Study of entrainment characteristics in cloud-like flows

English Abstract:

Clouds are one of the major sources of uncertainty in weather prediction (IPCC Fourth Assessment Report: Climate Change 2007). The present study involves laboratory simulation of orographic cloud-like flow. Orographic clouds are formed when the moist air parcels near the surface are forced to move up because of the presence of mountain. After rising to a certain height, condensation starts and the released latent heat adds extra buoyancy to the cloud. We considered planar buoyant wall jet with volumetric heat addition to the flow fluid (mimicking latent heat released in real scenario) as an appropriate low order fluid dynamical model to simulate orographic clouds at laboratory conditions. It was observed that the entrainment starts to reduce as heat is added to the flow. Also, it was found that this reduction starts at a bulk Richardson number (non dimensional heat release parameter) which was an order of magnitude lower that that seen in experiments of Narasimha et al. (2011) on free standing orographic clouds. This is in agreement with the observations in real orographic clouds where clouds always develop as a thin layer along the mountain slope, although the natural tendency of buoyancy being to make in spread in the direction opposite of gravity. We also developed a novel technique to get the instantaneous structure of the turbulent shear flow. We are applying this technique to cloud-like flows to study the evolution of vortical structures in the flow. We plan to determine parameters related to vorticity and turbulence structure which could be later incorporated to the current weather prediction models to improve their accuracy. Detailed results will be presented at the conference.