Thermo and Fluid Dynamics

1. 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 Thermo and Fluid Dynamics

2. 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). Thermo and Fluid Dynamics

3. 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. Thermo and Fluid Dynamics

4. 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) which dissipate most of energy are the same for all flows. • Ideas which evolved 1960 - 1980’s suggest small scales are more complicated, but still universal. • It has never really been possible to test these ideas because of the absence of large enough high quality research facilities, so they were more or less accepted by default until 1990’s. Thermo and Fluid Dynamics

5. … versus new ideas • By the late 1980’s, the old ideas began to be challenged on several fronts. • New theories suggested turbulence might depend forever on how it started - meaning control might be possible. • Old ideas about universality of the small scales were challenged with new ones based on equilibrium similarity of all scales, and new kinds of universality. • The validity of experiments which appeared to support the old ideas were called into question. Thermo and Fluid Dynamics

6. 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 free from the influence of the walls. or • have too high a background disturbance level to extract the features of primary interest. Thermo and Fluid Dynamics

7. Why can’t a super-computer do the job? • The computational box required to duplicate the capabilities of the proposed 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, then the 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. Thermo and Fluid Dynamics

8. 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. Thermo and Fluid Dynamics

9. 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 Thermo and Fluid Dynamics

10. The Large Wind Tunnel Facility would: • be the largest and longest turbulence research tunnel in the world 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. Thermo and Fluid Dynamics

11. 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 to turbulence scale, reasonably independent of Reynolds number effects. (This is crucial to computer modeling.) Thermo and Fluid Dynamics

12. Research (continued) • We will be able to study for the first time ever in a high Reynolds number laboratory flow how particulates diffuse and disperse beyond the initial (and least interesting) instants. (This has important implications to all sorts of important problems.) • We will be able to study for the first time in a laboratory flow at high Reynolds number how the smallest scales of turbulence really behave. (This information is crucial to the development of LES turbulence models, the great hope for engineers.) • These represent the most fundamental flows of turbulence, and those from which we can learn the most about the physics. Thermo and Fluid Dynamics

13. 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. Thermo and Fluid Dynamics

14. 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). Thermo and Fluid Dynamics

15. 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, Sweden Hassan Nagib -IIT/Chicago, USA Roger E. A. Arndt - Univ. of Minnesota, USA William Saric - Arizona State Univ., USA Anthony Perry - Univ. of Melbourne, Australia Yong C. Han - Yeugnam Univ., S. Korea Thermo and Fluid Dynamics

16. Turbulence expertsopinions: • The world’s senior turbulence scientists are enthusiastic, among them: John L. Lumley - Cornell U., USA William C. Reynolds - Stanford U., USA Fazle Hussain - U. of Houston, USA • Many want to participate directly in the research, including: Franz Durst - U. of Erlangen, Germany Marie Farge - U. of Paris, France Mohammed Gad-el-Hak - Notre Dame U., USA Mark N. Glauser - Clarkson U., USA Charles Meneveau - Johns Hopkins U., USA Zelman Warhaft - Cornell U., USA Thermo and Fluid Dynamics

17. A Nordic Partnership • Our Scandinavian partners will be enthusiastic participants in making 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 convection Preben Buchhave, optics and measurement NTU - Trondheim, NO Per Aage Krogstad, boundary layers KTH - Stockholm, SE Arne Johansson, turbulence Thermo and Fluid Dynamics

18. 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. Thermo and Fluid Dynamics

19. 1:100 scale model of proposed facility Thermo and Fluid Dynamics

20. 1:100 scale model of proposed facility Thermo and Fluid Dynamics

21. 1:100 scale model of proposed facility Thermo and Fluid Dynamics

22. 1:100 scale model of proposed facility Thermo and Fluid Dynamics

23. 1:100 scale model of proposed facility Thermo and Fluid Dynamics

24. 1:100 scale model of proposed facility Thermo and Fluid Dynamics

25. 1:100 scale model of proposed facility (vertical arrangement) Thermo and Fluid Dynamics