Aerodynamic Development Of Land Speed Record Car Engineering Essay

Aerodynamic victimisation Of overthrow Speed Record motorcar Engineering EssayThis project is foc workoutd on the baseline streamlined analyses and optimisation of a Land Speed Record fomite in scathe of actionance of tail and aerodynamic stability, and thereby, speed the fomite derriere attain. The fomite Stay Gold shown at a lower place belongs to the David Tremayne, a Formula One journalist. It is his plan to chemise the underway British Land Speed Record by achieving a speed of about 350 m/s. A photograph of the fomite in its current form stinker be seen below.CUsersCecilDesktopDSC07489.JPG jut out 1, (20)- Photograph of the Land Speed Record fomite in its current form.In aerodynamic analyses, the preventive costs of conventional wind testing along with the advent of computing power, characterised by its decreasing cost has brought the applications of Computational Fluid Dynamics (CFD) to the fore depend of research and industrial applications, (2). The complication s of actual wind tunnel testing ranging from differences in bounce conditions to the scale and mounting of the object is c everywhereed well in exist literature, (1). CFD is a method for analysing complex fluid scat problems using numerical methods to solve the Navier-Stokes goerning equations.This report begins with the study of superior speed vehicle aeromechanics to understand the important physical phenomena taking place, i.e. Air flows linked with opposite parts of the vehicle. CFD has been established as a proven tool used to perform baseline simulations with different turbulence models, demarcation conditions and control grids. Consequently, the influence of compressibility by running cases with progressively rapid operating speeds up to Mach 0.5 and the effects of varying the geometry of draw close and ashes of the vehicle using low-drag f line of creditings are studied.Literature Review eminent Speed Vehicle AerodynamicsAerodynamics is the study of discordant forces when a dead body is in motion. As we know, any vehicle moving finished a fluid experiences forces induced by the fluid on it. When a vehicle moves forrader it displaces the static air in front of it and hence disrupts the air flow rough the body. These induced fluid forces atomic number 50 be characterised into triad main forces which can be represented on a Cartesian coordinate system as shown in the go in below, (19). see to it 2, (19)- Forces acting on a vehicle represented on Cartesian coordinate systemThe vertical force along the Z axis is called lift. In this context, the vertical force is usually push button the car towards the ground. Lift force then would be negative. Instead, the term downforce will be used, which is the positive vertical force towards the ground.The horizontal force moving in the opposite direction as the vehicle along the X axis is called drag force. Drag force is created by the vehicles resistance to motion moving through the air. . Drag w ill always be negative with this axis system, although in the results it will be displayed as positive, (19).The horizontal lateral force along the Y axis is called locating force which occurs due to strong cross winds or by vehicles being in proximity to each other. The magnitude of these forces depends on various factors like the geometry speed of the vehicle, mass of the fluid, viscosity compressibility. These three forces are the basic aerodynamic forces that act on a moving solid body. We concentrate on the reducing the drag force alone to achieve higher speeds.Aerodynamic FlowsThere are various kinds of aerodynamic flows considered important in a vehicle ranging from flows associated with the external strain of the vehicle to the flows existing in the lubrication and cooling systems of the vehicle which are called external and internal flows respectively, (3).CUsersCecilDesktopUntitled.jpg kind 3, (4) Attached flows and separated flows over a body.The streamlines are the curves associated with a pictorial description of a fluid motion, in this case air particles move along the streamlines, (4). Using this definition we can differentiate the flows. When the streamlines near the solid bob up follow the shape of the body, the flow is considered to be attached and if the flow does not follow the shape of the body, the flow is considered to be separated, (4). As seen from the figure above, separated flows leave behind trailing vortices which result in an unsteady agitate flow which can be seen in the figure below.CUsersCecilDesktop1-s2_0-S0167610501001611-gr11.gif