Chalmers University of Technology Thermo and Fluid Dynamics The Nordic Wind Tunnel A proposal to...

Chalmers University of Technology

Thermo and Fluid Dynamics

The Nordic Wind Tunnel

A proposal to build the world’s largest turbulence research facility at Chalmers

by

William K. George, Martin Wosnik, Rolf Karlsson, Gunnar Johansson, Bert Johansson and Scott

Woodward


Turbulence

• is the random and chaotic motion of fluids (like air and water).

• causes intense mixing, increased drag and heat transfer compared to non-turbulent (laminar) state.

• is characterized by a huge range of scales, which makes computer solution nearly impossible and experiments difficult.

• is governed by highly non-linear equations, which makes even calculations of average motions impossible without ad hoc assumptions (more unknowns than equations).



Motivation for research

• Turbulence is one of the great unsolved mysteries of science.

• The lack of understanding has important practical effects (e.g.weather prediction, engineering design and practice, energy).

• Mankind copes — but at a price in safety margins, energy waste, limitations to innovation.

• Some believe we can do better, but a major research facility is required to resolve fundamental questions.



Old ideas ...

• Classical view of turbulence dates from 1930’s and 40’s.- turbulence evolves to a state independent of starting (initial) conditions.- smallest scales (typically 1 mm or smaller) whichdissipate most of energy are the same for all flows.

• Ideas which evolved 1960 - 1980’s suggest small scalesare more complicated, but still universal.

• It has never really been possible to test these ideas becauseof the absence of large enough high quality research facilities, so they were more or less accepted by default until 1990’s.



… versus new ideas

• By the late 1980’s, the old ideas began to be challenged on several fronts.

• New theories suggested turbulence might depend foreveron how it started - meaning control might be possible.

• Old ideas about universality of the small scales were challenged with new ones based on equilibrium similarityof all scales, and new kinds of universality.

• The validity of experiments which appeared to supportthe old ideas were called into question.



Existing Facilities:

• are too small to achieve reasonable Reynolds numbers with small scales large enough to be resolved.

• are too short for the turbulence to evolve from its upstream (or initial conditions).

• are too narrow for large energetic turbulence scales to be freefrom the influence of the walls.

or• have too high a background disturbance level to extract the features of primary interest.




Why can’t a super-computer do the job?

• The computational box required to duplicate the capabilities of theproposed wind tunnel is:

(3 X 105)3 = 27 X 1015 for each time step

• The largest turbulence simulation to-date is only 10243 109, AND then only for non-decaying (forced) isotropic turbulence

• If computer capacity continues to double every 18 months, thenthe simplest computer experiment of this scale can be done in 37 years!

• And even this will take hundreds of hours of processor time per run.



The proposed Large Wind Tunnel Facility will be:

• large enough to remove the effect of side walls on the energetic turbulence scales.

• fast enough and large enough to get the necessary high Reynolds numbers, yet still resolve the dissipative scales.

• long enough and with low enough background disturbances to obtain the necessary downstream development times.

• finally able to resolve some of the oldest questions in turbulence, yet also able to test conclusively the new ideas.



The proposed Large Wind Tunnel:

test section length: 40 m

cross-section: 3 m X 3 m

top speed (test section): 40 m/s background disturbance level: < 0.02%

overall dimensions: 80 m X 21 m X 7 m

total estimated cost*: 50 M SEK

*from design to operation excluding building



The Large Wind Tunnel Facility would:

• be the largest and longest turbulence research tunnel in theworld with very low background disturbance level.

• be large enough for all present and foreseeable fundamental research wind tunnel experiments.

• have an estimated useful life of 100 years

• be suitable for eventual commercialization for a variety of atmospheric, wind engineering and sporting applications — including urban building design testing, Olympic winter sports training, and racing yacht design.


What research would be carried out?

• We will learn for the first time ever how very high Reynolds number boundary layers behave, including those with pressure gradients, roughness, heat transfer, and wall jets.

• We will be able to establish whether or not turbulent flows with and without mean shear reach equilibrium similarity states.

• We will be able to establish the importance of upstream conditions to homogeneous and free shear flows.

• We will be able to examine the importance of box size toturbulence scale, reasonably independent of Reynolds numbereffects. (This is crucial to computer modeling.)




Research (continued)

• We will be able to study for the first time ever in a high Reynoldsnumber laboratory flow how particulates diffuse and disperse beyond the initial (and least interesting) instants. (This hasimportant implications to all sorts of important problems.)

• We will be able to study for the first time in a laboratoryflow at high Reynolds number how the smallest scales ofturbulence really behave. (This information is crucial tothe development of LES turbulence models, the great hopefor engineers.)

• These represent the most fundamental flows of turbulence,and those from which we can learn the most about the physics.



But weren’t these experiments all done before?

• Some of these experiments were indeed carried out over the last 40 to 50 years, but using facilities that were too short, too small, and primitive instrumentation.

• Since then, measuring techniques have been revolutionized by computers, lasers and microelectronics— in fact some say we are entering the Golden Age of Turbulence because of this revolution.

• And we also have new (and old) ideas to test.


How will these experiments be different from before?

• First, because of the overall size of the facility it will be possible to resolve the important smallest scales at high Reynolds number conditions — the scales which dissipate the energy.

• Second, for the same reason it will be possible for the large energetic turbulence scales to be small enough to be independent of the effects of walls, a serious short-coming of previous work (separation of scales).

• Third, because of the length and low background disturbances it will be possible for the very first time to see how turbulence really evolves downstream (or in time).




Our design consultants

• We have consulted many of the world’s experts on turbulence research wind tunnel design.

• Without exception, they are enthusiastic about the possibility of building a tunnel of this size for this purpose, and have offered to help us get it right. Among them:

Arne V. Johansson - KTH, SwedenHassan Nagib -IIT/Chicago, USARoger E. A. Arndt - Univ. of Minnesota, USAWilliam Saric - Arizona State Univ., USAAnthony Perry - Univ. of Melbourne, AustraliaYong C. Han - Yeugnam Univ., S. Korea



Turbulence experts opinions:

• The world’s senior turbulence scientists are enthusiastic, among them:

John L. Lumley - Cornell U., USAWilliam C. Reynolds - Stanford U., USAFazle Hussain - U. of Houston, USA

• Many want to participate directly in the research, including:Franz Durst - U. of Erlangen, GermanyMarie Farge - U. of Paris, FranceMohammed Gad-el-Hak - Notre Dame U., USAMark N. Glauser - Clarkson U., USACharles Meneveau - Johns Hopkins U., USA

Zelman Warhaft - Cornell U., USA



A Nordic Partnership

• Our Scandinavian partners will be enthusiastic participants inmaking this part of the globe the world’s leading center for turbulence research.

• Among them already expressing strong interest are:DTU - Lyngby, DK

Poul S. Larsen, thermal convectionPreben Buchhave, optics and measurement

NTU - Trondheim, NOPer Aage Krogstad, boundary layers

KTH - Stockholm, SEArne Johansson, turbulence


Who will use this unique research facility?

• The turbulence researchers of Chalmers (TRL).

• Our Scandinavian Collaborators, through the partnership we will establish for the Nordic Wind Tunnel.

• Turbulence researchers around the world, hopefully through an international and/or European institute we will establish here.

• In summary, anyone carrying out serious turbulence research is welcome and invited to participate.




1:100 scale model of proposed facility



1:100 scale model of proposed facility(vertical arrangement)

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