| The primary objective of this dissertation is to understand the effect of latent heat release on the entrainment behavior of cumulus clouds. A laboratory analogue consisting of an off-source volumetrically heated jet was constructed for this purpose. The scope of this work is mainly experimental, undertaken using PIV, LIF, and whole field thermometry. Some direct numerical simulations were also performed, and supplemented by new theoretical models, and detailed analysis.; The characteristics of a volumetrically heated jet are found to be very different from both a normal jet and a plume. The large eddies residing at the edge of the jet are disrupted by heat injection. The scalar width is reduced in the heat injection zone. The velocity width and mass flux grow initially and reach constant values. The streamwise velocity profile transforms from a Gaussian to a flat-top Gaussian, allowing a larger transport of both momentum and mass flux. A twin-peak Gaussian profile for temperature has been identified as the reason for the change in the streamwise velocity profile. The cross-stream velocity profile shows an absence of outflow region near the jet axis; this is attributed to acceleration of the jet due to the added buoyancy.; This is probably the first time that a detailed numerical analysis of a flow wherein velocities, scalar concentration and temperature are strongly coupled has been attempted. Our numerical results are in good agreement with the experiments. These computations indicate that the normalized fluctuations for the streamwise velocity, scalar concentration and temperature increase drastically with heating, while those of the radial and azimuthal velocity components remain virtually unaffected. Further, the mass and momentum flux for the heated jet are related through a simple relationship.; The insights gained from the heated jet experiment are successfully extended to a conceptual model for entrainment in cumulus clouds. The model describes a system with a constant mass flux, but a varying momentum flux. Cumulus clouds may have a constant mass flux because a redistribution of mass between the up and downdrafts is possible, unlike a volumetrically heated jet, which has only regions of positive moving velocity. |
