The Nordic Wind Tunnel - Turbulence Online

The Nordic Wind Tunnela proposal to construct the world’s premierturbulence research facility in Swedenby Jan-Eric Sundgren, William K. George, Rolf I. Karlsson,T. Gunnar Johannsson and Martin Wosnik

A world ofturbulence...2The Nordic Wind Tunnel

This is a proposal to construct the world's premierturbulence research facility in Sweden.The Nordic Wind Tunnel......will be a very large (test section: length 40m, cross-section 3m x 3m), low-speed windtunnel with very low background turbulence (u'/U < 0.02%). It will be the only faciltyin the world with this combination of size (length and width) and high flow quality....will enable turbulence experiments on a scale that will not be achievable with computersfor several decades. It will be used to address most of the fundamental questionsthat have held back turbulence research for half a century. This research will ultimatelytranslate to great value to society....also has tremendous potential for commercialization due to its unique size and flowquality. This ensures its long-term viability serving a variety of industries.Last, but not least, the Nordic Wind Tunnel, operated as a major Nordic andEuropean Facilty, would be a prestigious endeavor for the country of Sweden. Theworld's leading scientists have enthusiastically endorsed this facility (see appendedletters) and they expect high quality, award-winning work to result from it.The Nordic Wind Tunnel3

Turbulence...4Turbulence has been studied for a long time, butis nevertheless often cited as the last unsolvedproblem in classical mechanics. The lack ofunderstanding has many adverse effects, whichrange from poor weather prediction to limitationson engineering design and practice.Scientists and engineers cope, but at a price insafety margins, wasted energy resources and limitationsto innovation. Many classical ideas ofturbulence theory date back to the 1930s and40s. These ideas have evolved since, but it hasnever been possible to truly test most of thembecause of the absence of large and longenough, high quality (low background turbulence)research facilities.“Turbulence remains one of the most outstandingresearch problems facing the international engineering,physics and mathematics research communities”Charles R. Doering, Professor of Mathematics, TheUniversity of Michigan, USA.“The proposal by Professors George and Karlsson is quitea timely one, given the number of significant turbulenceresearch issues that remain unsolved.”Professor Robert A. Antonia, ARC Senior ResearchFellow, The University of Newcastle, Australia.“Turbulence in the high Reynolds number limit is somethingthat I consider the central problem today in fluiddynamics research. If we have a reliable understanding offlows in the asymptotic high Reynolds number limit, thatwill provide an anchor for all turbulence research.”Professor Roddam Narasimha, FRS, Director NationalInstitute of Advanced Studies, Indian Institute of Science,Bangalore, India.The Nordic Wind TunnelLeonardo’s observation of turbulent flow: Drawing ofa free water jet from a square hole flowing into a pool(courtesy of eFluids.com).Experimental work in a large research wind tunnelis needed to solve a number of fundamentalquestions and enable scientists and engineers tofurther improve computations of turbulent flow.Simply put, the problem is how to achieve a separationof length scales, energetic to dissipation,of 10 5 or larger – and still be able to resolve thesmallest scales occuring in the flow with thesmallest technically feasible probes (approximately10 µm).“The most important question is whether or not the vaststore of information and knowledge that has beenobtained at low Reynolds numbers for a variety of importantclasses of turbulent flows is applicable to the highReynolds numbers that are characteristic of most realengineering flows. In order to investigate this question, awind tunnel capable of reaching these high Reynoldsnumbers while permitting instrument resolutiuon typicalof experiments at much lower Reynolds numbers must beavailable. this is just what the Nordic Wind Tunnel isdesigned for.”Professor James M. Wallace, Univ. of Maryland, USA.

