energies

Article Aerodynamic Effect of the Gurney on the Front Wing of a F1 Car and Flow Interactions with Car Components

Mattia Basso, Carlo Cravero * and Davide Marsano

Dipartimento di Ingegneria Meccanica, Energetica, Gestionale e dei Trasporti (DIME), Università degli Studi di Genova, Via Montallegro 1, 16145 Genova, Italy; [email protected] (M.B.); [email protected] (D.M.) * Correspondence: [email protected]

Abstract: The design of a racing car needs several aerodynamic design steps in order to achieve high performance. Each component has an aerodynamic interaction with the others and high performance requires a good match between them. The front wing is undoubtedly one of the main components to determine car performance with a strong interaction with the downstream components. The Gurney Flap (GF) is a small appendix perpendicular to the pressure side of the front wing at the that can dramatically improve the front wing performance. In the literature, the performance of a GF on a single profile is well documented, while in this paper the GF mounted on the front wing of a racing car has been investigated and the interactions through the 3D flow structures are discussed. The global drag and performance on the main components of the vehicle have been examined by comparing the cases with and without a GF. The GF increases the downforce by about 24% compared to a limited increase in the drag force. A fluid dynamic analysis has been carried out  to understand the physical mechanisms of the flow interaction induced to the other components. The  GF, in fact, enhances the ground effect, by redistributing the flow that interacts differently with the Citation: Basso, M.; Cravero, C.; other components i.e., the wheel zone. Marsano, D. Aerodynamic Effect of the Gurney Flap on the Front Wing of Keywords: racing car; front wing; gurney flap; CFD a F1 Car and Flow Interactions with Car Components. Energies 2021, 14, 2059. https://doi.org/10.3390/ en14082059 1. Introduction In Formula 1 (F1), front wings are one of the main components for the aerodynamic Academic Editor: Jorge M. M. Barata performance of the car. They have been the subject of massive studies that have led to the current configurations after a continuous phase of development since the 1950s. The Received: 5 March 2021 introduction of CFD techniques, associated with an available computational resources Accepted: 6 April 2021 Published: 8 April 2021 increase, has significantly contributed to the development of ever-increasing aerodynamic performance for the entire vehicle. The changes made to the vehicles over the years have

Publisher’s Note: MDPI stays neutral been carried out according to variations that have undergone the various tracks of the with regard to jurisdictional claims in world championship. They have become increasingly short and complex over time, and published maps and institutional affil- the main objective for cars has moved from reaching their maximum speed to reaching iations. their maximum acceleration. The aerodynamic components designed to have as low drag as possible have been improved to enhance the tire traction during steering and braking, i.e., maximizing the downforce. Typically, the front wing is responsible for 25% of the total downforce generated. The complexity of a front wing has been studied [1] and it is still a crucial issue. The Gurney Flap (GF) is a small supplement mounted perpendicularly Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. to the pressure side of a wing along the trailing edge that brings a series of aerodynamic This article is an open access article improvements to the car. In racing vehicles, this component has a height of 1%–5% as distributed under the terms and the ratio between its height and the of the wing. The macroscopic effect of the flap conditions of the Creative Commons is an increased flow deflection due to both flow recirculation on the pressure side and Attribution (CC BY) license (https:// increased lower base pressure at the trailing edge [2]. This increases the aerodynamic creativecommons.org/licenses/by/ loading and therefore the downforce. Local effects of the suction side separation bubble at 4.0/). low height from the ground can increase the related drag. Nevertheless, the aerodynamic

Energies 2021, 14, 2059. https://doi.org/10.3390/en14082059 https://www.mdpi.com/journal/energies Energies 2021, 14, 2059 2 of 15

efficiency (downforce/drag) with a proper flap dimension can increase with respect to baseline airfoil configuration [3]. If the Gurney is mounted on thicker the drag can be reduced because the vortices break off further downstream on the profile, keeping the boundary layer attached and stable for a wider incidence and ground height range with respect to the baseline case [2]. In several experimental works, the geometrical data of the GF have been optimized according to the application [3–5]. Experimental analysis using hot anemometers has shown that the wing without a GF has a wake with less instabilities with respect to the case including it [6,7]. These studies indicate that although the flow downstream of the Gurney satisfies Liebeck’s hypotheses, its instantaneous structure consists of a vortex shedding. To explain how this wake contributes to raising the downforce, these vortices have been investigated on how they form and interact to give a Von Karman’s vortex shedding [8]. It has been shown that for a given incidence and height of the GF, the low pressure acting on the Gurney base remains constant along the surface. In simple bodies, Rosko [9] noted similar regions of constant low pressure between the separation points due to the vortex shedding that reduces pressure acting on the face downstream of the device in the trailing edge area. Bearman and Trueman [10] hypothesized that this balancing effect is responsible for the increase in the depression area. Bearman [11] also quantified the magnitude of the recirculation zone, introducing the concept of length of formation, defined as the axial distance from the base of the body to the position of maximum. Good and Joubert [12] have shown how for flat plates immersed in a turbulent boundary layer, the maximum pressure measured downstream on the plate increases with the height of the disturbing element. Kennedy and Marsden [13] demonstrated computationally and experimentally that an increase in the load acting on the entire wing is generated, introducing a finite pressure difference at the trailing edge. Aerodynamic studies of the GF have been conducted considering the ground effect [14,15]. The GF has been analyzed and optimized recently in different applications. Tang and Dowell [16] compared the experimental loading of an NACA 0012 airfoil with a static and oscillating trailing edge GF by using an incompressible Navier–Stokes solver. A movable GF on an NACA 4412 airfoil has been studied by Camocardi et al. [17] by investigating the flow structure near the airfoil wake. Lee [18] studied the impact of GFs of different sizes and perforations on an NACA 0012 profile discussing the growth and development of the tip vortex with particle image velocimetry. Recently, Cole et al. [19] studied the effect of different GFs by highlighting that the airfoil shape is also strategic for the aerodynamic performances. Min et al. [20] analyzed the vibration reduction in micro flaps rotors with a GF. Pastrikakis et al. [21] compared the performance of a helicopter rotor with a GF at different forward flight speeds. A enhancement above 10% has been observed by Mohammadi et al. [22] by comparing the clean DU91W(2)250 airfoil. Recently, Woodgate et al. [23] used an inhouse CFD solver to evaluate the implementation of a GF on wings and rotors. Fernandes-Gamiz et al. [24] used CFD RANS models to analyze and design the GF and micro tabs on a S810 airfoil and a DU91(2)250 airfoil; in addition, the proper orthogonal decomposition (POD) has been used to develop a reduced order method. Aramanedia et al. [25] used the same airfoil to show a parametric study on the GF length through RANS models; the Artificial Neural Networks (ANN) have been used to obtain an accurate prediction model of the aerodynamic behavior of the airfoil with a GF. Extensive aerodynamic analyses on the profile in ground effect have been performed and the simulation of the vortex shedding from the GF has been discussed [26]; a criterion to quantify the wake and the recirculation zone in the vortex shedding mechanism has been developed [27]. The accuracy in numerical prediction of unsteady flows is essential for the vortex shedding mechanisms, but also for other aerodynamic problems like tonal noise [28] or vibro-acoustic stability analysis [29,30]. In this paper the CFD analysis of the aerodynamic performance of the front wing of a Formula 1 car is presented to understand the effects of a GF on the multi-element wing. The flow structures with and without the GF are investigated to also highlight the interaction with downstream car components. Very few studies have been published on the interaction of the Gurney with the other Energies 2021, 14, 2059 3 of 15

