Methods Of Evaluation Of Vehicle Aerodynamics

Methods Of Evaluation Of Vehicle silklikesPart a) Different methods of evaluation of fomite sleeksIn recent years aerodynamics of vehicle has gained a lots of attention because of the major use of negative lift (down force) principle which improves the performance of vehicles. Thus evaluating vehicle aerodynamics has become an historic part of car engineering and it is no longer only limited to vehicles initial designing. Several method and tools be apply in this process such(prenominal) as rescind tunnel interrogation, computational liquified aerodynamics or track testing. Each of these tools has their special necessitate for e.g.- at initial design stage wrap tunnel can be use and after car is built it can be tested on the track. In the fol humbleding paragraphs i discuss three mostly used methods i.e. pervert tunnel testing, CFD package and track testing.http//www.atzonline.com/cms/images/sh05-09-20.jpgWind tunnel testingIn 1870s first arise tunnel was designed howe ver until 1960s it was just meant to use for aeronautical purposes that once this method brought to use for automotive purposes, inside no time it became an essential part of car developments and provided good environment for aerodynamic evaluation.In the wind tunnel testing method a geometric shapes or specimens is mounted in the test section of wind tunnel and air is blown over or sucked through a duct by a fan or turning of fans. To make measurements more finished stringently spaces vertical and horizontal air vane be used which smoothes the miffed come before it reaches the representative. Usually, measurements are taken from a balance on which model is mounted and various visualisation techniques such as smoke and tufts are used to understand the affect of some geometric features on aerodynamic performance.Wind tunnel helps to acquire lots of data such asAerodynamic forces drag, lift, side forceVariation of these forces and movements with yawVehicle cooling dragAffec t of aero featuresSurface squelch distributionThere are different display cases of wind tunnels which are as followsLOW SPEED WIND TUNNEL withal named as SUBSONIC WIND TUNNEL are of open return type or return flow in which air is moved with a propulsion system made up of a huge axial fan which helps in increasing dynamic pressure and thus helps to overcome viscous loss. In this type mach number is kept very low and speed is well-kept up to 400 km/hhttp//en.wikipedia.org/wiki/Subsonic_and_transonic_wind_tunnelSubsonic_tun)Staffordshire University logoHIGH SPEED OR TRANSONIC WIND TUNNEL is designed to reach the speed close to the speed of sound. Mach and Reynolds number both are important here due to viscous or in viscid interactions. As compared to subsonic wind tunnel, oftentimes large scale facilities and pressurized wind tunnels are used.(http//en.wikipedia.org/wiki/Subsonic_and_transonic_wind_tunnelSubsonic_tunnel)SUPERSONIC WIND TUNNEL generates supersonic speed. In superson ic wind tunnel, high pressure ratio is necessitate and to avoid occurrence of liquefaction or condensation drying or pre heating facility is required.http//upload.wikimedia.org/wikipedia/commons/thumb/f/f0/Supersonic-en.svg/400px-Supersonic-en.svg.png(http//reference.findtarget.com/search/supersonic%20wind%20tunnel/)HYPERSONIC WIND TUNNEL produces hypersonic flow field in test section. It runs with very high pressure ratio and like supersonic hypersonic likewise requires pre heating facility. As compared to other types of wind tunnels, hypersonic wind tunnel has more challenges in its designing.Staffordshire University logo(http//commons.wikimedia.org/wiki/FileLangley_hypersonic_wind_tunnels.jpg)WIND TUNNEL SCALEModel scale wind tunnel testing (MWT) plays an important power in aerodynamic development of motorsport vehicles, training and research though now it has been outmoded by CFD.wind_tunnel1Figure http//www.insightman.com/mag_photos/wind_tunnel1.jpgIt is an ideal way to dete rmine the affects of various features and ashes styles on aerodynamics of vehicles. In model scale testing, model lie between 30%,60%nand they can be be produced by various techniques such as fibre glass, stylist clay models, milled foam and rapid prototype models or a combination of all of these.Model scale testing doesnt needs high running cost as sophisticated test methods such as fitting a moving ground plane doesnt need high expense. In all, if styling method can be utilized than this testing method is a cheaper method to develop vehicle aerodynamics.Staffordshire University logoIn scandalize of all, model scale testing has its own limitation such asEnsuring geometric similarity some special features can be difficult to model at small model scale.Reynolds number effects Reynolds number (Re) of the flow around vehicles reduces with the reduction in scale which then requires an appropriate increase in the airflow.FULL SCALE WIND TUNNEL TESTING (FSWT)-FSWT has totally taken over MWT as it many problems approach during MWT are overcome by apply full scale testingIt eliminates the effect caused due to Reynolds number.It totally avoids the cost of production of models.It helps to determine the influence of small geometric changes.Aerodynamics Radical LMP2 in MIRAs Full Scale Wind Tunnel(http//www.mira.co.uk/Services/AerodynamicsMainPage.htm)COMPUTATIONAL FLUID AERODYNAMICS (CFD)It is a phenomenon or software used to improve the car aerodynamics. The software provides