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Bouyancy-driven asymmetric water boundary layer along a heated cylinder

Published online by Cambridge University Press:  19 April 2006

Lun-Shin Yao ,
Ivan Catton  and
J. M. Mcdonough
Lun-Shin Yao
Affiliation:
Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801
Ivan Catton
Affiliation:
University of California, Los Angeles, CA 90052
J. M. Mcdonough
Affiliation:
University of California, Los Angeles, CA 90052
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Abstract

The development of a three-dimensional water boundary layer along a heated longitudinal horizontal cylinder is studied by a finite-difference method. The secondary flow is induced in an otherwise axially symmetric laminar boundary layer by the buoyancy force. The development of the boundary layer is studied under two heating conditions: constant wall heat flux and constant wall temperature. In general, close to the leading edge, the magnitude of the secondary flow is small and the boundary-layer flow is forced-convection dominant. The secondary flow grows downstream, and the interaction of the free and forced convection becomes important. The flow becomes free-convection dominant further downstream. The temperature-dependent viscosity of water has the effect of thinning the heated boundary layer. The buoyancy effect and the variable viscosity effect enhance each other over the lower part of the cylinder and compete with each other over the upper part of the cylinder. The numerical results compare with the forced convection dominant asymptotic solution and indicate that the asymptotic solution is only valid when x < 0·1a/ε½. Since the boundary layer is thin compared with the radius of the cylinder, the transverse curvature effect is small and can be neglected. Therefore, the solution can be applied to the entrance region of heated straight pipes as the zeroth-order boundary-layer flow.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 98 , Issue 2 , 29 May 1980 , pp. 417 - 434
Copyright
© 1980 Cambridge University Press

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