A Numerical Simulation for Improving the aerodynamics of a pickup truck by use of diffusers, spoilers, and bumps

doi:10.21203/rs.3.rs-1781736/v1

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Research Article

A Numerical Simulation for Improving the aerodynamics of a pickup truck by use of diffusers, spoilers, and bumps

https://doi.org/10.21203/rs.3.rs-1781736/v1

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A pickup's aerodynamics characteristic for reducing drag force and increasing negative lift is studied; this study is performed to reduce fuel consumption and increase stability. The external flow devices such as a diffuser and a spoiler on the model which can change the direction of the airflow around the pickup to the desired direction are utilized. A diffuser at the rear end of the pick-up is studied to examine the effect of change of its length and angle on the aerodynamics characteristic of the Pickup. A spoiler length at the roof of the pickup spoiler as well as the change of its angle and the double spoiler are investigated; besides, the effect of the Bump's height on the tailgate of the pickup is studied. As a result of adding these devices to the pickup, increasing the diffuser length and angle, the drag coefficient and negative lift coefficient increase. In addition, the drag coefficient and negative lift coefficient will decrease if the spoiler length is increased. But with increasing double spoiler angle, the drag coefficient and negative lift coefficient increase. finally the drag coefficient and negative lift coefficient decrease with the addition of bumps on the tailgate of the Pickup truck.

CFD

Drag coefficient

Lift coefficient

Spoiler

Pickup

Numerical solution

Bumps

Since the beginning of the twentieth century, fuel prices and the speed of cars have increased gradually and this made it important to reduce aerodynamic drag [1]. Cooper et al [2] experimented with a wind tunnel to find that the rate of reduction in fuel consumption was directly related to vehicle aerodynamics. Delmore et al. [3] investigated the use of technology such as aerodynamics to reduce fuel consumption. Zolfa-Kassim et al. [4] analyzed the potential of fuel savings by reducing the drag force on heavy vehicles. Maxwell et al. [5] investigated the effect of adding a roof spoiler experimentally and numerically. Al Quran et al. [6] tested a vortex near a pickup truck experimentally. Cooper [7] tested the impact of a pickup tailgate on aerodynamic performance. Khalighi et al. [8] conducted a numerical Investigation and Formulation of Flow fields on Pickup vehicles. Holloway et al. [9] studied three different turbulence models to simulate drag force for a pickup vehicle and compared them with experimental results. Mokhtar et al. [10] analyzed the aerodynamics manner of a pickup car in both open and closed tailgate situations. Jia et al. [11] investigated experimentally and numerically about geometry variation of a bed and its length and height. Jong et al. investigated the effect of adding a flap on the back of a pickup truck cab on the drag coefficient reduction numerically and empirically [12]. Wang et al. succeeded in reducing the drag of a pickup truck by using deformation techniques, alternative models, and experimental optimization techniques [13]. Khaliqi et al. [14] investigated the reduction of drag force in a boat-shaped tail attached to a full-size tailgate numerically. Mousavi et al [15]. examined the effect of adding a vortex generator on the roof of a pickup truck numerically. Spike et al. [16] tried to reduce the drag force on the pickup car by adding 5 external flow control devices. Gucci et al. [17] investigated Front Spoiler, Deflectors on the side, and rear-wheel covers numerically and practically. Bahoosh et al. [18] studied numerically the aerodynamics effects of two tandem cars; the results revealed that the drag force on each two tandem cars is less than a single car. Bahoosh et al. [19] performed Numerical simulations of the airflow around a hatchback and a sedan vehicle without and with spoilers, the study on its effect on drag and lift coefficients with and without crosswinds.

In this study improving pickup aerodynamics characteristics by adding some features is investigated. the continuum and momentum equations were solved in a three-dimensional and steady; moreover, the k-epsilon Realizable model was used to simulate the turbulence equations. FLUENT and Solidworks software were utilized for this research. In the first step, the effect of adding a diffuser, changing its angle, and changing its length on the pickup car is investigated; after that, the effect of adding a roof spoiler and changing its length; moreover, the effect of the simultaneous presence of the rear spoiler and the roof spoiler on the model of the pickup car has been studied. Finally, the effect of adding bumps on the tailgate is considered.

