Exterior Styling Of An Intercity Bus For Improved Aerodynamics

[email protected] http://www.wix.com/arunrave/frontpage Exterior Styling of an Intercity Transport Bus for Improved Aerodynamic Performance Arun Raveendran1, D. Rakesh2, S.N. Sridhara3 1- (Engg) student, 2-Senior lecturer, 3-Professor and HOD, Automotive Engineering Centre M.S.Ramaiah School of Advanced Studies, Bangalore

Abstract Intercity buses travel about 250 to 350 km in a stretch and usually are of sleeper coach mode. The exterior styling, sleeper comfort and aerodynamically efficient design for reduced fuel consumption are the three essential factors for a successful operation in the competitive world. The bus body building companies prioritizes the exterior looks of the bus and ignore the aerodynamic aspect. Scientific design of sleepers for increased comfort of the passengers is seldom seen. The overall aim of this project was to redesign an intercity bus with enhanced exterior styling, reduced aerodynamic drag and increased comfort for the passengers. Extensive product study and market study were carried out and aspirations and frustrations of commuters were recorded. An operating intercity bus was benchmarked and analyzed for styling, aerodynamic performance and comfort. Fluent, a commercial CFD code was used to evaluate the aerodynamic performance. Principles of product design were used to analyse the styling and comfort. The benchmarked high floor bus was redesigned with low - floor for reduced aerodynamic drag. The exterior was redesigned with emphasis on improvised aerodynamic performance and appealing looks. The interior was modified to meet aspirations of the commuters. The results of the redesigned exterior body showed a reduction of Cd from 0.53 to 0.29 and overall aerodynamic drag reduction by 60% due to combined effect of reduced Cd and frontal area. The redesigned interior was found to be at the satisfaction of commuters. Key Words: Bus Aerodynamics, Drag Reduction, Low Floor Bus Design, Sleeper Coach efficient buses. The power generated in the engine is mainly used to overcome the rolling resistance, aerodynamic drag and climbing resistance. Out of these three components aerodynamic drag increases with respect to the vehicle speed. At high speeds at about 100 Km/hr the drag force exceeds the power spend on overcoming the rolling resistance [1]. So reducing the aerodynamic drag is of prime importance to achieve fuel efficiency. Vehicle aerodynamics deals with the study of forces acting on a vehicle body when it moves through air [2].Drag and lift are the two main phenomena observed on the vehicle body due to the effect of the wind. About 90% of drag is due to the pressure difference created between the various areas of the vehicle [2].

Nomenclature A Cd I k ρ ε µ

Frontal projected area (m2) Coefficient of drag Turbulent intensity (m) Turbulent kinetic energy (m2/s2) Density of air (kg/m3) Dissipation rate (m2/s3) Dynamic viscosity (Ns/m2)

Abbreviations CFD CAD PDS QFD

Computational fluid dynamics Computer aided design Product design specification Quality function deployment

1.1 Styling and aerodynamics

1. INTRODUCTION Buses are used as means for transporting large amount of people from one place to other. All the states governments are having its own intercity bus fleet in India which provides mobility for the people at a reasonable cost. Huge numbers of private bus firms are also in operation and are efficient in reducing the dependency on trains. Indian road conditions are significantly improved for the past 10 years and intercity bus travel time is reduced as they can travel with high speeds. In order to keep a low operating cost these buses have to deliver high efficiency at these speeds. Rising fuel prices and stringent government regulations force the vehicle manufactures and operators to produce and operate fuel

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Drag force acting on the vehicle depends on frontal projected area and the coefficient of drag value of the vehicle. Any reduction in these values will directly reduce drag force experienced by the vehicle. Frontal projected area of the intercity bus is decided by the interior packaging of the bus. Coefficient of drag value is determined by the shape of the vehicle. These two factors influence the exterior styling of the vehicle. Exterior styling of the vehicle is important due to the fact that the vehicle has to attract customers. The vehicle should project its performance and comfort capabilities through its exterior design. Finding harmony with the aerodynamic requirements and customer oriented styling will lead to a successful vehicle with low fuel consumption.