participate 4, (5) Trailing vortices in the wake of a conventional fastback carIt is also important for Race Car engineers to know whether the flow is stratified or turbulent since features such as flow interval and vehicle drag can change dramatically within these two flows, (4). When a body travels in an undisturbed environment, the flow can be considered laminar. Conditions such as wind s or the motion of other vehicles directly affects the flow causing turbulence. Turbulence is a chaotic and random state of motion develops in which the velocity and pressure sensation change continuously with cartridge holder, 22.Characteristic of Aerodynamic flowsExternal Automotive flows can be characterised as those involving excessive flow separation, transitional flows, strong cross flows and streamline curvature with a turbulent wake interacting with the ground term layers, (5). The prevailing rural areas where the separation of air flow takes place are the front and rear windshields. This separation of air flow leads to change in pressure over the surface of the vehicle which constitutes the aerodynamic drag of the vehicle. Pockets of high and low velocities are created around the vehicle because of this separation. The variation of pressure over a vehicle is shown in the figure below and is measured by a coefficient of pressure, denoted by Cp. According to Bernoullis eq uation, the low pressure region denotes high velocity and high pressure region denotes low velocity. Cp is addicted by the ratio of the difference in pressure on any point of the vehicle to the dynamic pressure.CUsersCecilDesktop109741_3mg.jpgFigure 5, (4) Variation of pressure over a vehicle leap LayerThe layer between the vehicle and the moving air where the fluid flow is stagnant or less is called the bourne layer and is a significant aspect at high speeds. When the body is in motion, a sexual congress velocity is created between the vehicle and the air around it due to the fluid viscosity. Boundary layers may be either laminar or turbulent depending on the value of the Reynolds number. For lower Reynolds numbers, the boundary layer is laminar and the velocity changes uniformly as one moves away from the wall and for higher Reynolds numbers, the boundary layer is turbulent and the velocity is characterized by unsteady (changing with time) swirling flows inside the boundary la yer, (7). In real environment it is inevitable that the boundary layer detaches from the solid body which results in a large increase in the drag on the body. So at high speeds, it is important to maintain an attached and laminar boundary layer with a streamlined shape (4).CUsersCecilDesktopboundlay.gifFigure 6, (7) Boundary layer on a surface of a vehicleCompressibility effectsCompressibility is the measure of change in people of the air relative to the speed. We are dealing with subsonic speeds (less than Mach 1) where the air acts as if its an incompressible fluid meaning the density will remain immutable though the velocity and pressure are variable, (6). By Bernoullis principle when air enters a body or part of the vehicle, air must travel faster to get to the other side as the bypass air varying the pressure and velocity. The velocity and pressure return to their original form at the outlet.Importance of the speed of sound hold up is the pressure disturbances radiating in a ll directions from the vehicle. In subsonic flight sound waves radiate from all points on the vehicle and can travel faster than the vehicle itself as shown on the figure on the left.CUsersCecilDesktopasw.pngFigure 6, (6) Propagation of sound waves in subsonic and supersonic speedsCUsersCecilDesktopas.pngAs the vehicle travels at higher speeds, these sound waves pile up at the twist of the aerofoil and create shock waves as shown in the figure on the right. These shock waves are created due to change in pressure velocity of air flow and these waves cannot get ahead the originating point at the speed of sound. There are different kinds of shock waves which are discussed below. Oblique Shock waves are formed on sharp edges of the body with the air surface changing in the direction of air flow, basically on leading and trailing edges of the airfoil, (6). Normal shock waves are formed in front of a blunt body or on the body itself. The molecules pile up at the front and form a detach ed wave called the bow wave, (6). Expansion shock waves are formed in the regions of separation on the body or airfoil. Shock waves are very important in high speed aerodynamics as it affects the change in direction of the fluid flow and are relatively negligible