AN EXPERIMENTAL STUDY OF THE AERODYNAMICS FORCES ACTING ON A TRUCK

  

AN EXPERIMENTAL STUDY OF THE AERODYNAMICS

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FORCES ACTING ON A TRUCK

  Mustofa *

Abstract

  

The aim of this project is to show the aerodynamics experiment results of a truck in terms of drag coefficient

(C ) within aerodynamics forces. The test was conducted in the Wind Tunnel laboratory at the University of

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South Australia in the school of Mechanical and Manufacturing Engineering. In addition to the test, fairing

and without fairing effects were investigated. Results, C truck with fairing was lower than that of with

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fairing by 0.108 or from 1.518 to 1.41. By adding the fairing on the truck’s cap, fuel consumption could be

saved.

  Keyword: drag coefficient and fairing

  1. Introduction

  2. Coefficient of drag (C ) d

  As one of the activities over the Aerodynamic efficiency of a car is development in vehicle technology is to conduct a determined by its Coefficient of Drag (C ).

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  practical study to obtain aerodynamic drag. This is Coefficient of drag is independent of area; it simply one of the most important factors for vehicles reflects the influence to aerodynamic drag by the which have great influence on fuel consumption. shape of object. Theoretically, a circular flat plate

  The effect of cross-wind on the aerodynamic forces has C 1.0, but after adding the turbulence effect

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  is very significant [1]. Traveling through still air the around its edge, it becomes approximately 1.2. The drag force acts on the relatively small frontal area most aerodynamic efficient shape is water drop, of the truck and is directed nearly parallel to its whose C is 0.05. However, we cannot make a car

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  longitudinal axis. However in the presence of a like this. A typical modern car is around 0.30. cross-wind the magnitude of the relative velocity between the truck and the air is increased and its

  2

  3. Calculating the frontal area (m ) and C of a

  direction is skewed to the direction of motion so d

  truck

  that the large side area of the trailer is exposed. The resulting drag force is much larger and it has According to the weight and height of the components both parallel and normal to the truck measured during the experiment, the frontal direction of the truck’s motion. Substantial lift can area can be calculated as follows: also be generated in cases of separated flow over the top of the trailer. The component of drag

  2 A = h . w (m ) ……………………(1) F

  normal to the longitudinal axis of the truck, referred [2]. Therefore, the more aerodynamic drag is

  Where: reduced, the more fuel can be saved. Wind tunnel A = frontal area experiment is traditionally method to obtain F h = height of frontal area (mm) aerodynamics characteristics. Currently, w = width of frontal area (mm)

  Computational Fluid Dynamics (CFD) method has been developed. Due to software obstacle, this method can not be uploading through such article.

  The result is depicted in Table 1.

• Staf Pengajar Jurusan Teknik Mesin Fakultas Teknik Universitas Tadulako, Palu

  An Experimental Study of the Aerodynamics Forces Acting on A Truck

  Table 1. Frontal Area

  2 Model Height (mm) Width (mm) Frontal Area (A ) m F

  Truck 158 98.7 0.01559 Table 2. Force balance calibration:

  Known mass (pounds) Horizontal force (N) Strain gauge reading

  1 4.5 211 2 9 427 3 13.5 633 4 18 855 5 22.5 1088

  Prior to conducting the test, the experiment set was

  ∆h = 160 / 5 → ∆h = 32 calibrated to get balancing as follow (Table 2).

  ∆p = ρ. g. ∆h → ∆p = 1.2 × 9.8 ×32 →

  There is only one coefficient of drag for an

• -2

  article which is exposed to a given wind in a certain

  ∆p = 376.5 Nm

  angel. This means that C is not dependent to the

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  wind speed (fan 1 or fan 1+2). If there is no error ₂

  2

  1 → V = (2 × 376.32) /1.2 →

  ρ

  Δ p =

  V

  during the experiment, the results acquired from

  2

  experiment 1, truck without fairing for both

  2 V = 627.2 = 25.04 m/s → V

  conditions (fan 1 was ON and fan 1 + 2 were ON) must be the same. However, as it can be observed

  F _D C =

  from the last right column in the table 3, the amount d ₂

  1 ρ AV

  2

  of C obtained from the experiment one (fan 1 is

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  ON) is slightly different from the second

  Cd = 9.0625 / (0.5 × 1.2 × 0.01559 ×

  experiment (fan 1 and 2 are ON) and this happened for both fairing and without faring truck. The 627.2) reason is some errors which normally happen over

  Cd = 1.54

  the experiments. The more accurate and calibrate are the measurement instruments, the more reliable With the same calculation for (fan 1+2 is outcomes would be achieved, ON), the coefficient of drag (C ) is 1.518.

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  Means that the higher the wind a. Truck without fairing speed/aerodynamics forces (fan is ON) is

  To calculate the coefficient of drag, the formula acting on the frontal area of the truck, the is: bigger is the drag coefficient (C ) on the

  d truck with no fairing.

