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TURBULENT DECAY BEHIND MULTI-SCALE AND CONVENTIONAL GRIDS

Per-Age Krogstad
Department of Energy and Process Engineering, Norwegian University of Science and Technology N-7491 Trondheim, Norway

Peter A. Davidson
Department of Engineering, University of Cambridge Cambridge CB2 1PZ, UK

Sinopsis

We investigate wind tunnel turbulence generated by a conventional and two multi-scale grids. The conventional and multi-scale grids were all designed to produce turbulence with the same integral scale, so that a direct comparison could be made between the different flows. The turbulent decay rate behind our multi-scale grids is virtually identical to that behind the equivalent conventional grid. In particular, all flows exhibit a power-law decay of energy, u2 ~ t−n, where n is very close to the classical Saffman exponent of n = 6/5. Our results are at odds with some other experiments performed on multi-scale grids, where significantly higher energy decay exponents and turbulence levels have been reported.