benefits from number crunching capability of computers used to solve the problems of fluid flow, heat transfer and related processes like chemical reactions with the use of simulations of fluid flow. The fluid here refers to a lot of substances as well which behave like fluids depending on the peck they are in, for example, winds blowing around buildings, cooling air flows in a laptop, drugs in asthma inhalers etc. It mainly focuses on affects made by pressure, temperature, density and the ve locity of the fluids. It is powerful technique software with a wide range of applications. It is very ordinarily used software in automotive assiduity (the method has an ability to calculate the air flows around a vehicle or car), especially in motorsports because of the massive competition. It first came in light in 1990s.The software is now owned by Bar Honda Formula 1 team. The software has always been updated at times as the as the newly computer technologies come in. since the software runs of a computer, the speed of the computer processor likewise plays an important role in improving the performance, in other intelligence activitys, more powerful the supercomputer, more accurate result of CFD process. As the time passes it has become cheaper and advanced.Staffordshire University logoStreamlines under a contain car (http//strangeholi daylight.com/oops/stuff/annurev.fluid.38.050304.092016.pdf)Working process of computational software is divided into phasesFirst of all, it divides the geometric structure of the object into a set of elements or stall which named as a mesh. The accuracy of the result of CFD totally depends upon the number of cells as higher their number is, more accurate result will be.Secondly, mesh representing meretriciousness occupied by the fluid is created. Now, when fluid flow comes into contact with the object, it gets separated into as many cells as possible.Then, computer starts finding out the problem it faced during the second phase. Besides this, it also set up a clear image of interaction of object and fluid flow. Finally, simulation is started and result obtained is analyzed.Staffordshire University logoINSTRUMENTED highroad OR TRACK TESTINGThis testing method has earned lots of popularity in short time as it a very cost efficacious testing method as all we need to perform this is good weather and cost of renting a track and instrumenting. Aerodynamic drag plays an important role to improve the performance (fuel cons umption, speed) of car. These tracks are constructed especially for the vehicles which are new or are under research. The tracks are made under such circumstances that when testing a car it gets the most relevant or most accurate results.DSC_05442Figurehttp//www.speedsportlife.com/wp-content/2009/11/DSC_05442.JPGThese tests are used to identify the different properties or aspects in different conditions such as traffic flow, weather (raining, dusty, snowing or at different wind flows) and time of day. The car is made run on the track at different and constant speeds to check the flow ratios with the help of the sensors fixed on both sides of the track. The sensors track the dynamic path of the car which give information about the flows and performance of the cars. The aerodynamic behaviour of the vehicle is then analyzed and the car is again made run on the track with meliorate or modified aerodynamic properties.Part 2Staffordshire University logoComputational Fluid Aerodynamics ( CFD)The science that tries to verify a numerical solution to the equations that govern the fluid flow is called CFD (Computational Fluid Dynamics). In the recent years, CFD methods have been utilized as an important tool of design analysis within research organisation and industry with the help of supercomputers. In fact, science is now trying for the theoretical-experimental treatment so that results which are obtained in wind tunnel testing can be used to standardize and prove the numerical models.As everything have its dual aspects, so as CFD. It has its own lots of advantages and some disadvantages too which are discussed as followsMERITS-A large number of CFD simulations can be performed rapidly and of course it is way cheaper than make a real model and running it in a wind tunnel or an instrumented track. With CFD there is always a greater probability of getting design right first time before manufacturing the actual vehicle because overall concept and shape can be tested. CF D enables the designer to analyze and visualize the flow around the vehicle. It can be done a number of times to facilitate the design optimization. It is much cheaper than to perform a wind tunnel test.Auto optimization is the advanced form of CFD and is considered to be more accurate. In it computational methods that accesses mathematically the obtained results and makes changes to the configuration and the shape of the vehicle. It automatically selects the most suitable design.Automatic mesh deformation is one of the advancement in auto optimization. perform computational optimization method and automatic mesh together, it is possible to explore geometry changes and the software alters the mesh along with the geometry.CFD technology helps to improve the aerodynamic performance of vehicles and also helps in reducing co2 emmision.Thus, this testing method not only serve a duty for automotive purposes but also helps in retention environment pollution free.Staffordshire University logoDemeritsNo doubt