The image of the pickup model utilized for the analysis is shown in Fig. 1 [20]. The car has a length of 5010 mm, a width of 1695 mm, and a height of 1585 mm. The length of the bed is 2265 mm and its inner height is 200 mm, its outer height is 510 mm. Solidworks software is used to draw the geometry of the simplified model of the Mitsubishi L200 car.

The Reynolds Averaged Naiver Stokes equation (RANS) was solved with a finite volume method. The governing equations were used as time averages of continuity and motion equations to simulate the flow over a pickup model for Newtonian fluids [21].

\(\frac{\partial {u}_{j}}{\partial {x}_{j}}=0\)	(1)
\(\frac{\partial {u}_{i}}{\partial t}+{u}_{j}\bullet \frac{\partial {u}_{i}}{\partial {x}_{j}}=-\frac{\partial p}{\partial {x}_{i}}+\nu \frac{{\partial }^{2}{u}_{i}}{\partial {x}_{j}\partial {x}_{j}}\)	(2)

So that u, p, and \(\nu\) are averaged velocity vector, averaged static pressure, and kinematic viscosity of the flow, respectively. The Realizable k-ԑ turbulence model is utilized [22].

\(\frac{\partial }{\partial {x}_{i}}\left(\rho k{u}_{i}\right)=\frac{\partial }{\partial {x}_{j}}\left[\left(\mu +\frac{{\mu }_{t}}{{\sigma }_{k}}\right)\frac{\partial k}{\partial {x}_{j}}\right]+{P}_{k}-\rho \epsilon\)	(3)
\(\frac{\partial }{\partial {x}_{i}}\left(\rho \epsilon {u}_{i}\right)=\frac{\partial }{\partial {x}_{j}}\left[\left(\mu +\frac{{\mu }_{t}}{{\sigma }_{\epsilon }}\right)\frac{\partial \epsilon }{\partial {x}_{j}}\right]+\rho {C}_{1}{S}_{\epsilon }-\rho {C}_{2}\frac{{\epsilon }^{2}}{k+\sqrt{\nu \epsilon }}\)	(4)

Where S is the strain rate.

\(S=\sqrt{2{S}_{ij}{S}_{ij}}\)

(5)

And \({C}_{1}=\text{m}\text{a}\text{x} (0.43,\frac{\eta }{\eta +5})\), \({\sigma }_{\kappa }\) and\({\sigma }_{ԑ}\) are the Prandtl turbulence numbers for k and ԑ, respectively. The turbulence viscosity (\({\mu }_{t}\)) is calculated as follows.

\({\mu }_{t}=\rho {C}_{\mu }\frac{{\kappa }^{2}}{\text{ԑ}}\)

(6)

So that \({c}_{\mu }\) is not constant and is calculated as follows.

\({C}_{\mu }={(4+{A}_{s }{U}^{\text{*} }\kappa /\text{ԑ})}^{-1}\)

where \({A}_{s}=\sqrt{6}\text{c}\text{o}\text{s}{\phi }\), \({\phi }=\frac{1}{3}\text{a}\text{r}\text{c}\text{c}\text{o}\text{s}\left(\sqrt{6}W\right)\), \(W={2}^{1.5}\frac{{S}_{ij}{S}_{jk}{S}_{ki}}{{S}^{3}}\), \({U}^{\text{*} }=\sqrt{{S}_{ij}{S}_{ij}+{\tilde{{\Omega }}}_{ij}{\tilde{{\Omega }}}_{ij}}\) ,

(7)

For the fixed model, the predefined values are used as follows.

