Aerodynamic Development Of Land Speed Record Car Engineering Essay

sleek Development Of institute belt along shew gondola car Engineering EssayThis project is foc employ on the baseline silky analyses and optimisation of a Land pelt along disc fomite in terms of performance of reap and aerodynamic stability, and thereby, upper the fomite fag end attain. The fomite Stay Gold shown infra belongs to the David Tremayne, a Formula One journalist. It is his plan to break the current British Land Speed place down by achieving a hurry of about 350 m/s. A photograph of the vehicle in its current form jackpot be seen below.CUsersCecilDesktopDSC07489.JPG count 1, (20)- Photograph of the Land Speed Record vehicle in its current form.In aerodynamic analyses, the prohibitive cost of conventional wind tribulationing along with the advent of computing power, characterised by its decreasing cost has brought the applications of Computational Fluid Dynamics (CFD) to the fore foregoing of research and industrial applications, (2). The complication s of actual wind tunnel testing ranging from differences in confines conditions to the scale and mounting of the object is c everyplaceed well in existing literature, (1). CFD is a method for analysing complex peregrine spring problems utilise numerical methods to act upon the Navier-Stokes g overning equations.This report begins with the study of graduate(prenominal) advance vehicle aero kinetics to sympathise the key physical phenomena taking place, i.e. line combines linked with distinct parts of the vehicle. CFD has been conventional as a turn up tool social occasiond to perform baseline simulations with different turbulence puts, bourne conditions and control grids. Consequently, the bring of compressibility by racecourse cases with progressively faster in operation(p) uppers up to Mach 0.5 and the personal effects of varying the geometry of nose and frame of the vehicle victimization low- sail fairings atomic number 18 studied.Literature Review spunky Speed Vehicle aeromechanics silklikes is the study of various effectivenesss when a proboscis is in motion. As we know, any vehicle touching through a swimming experiences forces bring forth by the fluid on it. When a vehicle moves ship it displaces the passive air in bet of it and hence disrupts the air flow virtu alto clan downhery the form. These induced fluid forces can be characterised into three main forces which can be represented on a Cartesian coordinate brass as shown in the signifier below, (19). externalise 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 pushing the gondola car towards the basis. Lift force then would be negative. Instead, the term downforce will be used, which is the positive vertical force towards the ground.The naiant force moving in the opposite caution as the vehicle along the X axis is called drag forc e. Drag force is created by the vehicles resistance to motion moving through the air. . Drag will invariably 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 facial expression force which occurs repayable to wet cross winds or by vehicles organism in proximity to each other. The magnitude of these forces depends on various factors wish well the geometry speed of the vehicle, mass of the fluid, viscosity compressibility. These three forces be the basic aerodynamic forces that act on a moving sohat body. We concentrate on the reducing the drag force al atomic number 53 to achieve in gamey spiritser speeds.Aerodynamic emanatesThere ar various kinds of aerodynamic flows considered important in a vehicle ranging from flows associated with the external shape of the vehicle to the flows existing in the lubrication and cool down systems of the vehicle which ar called extern al and internal flows respectively, (3).CUsersCecilDesktopUntitled.jpg haoma 3, (4) connect flows and unaffectionate flows over a body.The streamlines are the curves associated with a pictorial rendering 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 emerge follow the shape of the body, the flow is considered to be attached and if the flow does non follow the shape of the body, the flow is considered to be separated, (4). As seen from the figure above, separated flows leave behind(predicate) trailing vortices which result in an unsteady awake flow which can be seen in the figure below.CUsersCecilDesktop1-s2_0-S0167610501001611-gr11.gifFigure 4, (5) Trailing vortices in the wake of a conventional fastback carIt is in addition important for Race Car engineers to know whether the flow is laminar or turbulent since features such as flow separation and vehic le drag can change dramatically within these two flows, (4). When a body travels in an undisturbed purlieu, the flow can be considered laminar. Conditions such as winds or the motion of other vehicles directly affects the flow cavictimization turbulence. turbulence is a chaotic and random state of motion develops in which the fastness and press change continuously with time, 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 boundary points, (5). The prevailing subjects where the separation of air flow takes place are the front and rebel windshields. This separation of air flow leads to change in pressure over the come in of the vehicle which constitutes the aerodynamic drag of the vehicle. Pockets of high up and low velocities are created around the vehicle be piddle of this separa tion. 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 equation, the low pressure region denotes high stop number and high pressure region denotes low speeding. Cp is given by the ratio of the difference in pressure on any focalize of the vehicle to the dynamic pressure.CUsersCecilDesktop109741_3mg.jpgFigure 5, (4) Variation of pressure over a vehicleBoundary LayerThe forge mingled with the vehicle and the moving air where the fluid flow is stagnant or less(prenominal) is called the boundary layer and is a significant aspect at high speeds. When the body is in motion, a sexual intercourse stop number is created between the vehicle and the air around it overdue to the fluid viscosity. Boundary layers may be either laminar or turbulent depending on the value of the Reynolds number. For glare Reynolds numbers, the boundary layer is laminar and the velocity changes uniform ly as one moves away from the wall and for high Reynolds numbers, the boundary layer is turbulent and the velocity is characterized by unsteady (changing with time) swirling flows inside the boundary layer, (7). In real(a) surroundings 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 come out of a vehicleCompressibility effectsCompressibility is the measure of change in volume 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 constant 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 appreciation up 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. greatness of the speed of lumberingSound is the pressure disturbances radiating in all focalisations 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 nose of the aerofoil and create haze waves as shown in the figure on the right. These disaster 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 wallop waves which are discussed below. Oblique Shock waves are formed on sharp edges of the body with