Measurements in a two-dimensional thermal plume along a vertical adiabatic wall

Abstract

Mean velocities and temperatures were measured in a turbulent plume above a line heat source at the base of a vertical adiabatic wall. Various values of the buoyancy flux and distances above the source in the weakly buoyant regime of the flow were considered. Correlating expressions for the data were determined by assuming streamwise similarity of mean flow quantities, and a fixed entrainment constant and local skin-friction coefficient. The results yielded an entrainment constant based on the average velocity of 0·095±0·005. This value of the entrainment constant is in fair agreement with earlier work on wall plumes, but is less than half the value reported for free line plumes. Local flow properties are only weakly dependent upon the value of the skin-friction coefficient, with variations of 0-0·01 causing only a 3% change in the mean velocity and weight density defect. The results suggest that the presence of a wall, as opposed to a plane of symmetry, has a strong influence on entrainment, although the specific drag characteristics of the wall are of less importance. The reduced entrainment causes higher velocities and higher values of the weight density defect in a wall plume than in a comparable free plume.