The

Abdul Razzaque Ansari and Prashant Kumar Rana


description of the fuel energy used in modern vehicles at urban driving and highway driving. The shape of the vehicle uses about 3 % of fuel to overcome the resistance in urban driving, while it takes 11% of fuel for the highway driving. This considerable high value of fuel usage in highway driving attracts several design engineers to enhance the aerodynamics of the vehicle using minimal design changes [Krishnani (2009)]. The effect of drag on the moving vehicle is proportional to the square of velocity, so with increase in velocity (at approximately 50 km/h), aerodynamic drag becomes one of the most prominent factors contributing to the total drag experienced by the vehicle [Singh (2004)]. Aerodynamic evaluation of air flow over an object can be performed using analytical method or CFD approach. On one hand the analytical method of solving air flow over an object can be done only for simple flows over simple geometries like laminar flow over a flat plate. If air flow gets complex as in flows over a bluff body, the flow becomes turbulent and it is impossible to solve Navier-Stokes and continuity equations analytically. On the other hand obtaining direct numerical solution of Navier-Stokes equation is not yet possible even with modern day computers. In order to come up with a reasonable solution, a time averaged Navier-Stokes equation is being used (Reynolds Averaged Navier Stokes Equations- RANS equations) together with turbulent models to resolve the issue involving Reynolds Stress resulting from time averaging process. Aerodynamically designed cars may offer better stability at higher speed of air. While moving past, cars had two different aerodynamic models and were most crucial accept of car designs. It includes task of integration of advanced engineering and computer analysis. Aerodynamically designed cars require least power in overcoming drag exerted by air and exhibits higher performance with less fuel consumption [1-5].

1.1. Forces on the Car Surface 1. Tangential force induced by shear stress due to viscosity and velocity gradient at boundary surface. 2. The forces normal to the car surface resulting from pressure intensity varying along the surface due to dynamic effect. Sum of the two forces over complete surface is known as resulting force.

Component of these forces in the direction of relative velocity passed over car body is defined as aerodynamic drag. Aerodynamic is crucial factor in judging the performance of a car. It highly influences fuel consumption of car at higher speed. Streamlined aerodynamically design of a car may have Cd value from 0.3 to 0.5 drags in the surface of vehicle. Aerodynamic is a major of aerodynamic force which resists the forward motion of vehicle. This implies that vehicle body can move easily through the surrounding air with minimum air resistance. Whereas negative lift co-efficient indicates more stability and less charge of skidding [6-7].

Among the most important results obtained from wind tunnel experiments supporting design programs are the aerodynamic forces and moments acting on the test vehicle in a controlled and repeatable environment. Force and moment measurements are important for all ground vehicles. For some the principal interest is on drag because of its reflection on energy requirements [8-11].

1.2. Objectives 3-D computer aided modeling of a car of different make.

Computational fluid dynamics (CFD) analysis of 3-D car model to find the aerodynamic design parameters.

Field & experimental study to validate the CFD results.

CFD Analysis of Aerodynamic Design of Maruti Alto Car


2. MATHEMATICAL MODELING Relevant to the study-

Drag

Resistance to motion of vehicle

Rolling resistance

Gradient resistance

Air or wind resistance

Aerodynamic resistance

Total resistance

Boundary layer

2.1. Drag The drag coefficient is a function of several parameters like shape of the body, Reynolds Number, Froude number, Mach number and Surface. The drag coefficient is a common metric in automotive design pertaining to aerodynamic effects. As aerodynamic drag increases by the square of speed, a low value is preferable to a higher one. With about 60% of the power required to cruise at highway speeds being used to overcome aerodynamic effects minimizing drag translates directly into improved fuel efficiency [12].