\({C}_{2}=1.9, {\sigma }_{\kappa }=1.0 , {\sigma }_{\kappa }=1.2\)

(8)

3 − 1 Computational Domain

The computational domain contains a box; the dimensions of the box are 48000 mm long, 4000 mm in height, and width respectively. The vehicle is located at 12000 mm from the front of the tunnel, and 36000 mm from the rear of the tunnel. Both the flow tunnel and the four tires are considered stationary. Figure 2 shows the model and its location in the simulated wind tunnel. The input speed is 40\(\frac{m}{s}\); Atmospheric pressure constant is considered at the output. Symmetry conditions were used on the side; the uniform flow was applied to the top boundary condition; all vehicle surfaces are non-slip wall conditions. The total mesh volume is about 3 million. The initial layer of mesh on the surface of the car has about 1 mm in height.

Figure 3 illustrates the mesh layout on two cut plates; one is in the middle of the tunnel plate equal to the input and output; on the other side, the tunnel is cut longitudinally. Ansys Fluent 2019 software is utilized to simulate the 3D flow around the vehicle. The steady-state solution of the Reynolds averaged Navier-stocks equation is solved. Second-order upwind discretization is used for all calculations. The coupling scheme is used to treat the velocity-pressure coupling. The realizable k-epsilon turbulence model with a non-equilibrium wall function is used for the turbulence equations.

3 − 2 Mesh independence

A tetrahedral mesh with a boundary layer is utilized. The specification of the diffuser is a zero-degree angle, 229.6 mm length, and the ratio to the total length of the vehicle is 0.0457. The variations of drag coefficient and lift coefficient for the diffuser in different mesh numbers are shown in Fig. 4. As shown in the figure, with the increase of the mesh’s number to more than 2 million, no specific change has been achieved. To ensure the independence of the mesh network, the number of meshes around 3 million has been selected.

In a vehicle, the drag force is generally caused by the difference in pressure between the front and the rear of the vehicle. This pressure difference causes more than 70% of the total drag force to be compression drag force and the remainder of the drag force is due to viscous drag. To understand the effect of adding aerodynamics devices such as spoiler, diffuser, and bed bump to reduce drag and lift forces, we will investigate the flow field and local pressure distribution.

4 − 1 Validation

The flow around "Ahmed's body" has been studied. This geometry and its details are illustrated in Fig. 5. The results of the present numerical simulation are compared with the experimental data of Ahmed et al [23]. Figure 6 depicts the drag coefficient at various angles of the back of the body. As shown in this figure, the results of the numerical solutions are well-matched with the available experimental data.

4 − 2 Effect of the diffuser and its angle

In this section, we will study the effect of adding a diffuser and changing the diffuser angle from 0 to 50 degrees; in this case, the diffuser length is fixed at 230 mm; moreover, examining the length of the diffuser relative to the length of the entire vehicle is considered and in this case, the diffuser angle is assumed to be 10°. Diffuser length is considered from 129 mm to 629 mm with a 100 mm increment. all of the cases in this section are 6 different cases. The ratio of this diffuser length to the total length of the vehicle is 0.025 to 0.125 with a 0.02 increment. The diffuser angle is measured between the diffuser and the horizon line. The simulated pickup is illustrated in Fig. 7.

From Fig, 8 as the diffuser angle increases to 30 degrees, the drag coefficient increases to over 0.45 but then it falls from 40 degrees to almost 0.44, and then with an increase in diffuser angle to 50 degrees, the drag coefficient raise to approximant 0.45 again; on the other hand, as the diffuser length increases to 329 mm with the same trend the amount of drag raise to over 0.45, which is the highest drag amount. However, in the opposite trend, the drag amount falls to less than 0.45 with an increase in diffuser length up to 629 mm.

The reason for alter in drag amount when the diffuser angle increase can be explained in Fig. 9. This figure shows, that with increasing the diffuser angle, the pressure difference between the front of the car and its back increases; consequently, it causes to increase in the drag coefficient. Except for pickup truck cases with 40 degrees the diffuser angle has fluctuated pattern shown in Fig. 9. This is because while for all cases with increased spoiler degree, these difference increases, this case has the opposite influence. Therefore, the drag amount decreased and this caused a fluctuating pattern.