components of a racing car, in order to understand any additional beneficial effects. The first part of the paper examines the global drag and downforce on the main components of the vehicle located between the front wing and the tire. The second part discusses in some detail the differences in the flow structures that occur with or without a GF on the various car components using a set of control planes in the 3D domain. Studies on the of racing car wings using CFD have been published [31–33] and the Ansys CFX code, as in the present work, has been used to investigate the ground effect [34]. The CFD model setup is crucial to correctly represent different racing scenarios [35] or to investigate the effect of the wake on the following cars [36]. The 3D model of a real F1 car from the 2000s is used as reference geometry for the analysis. The car model is old, compared to current models, but it is an actual car configuration that participated in F1 championships for years. It can therefore be considered a relevant case in aerodynamic design for the scope of the present paper. It must be evident that a university research group cannot have access to the most recent geometrical designs to publish a research paper. Moreover, any experimental data are kept confidential and not made available to university groups to be published. With the above restrictions, the paper is aimed at the critical analysis of the flow structures around the front wing and the interactions between components (e.g., wheels, , etc.) to highlight: (1) the strong aerodynamic interactions between parts, (2) the dramatic effect of a small detail (the Gurney flap) on component performance and aerodynamic interactions. The CFD technology is used as a numerical application tool to investigate and to quantify the above effects. The use of CFD, properly set, is a current design practice for such configurations. The CFD model used has been set up in previous research activities with reference cases where detailed experimental data were available for validation. Only the front part of the car is considered with the rear part modelled with a boat tail to keep the car obstruction to flow close to the front wing. The attention is therefore focused on the GF aerodynamic effects and interactions with the front car components.

2. Geometry and CFD model 2.1. Application The geometry used for the analysis is a Formula 1 car of the early 2000s with a front wing composed of: a main wing (main) (c = 0.228 m, b = 0.639 m), a flap (c = 0.182], b = 0.626 m), and two endplates. The endplate facing the exterior of the has c = 0.501 m and b = 0.127 m, while the one facing inwards has c = 0.186 m and b = 0.137 m. The GF is installed perpendicularly to the trailing edge of the flap with the following reference geometry: • Central part with height of 1.35% of the aileron chord and thickness s = 1.75 mm; • Lateral part of variable height between 1.8% and 0.36%, with thickness s = 1.9 mm; • External part in contact with the endplate with h = 1.8% and s = 1.9 mm; • Internal endplate with h = 1% of chord of the complete aileron.

The above front wing is installed in a racing car with a lv = 3.5 m body and maximum width of 0.5 m, with a tire of diameter 620 mm and tread width w = 320 mm. The tire is supported by lower and upper suspensions with an aerodynamic section: the first has c = 77 mm and the second has a variable chord between 85 and 167 mm. A camera is installed with a wing profile with c = 168 mm and b = 100 mm. In Figure1, the geometry of the vehicle and the front wing with the GF is reported, by highlighting its location. Energies 2021, 14, 2059 4 of 15 Energies 2021, 14, x FOR PEER REVIEW 4 of 15