  F …………………. (2) _D =

  C d ₂

  1 ρ AV

  2 b.

  Truck with cab fairing Track with cab fairing where fan 1 was ON;

  Having the data for strain gauge and horizontal with the same above steps then C is 1.43 force, we can draw a line. The slope of the line is d For both fan 1 and fan 2 are ON, the C is 1.41.

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  calculated (m) and is used for calculating force According to the calculations under the below for other amounts of strain gauge; Calculation of table, the coefficient of drag (C ) calculated for

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  slop (m): the track with fairing and without fairing are as

  m= (427-211)/(9-4.5) Æ m = 48 follow (Table 3).

  So, m = (430-427)/(Fd-9) Æ 48=(430-

  427)/(Fd-9)

  ÆFd = 9.0625 N 197

  “MEKTEK” TAHUN XI NO.3 SEPTEMBER 2009 Table 3. Coefficient of drag (C

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  C

  There are a variety of fairings for trucks, many of which can considerably reduce the aerodynamic drag force. According to the pictures Figure 2, the percentage of reduction for each of them are given:

  The following pictures are two of the fairings which have been using for decreasing aerodynamic drag for many years (Figure 1):

  expected to obtain more reduction, provided the errors over the experiment are minimised.

  ×100 = 7.128 % decrease. However, this is

  (With fairing) = (1.43 + 1.41)/2 = 1.42 The percentage of reduction = 100 – (1.42/1.52)

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  (Without fairing) = (1.54 + 1.518)/2 = 1.529 C

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  Due to the error occurred over the experiment, the average is applied and the percentage of reduction is calculated as follows:

  ) for a truck with cap and without fairing

  1.41 Figure 1. Different type of trucks with fairings Figure 2. Splitter plate of a truck

  15.93

  1 Open 160 25.04 398 8.39 1.43 1 + 2 Open 310 34.58 755

  Truck with cab fairing

  1.54 1 + 2 Open 306 34.6 810 16.98 1.518

  1 Open 160 25.04 430 9.0625

  Truck without fairing

  Model fan slats Manometer reading V (m/s) Strain gauge reading F d (N) C d

  The Splitter plate decreases the effect of turbulence occurring at this stage. The wind tunnel experiment has shown that this type of fairing can reduce aerodynamic drag up to 4 % [5]. fairings

  An Experimental Study of the Aerodynamics Forces Acting on A Truck

  Figure 3. Skirts, base flaps and side extenders of a trailer Figure 4. Optimum shape for trucks fairings

  The percentage reduction of aerodynamic drag is optimum shape and design for truck fairings. For given below for each of the above fairings: instance, the figures below are ideas for aerodynamic drag reduction. NASA is one of the 4 % trailer base –flaps institutions which have been making trucks more 6 % trailer skirt aerodynamics [6]. 2 % gap splitter plate/side extenders

  Other improvements/modifications can be

• made to a truck to provide additional improvements

  Total: 12 % in drag reduction. Firstly, the truck frontal area has a significant role to determine its C . Therefore, one

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  In addition to the fairings shown above, approach can be reducing the frontal area as much many researches are being conducted to find out the

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  “MEKTEK” TAHUN XI NO.3 SEPTEMBER 2009 as possible. This results in reducing the height and

5. References width of the container behind and truck itself [4].

  L. Taylor, 2006, Lecture Notes in Development in Secondly, another approach would be covering the

  Vehicle Technology course, the School of

  spare space between the truck and its container Advanced Mechanical and Manufacturing using a cover made by fibre glass or plastic to avoid Engineering, UniSA, South Australia. vortex happening. Thirdly, using a under body fairing and/or modified spoiler at the back of the

  J. Bettle, A.G.L. Holloway, J.E.S. Venart, 2003, A vehicle to improve the separation and minimise computational study of the aerodynamic drag. Fourthly, according to the answer of previous

  forces acting on a tractor-trailer vehicle

  question, adding flaps, trailer skirt and gap splitter on a bridge in cross-wind, Journal of plate can be feasible approaches to improve in drag Wind Engineering and Industrial reduction. Lastly, using advance simulation Aerodynamics 91, page 573–592. software enables engineers to simulate and predict http://www1.eere.energy.gov, accessed 10 the effect of using different types of fairings on September 2006. aerodynamic drag reduction. http://gcep.stanford.edu/pdfs, accessed 2 October

  2006

4. Conclusion

  http://www.nhtsa.dot.gov/cars/testing/ncap, Over the experiment conducted about accessed 15 November 2006 aerodynamic drag, this is observed that the http://nasaexplores.nasa.gov/show, accessed 15 influence of fairing for reducing aerodynamic drag

  November 2006 for track is considerable. Due to the errors over the experiment associated with measurement instruments the result for C were slightly different

  d for each obstacle exposed to wind in wind tunnel.

  However, wind tunnel is a reliable and good experiment for acquiring C .

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