The Buoyancy and Variable Viscosity Effects on a Water Laminar Boundary Layer along a Heated Longitudinal Horizontal Cylinder
Small cross flow is induced in an otherwise axially symmetric laminar boundary layer when a uniform horizontal stream flows along the inner or outer surface of a heated horizontal cylinder. The magnitude of this cross flow depends on the ratio of the Grashof number to the square of the Reynolds number, based on the radius of the cylinder, and in its early stages grows linearly in the downstream direction. The report shows that the variable-viscosity effect can increase the velocity gradient and, hence, stabilize the laminar boundary layer; the cross-flow effect will decrease the velocity gradient and destabilize the laminar boundary layer over the upper half of the cylinder (or the pipe flow). Also, the boundary beyond which the cross-flow effect can overwhelm the variable-viscosity effect has been determined.