Figure 1. Geometry of the model and front wing with GF details. Figure 1. Geometry of the model and front wing with GF details. 2.2. Governing Equations 2.2. Governing Equations The Reynolds-averaged equation for conservation of mass and momentum form the The Reynolds-averaged equation for conservation of mass and momentum form the dynamic flow problem. The turbulence model adopted in the CFD approach is the k-ω dynamic flow problem. The turbulence model adopted in the CFD approach is the k-ω SST, in order to solve the boundary layer near the walls; it is based on the Boussinesq’s SST, in order to solve the boundary layer near the walls; it is based on the Boussinesq’s hypothesis to model the Reynolds stress tensor. This model was developed to combine hypothesis to model the Reynolds stress tensor. This model was developed to combine the the accuracy of the k-ω model near the wall and the robustness of the k-ε in the accuracy of the k-ω model near the wall and the robustness of the k-ε in the free-stream. It free-stream. It contains some different terms with respect to the standard k-ω formula- contains some different terms with respect to the standard k-ω formulation. A blending tion. A blending function activates the transformed models k-ω and k-ε depending on the function activates the transformed models k-ω and k-ε depending on the local value of local value of y+, i.e., near or far from the wall [37]. A different formulation for the eddy y+, i.e., near or far from the wall [37]. A different formulation for the eddy viscosity and viscosity and modified constants is introduced. The transport equations are: modified constants is introduced. The transport equations are: () + ( ) = + "− + # (1) ∂ ∂ ∂ ∂k (ρk) + (ρku )= Γ + G − Y + S (1) ∂t ∂x i ∂x k ∂x k k k i j j () + = + − + + (2) " # ∂ ∂  ∂ ∂ω (ρω) + ρωuj = Γω + Gω − Yω + Dω + Sω (2) The diffusivity is obtained∂ tby the following∂xj equations:∂xj ∂xj The diffusivity is obtained = by+ the following equations: (3) µt = + Γk = µ + (3) σk (4) µt The eddy viscosity is determined with: Γω = µ + (4) σω 1 = The eddy viscosity is determined1 with: (5) , ∗ ρk 1 µt = h i (5) The model constants are: σk,1 = 1.176, σω,1 = 2.0, σk,2ω = 1.0, σ1ω,2 SF= 21.168, α1 = 0.31, βi,1 = max a∗ , a ω 0.075, and βi,2 = 0.0828. 1

The model constants are: σk,1 = 1.176, σω,1 = 2.0, σk,2 = 1.0, σω,2 = 1.168, α1 = 0.31, 2.3. CFD Model βi,1 = 0.075, and βi,2 = 0.0828. The computational domain for the study of a Formula 1 front wing consists of a rectangular parallelepiped2.3. CFD Model sufficiently extended so that the boundary conditions do not influence the flow structureThe computational around the domainfront wing for and the studythe front of aof Formula vehicle. 1In front order wing to consists of a save a considerablerectangular amount parallelepiped of computational sufficiently resources, extended only one so-half that of the the boundary front wing conditions do not and the vehicleinfluence was modelled the flow, exploiting structure around its axial the symmetry. front wing T andhe domain the front has of vehicle. the fol- In order to save lowing geometricala considerable characteristics: amount the of ground computational has a surface resources, 3lv × only8lv, while one-half the of entire the front wing and domain has a heightthe vehicle of 2lv. In was addition modelled,, the exploitingsurface in front its axial of the symmetry. wing is placed The domain at 2lv, the has the following surface at the outletgeometrical is 5lv far. characteristics: Figure 2 shows the the ground calcula hastion a surfacedomain 3l andv × the8lv ,details while theof the entire domain has

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a height of 2lv. In addition, the surface in front of the wing is placed at 2lv, the surface at the outlet is 5lv far. Figure2 shows the calculation domain and the details of the vehicle vehiclegeometry.vehicle geometry. geometry. In order In toIn order studyorder to andto study study compare and and compare the compare case withthe the case andcase with without with and and a without GF, without one modela aGF GF, one, has one modelbeenmodel cleaned ha has beens been up cleaned bycleaned the GFup up fromby by the the the GF GF flap. from from the the flap. flap.

FigureFigureFigure 2. 2. 2.ComputationalComputational Computational domain domain domain and and and geometry geometry geometry detail detail detail of of the the vehicle vehicle simulated. simulated.

TheTheThe dom domain domainain has has has been been been discretized discretized discretized with with with an an an unstructured unstructured unstructured grid grid grid with with with prism prism layer layers layers snear near thethethe wall wall wall of of of the the the vehicle vehicle vehicle and and and its its its components components, components, in in, in order order order to to to solve solve solve the the the boundary boundary boundary layer. layer. layer. T The heThe size size ofofof the the the first first first cell cell cell has has has been been been set set set to to to have have have a a ay+ y+ y+ close close close to to to one one. one. A. A A local local local refinement refinement refinement is is is required required required on on the the leadingleadingleading edges edges edges of of of the the the wings wings wings and and and at at at th the the etrailing trailing trailing edge edges edges withs with with the the the GF GF, GF, setting setting, setting a a amaximum maximum maximum size size size ofofof 1 1 1mm. mm. mm. The The The global global global mesh mesh mesh size size size consists consists consists of of of about about about 45 45 45 million million million of of cells cells. cells. In In. In Figure Figure Figure 33, ,3 thethe, the meshmesh mesh forforfor the the casecase case withwith with aa GF aGF GF is is shown,is shown shown while, while, while Figure Figure Figure4 reports 4 4report report thes wallsthe the wall y+ wall contours y+ y+ contours contours along along thealong front the the frontwingfront wing of wing the of vehicle.of the the vehicle. vehicle. The meshThe The mesh usedmesh used has used beenhas has been designed been de designedsigned to have to to have ahave high a ahigh quality; high quality; quality; over over 90% over 90%of90% cells of of cells have cells have ahave quality a aquality quality higher higher higher than than 0.5 than and 0.5 0.5 and with and with anwith equi-angle a na nequi equi-angle-angle skewness skew skewness greaterness greater greater than than 0.55 than 0.55and0.55 theand andaspect the the aspect aspect ratio ratio is ratio higher is is higher thanhigher 0.6.than than This 0.6. 0.6. mesh This This strategymesh mesh strategy strategy with the with with same the the local same same refinement local local re- re- finementonfinement the wings on on the hasthe wings beenwings has selected has been been afterselected selected a grid after after dependency a agrid grid dependency dependency analysis performedanalysis analysis performed performed in a previous in in a a previousworkprevious [26 ]work onwork the [26] [26] wing on on the in the ground wing wing in effectin ground ground analyzed effect effect inanalyzed analyzed an isolated in in an an form isolated isolated with form and form withoutwith with and and a withoutGF.without In the a aGF. previous GF. In In the thework previous previous [26], work the work CFD [26], [26], model the the CFD CFD was model validatedmodel was was byvalidated validated comparing by by comparing thecomparing numerical the the numericalresultsnumerical with results detailed results with with experimental detailed detailed experimental dataexperimental [38,39] at data differentdata [38,39 [38,39 distances] ]at at different different from ground distance distance ands sfrom withfrom grounddifferentground and GFand with heights. with different different GF GF heights heights. .