Wind TunnelsWind tunnels are ducts through which air ismoved, usually by a fan, to generate a controlledexperimental flow environment.Existing research wind tunnels are too small toreach high enough Reynolds numbers while stillpermitting resolved measurements of the smallestscales. They are either too short for the turbulenceto evolve from its upstream (initial)conditions, too narrow for the large energeticturbulence scales to be free from the influenceof the walls, or have too high a background disturbance(free-stream turbulence) level toextract the features of primary interest.The Reynolds number:Ratio of inertial to viscous forces. In turbulencethe most important Reynolds number is also theratio of length scales at which energy is suppliedto the turbulence to that at which it is dissipated.In most problems of practical interest this isgreater than 10 4 , sometimes many orders of magnitudegreater...Overview of a selection of wind tunnelsExample 1: BLWT 2, University of Western Ontario:Good overall size, insufficient flow quality (designed aswind engineering facility).Example 2: MTL wind tunnel, KTH, Sweden: Good flowquality, insufficient size (limited by available building).The Nordic Wind Tunnel5

Are there alternatives?Despite the increases in computational powerand progress in numerical techniques, it is currentlynot possible to resolve the small scales athigh Reynolds number. Even with computationalpower doubling every 18 months, it wouldtake several decades before a model-free, directnumerical simulation (DNS) of the simplest flowcase of non-decaying isotropic turbulence couldbe performed with the separation of scales 10 5equivalent to the wind tunnel proposed here(tremendous resolution requirements for a comparablesimulation – number of grid pointsgreater than 10 15 ).“Despite the impressive developments in ComputationalFluid Dynamics over recent decades, [...] many of the fundamentalquestions still facing the turbulence communitycannot possibly be answered in the foreseeable futurewithout recourse to laboratory work.”“There are now a number of relatively small-scale facilitiesdesigned to allow study of very high Reynolds numberflows (via use of very high pressures, exotic gases, or whatever)butt these are all inherently limited by the technicaldifficulties in developing and applying appropriate instrumentation.In my view, there is much to be said for theonly possible alternative approach: going to much largerscales, so that existing, well-developed techniques can beused.Your proposal is therefore very exciting and, if I maysay so, very well thought out.”Ian P. Castro, Professor of Fluid Dynamics, University ofSouthampton, UK.“Computers cannot (and will not be able to in the foreseeablefuture) explore the high Reynolds numbers thatare required to understand the basic properties of turbulence.”Zellman Warhaft, Professor of Mechanical and AerospaceEngineering, Cornell University, USA.“There are many important questions about the physics oflarge Reynolds number turbulence that could beanswered with highly accurate measurements in your proposedtunnel and nowhere else. I can envisage quite a fewexperiments in your tunnel that will help validate my DNS[direct numerical simulation] results.”Said Elgobashi, Professor and Chair, Mechanical andAerospace Eng., University of California, Irvine, USA.“I am convinced that the turbulence community reallyneeds a large-scale wind tunnel, with sufficient separationbetween the large and small scales, with sufficiently lowturbulence intensity, and in which the smallest scales canbe probed with no special difficulty even for the largestReynolds numbers. Such a tunnel (none of the presentlyavailable ones possess such specifications because theyare either too small, or, for the largest ones, they are recycledindustrial tunnels with insufficiently clean and controlledaerodynamic conditions) will be of considerablevalue for testing new ideas or new theories, and even forproviding basic clean data on which the present theorieswill be tested”Professor Fabien Anselmet, Director of Research at CentreNational de la Recherche Scientifique (CNRS), TurbulenceResearch Group, University Aix-Marseille, France.6The Nordic Wind Tunnel

What makes the Nordic Wind Tunnel unique?The Nordic Wind Tunnel overcomes the shortcomingsof present research facilities and is proposedfor construction at Chalmers Universityof Technology. It would be• wide enough to remove the effect of sidewalls on the energetic turbulence scales• fast enough and large enough to get the necessaryhigh Reynolds numbers, yet still resolvethe dissipative scales• long enough and with low enough backgrounddisturbances to obtain the necessarydownstream development times and will thusprovide an experimental facility capable ofresolving some of the oldest questions in turbulencewhile also testing conclusively new ideas.In the unique inverse design process it was askedwhat length and time scales needed to beresolved to conduct “meaningful” measure-ments (e.g., resolution of wall layer to obtainshear stress) and what Reynolds numbers neededto be achieved in the experiments to be performed(e.g., zero pressure gradient boundarylayer, far wake, decay of isotropic turbulence) tohelp resolve fundamental questions and sortcompeting theories. These length and timescales and Reynolds number criteria depend onthe flow being measured. The size (length andcross-sectional area of the test section) and performance(maximum free stream velocity) of theproposed wind tunnel facility were then determinedby what can be resolved with existingprobes.The small scales of the flow become smaller withincreasing flow speed or pressure. To quoteProfessor Tony Perry, University of Melbourne,who realized the dilemma and – before hisuntimely death – stated that: ``Big and slow - isthe way to go''.Example of one design criterion:For wall-bounded turbulent flows therequirement was that one viscous lengthscale can still be resolved (using a micro-LDA or a micro-PIV system, with a measuringvolume height of 10 µm) whileachieving a Reynolds number based onmomentum thickness of at least 100,000.Other “base case flows”, e.g. decaying turbulenceor wake flows, also provided furthersize and flow quality criteria.The Nordic Wind Tunnel7

