Abstract
Free convection plumes usually rise vertically, but do not do so when in an asymmetrical environment. In such cases they are susceptible to a thermoconvective instability because warmer fluid lies below cooler fluid in the upper half of the plume. We analyse the behaviour of streamwise vortex disturbances in plumes that are close to being vertical. The linearised equations subject to the boundary layer approximation are parabolic and are solved using a marching method. Our computations indicate that disturbances tend to be centred in the upper half of the plume. A neutral curve is determined and an asymptotic theory is developed to describe the right hand branch of this curve. The left hand branch is not amenable to an asymptotic analysis, and it is found that the onset of convection for small wavenumbers is very sensitively dependent on both the profile of the initiating disturbance and where it is introduced.
Similar content being viewed by others
Abbreviations
- c :
-
Constant in Eq. 2.16
- C p :
-
Specific heat
- d :
-
Natural lengthscale
- f :
-
Reduced streamfunction
- g :
-
Acceleration due to gravity
- k :
-
Vortex wavenumber
- K :
-
Permeability
- p :
-
Fluid pressure
- P :
-
Perturbation pressure
- q′′′:
-
Strength of heat source
- T :
-
Temperature
- u, v, w :
-
Darcy velocities in the x, y and z-directions
- U, V, W :
-
Perturbation velocities
- x, y, z :
-
Cartesian coordinates
- Y :
-
Scaled form of η in asymptotic analysis
- α :
-
Thermal diffusivity
- β :
-
Coefficient of cubical expansion
- δ :
-
Orientation of the plume centreline
- ϵ:
-
Inclination of a horizontal boundary
- μ :
-
Fluid viscosity
- θ :
-
Non-dimensional temperature
- Θ:
-
Perturbation temperature
- \(\phi\) :
-
Angular coordinate
- \(\phi^+,\phi^-\) :
-
Orientations of bounding surfaces
- ψ :
-
Streamfunction
- ρ :
-
Fluid density
- η :
-
Similarity variable
- ξ :
-
Scaled value of x
- −:
-
Dimensional
- ^:
-
Non-dimensional
- ′:
-
Derivative with respect to η
- c :
-
Critical value
- ∞:
-
Ambient
- 0, 1, 2,...:
-
Terms in asymptotic series
References
Afzal N. (1985). Two-dimensional buoyant plume in porous media: higher order effects. Int. J. Heat Mass Transf. 28: 2029–2041
Bassom A.P., Rees D.A.S. and Storesletten L. (2001). Convective plumes in porous media: the effect of asymmetrically placed boundaries. Int. Comm. Heat Mass Transf. 28: 31–38
Hall P. (1982). Taylor-Görtler vortices in fully developed or boundary-layer flows: linear theory. J. Fluid Mech. 124: 475–494
Ingham D.B. (1988). An exact solution for non-Darcy free convection from a horizontal line source. Wärme-Stoffübertrag. 22: 125–127
Lewis S., Bassom A.P. and Rees D.A.S. (1995). The stability of vertical thermal boundary layer flow in a porous medium. Eur. J. Mech. B-fluids 14: 395–407
Nield, D.A., Bejan, A.: Convection in Porous Media, 3rd edn. Springer, New York (2006)
Rees D.A.S. (1993). A numerical investigation of the nonlinear wave stability of vertical thermal boundary layer flow in a porous medium. Z.A.M.P. 44: 306–313
Rees D.A.S. (2001). Vortex instability from a near-vertical heated surface in a porous medium. I Linear theory. Proc. R. Soc. A 457: 1721–1734
Rees D.A.S. and Hossain M.A. (2001). The effect of inertia on free convective plumes in porous media. Int. Comm. Heat Mass Transf. 28: 1137–1142
Rees D.A.S., Storesletten L. and Bassom A.P. (2002). Convective plume paths in anisotropic porous media. Transp. Porous Media 49: 9–25
Wooding R.A. (1963). Convection in a saturated porous medium at large Reynolds number of Péclet number. J. Fluid Mech. 9: 183–192
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Rees, D.A.S., Postelnicu, A. & Bassom, A.P. The Linear Vortex Instability of the Near-vertical Line Source Plume in Porous Media. Transp Porous Med 74, 221–238 (2008). https://doi.org/10.1007/s11242-007-9195-3
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11242-007-9195-3