1. Introduction
The front wing of a Formula One (F1) racing vehicle, when operated in close proximity to the ground, generates approximately 30% of total downforce [
1], which is utilised in conjunction with mechanical grip to boost acceleration, braking, and turning speed. The wing, being the first appurtenance subjected to fresh airflow, has a significant influence on management of downstream airflow, interacting with other aerodynamic devices such as bargeboards, the underfloor, and the rear wing. It can maintain not only a low level of turbulence but also high energy within the fluid. As a result of a great amount of aerodynamic loading exerted on the front wing, the focus lies in the structural design. The wing should be rigid enough to bear the aerodynamic forces through high-speed corners as well as sufficiently durable. Moreover, in order to enhance competitiveness in the motorsport world, the structural design should aim to reduce the weight.
In 2011 Australian Grand Prix, it was noticed that the front wing end of the Red Bull RB6 was deflected towards the ground far more than those of its competitors [
2]. It was revealed that the wing becomes flexible under aerodynamic loads due to the elastic characteristic induced by the composite structure, and this is exploited to gain an aerodynamic advantage. The aeroelastic behaviour of the composite wing allows F1 engineers to improve aerodynamic performance by circumventing the technical regulation stating that all aerodynamic components must be satisfied with the static deflection test as a rigid body.
Both experimental and numerical studies on the inverted wing in ground effect have been extensively performed. In the F1 car, addition of extra elements on the wing can be an option to enhance aerodynamic performance by delaying trailing edge separation. Following single-element wing studies [
3,
4,
5,
6], investigation was thoroughly carried out on the double-element wing. It was started by Ranzenbach and Barlow conducting an experimental work on a two-dimensional NACA
Mod B aerofoil with 30% flap gap at the fixed ground facility [
7]. It was observed that additional downforce is obtained compared to that of the single-element wing, and a region of force decrease was captured at large heights. Jasinski and Selig [
8] conducted another experiment with the double-element wing. The ride height was fixed for 0.3 chord length, and the ground was not moving. It was shown that two trailing edge vortices at the endplate were created, and their size increased with higher flap angle. Following their single-element wing experiment, Zhang and Zerihan also investigated the ground effect of a two-element wing [
9], which is a combination of the single-element wing extracted from the previous work [
6] with an extra flap downstream. The results obtained from LDA, PIV, and oil flow visualisation presented the surface pressure on both elements and the sectional forces with the ride height variation. The downforce increase was mainly attributed to the main element with the help of significant circulation caused by the flap. As the wing was approached, the downforce increased up to the maximum and fell off due to the vortex breakdown at the small height. The double-element wing in ground proximity was tested experimentally by Mahon [
10] with various configurations of flap position and ride heights. It was found that the forces generated by a wing with multiple elements in ground proximity were largely insensitive to variation in flap location. However, extreme values of flap gap and flap location resulted in significant reductions in aerodynamic forces (downforce and drag) and pitching moment due to the flap stalling. The same model as Mahon’s was experimentally tested by van den Berg [
11] with a goal of ensuring and refuting Mahon’s hypotheses. However, unlike Mahon’s idea, he claimed that the cause of reduction in downforce is mainly from the edge vortex breakdown instead of the reversed flow within the lower wake. A region of larger flow reversal occurred as the edge vortex broke down.
