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Drag reduction of a pickup truck by a rear downward flap
Abstract
The drag reduction of a pickup truck by a rear flap add-on was examined through CFD simulations and wind tunnel experiments.
When installed at the rear edge of the roof, the flap increased the cabin back surface pressure coefficient, causing the downwash
of the bed flow to be inclined on the tailgate. Thus, the attachment of the bed flow to the tailgate was eliminated; consequently,
the drag coefficient was reduced with increasing flap length and downward angle despite the enlarged reverse flow in the wake.
However, the drag coefficient did not decrease any further after a specific downward angle was reached because the bed flow
increased the drag force at the tailgate and the flap lowered the pressure field above the flap. To maximize the drag reduction
effect, the rear downward flap should be designed to have an optimum downward angle.
Key WordsPickup truck–Drag reduction–Rear flap–Downward angle–Bed flow–Attachment–Tailgate
... With budgets tight, gas prices on the rise, and fuel economy on everyone's mind, it is now more imperative than ever to invest in new energy-saving technologies among all products and services, including more energy efficient vehicles. In the automotive industry, trucks are known for their relatively higher drag coefficients [1][2][3][4][5][6][7][8] which suggest that there is room for improvement. ...
... Previous studies performed on academic geometries showed that proper modification of the flow topology around a vehicle can improve its aerodynamic performance by reducing drag [4][5][6][7][8]. Flow control devices, such as cabin flaps [6], continuous suction, and/or blowing solutions [9][10][11][12][13][14], were proven to offer promising results. ...
... Previous studies performed on academic geometries showed that proper modification of the flow topology around a vehicle can improve its aerodynamic performance by reducing drag [4][5][6][7][8]. Flow control devices, such as cabin flaps [6], continuous suction, and/or blowing solutions [9][10][11][12][13][14], were proven to offer promising results. A carefully designed cabin flap, for instance, can increase the cabin surface pressure coefficient and displace or even eliminate the attachment of the bed flow on the tailgate, eventually reducing the size of the reverse flow in the wake [6]. ...
The continuous surge in gas prices has raised major concerns about vehicle fuel efficiency, and drag reduction devices offer a promising strategy. In this paper, we investigate the mechanisms by which geometrically optimized bumps, placed on the rear end of the cabin roof of a generic truck, reduce aerodynamic drag. The incorporation of these devices requires proper choices of the size, location, and overall geometry. In the following analysis we identify these factors using a novel methodology. The numerical technique combines automatic modeling of the add-ons, computational fluid dynamics and optimization using orthogonal arrays, and probabilistic restarts. Numerical results showed reduction in aerodynamic drag between 6% and 10%.
... Previous studies have shown that improvement of vehicle performance and fuel efficiency is typically achieved by proper modifications of vehicle shape (Altaf et al., 2014;Fourrié et al., 2011;Ha et al., 2011;Hsu & Davis, 2010;Leuschen & Cooper, 2009;Mohamed-Kassim & Filippone, 2010;Nayeri et al., 2009;Zhang et al., 2019). Arbitrary modification of vehicle shape may lead to increase in aerodynamic drag and fuel consumption. ...
... Observations from this study agree with previous studies which show that reduction of aerodynamics drag (and in effect, improvement of vehicle performance and fuel efficiency) depends on proper modification of vehicle shape (Altaf et al., 2014;Fourrié et al., 2011;Ha et al., 2011;Hsu & Davis, 2010;Leuschen & Cooper, 2009;Mohamed-Kassim & Filippone, 2010;Nayeri et al., 2009;Zhang et al., 2019). A linear regression model is obtained from Figure 7 to predict as a function of . ...
Overspeeding and overloading contribute to road accidents. In developing countries, overloading is often indicated by open boot due to commercial transporters’ motivation to carry an excess load to boost revenue. Therefore, there is a need to provide measures to control or eliminate the practice of overspeeding and overloading. This study aims to conduct a parametric study to determine the effect of vehicle speed and boot opening on the aerodynamics of airflow around a typical minibus, fuel consumption, and CO2 emission, and recommend optimum boot opening. Computational Fluid Dynamics is employed using the FLUENT™ program. Results show the existence of a wavy pattern for drag coefficient, fuel consumption, and CO2 emission concerning boot opening. Furthermore, two boot opening regions exist: and . The first region exhibits low prediction error (maximum of 7.25%) and better fit of regression model to FLUENT™ data. The first region also has lower susceptibility to exhibit handling instability. Therefore, boot opening around is recommended as the optimum boot opening, to ensure minimum fuel consumption and CO2 emissions, improve handling and safety. The developed regression models could inform regulatory bodies’ formulation and implementation of policies to mitigate road accidents. Keywords—Boot Opening, CO2 emission, Fuel Consumption, Pressure drag, Total Drag, Minibus, Viscous Drag
... Several studies have concluded that proper vehicle design would be necessary to decrease the aerodynamic drag generated at the rear of vehicles [11]. In this sense, the literature identifies works focused on different vehicle devices, such as the state of the wheels [12] or the use of flaps [13]. Since air is a great source of energy in other energy systems such as wind energy, the concern of this research stems from the objective of taking advantage of the great force of the airflow impinging on vehicles, to transform a part of the problem into a competitive advantage. ...