CFD is a best tool among all other ways of determining vehicle aerodynamics but scaling issues can create some limitations to it such as reduicton of transition from laminar to turbulent flows (e.g. boundary layers) or the calculation of separated flow and irregular wakes.)CFD can make millions of calculations to achieve an accurate result but the final result can only be appropriate for some reasons like non accurate or less accurate data, scientific knowledge base or reduction in number of calculations by supercomputer.So, there are more chances of making numerical misconducts since everything relays on computers. Besides this, approximation of result can cause Truncation errors and round off errors are also possible due to the word size available on a particular computerThe bottom line is that solutions find by CFD rely upon user-defined elements like grid generation and upheaval modelling, which will be soon an obstacle facing code developers. It is not ye t possible to create full flow field model economically as in mostly vehicles the large scale flow regimes depends on inevitability of transition and turbulence.PART 325mphPressure imageE25MPH25mph Pressure.gifThe pressure is very low (-21.71446) on swiftness and put down come on of wing .It is more (33.87485) on apparent movement apex of wing and also it is less( 23.76770) on front upper and spurn rise, it also akin on back upper and lower surface of wing. fastness imageE25MPH25mph Velocity.gifThe velocity is very low (1.854647)on front tip of wing and it is high (6.536719) on upper and lower front surface of it. It is also same on back upper and lower surface of wing. Velocity is really low (9.658100) on lower surface and upper surface of wing but on mid portion of upper surface it is (7.317064)45mphPressure imageThe pressure is very low (-16.66089) on middle upper and lower surface of wing .It is more (38.92842)on front tip of wing and also it is less( 23.76770) on front upper and lower surface, it also same on back upper and lower surface of wing.E45MPH45mph pressure.gifVelocity imageThe velocity is very low (2.634993)on front tip of wing and it is high (8.097410) on upper and lower front surface of it. It is also same on back upper and lower surface of wing. Velocity is really high (9.658100) on lower surface and upper surface of wing but on mid portion of upper surface it is (7.317064)E45MPH45mph velocity.gif65mphPressure imageE65MPH65mph pressure.gifThe pressure is very low (-1.500165) on upper and lower surface of wing .It is more (33.87485) on front tip of wing and also it is less( 18.71413) on front upper and lower surface, it also same on back upper and lower surface of wing.Velocity imageThe velocity is high (6.536719)on upper and lower front surface of wing. It is also same on back upper and lower surface of wing. Velocity is really high (9.658100) on lower surface and upper surface of wing but on mid portion of upper surface it is (7.3170 64)E65MPH65mph velocity.gif85mphPressure imageE85MPH85mph pressure.gifThe pressure is very low (-16.66089) on upper surface and also low on lower surface(-11.60731) of wing .It is more (33.87485) on front tip of wing and also it is less( 23.76770) on front upper and lower surface, it also same on back upper and lower surface of wing.Velocity imageThe velocity is high (8.097410) on upper and lower front surface of it. It is also same on back upper and lower surface of wing. Velocity is really high (9.658100) on lower surface and upper surface of wing but on mid portion of upper surface it is (7.317064)E85MPH85mph velocity.gifPart 4 Conclusion Staffordshire University logoAs the technology improves day by day the things (automobiles) get cheaper, smaller (size) and advanced. Since there are a lot of ways of aerodynamic testing, but the CFD software is the best way of evaluating the aerodynamic performance of the car.There are a lot of thing which make CFD the best. Like we can also ev aluate the aerodynamic performance of the car using methods like wind tunnels but using wind tunnels it becomes far more expensive (making arrangements for the sample model), whereas in CFD we just need a CAD model and everything is done more quickly than any other method. Also if the model needs any changes or modifications it is very easy as compared to making new models for wind tunnels.CFD is more affordable and there is no maintenance required whereas wind tunnels and instrumented tracks needs a lot of maintenance at the time of consummation or when free.There are very less or no chances of any errors in CFD (since everything is done with the help of computer) only a human error could affect the results, whereas in the case of track testing and wind tunnels the probability of making errors is more as big machinery or equipments are used which are analyzed by humans (no doubt computers are more reliable).There are lots of models (heavy) which are dangerous to test in wind tunne ls in full scale, whereas in CFD the simulation can be performed without worrying about anything.Using the mesh deformation makes the calculations more clear, one can focus on each and every single part the vehicle or model tested as compared to an overall result obtained from track testing or wind tunnels. It takes very less time to carry out the results.So CFD is the best method for testing the aerodynamic performance and it will become better and cheaper as the computers get more powerful and cheaper.Staffordshire University logo