1. Rayleigh-Taylor Driven Mixing in a Multiply Stratified Environment Andrew Lawrie & Stuart Dalziel, Department of Applied Mathematics and Theoretical Physics University of Cambridge, UK

2. Outline Molecular mixing in the early stages of RT LIF with passive tracers MILES/ILES simulation Implications for Front-Tracking schemes

3. Prior Work Experimental setup –Dalziel et al. (1999) JFM Multiple stratifications –Jacobs & Dalziel (2005) JFM Incompressible Simulation –Almgren et al. (1998) JCP

4. Experimental Setup Atwood No. = 0.0037

5. Passive Tracer Transport

6. LIF with Passive Tracers Chemically benign tracer Chemically reactive tracer

7. Chemically Reactive Tracer

8. Calibration

9. Numerical Approaches Front-Tracking Spectral TVD-Finite Volume Mass diffusion affects(George et al. 2002)

10. Simulation Incompressible Immiscible Boussinesq

11. Comparison

12. Fractal Dimension

14. Mixing Surface

15. Mixed Volume

16. Conclusions Molecular mixing in the early stages of RT has been directly visualised with LIF Arguments based on growth rate used to justify accuracy of Front-Tracking schemes are shown to be inaccurate MILES simulations appear to provide a reasonable approximation to the mixing behaviour

17. Further Work Turbulent Diffusion over stable density interface Isolated vortex |ring impingement on stable density interface Influence of interfacial shear on turbulent diffusion

18. Prior Research Experimental setup –eg. Self-similarity and internal structure of turbulence induced by Rayleigh-Taylor instability (1999) Dalziel, S. B.,Linden, P. F., Youngs, D. L. Journal of Fluid Mechanics Multiple stratifications –Rayleigh-Taylor Instability in Complex Stratifications (2005) Jacobs, J. W. Dalziel, S.B. Journal of Fluid Mechanics Incompressible Simulation –A Conservative Adaptive Projection Method for the Variable Density Incompressible Navier-Stokes Equations (1998) Almgren, A.S., Bell J.B.,Collela, P., Howell, L.H., Welcome, M.L. Journal of Computational Physics Front Tracking Simulation –A comparison of experimental theoretical an numerical simulation rayleigh-taylor mixing rates. (2002) George, E., Glimm, J., Li, X.-L., Marchese, A., Xu, Z.-L. Proc. Natl. Acad. Sci.

19. Laboratory Acridine +Alcohol 2,3,5,6, - dibenzopyridine