In the automotive industry, the flow of air generates high resistance in the advance of vehicles. In light of this situation, the objective of the present invention is to take advantage of the force of the air itself to help propel vehicles and thus reduce fuel consumption. A channeling system has been designed based on a deflector that collects the air that impacts against the vehicle at the front, transferring it to the rear where it is expelled, allowing the vacuum zone to be filled so that the high pressures of the channeled air are repositioned in the depression zone, significantly increasing the values of the pressures, including those that were previously negative. The deflector has been built and incorporated into a model car so that comparative experimental wind tunnel tests could be carried out to verify that the vacuum in the rear area is eliminated, and positive pressure is obtained.
... 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 ap on the back of a pickup truck cab on the drag coe cient 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]. ...
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.
... Some studies have also been conducted on diverse aerodynamic passive control devices, for instance, splitter plates [12] and flaps [13,14]. However, sometimes disagreements have been encountered regarding the aesthetics and the performances of the cars, and these concepts were not applied. ...
The aerodynamic complexity of the underbody surfaces of conventional road vehicles is a matter of fact. Currently available literature is focused mainly on very simple Ahmed-body geometries as opposed to realistic car shapes, due to their complexity and computational cost. We attempted to understand the flow behaviour around different realistic conventional road car geometries, and we provide an extensive evaluation of the aerodynamic loads generated. The key findings of this article could potentially set a precedent and be useful within the automotive industry’s investigations on drag-reduction mechanisms or sources of downforce generation. The novelty of the work resides in the realistic approach employed for the geometries and in the investigation of barely researched aerodynamic elements, such as front diffusers, which might pave the way for further research studies. A baseline flat-underfloor design, a 7∘ venturi diffuser-equipped setup, a venturi diffuser with diagonal skirts, and the same venturi diffuser with frontal slot-diffusers are the main configurations we studied. The numerical predictions evaluated using RANS computational fluid dynamics (CFD) simulations deal with the aerodynamic coefficients. The configuration that produced the highest downforce coefficient was the one composed of the 7∘ venturi diffuser equipped with diagonal sealing skirts, achieving a CL value of −0.887, which represents an increase of around 1780% with regard to the baseline model. That achievement and the gains in higher vertical loads also entail a compromise with an increase in the overall air resistance. The performance achieved with diffusers in the generation of downforce is, as opposed to the one obtained with conventional wings, a cleaner alternative, by avoiding wake disturbances and downwash phenomena.
... Ha et al. researched the drag reduction of a pick-up by installing a downward flap at the rear edge of the roof. The results showed that the drag coefficient was reduced with the increasing flap length and downward angle [4]. Schaut et al. adopted trailer side-skirts and trailer boat-tail to reduce the aerodynamic drag of tractor-trailer and found that drag response was different under different operational constraints [5]. ...
... Their results showed that the two flaps on the rear side edges reduce the drag by 25%. Ha, et al. [9] used both experimental and computational approaches to study the effect of using a rear downward flap applied to a pickup truck. Their study reveals that the drag reduction is proportional to the flap length. ...
Road vehicles drag is a direct consequence of a large wake area generated behind. This area is created owing to the vehicle shape, which is determined by the class, functional and aesthetic of the vehicle. Aerodynamic characteristics are a ramification and not the reason for the vehicle architecture. To enhance pressure recovery in the wake region, hence reduce drag, three different passive flow control techniques were applied to sport-utility-vehicle (SUV). A three-dimensional SUV was designed in CATIA, and a numerical flow simulation was conducted using Ansys-Fluent to evaluate the aerodynamic effectiveness of the proposed flow control approaches. A closed rectangular flap as an add-on device modifies the wake vortex system topology, enhances vortex merging, and increases base pressure which leads to a drag reduction of 15.87%. The perforated roof surface layer was used to delay flow separation. The measured base pressure values indicate a higher-pressure recovery, which globally reflected in a drag reduction of 19.82%. Finally, air guided through side rams was used as steady blowing. A steady passive air jet introduced at the core of the longitudinal trailing vortices leads to a confined wake area. The net effects appear in a global increase in the base pressure values and the pronounced drag reduction of 22.67%.
... The general goal of these devices is to decrease the adverse aerodynamic drag force and to increase the favorable negative aerodynamic lift force (downforce) of race cars as to improve their overall aerodynamic performance. A decrease in the aerodynamic drag force reduces the fuel consumption of a car, which may be achieved with add-on devices such as downward flaps [4] and boat tails [5], using alternative surface smoothness [6] or modifying the synthetic jet array actuation [7]. Optimization of the cooling system may alter the drag force as well, [8]. ...
A computational model was developed to study aerodynamic forces acting on two closed-wheel race cars in the slipstreaming (drafting) arrangement, i.e., when the cars are characterized by the same driving speed and situated one directly behind the other one. A particular focus was on the influence of a distance between the two cars on flow characteristics and aerodynamic loads experienced by the cars. Computational fluid dynamics (CFD) simulations were performed for a steady viscous fluid flow using the realizable k-ε turbulence model and non-equilibrium wall functions. The results indicate some important findings. The leading car experiences the smaller drag force coefficient for all studied distances when compared to the single car case. For larger distances between the cars, the drag force coefficient of the trailing car is generally larger than for a single car due to a complex turbulent wake flow of the leading car (drag bubble) that impinges the trailing car. The drag force coefficient of the trailing car decreases when decreasing a distance from the leading car. The modifications of the lift force coefficient are more pronounced for the trailing car as there is a decrease in the negative lift force (downforce). The downforce coefficient is significantly smaller for the trailing car than for the single car configuration at all studied distances. A slight decrease in the downforce coefficient is present for the leading car as well.