the air surfac e 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 detached 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 precedent 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 instal 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 deno ted 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 up 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 rate of flow on, commonly associated with development of boundary layers, (11). Pressure drag is formed from the eddying (turbulent) motions develop up by the fluid as it passes over the body which is associated with the geological 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 square of speed.CUsersCecilDesktopUntitled.pngFigure 7, (11) Driving Speed Vs Vehicle SpeedIt is likewise 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 detailed experimentation on the hugely known Ahmed bewilder, (12). The Ahmed influence is a simple geometric body that retains the main flow features, especially the whirlpool wake flow where most of the drag is concentrated. This modelling 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(a) Computational domainThe 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 inlet no slip on the surface of the body and a n on-structural tetrahedral grid approach is applied to this geometry at Re= 4.25106, (13) . This flow was understand victimization incompressible Navier-Stokes formulations and the drag and pressure were measured. From the figure below, it is observed that the jibe pressure drag is minimal at the front portion and is high the rear slanted portion of the body. Subsonic interactions are fairly bleached as the length of the body is long. CUsersCecilDesktopUntitled.pngCUsersCecilDesktopUntitled.pngFigure 9A,(13) Contour make full 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 ordinate 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 has always been an inherent jabbing to push the automobile to its limits in terms of performance and speed. Land Speed Record is highest speed achieved by an automobile on land. There are different classes and organisations with respect to the kinds of the vehicle, operating speeds and environment. The current vehicle belongs to the unlimited 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 encompassing(prenominal) vehicle comparable to Stay Gold LSR is the JCB dieselmax (shown below) which holds the land speed insert for a diesel-powered vehicle having been driv en to over 350mph breaking the world al-Quran 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, skin force and downforce, (15). It has been observed that the Cd of the vehicle was 0.17. aft(prenominal) 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 streamliner some other 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 trim back allowing the driver to be placed at an inclined position keep safety in mind, (18) th ough the driver in middle (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 habitual loads on the tyres are not reducing, improving traction and veering stability, (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 chemic 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 dissolve fluid flow problems. NSE are the governing equations of Fluid dynamics which are shown below.CUsersCecilPicturesnseqs.gifFigure 16, 2 2 Navier-Stokes equations of three dimensional fluid flowsThe NSE consists of time-dependant doggedness equation for saving of mass, time dependant conservation of momentum equations and conservation of energy equations, 22. The integral forms of these equations are solved using Finite flashiness 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 grow 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 point areDefinition of geometry in the computational domainGri d propagation discretising the domain into smaller cells ( grid or mesh)Define fluid properties and constringe the appropriate boundary conditionsSolvingThere are different techniques to solve numerical equations. CFD uses finite volume method which is the most established method in different softwares. 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 visualize the data with heavy(p) graphics due to the increasing demand in the engineering field. most of the most popular data visualisation tools areDomain geometry and grid display2D and 3D surface and vector plotsStreamlined and shaded mannequin plotAt present, almost all Formula 1 teams use CFD to constantly optimise the aerodynamics of their cars for better performances in a r ace. The coarctation of CFD was quick and efficient construction of a functional grid which has become more user friendly in modern times which makes it blowsy for meshing, 22.Conclusions aeromechanics CFD play a key role in the optimisation of a Land Speed Record vehicle. The geometry, powerplant, 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 roentgen 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. lay a good grip on High Speed Aerodynamics. pack 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 sensitiveness and boundary conditions relevant to the problem.CFD Tutorials Tutorial 1 Create basic geometry for slow-witted facing step (2D).Tutorial 2 Create basic geometry for lid driven cavity (2D).Tutorial 3 Create 3D model of cylindrical body with a rectangular grid and run simulations.Gantt graphCUsersCecilDownloadsAerodynamic Development 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 trope Modeller for lid driven cavity. The mesh was created in ANSYS Mesh and running simulations with condition 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 speed contours on the top wall of the cavity CUsersCecilDesktopCavity.pngThe mesh was solved for kibibyte iterations and were run on the top wall with a transitional velocity of 1.4607e-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 leeward 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 velo city 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 rectangular 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 turn 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 Road vehicle 4th edition.3 New Directions in Race car aerodynamics, Joseph Katz.4 Joseph Katz, Race Car Aerodynamics, 2nd edition.5 Ahmed, S. R. , Gawthorpe, R. G. and Mackrodt, P. -A.(1985) Aerodynamics of Road- and Rail Vehicles, Vehicle System Dynamics, 14 4, 319-39 26 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 ,Racecar Aerodynamic optimisation for an E-1 Class Streamliner Using Arbitrary Shape Deformation , SAE Technical piece 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 self-aggrandizing Eddy Simulation,13 CFD Modelling 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 Aerodyn amic Development of Buckeye Bullet galvanising LSR, Carrington Bork, Department of Mechanical Engineering, Ohio State University.17 http//www.carsbase.com/photo/photo_full.php?id=4546918 www.buckeyebullet.com/BB3.html19 Fundamentals of Vehicle Dynamics, doubting Thomas D. Gillespie, Society of Automotive Engineers, 400 Commonwealth drive, Warrendale, PA 15096-0001.20 CFD tutorials, Dr. Carl Gilkeson, University of Leeds.21 http//www.grc.nasa.gov/WWW/k-12/plane/nseqs.html22 An Introduction to CFD, H K Versteeg and Malasekara, 2nd edition.