For the same reason aerodynamics are of increasing concern to truck designers, where greater surface area presents substantial potential savings in fuel costs. Reducing drag is also a factor in sports car design, where fuel efficiency is less of a factor, but where low drag helps a car achieve a high top speed. However, there are other important aspects of aerodynamics that affect cars designed for high speed, including racing cars. It is important to minimize lift, hence increasing down force, to avoid the car becoming airborne. It is also important to maximize aerodynamic stability. Some racing cars have tested well at some particular "attack angles", yet performed catastrophically. Flipping over, when hitting a bump or experiencing turbulence from other vehicles. For best cornering and racing performance, as required in Formula One cars, down force and stability are crucial and these cars must attempt to maximize down force and maintain stability while attempting to minimize the overall Cd value. In fluid dynamics, the drag coefficient (commonly denoted as: Cd is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment such as air or water. It is used in the drag equation, where a lower drag coefficient indicates the object will have less aerodynamic or hydrodynamic drag. The drag coefficient is always associated with a particular surface area [13-14].

The drag coefficient Cd is defined as:

Where:

Fd is the drag force, which is by definition the force component in the direction of the flow velocity, ρ is the mass density of the fluid, V is the speed of the object relative to the fluid, and A is the reference area.



The reference area depends on what type of drag coefficient is being measured. For automobiles and many other objects, the reference area is the projected frontal area of the vehicle. This may not necessarily be the cross sectional area of the vehicle, depending on where the cross section is taken. For example, for a sphere cross sectional area is A = πr2 (note this it is not the surface area = 4 πr2). For airfoils, the reference area is the platform area. Since this tends to be a rather large area compared to the projected frontal area, the resulting drag coefficients tend to be low: much lower than for a car with the same drag, frontal area and at the same speed. Two objects having the same reference area moving at the same speed through a fluid will experience a drag force proportional to their respective drag coefficients. Coefficients for un-streamlined objects can be 01 or more, for streamlined objects much less.

The drag coefficient of any object comprises the effects of the two basic contributors to fluid dynamic drag; skin friction and form drag. The drag coefficient of a lifting airfoil or hydrofoil also includes the effects of lift-induced drag. The drag coefficient of a complete structure such as an aircraft also includes the effects of interference drag.

The vehicle was accelerated up the gradient to a given speed. At station (1) the engine was switched off and deducted. The distance x that the vehicle travelled from station (1) was measured [15].

Next, the projected area of the vehicle was carefully measured and temperature of atmosphere and density of air was determined.

X = distance travelled after switching off the engine, m = mass of vehicle in kg, v = velocity at which the engine was switched off (in m/s), Cd = coefficient of drag, p = density of air, A= projected area, The force F opposes the motion of the vehicle for skew of simplicity we assume the

distinction of F is positive in direction of velocity V Rolling resistance and gradient resistance for a given vehicle and gradient respectively, are constant. Rolling resistance + Gradient resistance = b Drag force = C (ρv2/2) A = av2; Where a = ρv2/2 Force, F = (av2+b)

F = m = m

×

F = mv

.= mvdv Integrating-

∫ =∫ /F

∫ = ∫ /(a +b)

∫ = ∫ ( )

Let, =



∫ = ∫ ( )

X = ( )

The above equation has been solved for k on computer and the program has been

supplied. The negative value of drag coefficient shows that the opposing form sets in the direction

opposite to the motion of vehicle. Moreover, vehicle is important determinants of the safety and comfort of a passenger

vehicle or the capability of a race car in competition

3. INTRODUCTIONS TO THE FIELD STUDY In the field study determination of drag coefficient Cd, drag force Fd, Rolling resistance, distance, time and velocity. First of all it was required to arrange a car. These parameters were determined for the vehicles such as Maruti Alto, Tata Indica and Maruti Omni. When the engine of the car starts it was required to determine the distance travelled by the car when the engine is stopped without any application of the brake and also the precaution of any road unwanted gradients such as pits, cracks, stones, bumpers etc were taken into account which means for the successful completion of the test or reading. The road must be smooth and neat. Such type of suitable testing spot was selected at the Ring road of Kanke near Birsa Agriculture College at the capital Ranchi (Jharkhand).