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[email protected] http://www.wix.com/arunrave/frontpage This research is aimed to deliver an aerodynamically improved bus design with user oriented exterior styling. The popular Volvo 9400 bus was evaluated for its aerodynamic performance and guidelines for better aerodynamics were collected from literature survey. Based on these guidelines and user study concepts were generated. The model was analyzed using fluent and improvements in drag values were predicted.

comfort level. Semi Deluxe Bus is designed for a slightly higher comfort level and with provision for ergonomically designed seats. Deluxe Bus is designed for a high comfort level and individual seats and adjustable seat backs, improved ventilation and pleasing interiors. A.C. Deluxe Bus is Deluxe Bus which is air conditioned. The present intercity buses operate in India mainly comes under the deluxe and A/C deluxe class.

1.2 Literature study

The main parts which defines the exterior styling of an intercity bus are the windshield, grill, front bumper, headlights, indicators, wipers, side windows, passenger doors, driver door, luggage space, engine space, back windshield, number plate, brake light, back indicator, back bumper and radiator grill. Interior of the bus consists of driver’s cabin and passenger compartment. The driver’s cabin consists of seating for the driver, his assistant, dash board and steering. The passenger compartment consists of rows of seats or beads according to the type of bus. All the intercity buses are high floor buses with a floor height of 1200 mm from the road. Luggage space is provided under the floor with opening from both the side of the bus. Four steps are provided for boarding the bus. In most of the present bus design the passenger door is located at the front side corner of the bus.

Edwin J Saltzman and Robert R Meyer [3] carried out studies on reducing the drag of trucks and buses. The final model equipped with rounded horizontal and vertical corners, smoothed under body and a boat tail achieved Cd value of 0.242. Ludovico Consano and Davide Lucarelli [4] at IVECO truck building company came up with an aerodynamically efficient truck. They paid particular attention on the corner surfaces of the vehicle. A higher and smoother roof has been designed with DAM fully integrated into the frontal bumper. Moreover the lateral lowered side skirts have been added to mask the tanks, rear wheels and axles. To prevent flow detachment, many rounded surfaces have been added to the exposed surfaces, such as the roof window, side mirrors, sun visor, etc. The test results revealed a fuel reduction of 8%. R. Mc Callen, K. Salari, J. et al [5] in their experiments found out removal of rear view mirror alone will bring down the drag of the vehicle by 4.5%. Any gap in the vehicle body will result in flow separation and flow circulation. A Gilhaus [6] investigation reveled a reduction in drag value until the front leading edge radii value reaches 150 mm. Further increase in the radius did not affect the drag value of the bus. C W Carr [7] investigated the effects of streamlining the front end of the rectangular bodies in ground proximity. Experiments shown a stream lined front end with low leading edge resulted in a drag coefficient of 0.21. W H huco and H J Emmelmann [8] found that detailed shape optimisation of parts such as roof radii, rain channels, headlights will result in reduction of drag force. W T mason and P S Beebe [1] carried out experiments using horizontal and vertical splitter panels extending from vehicle body at the rear end, vanes and non ventilated cavities close to vehicle bodies. Splitter panels had no affect on the drag value and the vane arrangement increased the drag. The addition of non ventilated cavities reduced the drag coefficient by 5%.

2. Product Survey Under AIS-052 code of practice for bus body design and approval, present intercity buses comes under type 3 and 4. These are designed and constructed for long distance passenger transport, exclusively designed for comfort of seated passengers and not intended for carrying standing passengers. Type 4 buses are special purpose buses exclusively sleeper coaches which are getting popularized in these days. Intercity buses are classified according to the occupancy level as medium capacity buses as it can carry 35 to 50 passengers. Intercity buses are again classified according to the comfort level as non deluxe bus (NDX), semi deluxe bus (SDX), deluxe bus (DLX) and A/C deluxe bus (ACX). Non Deluxe Bus is designed for basic minimum