FigureFigureFigure 3. 3. 3.DetailDetail Detail of of of the the the calculation calculation calculation grid grid grid of of of the the the aileron’s aileron’s aileron’s vehicle vehicle. vehicle. .

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Figure 4. Wall y+ contours on the aileron’s vehicle.

The followings boundary conditions have been set: at the inlet of the domain a uni- Figure 4. Wall y+ contours on the aileron’s vehicle. form velocity of 70 m/s and a turbulence intensity of 5% are fixed, while at the outlet of Figure 4. Wall y+ contours on the aileron’s vehicle. the domainThe followings there is boundarya pressure conditions ambient condit have beenion. In set: the at thesymmetry inlet of theside, domain the surface a uniform has been fixed as a symmetry condition, while at the surface relative to the ground, a wall no velocityThe of followings 70 m/s and boundary a turbulence conditions intensity have of been 5% areset: fixed,at the whileinlet of at the the domain outletof a uni- the slip condition with the same velocity of the car is set; finally the remaining surfaces of the domainform velocity thereis of a 70 pressure m/s and ambient a turbulence condition. intensity In the of symmetry 5% are fixed side,, while the surface at the has outlet been of domain have been set as an inviscid wall. The car surfaces are set as a no slip condition. fixedthe domain as a symmetry there is a condition, pressure whileambient at thecondit surfaceion. In relative the symmetry to the ground, side, the a wall surface no slip has The flow is considered isothermal and incompressible. All the equations have been conditionbeen fixed with as a thesymmetry same velocity condition, of thewhile car at is the set; surface finally relative the remaining to the ground surfaces, a wall of the no solved with second order numerical schemes and steady flow simulations have been set domainslip condition have been with setthe as same an inviscid velocity wall.of the The car caris set surfaces; finallyare theset remaining as a no slipsurfaces condition. of the up.The flow is considered isothermal and incompressible. All the equations have been solved domain have been set as an inviscid wall. The car surfaces are set as a no slip condition. with second order numerical schemes and steady flow simulations have been set up. The flow is considered isothermal and incompressible. All the equations have been 3. Results 3.solved Results with second order numerical schemes and steady flow simulations have been set 3.1. Global Performance of the Main Components 3.1.up. Global Performance of the Main Components This section discusses the main differences concerning aerodynamic performance This section discusses the main differences concerning aerodynamic performance with with3. Results or without the GF on the front wing. As shown in Figure 5, both the global down- or without the GF on the front wing. As shown in Figure5, both the global downforce and force and drag in the front wing increased with the GF; the lift (downforce) and the drag drag3.1. Global in the Performance front wing increased of the Main with Components the GF; the lift (downforce) and the drag increased by increased by 23.98% and 28.19%, respectively, while the aerodynamic efficiency E de- 23.98%This and section 28.19%, discusse respectively,s the while main the differences aerodynamic concerning efficiency aerodynamic E decreased performance only by 5%. creased only by 5%. with or without the GF on the front wing. As shown in Figure 5, both the global down- force and drag in the front wing increased with the GF; the lift (downforce) and the drag increased by 23.98% and 28.19%, respectively, while the aerodynamic efficiency E de- creased only by 5%.

FigureFigure 5. 5. LiftLift and and drag drag coefficients coefficients of of the the complete complete aileron aileron with and without GF GF..

The Cl and the drag coefficient Cd have been defined as: The lift coefficient Cl and the drag coefficient Cd have been defined as: L Figure 5. Lift and drag coefficients of the completeC aileron Lwith and without GF. C l= 1 2 (6(6)) l 1  AU2 /22ρAU∞  The lift coefficient Cl and the drag coefficient Cd have been defined as:

DDRLR CC = (7) dCd l 1 2 2 (7) /12ρAU∞ 2 (6) 1 AUAU 22  The aerodynamic efficiency E is defined as: The aerodynamic efficiency E is defined as: D C  R E =dCl/CD = L/D (8) 1 AU 2 (7) 2  The aerodynamic efficiency E is defined as:

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Energies 2021, 14, 2059 7 of 15 C E l  L (8) CDD This parameter is very important to indicate how much lift (downforce)(downforce) isis obtainedobtained with the GF referred toto thethe dragdrag value.value. The lift and drag contributionscontributions of the the individual individual components components were calculated,calculated, by measuring,measuring, respectively,respectively the, the vertical vertical and and horizontal horizontal force force components components using using the commercial the com- post-processingmercial post-processing software Ansys software CFX-Post. Ansys In CFX Figure-Post6,. theIn contributionsFigure 6, the of contribution downforce ands of dragdownforce for the and main, drag the for flap, the and main, the the endplates flap, and are the shown. endplates are shown.

Figure 6. Cl and Cd performance comparison on main, flap, and endplates. Figure 6. Cl and Cd performance comparison on main, flap, and endplates.

With thethe GF,GF, a a downforce downforce increase increase of of about about 30% 30% on on the the flap flap and and on theon endplatesthe endplates and 20%and 20% for the for main the main wasobserved; was observed on the; on other the hand,other thehand drag, the increased drag increase by 33%d by and 33% 24% and on the24% flap on andthe flap on the and endplates, on the endplates respectively,, respectively, but decreased but decrease on the maind on by the 67%. main The by effects 67%. onThe the effects suspensions on the suspe (uppernsions and lower),(upper theand wheels, lower), andthe wheels the body, and of thethe vehiclebody of are the reported vehicle inare Table reported1. in Table 1.

