1. NUMERICAL AND EXPERIMENTAL STUDY OF A RAYLEIGH-TAYLOR MIXING FRONT José M. REDONDO Dept. de Fisica Aplicada Universidad Politécnica de Cataluña (UPC)

2. NUMERICAL AND EXPERIMENTAL STUDY OF A RAYLEIGH-TAYLOR MIXING FRONT 1.Introduction 2.Experiments 3.Simulations 4.Fractal Dimension 5.Conclusions

3. 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

4. 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

5. Experimental Visualizations LIF Fluoresceine Visualization – Elevation and Plane Views

6. 3. SIMULATIONS 2D LES SGS: Smagorinsky – Lilly Unsteady, 1st-Order, Implicit Boussinesq model 256² elements mesh Atwood 5x10 - ²

7. 2D LES of the RT Front

8. Velocity Magnitude Volume of Fluid Vorticity Magnitude 0÷1 0÷0,33 -106÷84 min max

9. Experimental results vs LES

10. The Density Variation - Mixing

11. 4. FRACTAL DIMENSION

12. Volume of FluidVelocity MagnitudeVorticity Magnitude  4.5 4.0 3.5  3.0  2.5  2.0 D

13. Fractal dimension by scalar values Overall

14. Volume of fluid and Vorticity

15. Fractal dimension by scalar values Mushroom

16. Fractal Dimension for the Overall, Mushroom and Front D

17. Fractal Dimension for the Experiments

18. 5. CONCLUSIONS

19. 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.