in subsonic flows.Relevance of Aerodynamic DragIn aerodynamics, drag is defined as the force that opposes forward motion of the vehicle through the atmosphere and is parallel in the direction of free stream velocity of the air flow which can be overcome by thrust in order to achieve forward motion, (8). Generally in racing it is important to have to downforce to keep the vehicle stable on the ground. When going at speeds over 100 mph, the real drag is experienced.The aerodynamic drag is denoted by Cd and is given by the formula,Cd= Drag force/ (Dynamic pressure*Area)A body moving through a fluid experiences drag which can be divided into two components, frictional or viscous drag and pressure drag, (11). Frictional Drag is developed due to friction of fluid and the surface it is flowing on, commonly associated with development of boundary layers, (11). Pressure drag is formed from the eddying (turbulent) motions behave up by the fluid as it passes over the body which is associated with the formation of wake behind the vehicle. Hence the geometry of nose and body shape plays an important role in reducing drag on vehicle, (12).The figure below shows the driving force required to propel the vehicle forward at a constant speed as a function of the aerodynamic drag. We can see that the aerodynamic drag increases proportional to the full-strength of speed.CUsersCecilDesktopUntitled.pngFigure 7, (11) Driving Speed Vs Vehicle SpeedIt is also established that the drag prediction over the front of the vehicle, especially involving attached boundary layers and, subsonic flow is far easier and more accurate than the analysis of the rear of the vehicle, (11).Review of existing research, (13)Extensive research has been made in this area with exact experimentation on the widely known Ahmed model, (12). The Ahmed model is a simple geometric body that retains the main flow features, especially the vortex wake flow where most of the drag is concentrated. This model is used as a reference model to compare our results with. An illustration of this model is shown in the figure below.CUsersCecilDesktopUntitled.pngFigure 8 Left Geometric dimensions of an Ahmed model, Right Computational worldThe Ahmed reference model is a general car type bluff body shape which is enough for accurate for flow simulations. boundary conditions used for this problem are uniform flow at the inhalation no slip on the surface of the body and a non-structural tetrahedral grid approach is applied to this geometry at Re= 4.25106, (13) . This flow was solved using incompressible Navier-Stokes formulations and the drag and pressure were measured. From the figure below, it is discover that the total pressure drag is min imal at the front portion and is high the rear slanted portion of the body. Subsonic interactions are fairly abstemious as the length of the body is long. CUsersCecilDesktopUntitled.pngCUsersCecilDesktopUntitled.pngFigure 9A,(13) Contour fill field pressure Figure 9B, (13) Contour fill field velocityAnd as for the pressure measurements, the presence of vortices at side edges of the slant surface appears to be two dimensional with parallel isobars running over the surfaceCUsersCecilDesktopUntitled.pngCUsersCecilDesktop2.pngFigure 10A Flow behind the rear side of the body, Figure 10B Streamlines in the wakeTurbulent flows are completely three dimensional and unsteady. Using a time average flow, some sort of macrostructure appears to govern the pressure drag on rear end. Figure 10A shows the different wakes created due to different shapes and edges and Figure 10B shows the streamlines in wake structure.Land Speed Record (LSR) RacingEver since the inception of automobiles, there ha s always been an inherent drive to push the automobile to its limits in terms of doing and speed. Land Speed Record is highest speed achieved by an automobile on land. There are different classes and organisations with respect to the configurations of the vehicle, operating speeds and environment. The current vehicle belongs to the inexhaustible class, which is a special class for thrust powered vehicles which may be propelled using turbo jet engines and without any limitations over wheeled power, (14).Existing researchThe close-set(prenominal) vehicle comparable to Stay Gold LSR is the JCB dieselmax (shown below) which holds the land speed record for a diesel-powered vehicle having been determined to over 350mph breaking the world record at the Bonneville Salt Flats. The aerodynamics of the car was designed entirely using ANSYS Fluent by aerodynamicist Ron Ayers whose goal was to achieve an optimal