Table 1.1. PercentagePercentage variationvariation ofof aerodynamicaerodynamic forcesforces onon suspension,suspension, tiretire andand vehiclevehicle body.body.

SuspensionsSuspensions Tire Vehicle Vehicle BodyBody DownforceDownforce Drag Downforce Downforce Drag Downforce Downforce Drag Upper:Upper: +22.7 Upper: Upper: +2.6+2.6 +37.9 −25.825.8 +62.9 +48.7 Lower:Lower: +62.8 Lower: Lower: +57.4

The above components are therefore therefore affected affected by by the the GF GF installation: installation: increase in in downforce and drag, with the exception of the wheels where there is a reduction inin dragdrag like for the main (see Figure6 6).).

3.2. Fluid Fluid-Dynamic-Dynamic Analysis To understandunderstand the mainmain differences onon thethe aerodynamicaerodynamic performanceperformance ofof thethe vehiclevehicle and its components, a fluidfluid dynamic analysis was carried outout onon aa set of control planes, as shown in Figure7 7..

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Figure 7. Characteristic plans considered for the fluid dynamics analysis in the x, y direction. Figure 7. CharacteristicFigure 7. Characteristic plans considered plans for considered the fluid dynamics for the fluid analysis dynamics in the analysis x, y direction. in the x, y direction.

On plane x1, FigureOn plane 8, the x comparison, Figure8, the of comparisonthe contours of for the pressure contours and for ve pressurelocity, with and velocity, with On plane x11, Figure 8, the comparison of the contours for pressure and velocity, with and without a GF, are plotted to understand the reason for the downforce increase and andand withoutwithout aa GF,GF, areare plottedplotted toto understandunderstand thethe reasonreason forfor thethe downforcedownforce increaseincrease andand drag reduction on the main wing with a GF. dragdrag reductionreduction onon thethe mainmain wingwing withwith aa GF.GF.

Figure 8. Comparison on the x1 plane of distributions between the case with (right) and without GF (left): (above) pressure Figure 8. Comparison on the x1 plane of distributions between the case with (right) and without GF (left): (above) pres- contoursFigure 8. with Comparison velocity vectors,on the x (1below plane )of velocity distributions contours. between the case with (right) and without GF (left): (above) pres- sure contours with velocity vectors, (below) velocity contours. sure contours with velocity vectors, (below) velocity contours. A large area of low pressure (high velocity) under the main wing is evident with the A large area of low pressure (high velocity) under the main wing is evident with the GF installedA large thatarea enhances of low pressure the ground (high effect. velocity) The flowunder is the affected main by wing the presenceis evident of with the GFthe GF installed that enhances the ground effect. The flow is affected by the presence of the andGF installed redistributed that enhances below the the main ground wing effect. and towards The flow the is endplate, affected asby seen the presence by the velocity of the GF and redistributed below the main wing and towards the endplate, as seen by the ve- vectors.GF and Theredistributed velocity increase below the along main the wing suction and side towards gives a the smaller endplate, wake as on seen the main by the wing ve- locity vectors. The velocity increase along the suction side gives a smaller wake on the aslocity seen ve inctors. Figure The9, wherevelocity the increase streamlines along on the the suction y 2 plane side aregives plotted. a smaller This wake is the on main the main wing as seen in Figure 9, where the streamlines on the y2 plane are plotted. This is reasonmain wing for the as dragseen reductionin Figure 9 on, where the main the wingstreamlines with a on GF the installed. y2 plane The are same plotted. figure This also is the main reason for the drag reduction on the main wing with a GF installed. The same showsthe main the reason typical for flow the structure drag reduction with recirculating on the main flows wing upstream with a GF and installed. downstream The same the figure also shows the typical flow structure with recirculating flows upstream and GFfigure on the also flap shows element the of typical the wing. flow structure with recirculating flows upstream and downstream the GF on the flap element of the wing. downstream the GF on the flap element of the wing.

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Figure 9. Comparison on the y2 plane of streamline between the case without (left) and with (right) GF. Figure 9. Comparison on the y2 plane of streamline between the case without (left) and with (right) GF. Figure 9. Comparison on the y2 plane of streamline between the case without (left) and with (right) GF. The same fluid dynamics analysis was performed on the x2 plane to understand the The same fluid dynamics analysis was performed on the x2 plane to understand the The same fluid dynamics analysis was performed on the x2 plane to understand the increase in drag and in downforcedownforce onon thethe endplate.endplate. Pressure and velocity contours are reportedincrease inin Figure drag and 10. in downforce on the endplate. Pressure and velocity contours are reported in Figure 10.

