The standard theory of pulsations deals with the frequencies and growth rates of infinitesimal perturbations in a stellar model. Modes which are calculated to be linearly driven should increase their amplitudes exponentially with time; the fact that nearly constant amplitudes are usually observed is evidence that nonlinear mechanisms inhibit the growth of finite amplitude pulsations. Models predict that the mass of DAV convection zones is very sensitive to temperature (i.e., MCZ∝T−90eff) leading to the possibility that even "small amplitude" pulsators may experience significant nonlinear effects. In particular, the outer turning point of finite-amplitude g-mode pulsations can vary with the local surface temperature, producing a reflected wave that is slightly out of phase with that required for a standing wave. This can lead to a lack of coherence of the mode and a reduction in its global amplitude. We compute the size of this effect for specific examples and discuss the results in the context of Kepler and K2 observations.
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Effects of symmetry on magnetohydrodynamic mixed convection flow in a vertical duct
Magnetohydrodynamic convection in a downward flow of liquid metal in a vertical duct is investigated experimentally and numerically. It
is known from earlier studies that in a certain range of parameters, the flow exhibits high-amplitude pulsations of temperature in the form
of isolated bursts or quasi-regular fluctuations. This study extends the analysis while focusing on the effects of symmetry introduced by twosided
rather than one-sided wall heating. It is found that the temperature pulsations are robust physical phenomena appearing for both types
of heating and various inlet conditions. At the same time, the properties, typical amplitude, and range of existence in the parametric space are
very different at the symmetric and asymmetric heating. The obtained data show good agreement between computations and experiments
and allow us to explain the physical mechanisms causing the pulsation behavior.
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- Award ID(s):
- 1803730
- NSF-PAR ID:
- 10282596
- Date Published:
- Journal Name:
- Physics of fluids
- Volume:
- 32
- ISSN:
- 1070-6631
- Page Range / eLocation ID:
- 094106
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/1.50020608