Result of the inverse design and dimensioningprocess:A wind tunnel with atest section of 40 m length,cross section after contraction 3x3m,maximum free stream speed 40 m/s and afree stream turbulence u’/U of < 0.02%.“It is our view that the facility [...] would be second-tononeas an experimental research tool for basic turbulenceresearch into high Reynolds number incompressibleflows. This is particularly true for the range of scalesof turbulence resolved.”Poul Scheel Larsen, Professor of Fluid Mechanics andKnud Erik Meyer, Associate Professor of ExperimentalFluid Mechanics, Denmark Technical University.The total dimensions of the facility are:length: 79 m,width: 21 m,height 7 m.1:100scale model40 m8The Nordic Wind Tunnel

Problems that can be adressed in theNordic Wind TunnelFirst, and foremost, the Nordic Wind Tunnelwill enable experiments specifically designed toanswer fundamental questions in turbulence.“[...] coherent structure identification in turbulent flows, acrucial aspect for drag reduction, noise, vibration, mixingetc.”Professor J. P. Bonnet, University of Poiters and CentreNational de la Recherche Scientifique (CNRS), France.“[...] this well designed wind tunnel will allow to focus thestudies in several directions, spanning from isotropic toinhomogeneous flows.”Professor Paolo Orlandi, University of Rome “LaSapienza”, Italy.“[...] we seek answers to large eddy and direct numericalsimulation results that can only come from experimentsperformed in an exquisite facility of the type proposed.We expect the data will enable us to critically assess validationissues.”Professor Andrew Pollard, Director of Computational andExperimental Fluid Dynamics Laboratory, QueensUniversity, Canada.“For boundary layer experiments this tunnel, with its verylarge fetch and low background turbulence levels, willoffer a unique opportunity.”“[It] will provide key insights into the applied problems ofturbulence mixing (and reactions) and drag reduction.Modelling, such as large eddy simulations (LES) relyheavily on experimental insights.”Zellman Warhaft, Professor of Mechanical and AerospaceEngineering, Cornell University, USA.“The current controversies over the law of the wall andthe law of the wake imply an uncertainty about boundarylayerbehavior at high Reynolds number - which shouldworry designers of aircraft, ships and other high-Re artifacts.My view is that "theoretical" arguments are unlikelyto settle the matter so that high-Re experiments areneeded”Professor Peter Bradshaw, Flow Physics andComputation, Stanford University, USA“[...] the facilty seems suitable for investigation of a turbulentboundary layer at high Reynolds numbers, whenits thickness reaches tens of centimetres as, for example,on a plane fuselage in real flight”Victor V. Kozlov, Professor of Experimental FluidMechanics, Siberian Branch of Russian Academy ofSciences, Russia.“Your rationale for the construction of this tunnel is wellpresented in the ERCOFTAC Bulletin paper and theAPS/DFD presentation. In addition to the fundamentalphysical questions about turbulence dynamics that canonly be answered in such a facility, there are a number ofmore practical phenomena in geophysics and technologythat are determined by the high Reynolds number behaviorof turbulence, and that can be explored in such a tunnel.”“You might consider constructing the tunnel in such a waythat it could be stratified at some time in the future. Thereare a number of interesting questions related to atmosphericand oceanic turbulence that could be investigatedin such a tunnel – e.g. transport in stably stratified media,plume development in stable stratification, shorelinefumigation, etc.”John L. Lumley, Carrier Professor of Engineering, CornellUniversity, USA.The Nordic Wind Tunnel9

