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The Nordic Wind Tunnela proposal to construct the world’s premier

turbulence research facility in Sweden

by Jan-Eric Sundgren, William K. George, Rolf I. Karlsson,T. Gunnar Johannsson and Martin Wosnik

The Nordic Wind Tunnel2

A world of turbulence...

The Nordic Wind Tunnel

This is a proposal to construct the world's premier turbulence 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 com-puters for several decades. It will be used to address most of the fundamental ques-tions that have held back turbulence research for half a century. This research will ulti-mately translate 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.

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Turbulence 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 limita-tions on engineering design and practice.Scientists and engineers cope, but at a price insafety margins, wasted energy resources and lim-itations to 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 turbu-lence) research facilities.

Experimental work in a large research wind tun-nel is 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 sep-aration of length scales, energetic to dissipation,of 105 or larger – and still be able to resolve thesmallest scales occuring in the flow with thesmallest technically feasible probes (approxi-mately 10 µm).

Leonardo’s observation of turbulent flow: Drawing ofa free water jet from a square hole flowing into a pool(courtesy of eFluids.com).

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Turbulence...

“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 most important question is whether or not the vaststore of information and knowledge that has beenobtained at low Reynolds numbers for a variety of impor-tant classes 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.

“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 some-thing that 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.


Wind 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 small-est scales. They are either too short for the tur-bulence to 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 dis-turbance (free-stream turbulence) level toextract the features of primary interest.

Wind Tunnels

Overview of a selection of wind tunnels

Example 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 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 104, sometimes many orders of mag-nitude greater...


Are there alternatives?

Despite the increases in computational powerand progress in numerical techniques, it is cur-rently not possible to resolve the small scales athigh Reynolds number. Even with computation-al power doubling every 18 months, it wouldtake several decades before a model-free, directnumerical simulation (DNS) of the simplest flowcase of non-decaying isotropic turbulence could

be performed with the separation of scales 105

equivalent to the wind tunnel proposed here(tremendous resolution requirements for a com-parable simulation – number of grid pointsgreater than 1015).

“Despite the impressive developments in ComputationalFluid Dynamics over recent decades, [...] many of the fun-damental questions 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 facili-ties designed to allow study of very high Reynolds numberflows (via use of very high pressures, exotic gases, or what-ever) butt these are all inherently limited by the technicaldifficulties in developing and applying appropriate instru-mentation. 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 fore-seeable future) explore the high Reynolds numbers thatare required to understand the basic properties of turbu-lence.”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 pro-posed tunnel 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 recy-cled industrial tunnels with insufficiently clean and con-trolled aerodynamic 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.

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The Nordic Wind Tunnel overcomes the short-comings of present research facilities and is pro-posed for 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 nec-essary high Reynolds numbers, yet still resolvethe dissipative scales• long enough and with low enough back-ground disturbances to obtain the necessarydownstream development times and will thusprovide an experimental facility capable ofresolving some of the oldest questions in turbu-lence while 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-

What makes the Nordic Wind Tunnel unique?

ments (e.g., resolution of wall layer to obtainshear stress) and what Reynolds numbers need-ed to be achieved in the experiments to be per-formed (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 per-formance (maximum free stream velocity) of theproposed wind tunnel facility were then deter-mined by 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 meas-uring volume height of 10 µm) whileachieving a Reynolds number based onmomentum thickness of at least 100,000.Other “base case flows”, e.g. decaying tur-bulence or wake flows, also provided fur-ther size and flow quality criteria.


Result of the inverse design and dimen-sioning process:

A wind tunnel with a test section of 40 m length,cross section after contraction 3x3m,maximum free stream speed 40 m/s and a free stream turbulence u’/U of < 0.02%.

The total dimensions of the facility are:length: 79 m,width: 21 m,height 7 m.

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40 m

1:100 scale model

“It is our view that the facility [...] would be second-to-none as an experimental research tool for basic turbu-lence research into high Reynolds number incompress-ible flows. 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.

Problems that can be adressed in the Nordic Wind Tunnel

First, and foremost, the Nordic Wind Tunnelwill enable experiments specifically designed toanswer fundamental questions in turbulence.


“[...] the facilty seems suitable for investigation of a tur-bulent boundary 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 behav-ior of turbulence, and that can be explored in such a tun-nel.”“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 atmos-pheric and 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.

“[...] 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.

“[...] 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 vali-dation issues.”Professor Andrew Pollard, Director of Computational andExperimental Fluid Dynamics Laboratory, QueensUniversity, Canada.