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Manufacturing of intercity buses are carried out in two stages. The OEM manufactures drive away chassis of the bus which include the engine, transmission and chassis of the vehicle. The bodies of the buses are manufactured by body building companies. In order to regulate the design of the bus coaches, Indian Ministry of Shipping, Road Transport & Highways introduced the standard AIS-052 which was published in September 2001. The major rules which are to be considered while designing an intercity bus are listed below Parameters Width of the bus Length of the bus Gangway Service doors Width of door Height of service door Width of windows Emergency exit

Height of first step Height of second steps Intrusion above seat

Regulations Shall not exceed 2.6 m Maximum 12 meters for transport vehicle with rigid frame having two or more axles, Minimum of 1800 mm height and 300 mm wide Minimum 1 Minimum 650 mm Minimum 1650 mm Minimum 550 mm (sliding type except for ACX) 2 numbers ( 1 at front half opposite to service door next one at rear with area not less than 4000 cm2) 425 mm maximum 350 mm maximum

100 mm at height 1350 from floor Wheel arch intrusion 200 mm from the seat front Table 1 bus regulations as per AIS - 052

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[email protected] http://www.wix.com/arunrave/frontpage 2.1Bus aerodynamics Drag force acting on the bus body is given by the formula Drag force = ½ ρv2 A Cd

(1)

It is evident that the drag force acting on the vehicle depends on the density of the air, velocity of the vehicle, frontal projected area and the coefficient of drag value of the vehicle. Reduction in air density or the vehicle speed is not a viable solution for reducing the drag value of the bus. Reducing the frontal projected area is a viable solution as it will directly reduce the drag significantly. It is found in the product study a huge number of low floor buses were operating in the urban areas for transporting people. These buses are having a low deck with a height of 350 mm or less compared to the 1200 mm of high floor buses as shown in fig1. Low floor buses are having kneeling mechanisms which can further reduce the overall height. These buses are having interior height of more than 1800 over 60 % of its inner space. By incorporating the low floor bus chassis in intercity bus design will reduce present bus height. A low floor intercity bus design will have low projected area which in terms results in reduction in drag force. Interaction with the bus manufacturers revealed that the Coach manufactures were hesitating to use a low floor chassis due to the following reasons listed below. A low floor bus design which overcomes the below listed difficulties will reduce the bus height from 3400 mm to 2600 mm.  Luggage space reduction  Large wheel arches reduces the number seats  Divides the floor area in to two decks  Less space for fuel tanks leads to low capacity  Difficult to reach the engine compartment for repairs  Psychologically people like t sit at high floor than the low floor area

(34%). Business trips contribute to 16% of the seat occupancy. 93% people prefer to travel in night compared to 7% day travelers.72% prefer to sleep while only 26% people like do other activities. If money is not a constrain, 82% people like to travel in sleeper coaches and rest preferred AC deluxe buses. Most of the people adopted bus travel over train due to the easy availability and comfort of the bus. Safety, speed and flexible pick up and drop points are also influence the decision. Maximum seat occupancy was observed on Fridays and Saturdays. Occupancy levels of sleeper coaches and AC deluxe coaches were high compared to deluxe and semi deluxe coaches for buses staring from Bangalore. People prefer to occupy the front rows seats than the rear. More than 80% of private intercity buses are operating at night between 7 pm and morning 10 am. It was evident from the study that the majority of intercity bus users comes under the age group of 18 to 35 and consists of middle class professionals and students. It was also found that people prefer sleeper coaches over semi sleeper (reclining seat) coaches. The target customer group was finalized as 18 to 35 and the coach arrangement was selected as sleeper coach. The major user frustrations gathered from the user survey are listed below       

Old aged and disabled persons find it difficult to board the bus due to high step height. Difficult to sleep in the present adjustable seats as it will not allow any body movement. Results in body pain and neck pain after long travel. Outside lights often disturb the sleep. Less leg room in semi deluxe and deluxe buses. Lack of toilets results in journey brakes and user discomfort. Platforms at the bus stations are not able to reduce the boarding height due to current door position.