Figure 10. Comparison on the x2 plane of distributions between the case with and without GF: (above) pressure contours withFigure velocity 10. Comparison vectors, (below on the) velocityx2 plane contours.of distributions between the case with and without GF: (above) pressure contours Figure 10. Comparison on the x2 plane of distributions between the case with and without GF: (above) pressure contours with velocity vectors, (below) velocity contours. with velocity vectors, (below) velocity contours. The velocity vectors have an evident upwash direction in the wing central area, whileThe laterally velocity velocity the vectors vectorsflow interacts have have an an evidentwit evidenth the upwash tire upwash and direction tends direction to in be the deviated in wing the wing central in all central area,directions. while area, Bylaterallywhile comparing laterally the flow thethe case interactsflow with interacts withand without thewith tire the a and tireGF, tends andan evident tends to be to deviatedlow be- pressuredeviated in all regionin directions. all directions. is located By incomparingBy the comparing lower the part the case of case the with withendplate and and without facingwithout a the GF, a GF,car an in evidentan the evident case low-pressure with low- apressure GF. Without region region is the locatedis GF,located the in abovethein the lower lowerdepression part part of ofarea the the endplate is endplate negligible. facing facing With the the the car car GF in in, the thethe case flowcase with iswith accelerated aa GF.GF. WithoutWithout under thethethe GF,GF,base thethe of theabove endplate depression causing area the is low negligible. pressure With zones. the GF,InGF these, thethe flow flowregions, isis acceleratedaccelerated due to the underunder redistribution thethe base of the endplate flow, higher causing causing velocities the the low low are pressure pressure observed zones. zones. downstream In In these these regions, from regions, the due dueendplate. to tothe the redistribution The redistribution flow rate of, andofthe the flow,cons flow,equently higher higher velocities the velocities axial arevelocity are observed observed, is distributed downstream downstream more from from evenly the the endplate. endplate.over the carThe The and flow flow in rate rate, the, bottomand consequentlycons areaequently of the the main axial wing velocity velocity, and, is the distributed flap. Therefore, more evenly the flow over passes the car through and inin thethe channelsbottom area area generated of of the the main by main thewing wing base and ofand the the flap. the endplate, Therefore,flap. Therefore, with the higher flow the passes velocities flow through passes giving thethrough channels rise to the a relevageneratedchannelsnt ground generated by the effect base by on of the thethe base endplate,endplate. of the endplate, with However, higher with at velocitiesthe higher endplate velocities giving exit rise the giving topressure a relevantrise to re- a mainsgroundreleva ntlower, effectground generating on theeffect endplate. on a largerthe endplate. However, wake with However,at thehigher endplate drag. at the Even exit endplate the in the pressure exitwheel the remains area pressure, the lower, flow re- differsgeneratingmains lower,between a larger generating the wake case withawi largerth higherand wake without drag. with Even a higher GF in. W the drag.ith wheel the Even GF, area, in the the fluid wheel flow being differs area deflected,, betweenthe flow carriesthediffers case outbetween with a greater and the without casepath wi acausingth GF. and With awithout greater the GF, akinetic the GF fluid. W energyith being the loss. deflected,GF, the For fluid this carries reasonbeing out deflected,, anear greater the tread,pathcarries causing in out the a low agreater greater region, path kinetic there causing energy are noa greater loss. marked For kinetic thisdepression reason, energy nearareas. loss. the TheFor tread, samethis in reason set the of low, contoursnear region, the ontheretread, plane arein thex no3 are markedlow shown region, depression in there Figure are areas.11 no to marked understand The same depression set the of phenomena contours areas. The on related same plane set to x3 oftheare contours perfor- shown manceon plane on xsuspensions3 are shown andin Figure wheel. 11 to understand the phenomena related to the perfor- mance on suspensions and wheel.

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Energies 2021, 14, x FOR PEER REVIEW 10 of 15 in Figure 11 to understand the phenomena related to the performance on suspensions and wheel.

Figure 11. Comparison on the on the x3 plane of distributions between the case with and without GF: (above) pressure Figure 11.11. ComparisonComparison on thethe onon thethe xx33 plane of distributionsdistributions between the case with and without GF:GF: ((aboveabove)) pressurepressure contourscontourscontours withwith with velocityvelocity velocity vectors,vectors, vectors, ((belowbelow (below)) velocity)velocity velocity contours, contcontoursours, andand vectors.vectors.vectors.

TheThe baseline baseline casecase withoutwithout a GF GF has has three three distinct distinct swirling swirling directions directions affected affected by bythe thethe presencepresence of of the thethe wheel.wheel. The The first first isis at isat the atthe thetop top topof of the the of wheel thewheel wheel (where (where (where high high pressures high pressures pressures and and sep- sep- and separationsarationsarations are are are generatedgenerated generated on onthe the tread tread andand and onon onthe the the rubber rubber rubber sides). sides). sides). The The The second second second is dueis is due to the to thethe turbulences created by the wheel (where low pressure is reached). The third is due to the turbulences cr createdeated by the wheel (where low pressure isis reached).reached). The third isis duedue toto thethe flow that externally and internally bypasses the wheel (influenced by the flow exiting the flowflow that externally and internally bypasses the wheel (influenced(influenced by the flowflow exitingexiting thethe endplate). In the area between the bottom of the car and the wheel, on the back of the endplate). In In the the area area between the the bottom of of the c carar and the wheel, on the back of thethe lower suspension, a low-pressure zone is created with upward motion. With the GF, the lower suspension, a low low-pressure-pressure zone is createdcreated with upward motion. With the GF,GF, thethe main difference concerns the flow pattern below the front wing near the ground; it is main difference concerns the flow pattern below the front wing near the ground; it is more mainmore difference swirling with concerns a smaller the flowextension pattern of the below low - thepressure front zones, wing nearwhile the the ground;velocities it is swirling with a smaller extension of the low-pressure zones, while the velocities remain moreremain swirling higher. with In this a region,smaller there extension is a different of the interactionlow-pressure between zones, the while mainstream the velocities and higher. In this region, there is a different interaction between the mainstream and the remainthe suspension higher. In with this aregion, greater there turbulence is a different than with interaction a GF. This between different the mainstream interaction is and suspension with a greater turbulence than with a GF. This different interaction is displayed thedisplayed suspension on the with y4 plane a greater of Figure turbulence 12 with the than velocity with contours.a GF. This different interaction is ondisplayed the y4 plane on the of y Figure4 plane 12 of withFigure the 12 velocity with the contours. velocity contours.