... The elliptical flap obtains a maximum of 11.1% drag reduction, and the rest were below 6%. Another study on a pickup truck model was conducted by (Ha et al. 2011) using a flap and achieved a 5.6% drag reduction at a particular size and angle of the flap. Inspired by the secondary feather of birds, a new automatic moving deflector was applied at the 25° slant Ahmed body model by (Kim et al. 2016). ...
In this paper, a simple passive device is proposed for drag reduction on the 35° Ahmed body. The device is a simple rectangular flap installed at the slant surface of the model to investigate the effect of slant volume, formed between the device and the slant surface, on the flow behaviour. The slant volume can be varied by changing the flap angle. This investigation is performed using the FLUENT software at a Reynolds number of 7.8 × 10 5 based on the height of the model. The SST k-omega model is used to solve the Navier-stokes equations. It is found that this passive device influences the separation bubbles created inside the slant volume and provides a maximum drag reduction of approximately 14% at the flap angle of 10°. Moreover, the device delays the main separation point, which changes the flow conditions at the back of the model. The drag reduction was found to mainly dependent on the suppression of the separation bubbles formed inside the slant volume, which leads to faster pressure recovery. The cause of this pressure recovery is found to be the reduction in recirculation length and width. Also, the addition of a flap reduces the turbulent kinetic energy, which lessened the wake entrainment in the recirculation region, leading to a drag reduction. Also, it hinders the formation of horseshoe vortex that provides a pressure recovery and influence the wake width. However, the investigation also reveals that this device does not reduce the induced drag due to longitudinal vortex from the side edges.
... As applied to some automobiles and SUVs, a rear flap might be installed on a pickup truck. Both experimental and numerical results imply that when a rear flap is placed on the rear part of a roof, the flap increases the cabin pressure coefficient and consequently causes the bed flow to move downward and incline on the tailgate [13]. It was concluded that the drag coefficient can also be reduced by attaching the bed flow to the tailgate and increasing length of the flap. ...
In the present study, aerodynamic properties of modified generic pickup trucks were investigated by means of finite volume method. Steady, three-dimensional and turbulent flows over the pickup trucks were solved by standard k-epsilon turbulence model. An experimentally investigated two-dimensional pickup truck found in the open literature was used as a benchmark case and some modifications were done on it by closing the sides of the bed first. Then a tonneau was used to close the top of the box and finally, a canopy was used to cover the box completely from the tailgate to the cab roof. Simulations reveal that such modifications that were done on the reference case improve the aerodynamic characteristics of the vehicles in terms of drag coefficient. With respect to the original case, the drag coefficient reduces approximately 50%, 30% and 20% by using a canopy, a tonneau and closing all sides except top of the bed. Such decreases in drag coefficient was achieved because every modification prevents the flow separation more effectively around the bed and behind the cab. Regardless of the shape of the bed, the drag coefficient decreases with increasing Reynolds (Re) number up to Re=120000. It seems that this is the critical Reynolds number since drag coefficient does not change considerably with Re any more.
... As applied to some automobiles and SUVs, a rear flap might be installed on a pickup truck. Both experimental and numerical results imply that when a rear flap is placed on the rear part of a roof, the flap increases the cabin pressure coefficient and consequently causes the bed flow to move downward and incline on the tailgate [13]. It was concluded that the drag coefficient can also be reduced by attaching the bed flow to the tailgate and increasing length of the flap. ...
In the present study, aerodynamic properties of modified generic pickup trucks were investigated by means of the finite volume method. Steady, three-dimensional and turbulent flows over the pickup trucks were solved by standard k-epsilon turbulence model. An experimentally investigated two-dimensional pickup truck found in the open literature was used as a benchmark case and some modifications were done on it by closing the sides of the bed first. Then a tonneau was used to close the top of the box and finally, a canopy was used to cover the box completely from the tailgate to the cab roof. Simulations reveal that such modifications that were done on the reference case improve the aerodynamic characteristics of the vehicles in terms of the drag coefficient. With respect to the original case, the drag coefficient reduces approximately 50%, 30%, and 20% by using a canopy, a tonneau and closing all sides except the top of the bed. Such decreases in drag coefficient were achieved because every modification prevents the flow separation more effectively around the bed and behind the cab. Regardless of the shape of the bed, the drag coefficient decreases with increasing Reynolds (Re) number up to Re=12010 3. It seems that this is the critical Reynolds number since the drag coefficient does not change considerably with Re any more.
... Chien-hsiung et al. used CFD to study the influence of loading rear wing on automobile, and the research showed that rear wing can improve the longitudinal stability of automobile [2]. J.Ha et al. used the sedan car model to study the influence of the rear wing on car, and studies show that it is better to load the rear wing above the rear trunk of car [3]. Kang S.O et al.'s research shows that changing the shape of the car's tail can also improve aerodynamic performance without the using rear wing [4]. ...
Using the MIRA model and rear wing of UIUC database model study the influence of the rear wing on the car's aerodynamics. The aerodynamics of seven different positions of the rear wing and unloaded rear wing are compared under the same attack angle. Numerical simulation finds that because of the rear wing's setting, the vortex at the top of the truck and rear of the car are decreased, so the pressure drag of the car and the drag coefficient are increased. The rear wing also destroy the vortex of the car, which increases the negative lift coefficient. The results show that the vehicle can acquire maximum lift coefficient when B/H is 45%. The influence of the car gradually disappeared when the height of the rear wing increases to a certain level. The vehicle will acquire greater negative lift in faster speed.
