Motorcycle Cornering Improvement: an Aerodynamical Approach Based on Flow Interference a Master Thesis in Fluid Mechanics
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Motorcycle Cornering Improvement: An Aerodynamical Approach based on Flow Interference A Master Thesis in Fluid Mechanics Author: Vojtech Sedlak Supervisor/Examiner: Alessandro Talamelli Technical Advisor: Stefan Wallin Department of Mechanics and Department of Aeronautical and Vehicle Engineering Royal Institute of Technology KTH 2012 Contents Nomenclature 1 1 Introduction 3 1.1 Early History of Motorcycle Aerodynamics . 3 1.2 Focus on cornering . 4 1.3 Serious Attempts on Wing Use . 6 2 Project Overview 8 2.1 Concept . 8 2.2 Mechanical aspects . 10 2.2.1 Calculations . 11 2.2.2 Evaluating the Effect of Interference . 12 2.2.3 Anhedral angle effect on Vertical and Horizontal Forces . 14 2.2.4 Overall performance . 14 2.3 Speed estimation . 17 2.3.1 Airfoil Selection: NACA 23015 . 18 3 Problem Specification 19 3.1 Identifying Variables - The Buckingham Pi Theorem . 19 3.2 Problem Overview . 20 3.3 Predicting Near-wall Cell Size . 21 4 Numerical Approach 23 4.1 Work Flow . 23 4.2 Meshing . 24 4.3 Numerical Solver . 25 5 Preliminary 2D test-case 26 5.1 Geometrical Setup . 26 5.2 Mesh . 27 5.3 Solver . 28 5.4 Results . 29 5.4.1 Airfoil Properties . 29 5.4.2 Interpretation of Interfered Airfoil results . 30 5.4.3 Interfered Airfoil at α = 0◦ ........................ 31 5.4.4 Interfered Airfoil at α = 4◦ ........................ 32 5.4.5 Interfered Airfoil at α = 8◦ ........................ 34 6 Simple 3D case 38 6.1 Geometrical Setup . 38 6.2 Mesh . 39 6.3 Solver . 40 6.4 Results . 41 7 Final Concept 43 1 8 Discussion 45 8.1 Additional Work . 45 8.2 Further improvements . 45 8.2.1 Higher top speed . 45 9 Conclusion 47 Acknowledgments 48 A Appendix: Data 49 A.0.2 Data for 2D cases . 49 A.0.3 Data for 3D cases . 50 B MotoGP Regulations 2012 52 2 Abstract A new aerodynamic device, based on flow interference effects, is studied in order to signifi- cantly improve the cornering performance of racing motorcycles in MotoGP. After a brief overview on why standard downforce devices cannot be used on motorcycles, the new idea is introduced and a simplified mechanic analysis is provided to prove its effec- tiveness. The concept is based on the use of anhedral wings placed on the front fairing, with the rider acting as an interference device, aiming to reduce the lift generation of one wing. Numerical calculations, based on Reynolds-averaged Navier-Stokes equations, are performed on simplified static 2D and 3D cases, as a proof of concept of the idea and as a preparation for further analysis which may involve experimental wind-tunnel testing. The obtained re- sults show that the flow interference has indeed a significant impact on the lift on a single wing. For some cases the lift can be reduced by 70% to over 90% - which strengthens the possibility of a realistic implementation. Abstract in Swedish: Sammanfattning Ett nytt aerodynamisk koncept som nyttjar effekter av fl¨odesinterferenser ¨arutv¨arderati syfte att p˚aett noterbart s¨attf¨orb¨attraen roadracing-motorcykels kurtagningsm¨ojligheter. Efter en kort genomg˚angav varf¨ordiverse klassiska \downforce" l¨osningarej ¨arapplicerbara p˚amotorcyklar, presenteras det nya konceptet. Varp˚aen mekanisk analys genomf¨orsi syfte att se ¨over dess till¨ampbarhet.Konceptet bygger p˚aanhedrala vingar som placeras p˚aden fr¨amrek˚apan,d¨arf¨orarenagerar som ett interferensobjekt, och f¨ors¨oker st¨oraut lyftkraften som den ena vingen genererar. Numeriska ber¨akningarbaserade p˚aRANS-ekvationer ¨ar utf¨ordai f¨orenklade statiska 2D och 3D fall. Som ett vidare steg rekommenderas vindtun- neltester. Resultaten visar att fl¨odesinterferenser ¨arytterst m¨arkbaraf¨orvingar och i vissa fall kan lyftkraften reducerats med 70{90%. Detta f¨orst¨aker m¨ojlighetenf¨oren realistisk implementering. Nomenclature Symbols 2 Aw area of a wing [m ] 2 bw half-span of a wing [m ] Cd, CD drag coefficient for 2D, 3D case [-] Cf friction coefficient [-] CI interference coefficient [-] Cl, CL lift coefficient for 2D, 3D case [-] cr airfoil chord length [m] dc diameter of interference device[m] F~ , F force vector, force [N] 2 g0 sea level gravity constant, 9.81 [m/s ] K turbulence kinetic energy [m2/s2] k number of fundamental dimensions [-] l∗ viscous length scale [m] M~ , M moment vector, moment [Nm] M1 free stream Mach number [-] m mass [kg] m0 mass motorcycle [kg] mr mass rider [kg] N normal force [N] n number of independent physical variables [-] P mean static pressure [N/m2] p static pressure [N/m2] p0 fluctuating pressure part [N/m2] R~, R reaction force vector, reaction force [N] rc radius of a corner [m] ~r distance vector [m] Recr Reynolds number for an airfoil chord[-] ReL Reynolds number for specific lenght[-] −1 Sij mean strain rate tensor [s ] T temperature [K] U mean velocity [m/s] u0 fluctuating velocity part [m/s] uτ friction velocity [m/s] v velocity [m/s] xc position of interference device in x-direction [m] yc position of interference device in y-direction [m] yn wall-distance [m] y+ normalized wall-distance [-] α angle of attack [◦] δij Kronecker delta [-] µ dynamic viscosity [kg/(m s)] µs static friction coefficient [-] ν kinematic viscosity [m2/s] 2 νt turbulence eddy viscosity [m /s] Π dimensionless product [-] Πcount number of dimensionless products [-] ρ density [kg=m3] 2 τw wall shear stress [N/m ] ◦ φwing anhedral angle of wing [ , rad] ◦ 'lean lean angle of motorcycle [ , rad] 1 Acronyms CAD Computer Aided Design CFD Computational Fluid Dynamics FIM F´ed´erationInternationale de Motocyclisme FL Finish Line RANS Reynolds-averaged Navier-Stokes equation VLM Vortex Lattice Method Constant values To avoid any misconceptions, due to different definition-style in various literature, following values yield throughout this document. They are mainly based upon the standard values provided by Ansys Fluent. −2 g0 9.81 [m=s ] 3 ρ1 1.225 [kg=m ] µ1 1.7894e-05 [kg=(m · s)] T1 288.16 [K] 2 Chapter 1 Introduction A first thing to identify is what motorcycle type should be subjected for improvement. Clearly when aerodynamics is the topic, the fast going road racing machines are the ones with most to gain. The road racing motorcycle is a definition that includes all types of motorcycles that may compete by doing laps or sprint races on paved, closed down, purpose built race tracks. These tracks have a high number of corners, thus making cornering speed and agility a key element for success. Within road racing, there are several different categories in which motorcycles may compete. Mainly there are two premier classes. One that is referred to as MotoGP - a category purely focused on prototype racing with less strict regulations in an attempt to encourage creative thinking and development. The other category is Superbike World Championship where the focus is to get as much racing for as small cost as possible. This results in production bikes that are heavily regulated. As this thesis aims to provide a plausible aerodynamic cornering improvement, the aim is to be within the more lenient MotoGP regulations. However, the aim is not to present a final concept, but merely to provide some basic analysis whether the idea is at all realistic or not. 1.1 Early History of Motorcycle Aerodynamics In the early years much of the focus regarding aerodynamics for motorcycles, was simply focused on streamlining. And very much so, various concepts that were brought to light, would challenge different speed-records of the day. The idea was basically to create a tear- drop shaped faring that would cover the rider as much as possible. They also tried to build the motorcycle as low and narrow as possible to reduce the frontal area. Figure 1.1: Left: In early 1950's the typical \dustbin" fairing were popular as shown by Giulio Carcano's Moto Guzzi. Right: In 1957 FIM banned these types of fairings and the \dolphin" shape quickly became the norm. [5] However, these massive fairings turned soon out to be dangerous in crosswinds and cumber- some when cornering. It soon became clear, that to make fast and safe motorcycles, which 3 can go around twisting race tracks, many other considerations had to be taken into account. This led to motorcycles with more open, yet sleek, fairings. A concept which seems to have stood the time, since the basics layout, appears to be similar to even todays machines. Knowing this, raises the question whether the industry is reluctant to change or if this basic concept is actually so good, that any radical changes will most likely fail. What is known, is that countless attempts have been made to improve on this classic design. How many and with which ideas, is something one can only speculate, since these sort of things are usually close guarded secrets. 1.2 Focus on cornering It is clear that if one would find a way of how to improve cornering, the advantage would be substantial. A typical MotoGP track consists of a high number of sweeping corners. Even the majority of road sections that are between corners, that may look like straights, are actually no real straights since the motorcycle has to prepare for the next corner right away. In section 2.3, an example is given of the traditional racing track TT circuit Assen. Notice how turn 1 to 4 can be considered as a one sweeping corner. Cornering can obviously be improved by aerodynamic means. Placing a wing that creates negative lift (downforce) increases the normal force, thus enabling the static friction force to reach higher values. Inuence of Lift coecient during Cornering on a vehicle for unbanked turns 600 2 1 2 mv equation: s ( mg 0 – 2 C L ρ ∞ v Aw ( = 500 rc values: s = 1 m = 600 kg A = 1.47 m2 CL = –2 400 w v [km/h] 300 CL = –1 200 CL = 0 100 50 100 150 200 250 300 rc [m] Figure 1.2: Visualization of the great speed advantage a higher downforce can provide.