Figure 1 Types of bus chassis 3. User study (Gemba study) User study was conducted to select the target customer group, understand user frustrations and aspirations. A survey was conducted among the users. Users want a comfortable speedy commute which is reasonably priced and looks good. It was found that intercity bus users consist of mainly professionals working in other cities (45%) and students

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Figure 2 QFD matrix

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[email protected] http://www.wix.com/arunrave/frontpage A quality function deployment matrix was prepared by converting the user frustrations and aspirations in to technical voices.QFD revels the areas of importance to achieve maximum user satisfaction. Low floor, kneeling mechanism, sleeper coach, door position and aerodynamic shape got highest points. A low floor bus design will eliminate the boarding problem of aged and disabled users. It is also favourable as the bus height can be reduced to improve the aerodynamics of the vehicle without reducing the interior space. A low floor sleeper coach eliminates the difficulty in sleeping due to reclining seat, arrested body movement, body pain and low leg room. Area below the bed arrangement inside the coach can be easily converted as luggage space and fuel tank. Incorporating electro sensitive side windows allows the users to adjust the opacity of their windows and will reduce the light disturbances from outside. A wash room with toilet system has to be incorporated inside the bus cabin. Positioning the door behind front wheel arches will reduce the boarding height with respect to the bus stop platforms.

4. Bench marking and baseline simulation The Volvo 9400 intercity bus was selected as bench marked model. It is the latest model in the Indian market and is very popular in the segment. Engineering parameters of this model was kept as same for the new bus design and was selected as the baseline for studying the aerodynamic performances. This vehicle model was used to understand the flow behaviour Pressure distribution, Coefficient of drag value, Contribution of different parts, Drag force acting at different speeds, Flow separation and pressure stagnation areas

Fluid domain of 96m x 12.75m x 17 m was created around the bus model which was 10 times the length, 5 times the width and height of the vehicle. Bus model was placed inside this domain in such a way that 1/3 length was kept in front of the vehicle. The larger domain was kept at the rear to capture the essential flow features. A smaller domain was created inside this domain to generate fine mesh in and around the bus body. Gambit pre processor was the software tool used to generate the mesh. Outer volume was meshed with coarse elements. 21,47,716 Unstructured tetrahedral hybrid elements were used to mesh the entire fluid domain.

4.2Boundary conditions Boundary conditions were applied on the meshed model using the Gambit pre processor. The analysis was carried out in moving road and rotating wheel condition. In the simulation only straight wind condition was considered at 3 different vehicle speed of 80, 100, 120 Km/hr. Constant velocity inlet condition was applied at the inlet to replicate the constant wind velocity conditions same as wind tunnel tests. Zero gauge pressure was applied at the outlet with operating pressure as atmospheric pressure. All the boundary conditions used in the analysis are listed in table 2 Boundary inlet

Boundary condition Constant velocity Turbulent intensity Length scale

Outlet

Pressure outlet

Road

Moving wall No slip

Tyres

Rotating wall No slip No slip – Stationery wall Stationery wall Specified shear

Bus body Domain top and side

value V= 22.22 m/s I = 1.97 V= 27.78 m/s I = 1.92 V= 33.33 m/s I = 1.88 Constant pressure = 0 pa V= 22.22 m/s V= 27.78 m/s V= 33.33 m/s Ang. V = 404.36 rpm Ang. V = 505.55 rpm Ang. V = 606.55 rpm Shear stress = 0

Table 2 Boundary conditions

4.3 Turbulent model

Figure 3 Volvo 9400 intercity bus and CAD model 4.1Geometry and mesh generation Three dimensional model of the baseline model was created using Alias studio tools and Catia as shown in fig 3. Small details and gaps in the vehicle body were eliminated as the purpose of the analysis was to understand the overall aerodynamic performance of the basic bus shape