balance between aerodynamic drag, scratch up force and downforce, (15). It has been observed that the Cd of the vehicle was 0.17. After running a number of simulations, it is shown that higher downforce generated by the wings increases the drag on the vehicle drastically, (16).CUsersCecilPicturesjcb_dieselmax.jpgFigure 11, (17) Picture of a JCB dieselmax streamlinerAnother example is the Buckeye Bullet 3 (BB 3), which operates on a battery. This vehicle was developed using an alternate aerodynamic method. In order to test the body shape and geometry a new wind tunnel model was constructed though it is time consuming and costly. The vehicles frontal area was significantly reduced allowing the driver to be placed at an inclined position keep safety in mind, (18) though the driver in centre of attention (DIM) configuration used in BB1 BB 2 has better performance compared to the former. BB 3 also achieves more stability because it maintains negative pitch over higher speeds ensuring the sane loads on the tyres are not reducing, improving traction and yaw stab ility, (18). BB 3 had a 17 % reduce in the Cd compared to its predecessors.CUsersCecilPicturesBuckeye-Bullet-3-thumb-450255.jpgFigure 12, (18) Photograph of a Buckeye Bullet 3 at the Bonneville Salt FlatsComputational Fluid DynamicsIntroductionComputational fluid dynamics or CFD is the analysis of systems involving fluid flow, heat transfer and associated chemical reactions by means of computer based simulation, 21. CFD is used in wide range of industries. CFd contains a set of codes structured around the Navier-Stokes Equations (NSE) that are used to solve fluid flow problems. NSE are the governing equations of Fluid dynamics which are shown below.CUsersCecilPicturesnseqs.gifFigure 16, 22 Navier-Stokes equations of three dimensional fluid flowsThe NSE consists of time-dependant continuity equation for conservation of mass, time dependant conservation of momentum equations and conservation of energy equations, 22. The integral forms of these equations are solved using Finite Volum e Method (FVM) which is the discretisation method ANSYS Fluent uses. Discretisation is a method of converting higher order integral equations into a system of algebraic equations. These set of algebraic equations are later solved by an iterative method, 23.As mentioned earlier, at higher Reynolds numbers flows are observed to become turbulent. We used turbulence models in CFD to approximately model the turbulence in real time environment and results obtained are deemed near accurate.All codes in CFD contain 3 main elements 1.) A pre-processor, 2.) A solver, 3.) A post processor, 22.Pre-processingThe activities involved in this stage areDefinition of geometry in the computational domainGrid generation discretising the domain into little cells ( grid or engagement)Define fluid properties and specify the appropriate boundary conditionsSolvingThere are different techniques to solve numerical equations. CFD uses finite volume method which is the most established method in different s oftwares. The steps involved in this stage areIntegration of NSE over control volumes of the domainDiscretisation of resulting integral equations into a set of algebraic equationsSolution of the algebraic equations using an iterative methodPost-processingA large amount of work has been put into CFD packages to realise the data with outstanding graphics due to the increasing demand in the engineering field. Some of the most popular data visualisation tools are celestial sphere geometry and grid display2D and 3D surface and vector plotsStreamlined and shaded contour plotAt present, almost all Formula 1 teams use CFD to constantly optimise the aerodynamics of their cars for better performances in a race. The bottleneck of CFD was quick and efficient construction of a functional grid which has become more user friendly in modern times which makes it easy for meshing, 22.ConclusionsAerodynamics CFD play a key role in the optimisation of a Land Speed Record vehicle. The geometry, powerp lant, wheel configurations and vehicle dynamics are important parameters in achieving reduced drag. Open wheel configurations cause more overall drag on the vehicle. Also the tyres effective radius changes with speed and is necessary to test the relationship between the vehicle speed and tyres geometric configuration due to constant downforce exerted on the vehicle by the wings. This was the case revealed in the JCB streamliner.Project PlanStudy Vehicle Aerodynamics Understand the various aerodynamic flows involved in a vehicle. Get a good grip on High Speed