Value to societyThe questions which will be answered by theNordic Wind Tunnel will ultimately translate togreat value to society. Examples of this are moreaccurate, long-term weather predictions (whichcould prevent catastropies due to surprisestorms) and improvements in energy efficiencyin power plants and transportation.Mixing in industrial processes could be mademore efficient and air conditioning systems andair planes quieter. Design costs for a variety offluid machinery would be greatly reduced.“A limited deep understanding of turbulence impacts thedesign of many devices ranging from aircraft and aircraftengines to the cooling of micro-circuits. There has beenlittle fundamental progress in the last 20 years, in part dueto a serious lack of experimental data which your tunnelwould provide. I can therefore offer my wholeheartedsupport for your project as I believe it will be an importantcontributor to solving the turbulence problem at the internationallevel.“Professor P. Hutchinson, FREng, Cranfield University,UK.“This unique wind tunnel will be specifically constructedto supplement already existing facilities around the worldand the ambitious design goal of the project is to set thestage for a more comprehensive understanding of the fundamentalnature of fluid turbulence.”B.A.Pettersson Reif, Senior Principal Scientist,NorwegianDefence Research Establishment, Norway.“[...] existing theories still fail to forecast important environmentalphenomena and to describe technical processesespecially in multi-component media.”“[...] I have carefully read different versions of the proposaland have come to the conclusion that the idea toconstruct wind tunnel of rather large sizes (cross-section 3x 3 m and working area length 40 m) with extremely lowbackground level of basic turbulence (less than 0.02 %)has come in time and looks very productive. [...]Exact and complete experimental results will help in creatingof new generation theory, more directly connectedwith basic laws of nature than part of contemporaryheuristic theories of turbulence. The results can be comparedwith measurements obtained in other media (stratified,multiphase) and leads to new more deep understandingof flow phenomena and essential improving oftechnologies. “Yuli D. Chashechkin, Professor of Fluid Mechanics, Headof the Laboratory of Fluid Mechanics, Russian Academyof Sciences, Russia.“The stated policy of inviting foreign visitors to use thetunnel for their own research is another aspect of tremendoussignificance. This could be important not only for thelocal activity by injection of new ideas but would alsoenhance the standing of the university on the internationalscene.”Professor S. K. F. Karlsson, Brown University, USA.“I am convinced of the scientific need for this tunnel, andexpect it will be fully subscribed by workers world-wide. Itshould place Chalmers University and Sweden in the forefrontof modern turbulence research, where it should be,considering the long and distinguished history of Swedishinvestigators in modern fluid dynamics.”Professor Russell J. Donnelly, Director of CryogenicHelium Turbulence Laboratory, University of Oregon,USA.10The Nordic Wind Tunnel

Viabilty as engineering faciltyThe Nordic Wind Tunnel will be designed as afacilty for turbulence research, but has tremendouspotential for commercialization due to itsunique size and flow quality. This ensures itslong-term viability as engineering facilty servinga variety of industries.“I am also convinced that industry in Sweden and abroadwill find such unique facilities indispensable for developmentand advancement of many technologies, to mentionespecially aviation, space research, road-, rail- and watervehicles, as well as for studies of atmosphere and oceandynamics. Last, but not least, such facilities will add muchto the already enviable international prestige of ChalmersUniversity of Technology and Sweden as a whole.”Professor Kemo Hanjalic, Head of Thermo-Fluids Section,Delft University of Technolgy, The Netherlands.“Thus, results obtained in facilities such as yours will beextremely useful to the fluid engineer designing practicaldevices as well as to the scientist involved in fundamentalresearch. [...] your planned facilty will attract top scientistsand engineers for unique opportunities to work with youand your high Reynolds number tunnel. I myself will behonored to work with you and your research team”Professor Mohamed Gad-el-Hak, Notre Dame University,USA..“A test case for flow control. [...]The size of the models inthe Nordic Wind Tunnel will be more appropriate to testdemonstrators close to the industrial applications.”Professor J. P. Bonnet, University of Poiters and CentreNational de la Recherche Scientifique (CNRS), France.“Perhaps we have learned nearly all we can from researchdone in small wind tunnels. The proposed Nordic WindTunnel will allow research to be conducted at higherReynolds numbers with fewer wall effects.This will give usgreater insight into turbulence and its control”Professor David E. Stock, Washington State University,USA.“These [fundamental physical questions] should not beconfused with the atmospheric, wind engineering andsporting commercial applications which are also a possibility..”John L. Lumley, Carrier Professor of Engineering, CornellUniversity, USA.The Nordic Wind Tunnel11