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The solver used for the analysis was Fluent 6.3.26 and it uses a control-volume-method to solve the governing equations that can be solved numerically. The solver selected was the pressure based implicit solver. In this type the equations of continuity and momentum are solved sequentially. This is used for incompressible flows where the density is constant and not related to pressure. This reduces the computational time when compared to the other methods. The flow is considered to be steady in nature and thus the equations are solved using implicit iterative methods. Reynolds number of the flow was calculated and found out to be fully turbulent. The turbulence model selected as k-ε model which is well known for its robustness. This model assumes the flow to be fully turbulent and is based on the turbulence kinetic energy and its dissipation rate.

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Figure 4 Boundary conditions and meshed bus model k-ε model was selected because of its ability to converge to a moderately accurate result in comparatively less time. Pressure velocity coupling was used to calculate the pressure field. As the flow is considered as incompressible there is no independent equation to calculate pressure. Hence the pressure velocity coupling was used to derive the pressure equations. The algorithm used was the semi implicit method for pressure linked equations (SIMPLE). This is based on the concept of mass flow between the cells and the flow occurs when there is a pressure difference. The method applied for the solution of the momentum, kinetic energy and the dissipation rate was the first order upwind method.

Figure 6 shows the path lines of flow around the bus body. The flow gets stagnated at the frontal area and gets accelerated at the front radius area. Flow separation was observed behind the mirrors. Flow remains attached along the sides and roof. Flow eventually gets separated at the rear and forms vortices. Another major flow separation area where vortices generation observed was at the rotating tyre region.

4.4 Results and discussion Static pressure distribution plot (fig 5) of the bus body at speed of 100 Km/hr reveals pressure concentration in front region of the vehicle as the air flow strikes at the front and brought momentarily to rest. Front mirrors show high static pressure stagnation. Rear wall of the bus experiences low pressure compared to the front due to the flow separation and circulation. This pressure difference leads to high pressure drag on the body.

Figure 5 Static pressure distribution in Pa

Figure 6 Flow circulation - mirrors and wheels MSc (Engg) in APD

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Figure 7 Path lines of velocity magnitude Drag force acting on the vehicle increases with the speed of the vehicle. Front area of the bus experience maximum pressure stagnation. A streamlined front end which allows better air flow will effectively improve the drag performance of the vehicle. Windshield angle, bonnet shape, rear view mirror and radius at the front corners were identified as areas to be improved in the new design for better aerodynamics. The rear low pressure region created by the flow separation must be brought to minimum for improving the pressure drag acting on the body. Incorporating optimum values obtained from the literature review and features such as roof tapering, roof end lowering, boat tailing, and radius improvements will reduce the drag of bus. The main values obtained from the analysis which are taken as reference for the new bus design are listed in table 3 Parameters

80Km/hr

100Km/hr

120Km/hr

Cd value

0.539

0.538

0.537

2

2

Projected area

9.47 m

9.47 m

9.47 m2

Pressure drag

1427.79 N

2230.94 N

3212.25 N

Skin friction drag 119.33 N

180.52 N

253.12 N

Total drag force

2411.46 N

3465.38 N

1547.13 N

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6. CONCEPT GENERATION

5. PRODUCT DESIGN SPECIFICATIONS (PDS) PDS defines all features that must be incorporated in an aerodynamically efficient, user friendly bus design. Final product design specifications were derived from all the studies and analysis done up to now. No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Parameters Length Width Height Wheel base Front over hang Rear over hang Chassis Capacity Interior Interior seating Coach type Entry height Interior height Door position Door width Door height Luggage space Side windows Toilet system

20 21 22 23 24 24 25

Engine Output Power Torque Emissions class Gearbox Suspension Tyres

Specifications 12000 mm 2550 mm 2600 mm 6200 mm 2590 mm 3210 mm B7R LE ( Low entry) 30 + 2 Fully Sleeper coach Foldable seats Air conditioned 340 mm 1800 mm Behind front wheel 650 mm 1800 mm Middle of bus , min 5000 L Electro sensitive glasses Behind drivers cabin Rear-mounted, 6-cylinder, 7-litre diesel 213 kW (290 hp) @ 2100 rpm 1200 nm @ 1050 - 1650 rpm Euro 3 6-speed manual Full Air Tubeless (295/80 R 22.5")