... These characteristics can be improved by employing various body shapes and add-on devices, e.g. Ha et al. (2011), Bruneau et al. (2012), Kang et al. (2012), Buljac et al. (2015). ...
Computational model was developed to investigate aerodynamic forces acting on a closed-wheel race car. A particular focus was on the effects of ground clearance and rake angle on aerodynamic drag and lift forces. Computations were performed for a steady viscous fluid flow using the realizable k-ε turbulence model and non-equilibrium wall functions. The computational results indicate a strong influence of ground clearance and rake angle on aerodynamic loading of a race car. The largest drag force coefficient was obtained for the largest ground clearance. The drag force coefficient for the squatting car is larger by 5% compared to the reference case, where the both front and rear ground clearances are 100 mm. For the nose-diving car, the drag force coefficient is equal to the reference case. Increasing the ground clearance caused a negligible increase in the lift force coefficient in comparison with the reference case. A decrease in the ground clearance yielded an increase in the lift force coefficient. The largest positive lift force coefficient was obtained for a squatting car, whereas the largest negative lift force coefficient was observed for a nose-diving car. While the favorable aerodynamic downforce acting on front wheels is larger for a nose-diving car, for rear wheels it is larger for a squatting car.
... The ability of these tools have been analyzed by different researchers [17][18][19][20][21][22] and the flow behavior has been studied in detail. There are different flow control strategies that have been offered by the literature [11,23,24] in which use of passive devices is one of the ways to reduce the drag [25][26][27][28] . Various approaches as regards to these devices were explored and their effect was evaluated. ...
This paper presents a numerical study of drag reduction technique using passive flow device around a realistic car model. The model used in this investigation is Ahmed body, at the rear top of which a deflector is installed. Model is generated using the commercial package GAMBIT and simulations are performed in FLUENT to obtain the flow characteristics. The investigation is performed by sorting out the grid independence issues so as to have the less deviation from the accurate results. The performance of deflector is thereafter analyzed to determine the angle at which maximum possible drag reduction can be obtained. The deflector angles are varied from −25° to 60° at two inlet flow velocities of 16 m/s and 40 m/s. The results obtained are subsequently compared with the already obtained experimental values in literature and a good conformity is acquired. Further, the effect of two extra inlet flow velocities i.e. 20 m/s and 30 m/s is also studied to have the meticulous scrutiny of the flow behavior. After carrying out the complete study, a 7% decrease in the drag coefficient is obtained with respect to the case when there is no deflector.
... Castejon et al. 14 achieved automobile drag reduction for the SAE model (proposed by Society of Automotive Engineers) without reducing the automobile aerodynamic stability. The drag reduction of a pickup truck by a rear downward flap was examined computationally and experimentally in the study of Ha et al. 15 Fourrie et al. 16 carried out experimental investigations to study the drag reduction in a generic car model using a deflector. They achieved a drag reduction of up to 9%. ...
In this study, we attempted a novel drag reduction technique for 25° and 35° Ahmed models by experimenting with two types of flap structures, respectively, added to the slant edges of the two models. Different pairs of flaps were added at various angles compared to the slant for the sake of comparison. The study comprehensively analyzed the effects of the "big-type" and "small-type" flaps on the aerodynamic drag and near wake of an Ahmed model in a greater range of flap mounting angles. Parametric analysis results confirmed that large and small flaps are most efficient when configured on the 25° Ahmed model at specific angles; up to 21% pressure coefficient reduction was achieved for the 25° Ahmed model (flap configurations at slant side edge) and 6% for the 35° Ahmed model (flap configurations at both slant side and top edges). The velocity and pressure contours indicated that the key to drag reduction is to weaken (if not eliminate) the longitudinal vortex created at the side edges of the rear slant.
... Wassen et al. [15] studied the drag reduction of a road vehicle by steady blowing. Ha et al. [16] researched the drag reduction of a pick-up truck by using rear flaps. ...
The most important consideration in " Formula One " (F1) car design is Aerodynamics. " Aerodynamics " is the way air moves around things [1]. It is the difference between championship challenging car and a tail car [2]. Simply, F1 car aerodynamics design has to consider primary concerns: minimizing drag resulting from air resistance; and increasing downforce to push the car tires onto the track and stabilize the car during cornering. This paper discusses the aerodynamics and the resulting forces on F1 car body using CFD. Solidworks 2015 software [3] was employed to create the 3D model used in the simulation. The model was available on GrabCAD [4]. Also, ANSYS Fluent, v.17.1 [5] was used to simulate and analyze the aerodynamics of the car when it is running in a straight line, and cornering. Drag and lift coefficients, velocity streamlines and pressure contours were calculated and presented as results of this simulation.
... For the front wing, the wind incidence angle considerably influences flow characteristics around the vehicle (Diasinos and Gatto, 2008). In addition to sedan-type vehicles, the rear wings proved to be effective for trucks as well (Ha et al., 2011), while aerodynamically shaping the rear part of the vehicles can yield improvements in vehicle aerodynamics, even though the wings and spoilers are not used . In addition to other important issues, wheel rotation is observed to influence aerodynamics of vehicles as well (Fackell and Harvey, 1975). ...
