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Fourth International Symposium on Turbulence and Shear Flow Phenomena
June, 27-29, 2005, Marriot Hotel, Williamsburg, Virginia, USA

DOI: 10.1615/TSFP4

2D FRACTAL FLOW GENERATED BY ELECTROMAGNETIC FORCING: LABORATORY EXPERIMENTS AND NUMERICAL SIMULATIONS

pages 485-490
DOI: 10.1615/TSFP4.810
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要約

Recent works have focused on flow topology and the distribution in space and "size" of the stagnation points. They show that this spatial distribution is closely linked to the energy spectrum and particle pair dispersion statistics. Here we realize flow simulations (laboratory experiments and DNS) where a multi-scale structure of electromagnetically generated stagnation points controls the flow. We thus control the flow's topology and the energy input at each scale. As a first step, we work with a fractal electromagnetic forcing (3 iterations in space) constant in time (step of forcing) of a shallow layer brine flow considered as quasi two dimensional.
• We generate and control a multi-scale "laminar" flow
• Its energy spectrum is E(k) ~ k−p with p=2.5. This is clearly different from small or large scale forcing (p=5/3 or p ≥ 3) for 2D turbulent flows.
• This exponent (p=2.5) is surprisingly close to theory and shows the possibility to control the energy spectrum by pertinent multi-scale forcing.
• This multi-scale laminar flow presents interesting characteristics for mixing: i) during the energy transient, Lagrangian statistics present a ballistic behaviour leading to fluid element pair dispersion statistics with mean square separation ~ tγ where γ ~ 3 as in Richardson diffusion in isotropic turbulent flow, ii) After the transient, pair dispersion remains strong. γ is found in the range 2.3 ≤ γ ≤ 2.5.