There are two coupled primary objectives for this study of buoyancy-driven turbulence.
The first objective is to create a new diagnostic for collection of measurements to capture the
physics of Rayleigh-Taylor (RT) mixing. The second objective is to use the new diagnostic to
specifically elucidate the physics of large Atwood number, ( )( )2 1 2 1 / ρ ρ ρ ρ + − = t A , RT
mixing. Both of these objectives have been satisfied through the development of a new hot-wire
diagnostic to study buoyancy-driven turbulence in a statistically steady gas channel of helium
and air ( 6 . 0 03 . 0 ≤ ≤ t A ). The capability of the diagnostic to simultaneously and instantaneously
measure turbulent velocity and density fluctuations allows for a unique investigation into the
dynamics of Rayleigh-Taylor mixing layers at large At, through measurements of turbulence and
mixing statistics. The new hot-wire diagnostic uses temperature as a fluid marker for helium and
air, which is possible due to the Lewis number ~ 1 (Le = ratio of thermal diffusivity to mass
diffusivity) for helium and air, and the new diagnostic has been validated in an At = 0.03 mixing
layer. The energy density spectrum of v′ ′ ρ , measured experimentally for the first time in RT
mixing, is found to closely follow the energy distribution of v′ , up to the Reynolds numbers investigated ( ( ) mix t h gA h υ 6 2 Re 2 / 3 = ~ 1450). Large At experiments, with At = 0.6, have
also been achieved for the first time in a miscible RT mixing layer. An asymmetric penetration
of the bubbles (rising fluid) and spikes (falling fluid) has been observed, resulting in measured
self similar growth parameters αb = 0.060 and αs = 0.088 for the bubbles and spikes, respectively.
The first experimental measurements of turbulent velocity and density fluctuations for the large
At case, show a strong similarity to lower At behaviors when normalized. However conditional
statistics, which separate the bubble (light fluid) and spike (heavy fluid) dynamics, has
highlighted differences in v′ ′ ρ and rms v′ in the bubbles and spikes. Larger values of v′ ′ ρ and
rms v′ were found in the downward falling spikes, which is consistent with the larger growth rates
and momentum of the spikes compared to the bubbles. These conditional statistics are a first in
RT driven turbulence.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2772 |
| Date | 15 May 2009 |
| Creators | Kraft, Wayne Neal |
| Contributors | Andrews, Malcolm |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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