Computational model is developed to analyze aerodynamic loads and flow characteristics for an automobile, when the rear wing is placed above the trunk of the vehicle. The focus is on effects of the rear wing height that is investigated in four different positions. The relative wind incidence angle of the rear wing is equal in all configurations. Hence, the discrepancies in the results are only due to an influence of the rear wing position. Computations are performed by using the Reynolds-averaged Navier-Stokes equations along with the standard k-ε turbulence model and standard wall functions assuming the steady viscous fluid flow. While the lift force is positive (upforce) for the automobile without the rear wing, negative lift force (downforce) is obtained for all configurations with the rear wing in place. At the same time, the rear wing increases the automobile drag that is not favorable with respect to the automobile fuel consumption. However, this drawback is not that significant, as the rear wing considerably benefits the automobile traction and stability. An optimal automobile downforce-to-drag ratio is obtained for the rear wing placed at 39 % of the height between the upper surface of the automobile trunk and the automobile roof. Two characteristic large vortices develop in the automobile wake in configuration without the rear wing. They vanish with the rear wing placed close to the trunk, while they gradually restore with an increase in the wing mounting height. © 2016, The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg.
... Additionally, Ha Jong Su and Obayashi did research on the about drag reduction of a pickup truck by using rear flaps (Int. J. Automotive Technology, 2011.)[11] Likewise, there are many studies and experiments on the aerodynamic performance of an automobile. ...
A paper submitted to the 6th SNU-Tohoku Joint Workshop on Next Generation Aero Vehicle, 13-14, Oct., 2011, Seoul National University
... Depending on various configurations, the drag could be reduced by 25% and lift by 107%. Ha et al. [7] carried out experimental and computational study of drag reducing capability of a rear downward flap on a pickup truck. They found that the C D was reduced with the increasing flap length. ...
This paper presents a review of the techniques used to reduce aerodynamic drag over bluff bodies such as cylinders, spheres, 2D bodies with blunt backs and their application to commercial road vehicles. The recent research carried out on the drag reduction is presented and categorised. A new classification of the techniques is introduced and major contributions under them are shown. It can be concluded that there is not much work done with realistic 3D bluff bodies, especially using passive methods.
... Wassen et al. (2010) investigated the drag reduction of a road vehicle by steady blowing. Finally, Ha et al. (2011) researched the drag reduction of a pick-up truck by using rear flaps. ...
This study proposes an aerodynamically optimized outer shape of a sedan by using an Artificial Neural Network (ANN), which focused on modifying the rear body shapes of the sedan. To determine the optimization variables, the unsteady flow field around the sedan driving at very fast speeds was analyzed by CFD simulation, and fluctuations of the drag coefficient (CD
) and pressure around the car were calculated. After consideration of the baseline result of CFD, 6 local parts from the end of the sedan were chosen as the design variables for optimization. Moreover, an ANN approximation model was established with 64 experimental points generated by the D-optimal methodology. As a result, an aerodynamically optimized shape for the rear end of the sedan in which the aerodynamic performance is improved by about 5.64% when compared to the baseline vehicle is proposed. Finally, it is expected that within the accepted range of shape modifications for a rear body, the aerodynamic performance of a sedan can be enhanced so that the fuel efficiency of the sedan can be improved. The YF SONATA, a sedan manufactured by Hyundai Motors Corporate, played a major role in this research as the baseline vehicle.
... solutions reviewed in previous studies for passive flow control, Gillieron and Kourta (2009) proposed the use of splitter plates as a type of drag reduction for a simplified form of car geometry. Beaudoin and Aider (2008) presented an experimental study of flow control using flaps over a classic 3D bluff-body and achieved a level of drag reduction. Ha et al. (2011) performed a study of the drag reduction of a pickup truck using rear flaps. Singh (2003) developed an aerodynamic design optimization process for an automotive vehicle that changes the shape of the trunk to achieve a reduction of drag. For active flow control, Geropp and Odenthal (2000) performed a jet-blowing experiment to increase the ...
This research aims to develop an actively translating rear diffuser device to reduce the aerodynamic drag experienced by passenger cars. One of the features of the device is that it is ordinarily hidden under the rear bumper but slips out backward only under high-speed driving conditions. In this study, a movable arc-shaped semi-diffuser device, round in form, is designed to maintain the streamlined automobile’s rear underbody configuration. The device is installed in the rear bumper section of a passenger car. Seven types of rear diffuser devices whose positions and protrusive lengths and widths are different (with the basic shape being identical) were installed, and Computational Fluid Dynamics (CFD) analyses were performed under moving ground and rotating wheel conditions. The main purpose of this study is to explain the aerodynamic drag reduction mechanism of a passenger car cruising at high speed via an actively translating rear diffuser device. The base pressure of the passenger car is increased by deploying the rear diffuser device, which then prevents the low-pressure air coming through the underbody from directly soaring up to the rear surface of the trunk. At the same time, the device generates a diffusing process that lowers the velocity but raises the pressure of the underbody flow, bringing about aerodynamic drag reduction. Finally, the automobile’s aerodynamic drag is reduced by an average of more than 4%, which helps to improve the constant speed fuel efficiency by approximately 2% at a range of driving speeds exceeding 70 km/h.