“[...] 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.

“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 boundary-layer behavior at high Reynolds number - which shouldworry designers of aircraft, ships and other high-Re arti-facts. My view is that "theoretical" arguments are unlike-ly to settle the matter so that high-Re experiments areneeded”Professor Peter Bradshaw, Flow Physics andComputation, Stanford University, USA


Value to society

The 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.

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“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 fore-front of 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.

“The stated policy of inviting foreign visitors to use thetunnel for their own research is another aspect of tremen-dous significance. This could be important not only for thelocal activity by injection of new ideas but would alsoenhance the standing of the university on the internation-al scene.”Professor S. K. F. Karlsson, Brown University, USA.

“[...] existing theories still fail to forecast important envi-ronmental phenomena and to describe technical process-es especially in multi-component media.”“[...] I have carefully read different versions of the pro-posal and 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 cre-ating of new generation theory, more directly connectedwith basic laws of nature than part of contemporaryheuristic theories of turbulence. The results can be com-pared with measurements obtained in other media (strat-ified, multiphase) and leads to new more deep under-standing of flow phenomena and essential improving oftechnologies. “Yuli D. Chashechkin, Professor of Fluid Mechanics, Headof the Laboratory of Fluid Mechanics, Russian Academyof Sciences, Russia.

“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 inter-national level.“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 fun-damental nature of fluid turbulence.”B.A.Pettersson Reif, Senior Principal Scientist,NorwegianDefence Research Establishment, Norway.

Viabilty as engineering facilty

The Nordic Wind Tunnel will be designed as afacilty for turbulence research, but has tremen-dous potential for commercialization due to itsunique size and flow quality. This ensures itslong-term viability as engineering facilty serv-ing a variety of industries.


“I am also convinced that industry in Sweden and abroadwill find such unique facilities indispensable for develop-ment and 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 possi-bility..”John L. Lumley, Carrier Professor of Engineering, CornellUniversity, USA.


Location

The 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 coinci-dence, it happenend after the basicdesign/dimensioning process. Surprisingly, thetwo laboratory halls (pictured below) combinedcan actually house the Nordic Wind Tunnel in itscurrent configuration!

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 sup-port construction of the wind tunnel facility.”Professor Charles Meneveau, Director of Center forEnvironmental and Applied Fluid Mechanics, JohnsHopkins University, Baltimore, USA.

22m40m

40m

SSPAtowingtank

10m

Available laboratory buildings on Chalmers campus.

“The team at Chalmers is very strong, the project is time-ly and 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.

Cost estimates for construction

The 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 contrac-tors.

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 sus-tained research 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.


Operation of Nordic Wind Tunnel –International Collaboration

There 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, theo-retical and 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 con-cept of Mobility of researchers.(E.g. inclusion by ERCOFTAC (EuropeanResearch Council on Fluids, Turbulence andCombustion) as part of their SixthFramework)

“I can envisage this wind tunnel becoming a strong cata-lyst of 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.

“The outstanding features of the Nordic Wind Tunnelshould involve the entire global turbulence communityand would be an excellent base for the international coop-eration of experienced research groups and scientists. Thiscertainly would improve the international position andimportance of the Chalmers Laboratory. [...] the outstand-ing features of the laboratory would certainly motivatethe international organizations like EC, various branchesof industry etc for co-financing serious research of inter-national teams which might be an unusual chance formany.”Professor J. Krzyzanowski, Polskiej Akademii Nauk,Gdansk, Poland.

“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 notice-able advances in our understanding of turbulence.”B.A.Pettersson Reif, Senior Principal Scientist,NorwegianDefence Research Establishment, Norway.

“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.

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“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 num-bers while maintaining a very low level of background tur-bulence is 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 par-tially dependent on initial conditions and may lead to pas-sive control 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 bound-ary layer 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, uni-versity of Erlangen, Germany.

“I attended with considerable interest your detailed pres-entation describing 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 turbu-lence research 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.

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“[...] 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.

Chalmers University of Technology, Gothenburg, Sweden

for more information on the

Nordic Wind Tunnel

http://www.tfd.chalmers.se/trl/windtunnel/

Jan-Eric Sundgren, President Chalmers University of Technology

William K. George, Professor of TurbulenceRolf I. Karlsson, Professor of Experimental Fluid Mechanics

T. Gunnar Johannsson, Associate Professor Martin Wosnik, Assistant Professor

Department of Thermo and Fluid DynamicsChalmers University of Technology

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