Atmospheric temperature was recorded with the help of psycho meter as D.B.T- 24 degree Celsius and W.B.T. as 19 degree Celsius and the wind flow was almost negligible. The road test began with three people sitting inside the car. The precaution of window pan to be closed for each test was taken so that the air effect does not enter inside the vehicle through these window pans. The distance completely travelled by the vehicles at the speed of 20, 30, 40, 50, 60, 70 and 80 km/hr after the engine is stopped for each vehicle was determined with the help of distance measurement reader available in the vehicle near the speedometer. For the uniform distance travelled at 20, 30, 40, 50, 60, 70 and 80 km/hr it was required to first allow the vehicle travel uniformly at 30, 40, 50, 60, 70, 80 and 90 km/hr and the accelerator pedal was released. As the speed comes down to the required speed then the vehicle was allowed at least to travel constantly at that speed for minimum 05 seconds. The road test of the vehicle took place in the N-S direction. After the completion of the test the weight of the three cars was successfully taken as, Alto – 887 kg,

Figure 1 Car used for the field study work.



3.1. Estimation of drag coefficient and drag force on the base of field study X = distance travelled after switching off the engine, m = mass of vehicle in kg, v = velocity at which the engine was switched off (in m/s), Cd = coefficient of drag, ρ = density of air, A = projected area,

The force F opposes the motion of the vehicle for skew of simplicity we assume the distinction of F is positive in direction of velocity V. Rolling resistance and gradient resistance for a given vehicle and gradient respectively, are constant. Drag force = C ( /2) A = a ; Where a = Cd ρA/2 Force, F = (a +b)

F = m = m

×

F = mv

.= mvdv Integrating-

∫ = ∫ /F

∫ = ∫ / (a +b)

∫ = ∫ ( )

Let =

∫ = ∫ ( )

After integration, we have got the value of distance travelled by the vehicle after switching off the engine.

X = ( )

Where; K = constant value = b/a V= velocity of the car, m/s m = mass of the car in kg a = Cd ρA/2 F = (av2+b)

The test begins with the Alto car and the readings observed are as follows Readings of the Alto car Mass-887kg, Area-1.740m2



4. SIMULATION OF VEHICLE AERODYNAMIC

4.1. Simulation Steps Adopted for the Vehicles Aerodynamic There are three steps involved in a typical CFD simulation. The three steps are:

Pre-Processing Stage

CFD Solving Stage

Post-Processing Stage

Table 1 Readings of the Alto car Mass-887kg, Area 1.740 m2

In the pre-processing stage, CFD users are needed to provide sufficient input to the computer in order to obtain the desired output. The pre-processing stage is divided into several steps:

Geometry Generation

Mesh Generation

Input for Boundary Condition

Flow Type (Steady/Unsteady)

Discretization Scheme Input

Turbulence and Near Wall Model Input Selected the Maruti Alto car to find out the CFD result where design in pro/E software

and to compare the other motor vehicle and validate the result of this car

Figure 2 Maruti Alto Car used for the field study and design work.

S.N Speed km/h Distance (m) Time (s) Drag coefficient Cd Drag force Fd 1 20 200 40.16 0.152 5 2 30 300 59.42 0.324 13 3 40 330 50.79 1.42 187 4 50 400 52.96 0.84 161 5 60 600 60 0.517 153 6 70 700 78 0.457 184 7 80 720 82 0.454 239



4.2. Geometry Generation Pro/Engineer wildfire 5.0 In the Pre Processing stage the models of the vehicles were creates using the Pro-e software. Pro/E Wildfire 5.0 is unmatched for developing and communicating stunning product concepts. It's a truly open solution you can use to share ideas or refine concepts using freeform surfacing and reverse engineering tools. Designs can be sent directly to a rapid prototyping machine, or transferred to downstream Pro/E applications.

Easy-to-use tools, blending 2D or 3D, curves and surfaces, and imported sketches for concept exploration and industrial design.

Advanced also to-rendering to create photorealistic images.

Interoperable with other CAD systems [13-15].

4.3. Realizable Benefits Increase the number of product ideas conceptualized an evaluated.

Improve the richness of product collateral.

Figure 3 Maruti Alto designed in pro/E software

The default shape checking acceptance criterion that is used by the Ansys Workbench was produced by an extensive and thorough study that correlated different element shape metrics to the quality of the solution achieved with a distorted mesh. The study concluded that the Ansys program, which supports many different types element formulations (such as p-elements), must enforce stricter shape parameter values than the Ansys Workbench, which only needed to support the solid and shell elements for the aforementioned analyses. One particular shape metric predicted whether the quality of the element would affect the numerical solution time and again.

