<strong>Turbulence</strong>...4<strong>Turbulence</strong> has been studied for a long time, butis nevertheless often cited as the last unsolvedproblem in classical mechanics. <strong>The</strong> 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. <strong>The</strong>se 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.“<strong>Turbulence</strong> remains one of the most outstandingresearch problems facing the international engineering,physics and mathematics research communities”Charles R. Doering, Professor of Mathematics, <strong>The</strong>University of Michigan, USA.“<strong>The</strong> 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, <strong>The</strong> University of Newcastle, Australia.“<strong>Turbulence</strong> 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.<strong>The</strong> <strong>Nordic</strong> <strong>Wind</strong> <strong>Tunnel</strong>Leonardo’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).“<strong>The</strong> 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 <strong>Nordic</strong> <strong>Wind</strong> <strong>Tunnel</strong> isdesigned for.”Professor James M. Wallace, Univ. of Maryland, USA.
<strong>Wind</strong> <strong>Tunnel</strong>s<strong>Wind</strong> 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. <strong>The</strong>y 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.<strong>The</strong> 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).<strong>The</strong> <strong>Nordic</strong> <strong>Wind</strong> <strong>Tunnel</strong>5
Change language