Aerodynamic force is known as one of the most important attributes, which has significant weight on fuel consumption and vehicle performance. In this paper, minimising drag coefficient is performed considering modification of rear end factors. To this end, five geometrical parameters of a hatchback car are chosen as design factors in two levels: (1) rear spoiler length, (2) rear spoiler angle, (3) rear diffuser angle, (4) boat tail angle (5) fifth door height. Main and interaction effects of these factors on drag coefficient are investigated using design of experiments and optimum level for each parameter is achieved. Computational fluid dynamic method is applied to evaluate air stream around the car. To reduce the number of simulations fraction, factorial design algorithm is applied which decreased the number of case studies to half. Characteristics of airflow around optimum car model are discussed and reported at the end.
Since high speed automobiles become common nowadays, reducing the lift coefficient to enhance stability on the road is not just the concern of race cars anymore. Underbody diffusers are one of the well known devices for reducing lift force of the moving vehicle. First, the three dimensional flow over simple car model, namely Ahmed model was simulated. Flow pattern and the results for aerodynamic forces were in good agreement with experimental results. In addition, the same method was utilized to investigate the effect of diffuser and additional splitters on lift and drag coefficients of the models. The popular SST k-ω turbulence model was used to assess aerodynamic forces as well as pressure and velocity distribution. The study provides a good comparison between different amounts of end plates which makes it easier to decide the optimum model.
In this study, the air resistance is studied by using flow analysis near automotive body due to the its shape. Flow velocities of airs entering into inlet plane are two kinds of 70 km/h and 100 km/h. Air resistance in case of high speed driving(100 km/h) becomes higher than regular speed driving(70 km/h) and the resistance in case of the car with wider cross section at front side becomes higher than narrower cross section. By using this analysis result, the shape of automotive body can be effectively designed in order to reduce the air resistance.
This study proposed an aerodynamically optimized outer shape of a sedan using Artificial Neural Network (ANN) and focused its attention on modifying the rear body shapes of the sedan. To determine the optimization variables, the unsteady flow field around the sedan cruising very fast was scrutinized by CFD simulation, and thereby, the fluctuations of the drag coefficient (CD) and pressure around were confirmed. Regarding the baseline result for CFD, 6 local parts of the end from the sedan were chosen as the design variables for the optimization. Moreover, the ANN approximation model was established with 64 experimental points generated by the D-optimal methodology. As a result, an aerodynamically optimized shape for the rear end of the sedan in which the drag was minimal was proposed with its aerodynamic performance improving by about 5.517%, compared with that of the baseline. Finally, it is expected that in the proper range of shape modifications for a rear body, the aerodynamic performance of a sedan can be enhanced, and thereby, the fuel efficiency of the sedan can be improved. The YF SONATA, a sedan manufactured by Hyundai Motors Company, played a major role in this research as the baseline vehicle.
The goal of this study is to develop an actively translating rear diffuser device to reduce the aerodynamic drag experienced by passenger cars. The feature of this device is hidden under the rear bumper ordinarily not to ruin the external design of the car and slips out backward under the high-speed driving condition. By this study, a movable arcshaped semi-diffuser device is designed to maintain the streamlined automobile rear underbody configuration. It's installed under the rear bumper of a passenger car.
Aerodynamic force plays an important role in vehicle performance and its stability when vehicle reaches higher speed. Nowadays the maximum speed of car has been increased above 180 km/hr but at this speed the car has been greatly influenced by drag and lift forces. So the researchers are mainly focused in reduction of coefficient of drag and lift in car model at higher speed. Even though the various techniques are found by researchers for improving vehicle performance and its stability still we are in need of further improvement So we are implementing vortex generator as a aerodynamic add on device at rear portion of vehicle. The various yaw angles and location of vortex generator are analyzed to obtain the efficient one to reduce the aerodynamic forces. An approximate outer profile of the typical sedan car body (Hyundai Elantra) which has a Coefficient of drag value CD (0.35) has been generated in two configurations of with and without vortex generator by using solid modeling software and it has been analyzed using computational fluid dynamics (CFD) tool to reduce the aerodynamic drag and lift forces. Results show good improvement in reduction of above two forces by implementation of vortex generators on the car body.
An experimental investigation of turbulent flow over complex two-dimensional bluff bodies using a particle image velocimetry (PIV) technique is reported. The study obtained extensive data sets and documented the salient features of these complex flows using the mean flow and turbulent quantities as well as proper orthogonal decomposition (POD) analysis. The results indicate that all the turbulent quantities increased with downstream distance and test model distance from the test section floor as well as cavity depth but no significant increase in turbulence with the cavity length. The triple velocity correlations indicate that there is negative transport of turbulence kinetic energy in the streamwise direction close to the test section floor but positive transport away. The bulk of turbulence was produced close to the test models and transported away. The POD modes with the same symmetry appeared to be similar in shape, but shifted in the streamwise direction. This similarity in symmetry suggests "pairing" between the first and second POD modes.
Bluff body vehicles such as trucks and buses do not have a streamlined shapes and hence have high drag which can be reduced to make great savings in operational cost. While rectangular flaps have been widely studied as both passive add-ons and in active drag reducing systems for bluff bodies, changing the basic geometry of the flap has not been explored in literature. In this work, a baseline drag value is obtained for a simplified MAN TGX series truck in a CFD software, and the drag reduction of a proposed elliptically shaped flap is compared to aerodynamically equivalent rectangular flaps. The optimal mounting angle for both flaps is found to be 50°. A parametric study of changing the ellipse semi-major axis is carried out to find the optimal length for drag reduction. A maximum drag reduction of 11.1% is achieved using an elliptical flap with 0.12 m semi-major axis; compared to 6.37% for a length equivalent rectangular flap, and 6.84% for a surface area equivalent rectangular flap. Results of the pressure distribution and velocity flow behind the rear of the truck are also given and analyzed.