4.4. The results obtained after the successful meshing procedure of Maruti Alto car: In the Ansys Workbench are as follows:

Total Number of Nodes – 378862

Total Number of Elements – 1988620

Type of Meshing- Mixed Triangular Mesh



Figure 4 Maruti Alto meshed in Ansys work bench

Table 2 Total Grid Size

Table 3 Input Boundary Condition of Solving Stage of Alto cars of various Parameters

Mass Area (m2) Solver Formulation Velocity(m/s) 884 kg 1.740 Pressure Based Implicit 19.44

Table 4 Input Boundary Condition of Solving Stage of Alto Car of Various Parameters

Model Density kg3

Viscosity kg/m--s Operating Pressure (Pascal)

Turbulence intensity

k-epsilon 1.225 1.789 4e-05 101325 2%

4.5. Velocity Magnitude of Alto Car By the help of CFD Software

4.5.1. Velocity Magnitude The velocity magnitude of an object is the rate of change of its position with respect to a frame of reference and is a function of time. Velocity is equivalent to a specification of its speed and direction of motion in km/h.

Figure 5 Velocity magnitude profile interior zone of Maruti Alto obtained from contours

Car Level Cells Faces Nodes Alto 0 1110814 2274958 213892



Figure 6 Velocity magnitude profile of Maruti alto obtained from vectors.

Table 5 The results obtained for the Velocity Magnitude profile from contours and vectors

Car Maximum value in m/s

Minimum value in m/s

Observe value m/s

Drag coefficient (Cd)

Drag force(Fd)

Alto 38.1 7.76 22.3 0.784 315 Note – For the drag coefficient (Cd) and drag force (Fd) Calculation assumed from the constant experimental distance

4.5.2. Turbulence Intensity

Figure 7 Turbulent Intensity of Maruti Alto obtained from contours.

Table 6 Estimate the turbulent intensity.

Car Maximum value in %

Minimum value in %

Mean value in % Turbulence Intensity I=u’/U

Alto 95 34 64.5 1.82 %

4.6. Post Processing

4.6.1. Discretization of Scheme Input In this stage the model of all the three cars Maruti Alto, which were modeled using the Pro-E 5.0 software were exported in Ansys workbench V12 for the purpose of meshing. After successful meshing it was then exported to Fluent 6.3.26 software. After giving the input conditions, for the purpose of Iteration



4.7. Iterations of Car Model

Table 6 no. of iteration of Maruti Alto

Figure 8 Iteration of Maruti Alto

5. RESULTS AND DISCUSSIONS

5.1. Results After the successful completion of the practical calculation and computer software simulation for Analysis of Aerodynamic design of vehicles have found the drag coefficient and drag force are as follows-

Table 7: Result of Cd and Fd of Maruti Alto

5.2. Discussions If the car turbulence intensity of the car is more than the drag coefficient will be more and vice- versa. Initially there is no drag force between 0-25 km/hr speeds of the vehicle. But after 25 km/hr the drag coefficient increases and after 60 km/hrs the drag coefficient becomes constant.

When setting boundary conditions for a CFD simulation it is often necessary to estimate the turbulence intensity on the inlets. To do this accurately it is good to have some form of measurements or previous experience to base the estimate on. Here are a few examples of common estimations of the incoming turbulence intensity.

Model of Car Mean Drag coefficient, Cd Mean Drag force, Fd Practical 0.592 134.57 Theoretical 0.784 315

Model of the car No. of Iteration Iteration time Hours Maruti Alto 880 27



6. CONCLUSION The drag coefficients found theoretically and experimentally are very near. The results vary by only 0.24 values, in case of Maruti alto for drag coefficient. This shows the accuracy of the results obtained by us during this design process If the present design will be implemented for the model generation of the car we will obtain the exact values of the drag coefficient and drag force,

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[16] Abdul Razzaque Ansari, CFD Analysis of Aerodynamic Design of Tata Indica Car, International Journal of Mechanical Engineering and Technology , 8(3), 2017, pp.344–355.

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CFD ANALYSIS OF AERO DYNAMIC DESIGN OF … MARUTI ALTO CAR Abdul Razzaque Ansari Department of...

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