Evolution of highly buoyant thermals in a stratified layer

Brandenburg, Axel; Hazlehurst, John

doi:10.1051/0004-6361:20010273

Cited by 4 publications

(3 citation statements)

References 9 publications

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“…Such a deceleration may cause the thermals to move so slowly they would diffuse away their entropy perturbation before reaching the bottom of the solar convection zone. Brandenburg & Hazlehurst (2001) found that hot, buoyant thermals in stratified domains behave qualitatively similar to Boussinesq thermals. However, we are not aware of past work which carefully examines the effects of stratification on negatively buoyant thermals.…”

Section: Introductionmentioning

confidence: 78%

Entropy Rain: Dilution and Compression of Thermals in Stratified Domains

Anders

Lecoanet

Brown

2019

ApJ

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Large-scale convective flows called giant cells were once thought to transport the Sun's luminosity in the solar convection zone, but recent observations have called their existence into question. In place of large-scale flows, some authors have suggested the solar luminosity may instead be transported by small droplets of rapidly falling, low entropy fluid. This "entropy rain" could propagate as dense vortex rings, analogous to rising buoyant thermals in the Earth's atmosphere. In this work, we develop an analytical theory describing the evolution of dense, negatively buoyant thermals. We verify the theory with 2D cylindrical and 3D cartesian simulations of laminar, axisymmetric thermals in highly stratified atmospheres. Our results show that dense thermals fall in two categories: a stalling regime in which the droplets slow down and expand, and a falling regime in which the droplets accelerate and shrink as they propagate downwards. We estimate that solar downflows are in the falling regime and maintain their entropy perturbation against diffusion until they reach the base of the convection zone. This suggests that entropy rain may be an effective nonlocal mechanism for transporting the solar luminosity.

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Section: Introductionmentioning

confidence: 78%

Entropy Rain: Dilution and Compression of Thermals in Stratified Domains

Anders

Lecoanet

Brown

2019

ApJ

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“…In addition, several papers have addressed the detectability in radio and X-rays of cluster bubbles, including Churazov et al (2001), , Ensslin and Heinz (2002), and Soker et al (2002). Finally, bubbles in stratified atmospheres have been studied in the context of contact binary stars by Brandenburg and Hazlehurst (2001).…”

Section: Introductionmentioning

confidence: 99%

Morphology of Rising Hydrodynamic and Magnetohydrodynamic Bubbles from Numerical Simulations

Robinson

Dursi

Ricker

et al. 2004

ApJ

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Recent Chandra and XMM-Newton observations of galaxy cluster cooling flows have revealed X-ray emission voids of up to 30 kpc in size that have been identified with buoyant, magnetized bubbles. Motivated by these observations, we have investigated the behavior of rising bubbles in stratified atmospheres using the Flash adaptive-mesh simulation code. We present results from 2-D simulations with and without the effects of magnetic fields, and with varying bubble sizes and background stratifications. We find purely hydrodynamic bubbles to be unstable; a dynamically important magnetic field is required to maintain a bubble's integrity. This suggests that, even absent thermal conduction, for bubbles to be persistent enough to be regularly observed, they must be supported in large part by magnetic fields. Thermal conduction unmitigated by magnetic fields can dissipate the bubbles even faster. We also observe that the bubbles leave a tail as they rise; the structure of these tails can indicate the history of the dynamics of the rising bubble.

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“…The idea that buoyancy plays an important role in the evolution of the radio lobes in galaxies has been first proposed by Gull & Northover (1973) and has been used to estimate the lifetime of the radio lobes in M87 by Böhringer et al (1995). Three-dimensional simulations of hot bubbles in a stratified atmosphere have also been presented by Brandenburg & Hazlehurst (2001).…”

Section: Introductionmentioning

confidence: 99%

Simulation of radio plasma in clusters of galaxies

Brüggen

Kaiser

Churazov

et al. 2002

Monthly Notices of the Royal Astronomical Society

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We present three-dimensional hydrodynamical simulations of buoyant gas in a typical cluster environment. The hot matter was injected continuously into a small region off-set from the cluster centre. In agreement with previous analytic estimates we found that the bubbles evolve very differently depending on their luminosity. Using tracer particles we computed radio maps of the bubbles based on different assumptions about the magnetic field. In the radio band the bubbles closely resemble FRI sources. For the bubbles to be detectable for long enough to account for FRI sources, we found that reacceleration has to take place. The bubbles are generally difficult to detect, both, in the radio and in the X-ray band. Thus it is possible to hide a significant amount of energy in the form of bubbles in clusters. Finally, we compute the efficiency of the bubbles to stir the ICM and find that recurrent low-power sources may be fairly effective in mixing the inner cluster region.Comment: submitted to MNRAS. Full resolution colour figures at http://www.mpa-garching.mpg.de/~ensslin/Paper/hydra.ps.g

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Evolution of highly buoyant thermals in a stratified layer

Cited by 4 publications

References 9 publications

Entropy Rain: Dilution and Compression of Thermals in Stratified Domains

Entropy Rain: Dilution and Compression of Thermals in Stratified Domains

Morphology of Rising Hydrodynamic and Magnetohydrodynamic Bubbles from Numerical Simulations

Simulation of radio plasma in clusters of galaxies

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