Aerodynamics. Read about Importance of the speed of sound in achieving high speeds and influence of compressibility.Computational Fluid Dynamics (CFD) Reading on the background of CFD and understand how Navier-Stokes equations are derived, Numerical discretisation of equations using Taylor series. Understand turbulence modelling, grid sensitivity and boundary conditions relevant to the problem.CFD Tutorials Tutorial 1 Create basic geometry for backward facing step (2D).Tutorial 2 Create basic geometry for lid drive cavity (2D).Tutorial 3 Create 3D model of cylindrical body with a rectangular grid and run simulations.Gantt chartCUsersCecilDownloadsAerodynamic suppuration of LSR (1).pngProgress to dateWith the help of Dr. Carl Gilkesons CFD tutorials, creating meshes of basic geometrical shapes and running simulation on them was possible. The first tutorial involves creating the geometry in Design Modeller for lid driven cavity. The mesh was created in ANSYS Mesh and running simulations with undertake boundary conditions, velocity pressure was done in ANSYS Fluent.In the figure below, the mesh for the lid driven cavity is shown.CUsersCecilDesktopCavity- Vel Contours.pngFigure 13A Mesh for lid driven cavity Figure 13B Velocity contours on the top wall of the cavity CUsersCecilDesktopCavity.pngThe mesh was solved for 1000 iterations and were run on the top wall with a transitional velocity of 1.4607 e-03 (Re=100), ensuring the flow is laminar. The velocity contours are filled and can be seen in figure 13B.The second tutorial involves creating a backward facing step. This model is solved (1000 iterations) for turbulent conditions so a turbulence model (k-epsilon) was created and specified with an inlet velocity of 40m/s. Also this model is discretised to second order upwind for momentum, turbulent kinetic energy and turbulent dissipation rate. The results are shown below.CUsersCecilDesktopUntitled.pngFigure 14A- Mesh for Back Facing Step Figure 14B- Velocity contours on the backstepCUsersCecilDesktopMesh Backw step.pngIt is noted that the horizontal component of the velocity is negative behind the step as the flow reattaches after detaching due to high Reynolds number, 20.3D model of a cylinderIAnsys projectscylinder.jpgFigure 15A 15B(below) Mesh for 3D cylinder in a rectangular gridIn the figure above, a cylindrical mesh in a rectangular grid was created in ANYSYS Mesh. A re ctangular grid is created in the domain to solve finite volume system of equations and to get more accurate solutions. The model was solved for constant pressure at the inlet to get reversed flow on all faces using hybrid initialisation as seen below.IAnsys projects12.jpgReferences1 P.R. Spalart, Strategies for turbulence modelling and simulations, Boeing Commercial Planes(Feb 1999).2 W.H.Hucho, Aerodynamics of avenue vehicle 4th edition.3 New Directions in Race car aerodynamics, Joseph Katz.4 Joseph Katz, Race Car Aerodynamics, second edition.5 Ahmed, S. R. , Gawthorpe, R. G. and Mackrodt, P. -A.(1985) Aerodynamics of Road- and Rail Vehicles, Vehicle System Dynamics, 14 4, 319-3926 High Speed Aerodynamics, Seminar, Harry L Whitehead.7 http//galileo.phys.virginia.edu/classes/311/notes/fluids2/node11.htm8 http//www.pilotfriend.com/training/flight_training/aero/drag.htm9 http//www.princeton.edu/asmits/Bicycle_web/blunt.html10 Miles Jackson , B. Taylor Newill and Perry Carter ,Race car Aerodynamic Optimization for an E-1 Class Streamliner Using Arbitrary Shape Deformation , SAE Technical paper 2007-01-3858.11 Hiroyuki Ozawa, Dai Higashida,Development of Aerodynamics of a Solar Race Car, Honda RD, 1998 SAE.12 Sinia Krajnovic, Lars Davidson, Flow Around a Simplified Car Part 1 Large Eddy Simulation,13 CFD exemplar of Flow around the Ahmed vehicle model, Gerardo Frank and Jorge DElia, Centro Internacional de Metodos Compucionales en Ingeneria.14 http//www.landspeed.com/archive/classroom/classlsrbasics.html.15http//www.newmaterials.com/News_Detail_Aerodynamics_of_jcb_dieselmax_car_designed_entirely_with_cfd_code_fluent_9408.aspaxzz2H86gSGFW16 Aerodynamic Development of Buckeye Bullet Electric LSR, Carrington Bork, Department of Mechanical Engineering, Ohio secernate University.17 http//www.carsbase.com/photo/photo_full.php?id=4546918 www.buckeyebullet.com/BB3.html19 Fundamentals of Vehicle Dynamics, Thomas D. Gillespie, Society of Automotive Engineers, 400 Commo nwealth drive, Warrendale, PA 15096-0001.20 CFD tutorials, Dr. Carl Gilkeson, University of Leeds.21 http//www.grc.nasa.gov/WWW/k-12/airplane/nseqs.html22 An Introduction to CFD, H K Versteeg and Malasekara, 2nd edition.