NUMERICAL AND EXPERIMENTAL STUDY OF A RAYLEIGH-TAYLOR MIXING FRONT José M. REDONDO Dept. de Fisica Aplicada Universidad Politécnica de Cataluña (UPC)
NUMERICAL AND EXPERIMENTAL STUDY OF A RAYLEIGH-TAYLOR MIXING FRONT 1.Introduction 2.Experiments 3.Simulations 4.Fractal Dimension 5.Conclusions
1.INTRODUCTION Important parameters to consider in Rayleigh Taylor Instability study The Atwood Number, A The width of the mixing zone, The non-dimensional time, The Fractal Dimension
2.EXPERIMENTS ON RTI Experiments in a Perspex tank; H=500mm L x =400mm L y =200mm Linden, Redondo & Youngs (1994) J. Fluid Mech. 265 Dalziel, Linden & Youngs (1997) 6 th IWPCTM
Experimental Visualizations LIF Fluoresceine Visualization – Elevation and Plane Views
3. SIMULATIONS 2D LES SGS: Smagorinsky – Lilly Unsteady, 1st-Order, Implicit Boussinesq model 256² elements mesh Atwood 5x10 - ²
2D LES of the RT Front
Velocity Magnitude Volume of Fluid Vorticity Magnitude 0÷1 0÷0, ÷84 min max
Experimental results vs LES
The Density Variation - Mixing
4. FRACTAL DIMENSION
Volume of FluidVelocity MagnitudeVorticity Magnitude 3.0 2.5 2.0 D
Fractal dimension by scalar values Overall
Volume of fluid and Vorticity
Fractal dimension by scalar values Mushroom
Fractal Dimension for the Overall, Mushroom and Front D
Fractal Dimension for the Experiments
5. CONCLUSIONS
Conclusions 1.Fractal dimension anlaysis probed that the mixing occurs mainly at the sides of the blobs and that in the front there is no mixing 2.The fractal dimension differs for the various scalar fields even when there is presence of similar topology and structure. These differences seem to be related with a complex system of cascades of direct and inverse vorticity. 3.The range of scales is very active and complex and in the future the application of Fractal Analysis can be helpful to decompose and analyse these scales. 4.A three dimensional simulation (even better if DNS is used) analyzed with Fractal Analysis may give a better approach to the experimental results.