Density ratio dependence of Rayleigh-Taylor mixing for sustained and impulsive acceleration histories
- Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)
The turbulent Rayleigh-Taylor instability is investigated over a comprehensive range of fluid density ratio (R)1.3{<=}R{<=}50 [0.15{<=}A=(R-1)/(R+1){<=}0.96] and different acceleration histories g(t) using the Linear Electric Motor. The mixing layer is diagnosed with backlit photography and laser-induced fluorescence. For a constant acceleration, the bubble (2) and spike (1) amplitudes are found to increase as h{sub i}={alpha}{sub i}Agt{sup 2} with {alpha}{sub 2}{approx}0.05{+-}0.005 and {alpha}{sub 1}{approx}{alpha}{sub 2}R{sup D{}sub {alpha}} with D{sub {alpha}}{approx}0.33{+-}0.05. For temporally varying accelerations Ag(t)>0, this can be generalized to h{sub i}=2{alpha}{sub i}AS using S=[{integral}(sq root)(g)dt]{sup 2}/2 rather than the displacement Z={integral}{integral}gdt{sup '} dt. For impulsive accelerations, S remains constant during the coast phase and the amplitudes obey a power law h{sub i}{approx}t{sup {theta}}{sup {}sub i} with {theta}{sub 2}{approx}0.25{+-}0.05 and {theta}{sub 1}{approx}{theta}{sub 2}R{sup D{}sub {theta}} with D{sub {theta}}{approx}0.21{+-}0.05. These values of D{sub {alpha}} and D{sub {theta}} compare favorably with numerical simulations and mix models. The average diameter at the mixing front for bubbles is found to increase as d{sub 2}{approx}h{sub 2}(1+A)/4 in qualitative agreement with ''merger'' models, but the associated dh{sub i}/dt is two times larger than the terminal velocity of an isolated bubble. The spikes become relatively narrow at large R, yet they still grow as gt{sup 2}. (c) 2000 American Institute of Physics.
- OSTI ID:
- 20215070
- Journal Information:
- Physics of Fluids (1994), Vol. 12, Issue 2; Other Information: PBD: Feb 2000; ISSN 1070-6631
- Country of Publication:
- United States
- Language:
- English
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