Table 4 product design specifications No 1 2 3 4 5 6 7 8 9 10 11

Aerodynamic Specifications Minimum front corner radius of 150 mm Minimum windshield angle 15 degrees Smooth and covered under body Minimum trailing edge radius of 150 mm Side panel tapering Rear roof tapering Diffuser Rear view mirror elimination Curved front end Boat tailing Roof end lowering

Using the data collected from the user study the target customer selected was students and working professionals at the age of 18 to 35.To understand the different activities in their day to day life a lifestyle board was prepared. It was observed that they lead an energetic, fast and fun loving life in this age period. They never want to waste any time in their life and were constantly on the move between college, office, friends and family. Most of them were obsessed with travelling, adventure trips, fast bike and cars. Most of them travel in the intercity bus to their vacation destination or to a busy business meeting. After the completing the journey in the bus most of them go to office or to their planned work just after a quick fresh up. So they don’t want to waste the rest of the day in their busy life. This age group people have lots of energy in them and are at the peaks of their life. From the life style board a mood board was prepared which shows the different emotions and situation this age group goes through in their life. From the mood board the most suitable theme for the bus design was found to be adventure, fast and speed. This theme was also selected because it directly related with the aerodynamics. A theme board was prepared which was related to the adventure theme. The theme board includes objects and things directly related to speed and adventure. Nature is composed of animals which are very fast and have good aerodynamic shape. Even though Killer whales are fearsome animals they are always the main attractions in big aquariums on the vacation trips. They can move through water very easily and are having huge body which is similar to the requirements of an intercity bus. The shape of the bus is derived from the killer whale shape. Constrains listed in the PDS and aerodynamic specifications were incorporated on the concept. Maroon colour was selected for the exterior as it truly expresses the adventure theme. The windshield is curved and angled. Front area is curved to improve the flow in that area which is derived from killer whale face. Front corner radii were kept more than 150 mm, roof tapering, roof end lowering, side panel tapering and boat tailing also incorporated.

Figure 8 New bus concept design

Table 5 Specifications for aerodynamics improvements

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Figure 9 Comparison of new interior with the present design Interior of the bus was designed for transporting 30 passengers, one driver and his assistant. Coats for sleeping were arranged on each side of the gangway of width 600 mm. Each side was having two rows of beds stacked on another. A comfortable gap of 600 mm was kept between coats. On the left side of the gangway two beds were arranged and right side single bed was arranged. Beads were made foldable so that it will converts as temporary seats if the passenger wants to sit. Interiors were made up of wood finish materials to induce the feeling of being at home bed. Each cabin was equipped with individual bead lamps and fall protection guide rails. A minimum of 1800mm roof height was maintained throughout the gangway. The luggage space was incorporated below the coats in the middle of the bus with a capacity of 4914 L. A survey was conducted among the users of the intercity bus to understand the acceptance level of the new design. Majority of the users were found to be happy with the new design as the problems listed by them are solved in the new design. People were found to be excited with the low floor bus design and the toilet system inside which was not present in the existing intercity bus. These added features found to attract older people as they found it difficult to board the existing bus. Incorporation of the toilet system was appreciated by the users as many of them ignored the bus travel due to lack of sanitation in the present design.