Figure 10 shows the rise in the diffuser length, the difference between front pressure and pressure at the end of the pickup truck with the same trend increased. As a result of this, the drag coefficient rises. Although, this pattern changed after the 329 mm diffuser length. This means that the pressure difference decrease with an increase in diffuser length, therefore, the drag coefficient drops with length increase.

As you can see from Fig. 11 as the diffuser angle is increased to 30 degrees, the negative lift coefficient increases, and the stability of the vehicle increases but as the angle increases, the negative lift coefficient decreases. On the other hand, as the diffuser length increases, the negative lift coefficient increases as the separation zone expands, and the stability of the vehicle increases.

Figure 12 illustrates that the diffuser attached to the rear end of the car raises the upper surface local air pressure which effectively increases the downward force that is known as negative lift; moreover, the rear diffuser not only changes the pressure on the top of the vehicle, which causes a pressure increase but the pressure on the underside is decreased. Therefore, with an increase in diffuser angle to 30 degrees, upper surface air pressure increases while at 40 degrees this amount decreases. This means a more negative lift in the 30-degree case than the 40-degree case. In addition, with an increase in diffuser length, upper surface air pressure increases this case raise in the negative lift.

4 − 3 Spoiler length and Double spoiler

To investigate the effect of the spoiler’s length, a zero-degree spoiler is placed behind the pickup cab. We increase the spoiler length from 200 mm to 600 mm with a difference of 100 mm; moreover, to study the simultaneous impact of two spoilers, insert a zero-degree ceiling spoiler at the back end of the pickup cabin and another spoiler at the downstream end of the pickup bed. Increase the spoiler angle at the end of the pickup room from negative 10 degrees to positive 40 degrees with a 10-degree angle difference. The modeled pickup truck with spoiler and double spoiler are depicted in Fig. 13.

it can be seen from Fig. 14 as the spoiler angle increases to 30 degrees, the drag coefficient increases to over 0.5 but then it falls in 40 degrees to almost 0.48. On the other hand, as the spoiler length increases to 500 mm with the opposite trend the amount of drag decrease to almost 0.42, which is the lowest drag amount. However in the opposite trend, the drag amount rais to over 0.42 with the increase in spoiler length up to 600 mm.

Figure 15 illustrated, that with an increase in the spoiler length, the pressure difference between the front of the pickup truck and the end decrease, this is less than pressure diffraction in the case without a spoiler. As a result, this causes a dropping pattern in drag amount. However, with an increase in spoiler degree, the pressure difference increases even more than the case without a spoiler. Therefore, the drag amount has the same increasing trend

As you can see from Fig. 16 by adding a spoiler and increasing its length behind the cabin roof, the negative lift coefficient decreases. On the other hand, Fig. 14 shows that by adding a spoiler behind the tailgate and changing its angle in the presence of a ceiling spoiler whose length and angle are constant, the negative lift coefficient increases with increasing angle.

Figure 17 illustrates that the spoiler attached to the car raises the upper surface local air pressure which effectively increases the downward force known as negative lift; moreover, using the rear spoiler and another spoiler behind the cabin roof together not only changes the pressure on the top of the vehicle, which causes a pressure increase; but the pressure on the underside is decreased. Therefore, an increase in rear spoiler angle causes to increase in the upper surface air pressure. This means more negative lift to be created. In addition, with an increase in spoiler length, upper surface air pressure increases and performs to raise in the negative lift.

4–4 Tailgate bumps

An aerodynamic device has been added to the top surface of the tailgate. This is a bump on the tailgate. To investigate the effect of this device on the drag coefficient and lift coefficient, we have increased its height from 65 mm to 225 mm by a ratio of 50 mm, and the results are compared with the no-bump model. The pickup truck model and tailgate bumps are depicted in Fig. 18.

Figure 19 shows the drag coefficient graph for the pickup, with no bumps and with bumps as you see up to 115 mm height, the addition of bumps reduces drag coefficient while with an increase in bumps height drag raise. Moreover, the case with 215 height of the bumps has more drag than the case without a bumper. On the other hand, Fig. 16 shows that adding bumps behind the tailgate and changing its height causes the negative lift coefficient to decrease.