Figure 12. Comparison on the y4 plane of velocity contours between the case with and without GF. Figure 12. Comparison on the y plane of velocity contours between the case with and without GF. Figure 12. Comparison on the y4 plane of velocity contours between the case with and without GF. A large recirculation bubble is generated below the lower suspension without the GF; Athe large incoming recirculation flow on bubblethe suspension, is generated induced below by thethe lowerGF, has suspension a correct incidence without with the GF; A large recirculation bubble is generated below the lower suspension without the thethe incoming suspension flow rod on that the strongly suspension, reduces induced its wake. by theThe GF, radically has a correctdifferent incidence flow structure with the GF; the incoming flow on the suspension, induced by the GF, has a correct incidence with suspensionthat forms rodin the that tires strongly wake, reducesunder the its suspensions wake. The, radicallycan be ob differentserved in flowFigu structurere 13 using that the suspension rod that strongly reduces its wake. The radically different flow structure formsthe streamlines in the tires visualization wake, under. the suspensions, can be observed in Figure 13 using the that forms in the tires wake, under the suspensions, can be observed in Figure 13 using streamlines visualization. the streamlines visualization.

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Figure 13. Comparison of the streamlines below the vehicle between the case with and without GF. FigureFigureFigure 13. 13. ComparisonComparison Comparison of of of the the the streamlines streamlines streamlines below below the the vehicle vehicle between between the the case case with with and and without without GF.GF GF. . Figure 14 shows the streamlines pattern on a transversal plane close to the endplates FigureFigure 14 14 shows shows the the streamlines streamlines pattern pattern on on a a transversal transversal plane plane close close to to the the endplates endplates (plane y4) where the flow without a GF (left) is slower close to ground and gives rise to a (plane(plane y 4y)) 4where) where where the the the flow flow flow wi without withoutthout a a aGF GF GF (left) (left) is is slower slower close close to to ground ground and and give gives gives srise rise to to a a large recirculation area due to interaction with the tire. The configuration with the GF, as largelargelarge recirculation recirculation recirculation area area due due to to interaction interaction with with the the tire. tire. The The The configuration configuration configuration with with with the the the GF, GF, as as previously discussed, has higher velocity close to ground and the above recirculation previouslypreviously discussed, discussed, discussed, has has has higher higher higher velocity velocity velocity close close close to groundto to ground ground and and the and abovethe the above above recirculation recirculation recirculation area area is absent; the flow is deflected upward with a positive interaction with the suspen- areaisarea absent; is is absen absen thet; flow t;the the flow is flow deflected is is deflected deflected upward upward upward with with a with positive a apositive positive interaction interaction interaction with with the with suspensions, the the suspen- suspen- sions, as previously discussed. However, in this last case, the wake of the car is wider sionsassions previously, as, as previously previously discussed. discussed. discussed. However, However However in this, in, last in thi case,this slast last the case case wake, the, the of wake thewake car of of isthe the wider car car is (stream- is wider wider (streamlines deflection) thus giving more overall drag, but also beneficial effects on the (streamlineslines(streamlines deflection) deflection) deflection) thus giving thus thus moregiving giving overall more more overall drag, overall but drag, drag, also but beneficialbut also also beneficial beneficial effects oneffects effects the tire,on on the asthe tire, as previously claimed. tpreviouslyire,tire, as as previously previously claimed. claimed. claimed.

Figure 14. Comparison on the y4 plane of the streamlines. Without (left) and with (right) GF. 4 FigureFigure 14. 14. Comparison Comparison on on the the y 4y planeplane plane of of of the the the streamlines. streamlines. streamlines. Without Without Without ( leftleft (left)) and and) and with with with ( right (right) GF. ) GF.

In Figure 15 the pressure contours on the y3 plane are shown. They highlight that a InInIn Figure Figure Figure 1515 15 thethe the pressure pressure pressure contours contours contours on on on the the the y y3y 3plane3 planeplane are areare show shown.shown.n They. They highlight highlight that that that a a large low-pressure area is generated on the nose of the connector with the GF and a re- largealarge large low low low-pressure-pressure-pressure area area area is is generated is generated generated on on onthe the the nose nose nose of of the of the the connector connector connector with with with the the theGF GF GFand and and a are- re- a duction of the high-pressure zone below the suspension. These combined effects give ductionreductionduction of of of the the high high-pressurehigh-pressure-pressure zone zone below below below the the the suspension. suspension. suspension. These These These combined combined combined effects effects give give more downforce with the GF installed. moremore downforce downforce with with the the GF GF installed installed. installed. .

Figure 15. Comparison on the y3 plane of pressure contours. Case without (left) and with (right) Figure 15. ComparisonFigureFigure on15. 15. the Comparison Comparison y3 plane of on pressureon the the y 3y plane3contours. plane of of pressure pressure Case without contours. contours. (left Case )Case and without withwithout (right (left (left)) GF.and) and with with (right (right) ) GF. GF.GF. The pressure contours on the x4 plane are shown in Figure 16 to discuss the various aerodynamic effects acting on the other parts of the vehicle.

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TheThe pressure pressure contourscontours on the xx44 planeplane are are shown shown in in Figure Figure 16 16 to todiscuss discuss the the various various aerodynamicaerodynamic effects effects actingacting on the otherother parts parts of of the the vehicle vehicle. .