Figure 10 Meshed bus model Static pressure contours of the bus model at vehicle speed of 100 km/hr are shown in fig 11. The plot shows considerable reduction in pressure stagnation area in the front of the vehicle. The static pressure value also reduced compared to the baseline model. Static pressure plot at the rear end of the vehicle reveals an increase in pressure. The pressure difference between the front and the rear area was reduced which reduces the pressure drag acting on the body

7. Simulation The new bus design was analysed for its aerodynamic efficiency. Model was meshed using the same procedure explained in section 3. Fluid domain of 96m x 12.75m x 13m was created around the vehicle. Area around the bus model was meshed with fine elements and coarse elements were used at the outer areas. 24,36,871 Unstructured tetrahedral hybrid elements were used to mesh the fluid domain fig 9. The only boundary condition which differs from the baseline analysis was the length scale value which is 0.91.Grid independent study was carried out on the modal. It was found that a difference in 8,68,073 elements produced a change in Cd value of 0.023 which was well within the acceptable limits.

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Figure 11 static pressure contours in Pa Large numbers of vortices were generated and flow separation was observed at the rear of the baseline model fig 12. In the new design these were brought to a minimum value. It is evident from the fig 13 that the low velocity area behind the new bus design is considerably reduced due to the effect of roof tapering, roof lowering boat tailing and diffuser at the rear. Flow is directed at the rear to minimise the low pressure area behind the vehicle. No flow separation is occurring at the front of the vehicle as due to the improvement in the front corner radii and elimination of the rear view mirror

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Figure 12 Comparison of vortices at the rear



Base line – Mid plane



The present high floor sleeper coach was modified to a low floor version with substantially reduced aerodynamic drag. The drag coefficient of 0.53 of present bus was found to be reduced to 0.29 in the modified design. The exterior was redesigned giving emphasis to both aerodynamics and aesthetics. The interior was also modified to improve the comfort of the commuters. The proposed concept was well received by the commuters.

7. References [1]

New design – Mid plane

Wolf Heinrich Hucho., (2001), “Aerodynamics of road vehicles”, 4 th edition, SAE International, vol.1, pp. 11-88.

[2]

Fred Browand., (2005), “Reducing the drag and fuel consumption”, Advanced transportation workshop. October, 10 -11.

[3]

Edwin. J. Asltzman and Robert. R. Meyer., (1999), “A reassessment of heavy duty truck aerodynamic design features and priorities”, NASA/tp-1999-206574

[4]

Mr. Ludovico Consano and Davide Lucarelli., (2007), “Fuel Reduction on a Tractor-Trailer Truck at IVECO IVECO S.p.A”, 3 rd European automotive CFD conference, EACC 2007

[5]

R.. Mc. Callen, K. Salari, J. Ortega, F. Browand, M. Hammache, T. Hsu., (2004), “Effort to Reduce Truck Aerodynamic Drag – Joint Experiments and Computations Lead to Smart Design”, AIAA Fluid Dynamics Conference, June 28 – July 1,

[6]

Gilhaus A., “Main parameters determining the aerodynamic drag of buses, colloque construire avec le vent, vol 2,

[7]

Carr.G.W., (1982), “The aerodynamics of basic shapes of road vehicles, part 1, Simple rectangular bodies”, MIRA report No.1982/2

[8]

Hucko,W.H Emmelmann. H.J (1977) “Aerodynamiche Formoptimierung,ein weg zur steigerung der wirtschsftlichkeit von nutzfahrzeugen,” Series.12, NO.31 1977.

Drag force in N

Figure 13 Velocity contours comparison 4000 3500 3000 2500 2000 1500 1000 500 0

New design

3465

Volvo 9400

2411 1547 608 80 Km/hr

947

1357

100 Km/hr 120 Km/hr

Vehicle speed Figure 14 Drag force comparison The coefficient of drag value of the new design is found to be 0.296 which 44 % improvement compared to the baseline model. Use of low floor bus chassis led to the height reduction of bus from 3.4 m to 2.6 m which reduced the projected area to 6.75 m2. Clear decrease in the drag force is visible in the analysis and the total drag force is reduced from 2411 N to 955N.This is an improvement of 60.39 %.figure 14 shows the comparison of drag force acting on the base line model and the new design at different vehicle speeds.

8. Conclusion A detailed investigation of the present bus in the field of styling and aerodynamics was carried out. The results of these investigations were used to come up with an

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