Abstract
Free convective onset in a bottom heated porous medium under the influence of transverse magnetic field is studied within the framework of nonlinear theory. Simple harmonic time modulation is imposed on either the bounding surface temperature or the gravitational field acting on the medium. The Darcy–Lapwood–Brinkman model of flow through porous media is employed with two basic types of physical boundary conditions. The generalized energy approach coupled with the variational principles is followed. Higher order Galerkin method is then used to determine the unconditional and sharp stability limits for arbitrary values of modulational parameters. The increase in the Hartmann number is found to inhibit instability, thereby delaying the onset of two dimensional rolls. Moreover the initiation of instability mechanism can be well adjusted through a good knowledge of the parameters involved.
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Abbreviations
- a :
-
Thermal modulation amplitude
- \(A_m, B_m\) :
-
Adjustable functions
- \(\mathbf {B}\) :
-
Applied magnetic field
- \(c_p\) :
-
Specific heat
- d :
-
Porous medium depth
- Da :
-
Darcy number
- E :
-
Disturbance energy
- \(g_0\) :
-
Reference acceleration level
- H :
-
Darcy-Hartmann number
- Ha :
-
Hartmann number
- \(\mathbf {j}\) :
-
Electric current density
- k :
-
Permeability
- \(\mathbf {k}\) :
-
Vertical unit vector
- K :
-
Thermal conductivity
- p :
-
Pressure
- \(p_b\) :
-
Basic state pressure
- \(p\prime\) :
-
Perturbed pressure
- Pr :
-
Prandtl number
- \(\mathbf {q}\) :
-
Filtration velocity, (u, v, w)
- \(\mathbf {q_b}\) :
-
Basic state velocity
- \(\mathbf {q\prime }\) :
-
Perturbed velocity
- R :
-
Darcy–Rayleigh number
- Ra :
-
Rayleigh number
- t :
-
Time
- T :
-
Temperature
- \(T_b\) :
-
Basic state temperature
- \(T_r\) :
-
Reference temperature
- V :
-
Volume of porous media
- x, y, z :
-
Space coordinates
- \(\alpha\) :
-
Wavenumber, \(\sqrt{\alpha _x^2+\alpha _y^2}\)
- \(\alpha _x\) :
-
Wavenumber in the x-direction
- \(\alpha _y\) :
-
Wavenumber in the y-direction
- \(\rho\) :
-
Fluid density
- \(\theta\) :
-
Perturbed temperature
- \(\vartheta\) :
-
Porosity
- \(\nu\) :
-
Kinematic viscosity
- \(\mu\) :
-
Coefficient of thermal expansion
- \(\epsilon\) :
-
Gravity modulation amplitude
- \(\kappa\) :
-
Thermal diffusivity
- \(\phi\) :
-
Phase angle
- \(\lambda\) :
-
Coupling parameter
- \(\delta\) :
-
Variation of a quantity
- \(\psi\) :
-
Lagrange multiplier
- \(\sigma\) :
-
Electric conductivity
- \(\varGamma\) :
-
Space of admissible functions
- \(\varOmega\) :
-
Modulation frequency
- \(\omega\) :
-
Non-dimensional modulation frequency
- \(\zeta\) :
-
Isoperimetric constant
- \(\varDelta T\) :
-
Temperature difference
- D :
-
\(\partial /\partial z\)
- \(\nabla ^{2}\) :
-
Laplacian operator
- b :
-
Basic state
- cr :
-
Critical value
- L :
-
Linear
- N :
-
Nonlinear
- \('\) :
-
Perturbed quantity
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Acknowledgements
The second author thanks DST, India for providing financial assistance in the form of INSPIRE Fellowship. This work was supported by UGC, India through DRS Special Assistance Programme in Differential Equations and Fluid Dynamics.
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Saravanan, S., Meenasaranya, M. Energy stability of modulation driven porous convection with magnetic field. Meccanica 56, 2777–2788 (2021). https://doi.org/10.1007/s11012-021-01420-5
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DOI: https://doi.org/10.1007/s11012-021-01420-5