A complete transient, three dimensional simulation of the flow-field around a generic pickup truck geometry is carried out. A 1/12-scale replica of an actual pickup truck, with simplified features such as a smooth underbody, is considered in the study. The purpose of the study is twofold. First, it seeks to improve our understanding of the complex flow field around a pickup truck, which is predominantly a bluff body with a prominent wake. To this end a detail description of the time-averaged pressure distribution on the vehicle body as well as time-averaged velocities in the wake of the truck is provided. Secondly, the study seeks to judge the accuracy with which modern CFD techniques can predict complex, practical, bluff-body wake flows. This is accomplished by making a close comparison of the time-averaged wake velocity profiles predicted by CFD with analogous measurements made in a wind tunnel experiment using particle image velocimetry. CFD simulations are carried out with an unstructured finite-volume method based Navier-Stokes solver in conjunction with the RNG k-e and LES turbulence models. Simulation results are compared with experimental data reported elsewhere in literature.
This paper describes a computational and experimental effort to document the detailed flow field around a pickup truck. The major objective was to benchmark several different computational approaches through a series of validation simulations performed at Clemson University (CU) and overseen by those performing the experiments at the GM R&D Center. Consequently, no experimental results were shared until after the simulations were completed. This flow represented an excellent test case for turbulence modeling capabilities developed at CU. Computationally, three different turbulence models were employed. One steady simulation used the realizable k- model. The second approach was an unsteady RANS simulation, which included a turbulence closure model developed in-house. This simulation captured the unsteady shear layer rollup and breakdown over the front of the hood that was expected and seen in the experiments but unattainable with other off-the-shelf turbulence models. Details of the high performance computing effort required to produce these results are discussed. The third simulation employed a new closure model designed to include the effects of small-scale unsteadiness on the mean flow without actually performing time-accurate simulations. As expected, this reduces CPU time, disk storage, and data I/O times significantly. In this case, CPU time was reduced by 95%. An approach of this nature would greatly reduce design time and make CFD a more feasible option.
Simple devices have been shown to be capable of tailoring the flow field around a vehicle and reducing aerodynamic drag. An experimental and computational investigation of a drag reduction device for bluff bodies in ground proximity has been conducted. The main goal of the research is to gain a better understanding of the drag reduction mechanisms in bluff-body square-back geometries. In principle, the device modifies the flow field behind the test model by disturbing the shear layer. As a consequence, the closure of the wake is altered and reductions in aerodynamic drag of more than 20 percent are observed. We report unsteady base pressure, hot-wire velocity fluctuations and Particle Image Velocimetry (PIV) measurements of the near wake of the two models (baseline and the modified models). In addition, the flows around the two configurations are simulated using the Reynolds Averaged Navier-Stokes (RANS) equations in conjunction with the V2F turbulence model. In order to capture the oscillating behavior of the wake the equations are solved in their unsteady form. The mean pressure results show a significant increase in the base pressure with the drag reduction device. For the present geometries, the drag reduction device suppresses large-scale turbulent motions in the wake. The results show a reduction of the turbulence intensity as well as a rapid upward deflection of the underbody flow with the device in place. The effect of the drag reduction device on the length of the recirculation region in the near wake is small. Furthermore, the results confirm that the separated flow from the trailing edge of the model reattaches on the extended plate (add-on device) which is similar to that of a boat-tail effect. This boat-tail effect is documented by mean flow streamlines that show the dividing streamlines originating at the tip of the plates making the recirculation region narrower even though the main recirculation length does not change. Finally, both the measurements and simulations reveal that the instantaneous flow fields differ significantly from the averaged ones.
The results of an experimental investigation of the flow over a pickup truck are presented. The main objectives of the study are to gain a better understanding of the flow structure in near wake region, and to obtain a detailed quantitative data set for validation of numerical simulations of this flow. Experiments were conducted at moderate Reynolds numbers (~3×10 5 ) in the open return tunnel at the University of Michigan. Measured quantities include: the mean pressure on the symmetry plane, unsteady pressure in the bed, and Particle Image Velocimetry (PIV) measurements of the flow in the near wake. The unsteady pressure results show that pressure fluctuations in the forward section of the bed are small and increase significantly at the edge of the tailgate. Pressure fluctuation spectra at the edge of the tailgate show a spectral peak at a Strouhal number of 0.07 and large energy content at very low frequency. The velocity field measurements in the symmetry plane show that shear layers form at the top of the cab and the underbody flow region. The cab shear layer evolves more slowly than the underbody flow shear layer and does not interact strongly with the tailgate for the present geometry. Behind the tailgate there is no recirculating flow region in the symmetry plane believed to be due to downwash from streamwise vorticity in the near wake. There are small recirculating regions on the sides of the tailgate symmetry plane extending approximately one tailgate height downstream.