LocationThe Nordic Wind Tunnel will be built atChalmers University of Technology. Chalmers isa major technical university located inGothenburg on the west coast of Sweden.The Nordic Wind Tunnel will be housed in anexisting, currently underused building, adjacentto SSPA. Finding this building was a coincidence,it happenend after the basicdesign/dimensioning process. Surprisingly, thetwo laboratory halls (pictured below) combinedcan actually house the Nordic Wind Tunnel in itscurrent configuration!“The team at Chalmers is very strong, the project is timelyand clearly stated. It could well become a majorresource for Europe, the US and other countries – aCERN for turbulence.”Zellman Warhaft, Professor of Mechanical and AerospaceEngineering, Cornell University, USA.The scientific infrastructure at Chalmers isalready in place with both W.K. George andR.I. Karlsson joining the faculty at Thermo andFluid Dynamics, and the moves of theirrespective laboratories to form the newTurbulence Reseach Laboratory (TRL) atChalmers.“The two researchers (Prof. W.K.George and Prof R.I.Karlsson) have an outstanding international reputation inthe field and will be first-rate users of the proposed windtunnel facility. Moreover, such a facilty will greatlyenhance the already high visibility of Chalmers in the areaof turbulence and fluid mechanics. I wholeheartedly supportconstruction of the wind tunnel facility.”Professor Charles Meneveau, Director of Center forEnvironmental and Applied Fluid Mechanics, JohnsHopkins University, Baltimore, USA.Available laboratory buildings on Chalmers campus.22m40m10m40mSSPAtowingtank12The Nordic Wind Tunnel

Cost estimates for constructionThe cost of construction has been estimated atSEK 60 million.The estimated engineering design cost is onetenth of the total cost, SEK 6 million.We are hereby asking for funding of the designphase. The engineering design phase will endwith a bidding conference, at which the facility– in parts or whole – can be bid on by contractors.Timetable:- design: 1 year- construction: 1-2 years“I am thus heartened that you are undertaking to build awind tunnel that will be able to resolve a number of theoutstanding questions in turbulence. [...] I have no doubtthat the expenses involved will be amply justified if sustainedresearch activities in it can be pursued.”Professor Katepalli R. Sreenivasan, Director of Institutefor Physical Science and Technology, University ofMaryland. Also in Engineering, Physics and Mathematics,Yale University, USA.“I admire the careful thought which has gone into thisfacility design, which when built will surely put Sweden ina leading position in wind tunnel research. I also admirethe great ingenuity in picking a design for building thisfacility at a very modest total cost.”Professor Russell J. Donnelly, Director of CryogenicHelium Turbulence Laboratory, University of Oregon,USA.The Nordic Wind Tunnel13

