An experimental study of nonlinear disturbance behaviour in natural convection

Abstract

An experimental investigation has been carried out to determine the behaviour of three-dimensional disturbances in laminar natural convection flow adjacent to a flat vertical surface with uniform heat flux input. A controlled two-dimensional disturbance, with a superimposed transverse variation, was introduced into the boundary region by a vibrating ribbon. The downstream propagation and amplification of these disturbances were studied in detail. Of principal interest was their nonlinear interaction with the base flow and any secondary mean flows that might arise therefrom. Measurements of the transverse mean velocity component indicate a double longitudinal vortex system. These results also show a distortion of the longitudinal base velocity profile which rapidly increases downstream. An alternate spanwise steepening and flattening of the profile is found to result. These mean flow modifications are found to be in good general agreement with existing theoretical and experimental studies of such flows. Our results are also compared with those obtained for forced flow. Several very important differences and similarities are indicated.