Computational studies have been extensively performed on the double-element wing in ground effect. Ranzenbach and Barlow also examined the flow field around their double-element aerofoil using variants of the Standard k-ε model in a structured domain including a moving ground [
12]. At low ride heights, they only noticed minor variations in downforce, but this did not affect their original conclusion on the cause of force reduction. The influence of various turbulence models was evaluated by Mahon and Zhang [
13] using Zerihan’s double-element aerofoil [
9]. It was noted that more than 80% of total downforce is generated by the primary element, whereas the flap creates a great deal of drag. With the limited dimensionality, it was argued that the numerical solution anticipates the boundaries of the wake inaccurately. Mahon also used a three-dimensional double-element wing to undertake a thorough computational examination [
10]. The underestimated lower surface suction pressure caused weaker edge vortices and they showed close relationship with the pressure discrepancy between the wing’s bottom and upper surfaces. The three-dimensionality helped to better predict the wake profile compared to the two-dimensional result. Following the work of Mahon [
10], the same wing model was numerically studied by van den Berg [
14], focusing on improving the quality of the computational domain to obtain better results. Consequently, the correlation between experiment and numerical solution was improved in comparison with the work of Mahon [
10]. However, the RANS results failed to converge for a region of the non-dimensionalised ground height (h/c) ranging between 0.158 and 0.317 due to limitation of capturing unsteady characteristic of the flow caused by the vortex breakdown. Heyder-Bruckner conducted a computational study on a double-element wing in ground proximity with ride height variation using RANS and detached eddy simulation (DES) [
15]. The DES produced better prediction of the general feature of downforce and breakdown of the main edge vortex than that of RANS. It was also found that the wing downforce was only influenced at higher ride heights before the vortex breakdown occurred. Recent research carried out by Benjamin [
16] was also focused on aerodynamic investigation of the double-element wing used for the motorsport application. It was observed that a bio-mimicked modification inspired by tubercles of a humpback whale flipper implemented on the leading edge of the wing has potential to enhance aerodynamic performance.
Despite the importance of the structural design of the inverted wing in ground effect, there have been few studies considering integration of the wing aerodynamics and structure. As a result of significant non-linear and interdisciplinary characteristics of the aero-structural coupled phenomenon, a numerical technique known as fluid-structure interaction (FSI) may be alternatively used because existing experiments and computations are restricted. The advent of numerical solutions can address complicated FSI engineering problems in an efficient manner in many industries such as aerospace, automotive, hemodynamics, and hydrodynamics. Aeroelastic behaviour of aircraft wings is one of the essential aspects to be taken into consideration to prevent the wing from static or dynamic aeroelastic problems [
17,
18,
19]. In mechanical engineering, hydraulic system geometry consisting of hydrofoils can be developed by using the FSI approach to study effect of the interaction between the foils and flow on their performance [
20,
21]. In hydrodynamics, cavitation, which has a negative effect on the flow behaviour, was investigated by implementing the FSI analysis [
22], and a new FSI method coupling the smoothed particle hydrodynamics (SPH) and finite element method (FEM) was developed to study a dam break problem with an elastic gate [
23]. A new form of two-way coupling FSI modelling for a three-dimensional model for an asymmetric serpentine was introduced by using COMSOL and an arbitrary Lagrangian–Eulerian (ALE) method [
24]. The reduced basis method (RBM) was integrated with the FSI modelling approaches to solve the complicated coupled problems in a more efficient manner [
25,
26]. However, the focus should lie on implementation of a separate method into existing modelling techniques, especially remeshing process. In addition, code implementation may be a lengthy process when the complexity of the problem is increased. Recently, many studies on hemodynamics using FSI analysis have been carried out [
27,
28,
29,
30]. Despite assessing different parts of the body or diseases, the main objective is to investigate the dynamic behaviour between blood flow and flexible aortic wall deformation and ultimately to better understand causes attributed to diseases.
Aeroelastic behaviour of car components has been the subject of research in the automotive industry. FSI analysis based on one-way coupling was employed to predict a potential panel problem caused by vibration of an elastic vehicle hood interacting with flow field, which is of great help in the preliminary design stage [
31]. Ratzel et al. [
32] carried out FSI simulations coupled to transient flow to investigate aerodynamic performance of a flexible flap attached to the rear of a generic vehicle model. Based on a geometric parameterisation study using the FSI technique, the flap shape was optimised in order to minimise deformation. A front spoiler was numerically analysed using a two-way FSI weakly coupled method to evaluate the effect of interaction between the component and near/far flow fields on vehicle drag [
33]. The computational results were supported in comparison with the experiments performed in a wind tunnel. Hydroplaning, which occurs between the tyre surface and a layer of water on the road, was evaluated by coupling the finite element method and Navier–Stokes equation [
34]. Despite more computational resources being required to simulate the FSI analysis, more accurate prediction for hydroplaning speed and associated tyre performance was achieved. There are few studies on development of race car wing performance using the FSI analysis. A Formula One car front wing was simulated by a CFD and FEA coupled method in order to investigate the wing performance regarding lift and drag [
35]. However, the ground effect was not taken into consideration in this research. Castro et al. [
36] performed an aero-structural coupled numerical analysis of a multi-element wing created based on 2022 F1 technical regulations. Several variations of the structural design of the wing were studied to quantify its behaviour related to aerodynamic forces applied. Another recent work studied aeroelastic behaviour of the wing in ground effect [
37]. The single-element composite wing in ground effect was used to investigate and quantify the aeroelastic effect on the aerodynamic and structural performance of the wing using a two-way coupling method in ANSYS software, which has great benefits in reducing the resources required to develop a specific code and associated implementation procedure. A modified FSI framework using existing fluid and structural modules within the software was proposed in conjunction with the high performance computing system. The equivalent methodology was applied in a more complicated model in this study.