Operation of Nordic Wind Tunnel –International CollaborationThere is great and increasing interest for theproject throughout the international fluidmechanics community. The Nordic WindTunnel will be made available for researchersfrom all over the world.Leading international scientists are lookingforward to use it in their experimental, theoreticaland numerical research. They anticipatethat very high quality work will result from theNordic Wind Tunnel.It is anticipated that a significant part of theoperating costs of the Nordic Wind Tunnel canbe covered by the EU, particularly by formingNetworks of Excellence and utilizing the conceptof Mobility of researchers.(E.g. inclusion by ERCOFTAC (EuropeanResearch Council on Fluids, Turbulence andCombustion) as part of their SixthFramework)“I welcome this proposal, not just because it will providea proper modern experimental facility in Europe, butbecause it will also provide a focus for collaboration fromall sides of the European turbulence community.”Professor J. D. Gibbon, Imperial College, London, UK.“I can envisage this wind tunnel becoming a strong catalystof European research in turbulence and Chalmersbecoming an important center for turbulence research asa result.”J. C. Vassilicos, Imperial College, London, UK.“We would liked to express our general support for theinitiative, also because it would provide new opportunitiesfor Nordic research collaboration.”Poul Scheel Larsen, Professor of Fluid Mechanics andKnud Erik Meyer, Associate Professor of ExperimentalFluid Mechanics, Denmark Technical University.“I am very exited about the prospects for your proposednew wind tunnel, as I believe that the collaborations andstate-of-the-art research that will arise will lead to noticeableadvances in our understanding of turbulence.”B.A.Pettersson Reif, Senior Principal Scientist,NorwegianDefence Research Establishment, Norway.“The outstanding features of the Nordic Wind Tunnelshould involve the entire global turbulence communityand would be an excellent base for the international cooperationof experienced research groups and scientists. Thiscertainly would improve the international position andimportance of the Chalmers Laboratory. [...] the outstandingfeatures of the laboratory would certainly motivatethe international organizations like EC, various branchesof industry etc for co-financing serious research of internationalteams which might be an unusual chance formany.”Professor J. Krzyzanowski, Polskiej Akademii Nauk,Gdansk, Poland.14The Nordic Wind Tunnel

“Build it and they will come...”( from the movie: A Field of Dreams )“The scale and quality of the proposed Nordic WindTunnel is truly world class. A facility that will enable us toexplore turbulent wall flows, and other canonical flows,such as introducing curvature, temperature gradients andeven concentration gradients, at such high Reynolds numberswhile maintaining a very low level of background turbulenceis exactly what we need. It will enable for the firsttime the dissipative scales to be explored as well as howthese interact with other mechanisms. It will enable us toanswer the question whether turbulence is wholly or partiallydependent on initial conditions and may lead to passivecontrol strategies.”Professor Andrew Pollard, Director of Computational andExperimental Fluid Dynamics Laboratory, QueensUniversity, Canada.“With our own research facilities, we cannot achieve thehigh Reynolds number flows we would like to investigateand we therefore hope to collaborate with you on boundarylayer research at high Reynolds numbers. We are alsointerested in flow around obstacles and we would like tocarry out this experimental work at low blockage ratios.Your planned wind tunnel will permit this kind ofresearch.”Dr.Dr.h.c. Franz Durst, Professor of Fluid Mechanics, universityof Erlangen, Germany.“I attended with considerable interest your detailed presentationdescribing the project at the APS/DFD meetingin San Diego last November 2001. I would like to state inno-uncertain terms that building such a large wind tunnelfacility is of timely and crucial importance for our turbulenceresearch community.”Fernando F. Grinstein, Chair Elect, AIAA FluidDynamics Technical Committee, Research Physicist,Naval Research Laboratory, USA.“Together with many of my colleges I would be very keenin research collaborations with the Nordic Wind Tunnelonce this project is completed. I see the boundary layerand wake flows as the main topic of collaboration betweenthe BLWTL and the Nordic Wind Tunnel .”Professor H. Hangan, Boundary Layer Wind TunnelLaboratory, University of Western Ontario, Canada.“[...] the proposed Nordic Wind Tunnel will be a uniqueopportunity to create a somewhat European center forexperimental research in turbulence, that will be used forseveral groups in Europe and overseas, among those, mylaboratory will take an active part”Professor J. P. Bonnet, University of Poiters and CentreNational de la Recherche Scientifique (CNRS), France.The Nordic Wind Tunnel15

Jan-Eric Sundgren, PresidentChalmers University of TechnologyWilliam K. George, Professor of TurbulenceRolf I. Karlsson, Professor of Experimental Fluid MechanicsT. Gunnar Johannsson, Associate ProfessorMartin Wosnik, Assistant ProfessorDepartment of Thermo and Fluid DynamicsChalmers University of Technologyfor more information on theNordic Wind Tunnelhttp://www.tfd.chalmers.se/trl/windtunnel/Chalmers University of Technology, Gothenburg, Sweden