Methods Of Evaluation Of Vehicle Aerodynamics

Methods Of Evaluation Of vehicle silkysPart a) Different systems of evaluation of vehicle streamlinedsIn recent years flowings of vehicle has gained a spile of guardianship beca hold of the major use of negative lift (down force) principle which breaks the serveance of vehicles. olibanum evaluating vehicle aerodynamics has be get in an consequential place of car engineering science and it is no longer only limited to vehicles initial objectiveing. Several rule and tools ar utilise in this physical process such(prenominal)(prenominal) as farting dig examen, computational fluid aerodynamics or track testing. sever tout ensembley of these tools has their special need for e.g.- at initial design stage arc delve bottom be utilize and after car is make it groundwork be tested on the track. In the fol downcasting paragraphs i discuss three close toly utilise methods i.e. travel tunnel testing, CFD softw be system and track testing.http//www.atzonline.com/cm s/ effigys/sh05-09-20.jpgWind tunnel testingIn 1870s first principal tunnel was designed but until 1960s it was fitting meant to use for aeronautical purposes but once this method brought to use for self-propelling purposes, within no sentence it became an essential part of car developments and provided good environment for aerodynamic evaluation.In the land up tunnel testing method a geometric shapes or simulates is mounted in the test section of slue tunnel and air is b downcastn over or sucked through a line by a fan or turn of events of fans. To make measurements much(prenominal) finished closely spaces vertical and horizontal air vane be used which smoothes the disruptive f emit before it pertaines the model. Usually, measurements are interpreted from a balance on which model is mounted and conglomerate visualisation proficiencys such as smoke and tufts are used to understand the affect of to a greater extent than(prenominal) or less geometric features on aerodynamic performance.Wind tunnel helps to acquire scores of data such as sleek forces drag, lift, side force diversity of these forces and movements with yawVehicle change dragAffect of aero featuresSurface insistence distributionThere are different types of wind tunnels which are as followsLOW SPEED WIND TUNNEL besides named as subsonic WIND TUNNEL are of open return type or return flow in which air is moved with a actuation system do up of a huge axial fan which helps in increasing dynamic pressure and thus helps to overcome saccharine loss. In this type mach number is kept truly low and amphetamine is maintained up to 400 km/hhttp//en.wikipedia.org/wiki/Subsonic_and_transonic_wind_tunnelSubsonic_tun)Staffordshire University logotypetype senior high SPEED OR TRANSONIC WIND TUNNEL is designed to reach the speed close to the speed of sound. Mach and Reynolds number both are primary(prenominal) here due to viscous or in viscid interactions. As compared to subsonic wind tunnel, much large cuticle facilities and pressurized wind tunnels are used.(http//en.wikipedia.org/wiki/Subsonic_and_transonic_wind_tunnelSubsonic_tunnel)SUPERSONIC WIND TUNNEL generates ultrasonic speed. In supersonic wind tunnel, high pressure ratio is required 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 actually high pressure ratio and deal supersonic hypersonic too requires pre heating facility. As compared to opposite types of wind tunnels, hypersonic wind tunnel has to a greater extent challenges in its designing.Staffordshire University logo(http//commons.wikimedia.org/wiki/FileLangley_hypersonic_wind_tunnels.jpg)WIND TUNNEL carapaceModel scale wind tunnel testing (MW T) plays an important share in aerodynamic development of motorsport vehicles, training and search though instanter it has been outmoded by CFD.wind_tunnel1Figure http//www.insightman.com/mag_photos/wind_tunnel1.jpgIt is an ideal way to determine the affects of various features and body styles on aerodynamics of vehicles. In model scale testing, model lie between 30%,60%nand they erect be be produced by various techniques such as fibre glass, stylist clay models, urbane foam and rapid prototype models or a combination of all of these.Model scale testing doesnt postulate high running follow as sophisticated test methods such as fitting a moving ground plane doesnt need high expense. In all, if styling method fag be apply than this testing method is a cheaper method to develop vehicle aerodynamics.Staffordshire University logoIn spite of all, model scale testing has its own limitation such asEnsuring geometric relation m some(prenominal) special features can be difficult to model at small model scale.Reynolds number effects Reynolds number (Re) of the flow al or so 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 umteen problems faced during MWT are overcome by use expert scale testingIt eliminates the effect caused due to Reynolds number.It totally avoids the greet 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/service/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 dissolve 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 fountainhead which behave like fluids depending on the circumstances they are in, for example, winds blo elongation around buildings, cooling air flows in a laptop, drugs in asthma inhalers etc. It in general focuses on affects made by pressure, temperature, density and the focal ratio of the fluids. It is ruling technique software with a wide range of applications. It is very commonly used software in automotive industry (the method has an ability to purport the air flows around a vehicle or car), specially in motorsports because of the massive competition. It first came in light in 1990s.The software is at once owned by Bar Honda Formula 1 team. The software has perpetually been updated at times as the as the new computer technologies come in. since the software runs of a computer, the speed of the computer processor as well plays an important role in improving the performance, in other words, more powerful the supercomputer, more accurate number of CFD pr ocess. As the time passes it has become cheaper and advanced.Staffordshire University logoStreamlines under a stock car (http//strangeholiday.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 fair game into a set of elements or cell which named as a electronic network. The truth of the go away of CFD totally depends upon the number of cells as higher their number is, more accurate result will be.Secondly, mesh representing volume occupied by the fluid is created. Now, when fluid flow comes into contact with the object, it gets separated into as many cells as come-at-able.Then, computer starts finding out the problem it faced during the entropy phase. Besides this, it also set up a clear meet of interaction of object and fluid flow. Finally, simulation is started and result obtained is canvass.Staffordshire University logoINSTRUMENTED track OR TRACK TESTING This testing method has earned lots of popularity in short time as it a very cost effective 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 consumption, 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 gives 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, sno move 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 giv e 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 better or modified aerodynamic properties.Part 2Staffordshire University logoComputational still Aerodynamics (CFD)The science that tries to verify a numerical solution to the equations that reign 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 toilsome 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 making a sincere 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. CFD enables the designer to analyze and fancy the flow around the vehicle. It can be d one and only(a) 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. Performing 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 engine room 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 keeping environment pollution free.Staffordshire University logoDemeritsNo doubt CFD is a outstrip 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 unsteady 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 misapprehensions since everything relays on computers. Besides this, approximation of result can ca use Truncation errors and round off errors are also possible due to the word size available on a grouchy computerThe bottom line is that solutions find by CFD rely upon user-defined elements like grid generation and turbulence modelling, which will be soon an obstructer facing code developers. It is not yet possible to create full flow field model economically as in largely vehicles the large scale flow regimes depends on inevitability of transition and turbulence. get off the ground 325mphPressure moving-picture showE25MPH25mph Pressure.gifThe pressure is very low (-21.71446) on top(prenominal) and deject summon of wing .It is more (33.87485) on attend tip of wing and also it is less( 23.76770) on front swiftness and depress come out of the closet, it also very(prenominal) on buttocks pep pill and tear down heighten of wing. swiftness imageE25MPH25mph swiftness.gifThe velocity is very low (1.854647)on front tip of wing and it is high (6.536719) on upper and note f ront climb up of it. It is also same on back upper and refuse surface of wing. Velocity is really low (9.658100) on lower surface and upper surface of wing but on mid(prenominal) 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 fron t 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 (7.317064)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 evaluate 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 operation or when free.There are very less or no chan ces 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 tunnels 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