Figure 16. Comparison on the x4 plane of pressure contours with velocity vectors. Case without (left) and with (right) GF. Figure 16. Comparison on the x 4 planeplane of of pressure pressure contours with velocity vectors. Case without ( leftleft)) and and with with ( (right) GF. GF. Low-pressure zones around the car and under the body are generated by vortices LowLow-pressure-pressure zoneszones aroundaround the the car car and and under under the the body body are are generated generated by vorticesby vortices that developthat develop from from the ground the ground at the at cornersthe corners of the of the body body sections. sections. These These vortices vortices and and their their low thatlow develop pressure from are useful the ground to both at feed the cornersthe cooling of the sections body (mainsections. radiator These and vortices brakes) and and their lowpressure pressure are usefulare useful to both to both feed feed the the cooling cooling sections sections (main (main radiator radiator and and brakes) brakes) and and to generateto generate additional additional downforce. downforce. In theIn the case case with with the the GF, GF the, the low-pressure low-pressure regions regions are are more tomore generate extended additional below thedownforce. body, resulting In the incase more with downforce. the GF, the However low-pressure, the drag regions gener- are extended below the body, resulting in more downforce. However, the drag generated at moreated extendedat the rear belowof the vehiclethe body is higher., resulting This in can more be argue downforce.d from theHowever analysis, the of Figure drag gener- 17, the rear of the vehicle is higher. This can be argued from the analysis of Figure 17, where atedwhere at thethe rearpressure of the contours vehicle onis higher. a plane This downstream can be argue of thed fromvehicle the are analysis shown. of The Figure flow 17, the pressure contours on a plane downstream of the vehicle are shown. The flow structure wherestructure the inpressure the wake contours with a onGF a has plane a larger downstream and stronger of the recirculat vehicle ingare zoneshown. with The low flow in the wake with a GF has a larger and stronger recirculating zone with low pressure that structurepressure inthat the increases wake with the pressure a GF has drag a larger of the vehicle.and stronger recirculating zone with low increases the pressure drag of the vehicle. pressure that increases the pressure drag of the vehicle.

Figure 17. Comparison of pressure contours with velocity vectors on a downstream plane. Case with (left) and without

(right) GF. Figure 17. Comparison of pressure contours with velocity vectors on a downstream plane. Case with (left) andand withoutwithout (right) GF. (right) GF. The pressure coefficient distributions on the wing and flap sections at planes y1, y2, and y3 are reported in Figure 18. From these graphs, it is clear that the aerodynamic loads The pressure coefficient distributions on the wing and flap sections at planes y1, y2, are higherThe pressure with the coefficient GF installed distributions, giving more on downforce the wing from and flapboth sections wing and at flap. planes y1, y2, and y3 are reported in Figure 18. From these graphs, it is clear that the aerodynamic loads and y3 are reported in Figure 18. From these graphs, it is clear that the aerodynamic loads are higher with the GF installed installed,, giving more downforce from bothboth wingwing andand flap.flap.

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FigureFigure 18. 18. PressurePressure coefficients coefficients on on wing wing (upper (upper) )and and flap flap (lower (lower) )sections sections on on plans plans y y11, ,y y2 2andand y y3 3withwith (red (red lines) lines) and and withoutwithout (blue (blue lines) lines) GF. GF.

4.4. Conclusions Conclusions TheThe results results of of detailed detailed CFD CFD analysis analysis on on a avehicle vehicle configuration configuration representative representative of of a ann F1F1 car car have have been been used used to to in investigatevestigate the the effects effects of of GF GF installation installation on on the the flow flow structure structure andand on on component component performances. performances. It It can can be be observed observed that that the the addition addition of of this this small small device device hashas a a dramatic dramatic effect effect on on the the overall overall flow flow structure structure around around the the car. car. The The flow flow structure structure fromfrom the the front front wing wing affected affected by by the the GF GF will will interact interact with with the the other other car car components components with with evidentevident aerodynamic aerodynamic performance changes changes withwith respect respect to to the the baseline baseline configuration. configuration. The Toverallhe overall front front wing wing downforce downforce increases increases of of almost almost 24%, 24% while, while the the drag drag force force increase increase is is28%. 28%. The The contribution contribution of of this this paper paper is is to to highlight highlight the the effects effects that that the the GF GF can can have have on on the thecar car components, components, to giveto give an interpretationan interpretation of theof the aerodynamic aerodynamic performance performance from from the flowthe flowstructures, structures and, toand stress to stress the strong the strong aerodynamic aerodynamic interaction interaction between between components components from the fromaddition the addition of the GF. of Thethe G mainF. The difference main difference with a GF, with consists a GF, consists in a large in area a large of low area pressure of low pressureunder the under main the wing main that wing enhances that enhances the ground the effect, ground which effect, causes which a redistribution causes a redistri- of the butionflow in of the the other flow components: in the other acomponents: flow acceleration a flow under acceleration the base under of the the endplate base of and the a endplatebetter interaction and a bett wither interaction the wheel with group. the On wheel the contrary, group. On without the contrary a GF large, without recirculation a GF largebubbles recirculation on the lower bubble parts on of thethe vehicle lower part are detected. of the vehicle It has are been detected highlighted. It has that been the highlightedcorrect dimensioning that the correct and installation dimensioning of the and GF installationcan increase of the the aerodynamic GF can increase downforce the aerodynamicfrom different down car components,force from different with an increasecar components in the aerodynamic, with an increase efficiency in the compared aerody- to namicbaseline. efficiency The CFD compared technology to baseline. is an essential The CFD tool technology to support theis an design essential and aerodynamictool to sup- porttuning the ofdesign the car. and aerodynamic tuning of the car.

Author Contributions: M.B., C.C., D.M. have equally contributed to the concept of the research activity, the setup of the model, the discussion of the results, and the writing of the paper. All au- thors have read and agreed to the published version of the manuscript.

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Author Contributions: M.B., C.C., D.M. have equally contributed to the concept of the research activity, the setup of the model, the discussion of the results, and the writing of the paper. All authors have read and agreed to the published version of the manuscript. Funding: No external findings have to be cited. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.

Nomenclature

A Area b Wing span c Wing chord Cd Drag coefficient Cl Lift coefficient (downforce) Cp Pressure coefficient d Diameter DR Drag coefficient E Aerodynamic efficiency h Height of Gurney flap (percentage of the airfoil chord) k Turbulent kinetic energy L Lift (downforce) lv Vehicle length p Static pressure s Thickness u Velocity u’ Axial local velocity U∞ Velocity at the domain inlet w Width y+ Non dimensional boundary layer distance from wall µ Dynamic viscosity ρ Density ω Specific rate of dissipation

Acronyms

ext External GF Gurney Flap inf Inferior int Internal sup Superior

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