The multi-element wing in close ground proximity has been extensively researched in experimental and numerical studies due to its significant performance advantage. However, few comparative studies have been conducted to anticipate the aerodynamic and structural performance of the wing concerning the aeroelastic characteristics. Furthermore, limitations of the FSI modelling approaches have been found in previous studies [
24,
25,
26,
36], such as that the additional resources required to develop an code for specific problems which may take a substantial amount of time. Focus should also be placed on integration of the separate code into the existing coupling process between CFD and FEA and stability of the correlation of fluid and structural algorithms. The aim of this work was to implement a two-way coupled FSI approach using commercial CFD and FEA solutions to examine the effect of aeroelastic behaviour of a double-element wing operating in close ground proximity on the wing’s aerodynamic performance. This would be of great help for engineers to reduce computational resources for solving sophisticated the aero-structural problem as well as increasing accessibility to the software usage. In order to enhance credibility of the solution and to minimise uncertainty, a grid sensitivity study was performed, followed by a turbulence model study. Numerical results are presented in terms of surface pressure distribution, aerodynamic forces, and wake profile. In the next section, a modified two-way coupling method is presented that couples the aerodynamic and structural behaviour of a simplified double-element composite front wing of an F1 vehicle in the context of high performance computing (HPC) using the ANSYS software package.
4. Conclusions
In the present work, a modified two-way coupling method was employed for the purpose of investigation into the fluid flow field around the composite-material multi-element wing to assess the aerodynamic performance of the wing induced by the aeroelastic effect. Our computational approach focused on a novel coupling of the aerodynamic and structural behaviour of the double-element composite front wing of an F1 vehicle in the context of high performance computing (HPC) to simulate a steady-state fluid-structure interaction (FSI) configuration using the ANSYS software package. The objective of these investigations was to understand the suitability of computational techniques for FSI modelling and to quantify the influence of aeroelastic behaviour of the composite wing on the aerodynamic performance in ground effect.
It was found that when the wing approaches the ground, substantial suction loading is created on the bottom surface of the main element, whereas the pressure around the flap remains relatively unaffected by the ride height variation as it is far above the ground. For the spanwise pressure around the wing due to the aeroelastic effect, a smaller amount of the suction pressure is obtained through simulations on both main elements and the flap across the span compared to experimental data. The largest numerically predicted downforce occurs at a higher ride height, followed by a larger drop in downforce at the lowest height as shown in comparison with experimental data. The FSI simulation generates additional drag compared to the experiments by a broadly constant value across the ride heights. As the height of the primary element is lowered, the velocity deficit inside the wakes grows, owing to an increase in the unfavourable pressure gradient underneath it.
It is important to note that the practical contribution of our investigation was to quantify the coupled effect on the aerodynamic and structural performance of the wing because the quantification of these physical processes is in the mainstream research focus. Overall, we focused on the development of an accurate FSI numerical modelling framework in conjunction with computational fluid dynamics (CFD) techniques and structural finite element analysis (FEA) for an F1 application. In future work, a more realistic F1 front wing could be investigated through computational methods in addition to wind tunnel testing of the ground effect to improve the applicability of current models.