Copyright © 2002 SAE International. This paper is posted on this site with permission from SAE International, and is for viewing only. Further distribution and use of this paper is not permitted without permission from SAE. This paper was part of the SAE 2002 World Congress, Detroit, Michigan, March 4th-7th 2002. Growing concerns about the environmental impact of road vehicles will lead to a reduction in the aerodynamic drag for all passenger cars. This includes Sport Utility Vehicles (SUVs) and light trucks which have relatively high drag coefficients and large frontal area. The wind tunnel remains the tool of choice for the vehicle aerodynamicist, but it is important that the benefits obtained in the wind tunnel reflect improvements to the vehicle on the road. Coastdown measurements obtained using a Land Rover Freelander, in various configurations, have been made to determine aerodynamic drag and these have been compared with wind tunnel data for the same vehicle. Repeatability of the coastdown data, the effects of drag variation near to zero yaw and asymmetry in the drag-yaw data on the results from coastdown testing are assessed. Alternative blockage corrections for the wind tunnel measurements are examined. A reasonable correlation between wind tunnel and on-road aerodynamic drag data is established for the configurations tested. Published
Aim of this study is to investigate an aerodynamic effect of a drag-reducing device on a heavy-duty truck. The vehicle experiences two different kinds of aerodynamic forces such as drag and uplifting force (or downward force) as it is traveling straight forward at constant speed. The drag force on a vehicle may cause an increase of the rate of fuel consumption and driving instability. The rolling resistance of the vehicle may be increased as result of the negative uplifting or downward force on the vehicle. A device named roof-fairing system has been applied to examine the reduction of aerodynamic drag force on a heavy-duty truck. As for a engineering design information, the drag-reducing system should be studied theoretically and experimentally for the best efficiency of the device. Four different types of roof-fairing model were considered in this study to investigate the aerodynamic effect on a model truck. The drag and downward force generated by vehicle has been obtained from numerical calculation conducted in this study. The forces produced on four fairing models considered in this study has been compared each other to evaluate the best fairing model in terms of aerodynamic performance. The result shows that the roof-fairing mounted truck has bigger negative uplifting or downward force than that of non-mounted truck in all speed ranges, and drag force on roof-fairing mounted truck has smaller than that of non-mounted truck. The drag coefficient (CD) of the roof-fairing mounted truck (Model-3) is reduced up to 41.3% than that of non-mounted trucks (Model-1). A downward force generated by a roof-fairing mounted on a truck is linearly proportional to the rolling resistance force. Therefore, the negative lifting force on a heavy-duty truck is another important factor in aerodynamic design parameter and should be considered in the design of a drag-reducing device of a tractor-trailer. According to the numerical result obtained from present study, the drag force produced by the model-3 has the smallest of all in all speed ranges and has reasonable downward force. The smaller drag force on model-3 with 2/3h in height may results of smallest thickness of boundary layer generated on the topside of the container and the lowest intensity of turbulent kinetic energy occurs at the rear side of the container.
Low speed wind tunnel measurements are made on a 1/16th scale generic tractor-trailer model at a width-based Reynolds number of 325,000. The model is fixed to a turntable, allowing the yaw angle to be varied between {+-}14 degrees in 2 degree increments. Various add-on drag reduction devices are mounted to the model underbody and base. The wind-averaged drag coefficient at 65 mph is computed for each configuration, allowing the effectiveness of the add-on devices to be assessed. The most effective add-on drag reduction device for the trailer underbody is a wedge-shaped skirt, which reduces the wind-averaged drag coefficient by 2.0%. For the trailer base, the most effective add-on drag reduction device is a set of curved base flaps having a radius of curvature of 0.91 times the trailer width. These curved base flaps reduce the wind-averaged drag coefficient by 18.8%, providing the greatest drag reduction of any of the devices tested. When the wedge-shaped skirt and curved base flaps are used in conjunction with one another, the wind-averaged drag coefficient is reduced by 20%.
In this study, a numerical simulation has been carried out for three-dimensional turbulent flows around a bluff-based bus-like body and actual bus body. The first step of this study is to verify the effectiveness of the CFD analysis. In the second step, to reduce the drag of the actual bus model, parameter studies are performed with attention to effective utilisation of the rear-spoiler equipped at the roof-end of upper body. From the results of this study, it is clear that the adoption of RNG k-ε turbulence model and nonlinear quadratic turbulence model with the second order accurate discretisation scheme predicts, fairly well, the aerodynamic coefficients. The results also show that the aerodynamic drag for a commercial bus can be reduced by 14% with the use of a drag reduction device.
The bed is one of the most important parts of a pickup truck for aerodynamic performance. The flow characteristics of a pickup truck were examined in a series of wind tunnel experiments and numerical simulations with regard to the bed geometry variation, the bed length, and the bed height. The drag coefficient was changed in accordance with the bed geometry variation so that the bed length and bed height had a significant interaction effect. The main factors that affected the drag coefficient were the bed recirculation flow over the bed and the reverse flow in the wake. The drag coefficient increased when the downwash of the bed flow was not recirculated into the bed but was attached to the upper part of the tailgate. The larger reverse flow in the wake and the enlarged adverse pressure area inside the bed influenced the drag increment when there was no attachment of the bed flow. For a low-drag pickup truck, the bed should be designed such that the bed flow is not attached to the tailgate and the reverse flow in the wake is small.
Two new two-equation eddy-viscosity turbulence models will be presented. They combine different elements of existing models that are considered superior to their alternatives. The first model, referred to as the baseline (BSL) model, utilizes the original k-omega model of Wilcox In the inner region of the boundary layer and switches to the standard k -epsilon model in the outer region and in free shear flows. It has a performance similar to the Wilcox model, but avoids that model's strong freestream sensitivity. The second model results from a modification to the definition of the eddy-viscosity in the BSL model, which accounts for the effect of the transport of the principal turbulent shear stress. The new model is called the shear-stress transport-model and leads to major improvements in the prediction of adverse pressure gradient flows.