As we can see from Fig. 20, with an increase in spoiler height, the pressure difference between the front of the pickup truck and the end increase which at the beginning is less than pressure diffraction in the case without tailgate bumps. As a result, this causes an increasing pattern in drag amount. In addition, with an increase in tailgate bumps height to 215, the pressure diffraction increased more than tailgate bumps less case. Therefore, this has more drag amount than a simple case.

Figure 20 illustrates that attaching tailgate bumps to a car decrease the upper surface local air pressure which effectively decreases the downward force known as negative lift; moreover, using tailgate bumps not only changes the pressure on the top of the vehicle, where it causes a pressure decrease but the pressure on the underside is increased. Therefore, with an increase in tailgate bumps height, cases upper surface air pressure decrease. This means less negative lift to be created.

This paper examines the strategies of reducing drag and increasing the negative lift applied to a pickup truck using computational fluid dynamics. External aerodynamic devices are positioned behind the roof of the cabin, at the rear end of the pickup bed, and on the tailgate. Three types of devices are evaluated: 1-The diffuser, which is at the lower end of the rear pickup 2-Spoiler, first by adding a spoiler to the back of the pickup cabin and Then add a spoiler to the end of the pickup in the presence of a roof spoiler 3-Bumps on pickup tailgate. Among these the best achievable reduction for the drag coefficient is achieved by adding the 500 mm ceiling spoiler; the drag coefficient reduction, in this case, is 9%. Moreover, the highest negative lift gain in the case of the 40-degree angle double spoiler with a difference of lift coefficient of 0.297. in addition, by reducing the diffuser length at a constant angle, the drag coefficient is reduced to 1%; moreover, adding bumps on the tailgate, reduces the drag coefficient by up to 3%.

Availability of data and materials

All data all are available in the manuscript

Competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Funding

The Shahid Chamran University of Ahvaz, Reza Bahoosh Grant number: SCU.EM1400.376.

Authors' contributions

1-Three types of devices are studied:

a-The diffuser, which is at the lower end of the rear pickup

b-Spoiler, first by adding a spoiler to the back of the pickup cabin and then add a spoiler to the end of the pickup in the presence of a roof spoiler

3-Bumps on pickup tailgate.

2- the drag coefficient is achieved by adding the 500 mm ceiling spoiler; the drag coefficient reduction, in this case, is 9%.

3. the highest negative lift achived in the case of the 40-degree angle double spoiler with a difference of lift coefficient of 0.297.

4. by reducing the diffuser length at a constant angle, the drag coefficient is reduced to 1%; moreover, adding bumps on the tailgate, reduces the drag coefficient by up to 3%.

Acknowledgment

The authors thank the reviewers and editor for the constructive comments. The authors would like to thank the Vice-chancellor for research, Shahid Chamran University of Ahvaz (Grant number: SCU.EM1400.376).

Authors' information

Reza Bahoosh: Associated Professor of the Mechanical Department of the Shahid Chamran University of Ahvaz, Ahvaz, Iran

Milad Rohani: MSc Student of Mechanical Department of the Shahid Chamran University of Ahvaz, Ahvaz, Iran

Mohammadreza Safarian: Associated Professor of the Mechanical Department of the Shahid Chamran University of Ahvaz, Ahvaz, Iran

*. Corresponding author: [email protected], [email protected]

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You are reading this latest preprint version

A Numerical Simulation for Improving the aerodynamics of a pickup truck by use of diffusers, spoilers, and bumps

Status:

Version 1

Abstract

Figures

1. Introduction

2. Geoetry Of Model

3. Governing Equations And Computational Domain

3 − 1 Computational Domain

3 − 2 Mesh independence

4. Results

4 − 1 Validation

4 − 2 Effect of the diffuser and its angle

4 − 3 Spoiler length and Double spoiler

4–4 Tailgate bumps

Conclusion

Declarations

Availability of data and materials

Competing interests

Funding

Authors' contributions

Acknowledgment

Authors' information

References

Status:

Version 1