scholarly journals Reduced modeling of porous media convection in a minimal flow unit at large Rayleigh number

2018 ◽  
Vol 371 ◽  
pp. 551-563 ◽  
Author(s):  
Baole Wen ◽  
Gregory P. Chini
Keyword(s):  
Porous Media ◽  
Rayleigh Number ◽  
Flow Unit ◽  
Minimal Flow ◽  
Reduced Modeling ◽  
Large Rayleigh Number

Plume formation and resonant bifurcations in porous-media convection

1994 ◽  
Vol 272 ◽  
pp. 67-90 ◽  
Author(s):  
Michael D. Graham ◽  
Paul H. Steen
Keyword(s):  
Boundary Layer ◽  
Porous Media ◽  
Rayleigh Number ◽  
Scaling Laws ◽  
Thermal Plumes ◽  
Scaling Behaviour ◽  
Parametric Resonances ◽  
Classical Boundary ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

The classical boundary-layer scaling laws proposed by Howard for Rayleigh–Bénard convection at high Rayleigh number extend to the analogous case of convection in saturated porous media. We computationally study two-dimensional porous-media convection near the onset of this scaling behaviour. The main result of the paper is the observation and study of instabilities that lead to deviations from the scaling relations.At Rayleigh numbers below the scaling regime, boundary-layer fluctuations born at a Hopf bifurcation strengthen and eventually develop into thermal plumes. The appearance of plumes corresponds to the onset of the boundary-layer scaling behaviour of the oscillation frequency and mean Nusselt number, in agreement with the classical theory. As the Rayleigh number increases further, the flow undergoes instabilities that lead to ‘bubbles’ in parameter space of quasi-periodic flow, and eventually to weakly chaotic flow. The instabilities disturb the plume formation process, effectively leading to a phase modulation of the process and to deviations from the scaling laws. We argue that these instabilities correspond to parametric resonances between the timescale for plume formation and the characteristic convection timescale of the flow.

Convection fluid dynamics in a model of a fault zone in the earth's crust

1978 ◽  
Vol 88 (4) ◽  
pp. 769-792 ◽  
Author(s):  
D. R. Kassoy ◽  
A. Zebib
Keyword(s):  
Fluid Dynamics ◽  
Rayleigh Number ◽  
Porous Material ◽  
Fault Zone ◽  
Slug Flow ◽  
Tectonic Activity ◽  
Two Dimensional ◽  
Core Flow ◽  
Number Flow ◽  
Large Rayleigh Number

Faulted regions associated with geothermal areas are assumed to be composed of rock which has been heavily fractured within the fault zone by continuous tectonic activity. The fractured zone is modelled as a vertical, slender, two-dimensional channel of saturated porous material with impermeable walls on which the temperature increases linearly with depth. The development of an isothermal slug flow entering the fault at a large depth is examined. An entry solution and the subsequent approach to the fully developed configuration are obtained for large Rayleigh number flow. The former is characterized by growing thermal boundary layers adjacent to the walls and a slightly accelerated isothermal core flow. Further downstream the development is described by a parabolic system. It is shown that a class of fully developed solutions is not spatially stable.

Nanofluid Impinging Jets in Porous Media

2016 ◽  
Vol 7 ◽  
pp. 84-113
Author(s):  
Bernardo Buonomo ◽  
Oronzio Manca ◽  
Sergio Nardini ◽  
D. Ricci
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Rayleigh Number ◽  
Peclet Number ◽  
Pure Water ◽  
Particle Diameter ◽  
Target Surface ◽  
Impinging Jets ◽  
Local Thermal Equilibrium ◽  
Péclet Number

Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in many applications in the fields of automotive, aerospace, electronics and process industry. A possible solution to obtain efficient cooling systems is represented by the use of confined impinging jets. Moreover, the introduction of nanoparticles in the working fluids can be considered in order to improve the thermal performances of the base fluids. In this paper a numerical investigation on mixed convection in confined slot jets impinging on a porous media by considering pure water or Al2O3/water based nanofluids is described. A two-dimensional model is developed and different Peclet numbers and Rayleigh numbers were considered. The particle volume concentrations ranged from 0% to 4% and the particle diameter is equal to 30 nm. The target surface is heated by a constant temperature value, calculated according to the value of Rayleigh number. The distance of the target surface is five times greater than the slot jet width. A single-phase model approach has been adopted in order to describe the nanofluid behaviour while the hypothesis of non-local thermal equilibrium is considered in order to simulate the behaviour in the porous media which is featured by a porosity value of 0.87. The aim consists into study the thermal and fluid-dynamic behaviour of the system. Results show increasing values of the convective heat transfer coefficients for increasing values of Peclet number and particle concentration. This behaviour is more evident at low Peclet number values and Rayleigh number ones.

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