Convective instabilities in two liquid layers
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We perform linear stability calculations for horizontal fluid bilayers, taking into account both buoyancy effects and thermocapillary effects in the presence of a vertical temperature gradient. To help understand the mechanisms driving the instability, we have performed both long-wavelength and short-wavelength analyses. The mechanism for the large wavelength instability is complicated, and the detailed form of the expansion is found to depend on the Crispation and Bond numbers. The system also allows a conventional Rayleigh-Taylor instability if heavier fluid overlies lighter fluid, and the long-wavelength analysis describes this case as well. In addition to the asymptotic analyses for large and small wavelengths, we have performed numerical calculations using materials parameters for a benzene-water system.Keywords:
Rayleigh–Taylor instability
Convective instability
Experimental evidence of two distinctive mechanisms of transition from localized (LTW) to extended (ETW) traveling waves in convecting binary mixtures is presented. Both are related to the convectively unstable nature of LTW, and reflect its different manifestations. In short cells the mechanism which is responsible for the LTW instability is related to the transition from convective to absolute instability. In long cells and negative enough values of the separation ratio \ensuremath{\psi}, transition from LTW to ETW occurs due to the interaction of convectively growing perturbations and LTW. Crossover between the two mechanisms is demonstrated.
Convective instability
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Observational tests of cumulus parameterizations are difficult. Since cumulus convection is generally embedded in a larger-scale flow pattern in which many feedbacks are acting, it is hard to tell what is causing what to happen. For those aspects of convection tightly embedded in feedback loops, the change in convective behavior caused by environmental changes needs to be correctly represented in parameterizations. However, it is precisely these changes that are difficult to observe, since negative large-scale feedback often minimizes the range of naturally occurring variations. For instance, suppose the convective mass flux were very sensitive to environmental instability, such that a slight increase in instability resulted in a large increase in convective mass flux. This in turn would generate large amounts of convective heating, which in turn would quickly stabilize the environment, thus reducing the vertical mass flux. In normal circumstances, large deviations from neutral stability would rarely occur, and observations of convective behavior in highly unstable conditions would be difficult to obtain. However, it is this abnormal behavior that needs to be studied in order to understand the feedback mechanisms that prevent it from occurring more frequently.
Convective instability
Mass flux
Convective flow
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By means of phenomenological arguments generalized Ginzburg-Landau equations for a certain secondary convective instability are proposed. These equations allow to simulate a system where stationary convection can interact with supercritical oscillatory modes. The results are very similar to that obtained in recent experiments on forced bimodal convection.
Convective instability
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The present article reviews recent progress in the study of pattern formation in convective instabilities. After a brief discussion of the relevant basic hydrodynamic equations as well as a short outline of the mathematical treatment of pattern formation in complex systems the self-organization of spatial and spatio-temporal structures due to convective instabilities is considered. The formation of various forms of convective patterns arising in the Bénard experiment, i.e. in a horizontal fluid layer heated from below, is discussed. Then the review considers pattern formation in the Bénard instability in spherical geometries. In that case it can be demonstrated how the interaction among several convective cells may lead to time dependent as well as chaotic evolution of the spatial structures. Finally, the convective instability in a binary fluid mixture is discussed. In contrast to the instability in a single component fluid the instability may be oscillatory. In that case convection sets in in the form of travelling wave patterns which in addition to a complicated and chaotic temporal behaviour exhibit more or less spatial irregularity already close to threshold.
Convective instability
Pattern Formation
Component (thermodynamics)
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Semi-convective mixing, as an example of double-diffusive convection, is of general importance in multi-component fluid mixing processes. In astrophysics it occurs when the mean molecular weight gradient caused by a mixture of light material on top of heavier one counteracts the convective instability caused by a temperature gradient. Direct numerical simulations of double-diffusive fluid flows in a realistic stellar or planetary parameter space are currently non-feasible. Hence, a model describing incompressible semi-convection was developed, which allows to investigate semi-convective layer formation. A detailed parameter study with varying Rayleigh number and stability parameter has been performed for the giant planet case. We conclude that semi-convective layering may not play that important role as suggested in earlier works for the planetary case.
Convective instability
Free convective layer
Convective mixing
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�������� ��������� ���� �.�. ������� , �.�. ������ � ������� ������ � ����������� ������������ ����� �������������� ������ � �� ��� ��!� �������� �������� ����� ������������ ������������ ��������� � ������������� ������ �������� ��� ����������� ���� ������� �������� ������� . �������� ������ ����������� ������� ������ ������ � ����������� ������������ ����� , ��������� ������� ������� ��� ������� �� �������� ����������� ������� . �������� ����������� ������� ��� ������� , ��� ������� ������� ������������ ������������ ������ �������� . ���������������� , ��������� ����������� , ����� ������� . The numerical analysis of convective Marangoni instability in nonstationary process of gas absorption by motionless liquid layer of finite thickness was made. The estimation of a critical time of transition to the convective unstable regime was obtained, the influence of the thickness of liquid layer to the critical time was investigated. The minimum thickness of liquid layer, which allows the convective instability of the absorptive process is computed.
Convective instability
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Convective flow
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Two major mesoscale convective clusters of different characters occurred during the heavy rainfall event in Guangxi Region and Guangdong Province on 20 June 2005,and they are preliminarily identified as a frontal mesoscale convective system(MCS1;a frontal cloud cluster) and a non-frontal MCS(MCS2;a warm sector cloud cluster).Comparative analyses on their convective intensity,maintenance mechanism, and moist potential vorticity(MPV) structure were further performed.The convective intensity analysis suggests that the ascending motion in both the frontal MCS1 and the warm sector MCS2 was strong,so it is hard to conclude whether the intensity of the frontal convective cluster was stronger than that of the nonfrontal convective cluster,and their difference in precipitation might result from differences in their moisture conditions.The comparative analysis of the maintenance mechanisms of matured MCS1 and MCS2 show that in MCS1 there were strong northerly inflows at middle and upper levels,and the convection was mainly maintained through convective-symmetric instability;while in MCS2,the water vapor was abundant,and the convection was maintained by moist convective instability.The structural analysis of MPV indicates that(1) the two clusters were both potentially symmetric unstable at middle and low levels;(2) there were interactions between the cold/dry air and the warm/wet air in the frontal MCS1,and the interactions between the upper- and low-level jets in the warm sector MCS2;(3) the high- and low-level jets and moisture condition nearby the convective clusters exerted different impacts on the two types of convective systems, respectively.
Mesoscale convective system
Convective instability
Free convective layer
Convective inhibition
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The evolution of material interpenetration boundary induced by Rayleigh-Taylor instability is calculated under various acceleration histories and density ratios using a buoyancy-drag model,which reveals that the mixing development under a constant acceleration is very different from that under a variable acceleration,and that the asymmetry between a bubble and a spike enhances with the increase of the density ratio.The calculation results are compared with detailed experiment data to prove the validation of the choice of model constants,the addition of phenomenal ratio factors and model assumption used.These results provide theory guides for applying a buoyancy-drag model to related engineering designs directly and for replacing existing empirical expressions,which greatly promote the development of engineering fields related to mixing phenomenon induced by instabilities.
Rayleigh–Taylor instability
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Convective instability
Convective flow
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