K. R. Sreenivas

Vortex-dynamics model for entrainment in jets and plumes

Recent experimental results of Bhat and Narasimha (1996) have revealed a dramatic difference in the entrainment between jets and plumes subjected to off-source volumetric heating and their unheated counterparts. Experimental observations show that plumes entrain more rapidly than jets; the greater entrainment by the plume is typically attributed to the presence of buoyancy in the plume. In contrast, the addition of buoyancy away from the source by volumetric heating produces the opposite effect of reduced entrainment. Apart from buoyancy, other factors such as acceleration due to pressure gradients or other body forces can also affect the rate of entrainment. In this paper, we develop a model for entrainment to explain the mechanism by which buoyancy produces contrasting effects on entrainment in volumetrically heated flows in comparison to their unheated counterparts. The model highlights the role of density stratification in the process of vortex sheet roll-up in free shear flows. With this model, we ar...

Levitation of a drop over a film flow

A vertical jet of water impinging on a horizontal surface produces a radial film flow followed by a circular hydraulic jump. We report a phenomenon where fairly large (1 mi) drops of liquid levitate just upstream of the jump on a thin air layer between the drop and the film flow. We explain the phenomenon using lubrication theory. Bearing action both in the air film and the water film seems to be necessary to support large drops. Horizontal support is given to the drop by the hydraulic jump. A variety of drop shapes is observed depending on the volume of the drop and liquid properties. We show that interaction of the forces due to gravity, surface tension, viscosity and inertia produces these various shapes.

Modeling the dynamics of the mixed layer in solar ponds

A new model is proposed to explain the Nielsen’s equilibrium condition. This model takes into account the effects of both turbulent entrainment and diffusion on the growth/erosion of the gradient zone. The existing turbulent entrainment model is modified to make it applicable near the equilibrium condition. The new model predictions indicate the dependence of the equilibrium condition on the mixed layer depth, apart from the salinity and temperature gradients in the gradient zone.

Study of the erosion of stably stratified medium heated from below

We present, results from a two dimensional numerical simulation of a stably stratified layer heated from below. The aim of the simulation is to study the mechanism of erosion of a stably stratified medium by the convective velocity. We solve transport equations for momentum, heat and species using Patankars SIMPLER method. Tracer particles are used to get flow pattern inside the mixed layer and in the gradient zone. We have observed randomly moving thermals issuing from the bottom heated surface and from the interface separating the mixed layer and the gradient zone. Stable fluid from the gradient zone gets entrained into the mixed layer with the falling thermal from the interface. This is the main mechanism of the turbulent entrainment. Results from the numerical simulation indicate the need to include the effects of the turbulent entrainment in modelling the equilibrium condition

Natural Ventilation in a Model Room

Natural ventilation of a model room with water as the fluid medium is studied. It is insulated by air gaps on the four sides and at the top. A constant heat flux has been maintained on the bottom surface of the room. This room is surrounded by a large exterior tank containing water. There are three openings each on two opposing sides of the model room. For any experiment, only one opening on each side is kept open. Fluid enters or leaves these openings and the flow is driven entirely by buoyancy forces. Shadowgraph technique is used for visualization. The buoyancy causes flow to enter through the bottom opening and leaves through the top opening. At the openings, buoyant jets are observed and which have higher or lower relative density compared with that of its environment. The buoyant jet at the inlet interacts with the plumes on the heated bottom plate. From these visualizations, it appears that free convection at bottom plate will be affected by the buoyant jets at the openings and the degree to which it is affected depends on the position and size of openings and distance between inlet and outlet. The flow rate due to the natural ventilation depends on the bottom surface heat flux and the height difference between the openings. The temperatures of the floor, the interior and the exterior are calculated using a simple mathematical model. The values of temperatures obtained in the experiments are reasonably well predicted by the mathematical model.

Study of Submerged Jet for Suction of Fluid

This paper deals with the study of a submerged jet for the suction of unwanted fluid. This submerged jet is caused by the fluid coming out from a source. The presence of a sink in front of this source facilitates the suction of the fluid depending upon the source and sink flow rates, the axial and lateral separations of the source and sink, and the angle between the axes of the source and sink. The main purpose is the determination of the sink flow rate for 100% removal of the source fluid as a function of these parameters. The experiments have been carried using a source nozzle 6 mm in diameter and two sizes for the sink pipe diameter: 10 mm and 20 mm. The main diagnostics used are flow visualization using dye and particle image velocimetry (PIV). The dependence of the required suction flow rate to obtain 100% effectiveness on the suction tube diameter and angle is relatively weak compared to the lateral separation. DOI: 10.1115/1.4007266]

Hydrodynamic lubrication: Experiment with ‘Floating’ drops

This article gives the principle of hydrodynamic lubrication and also presents the new phenomenon of levitating drops over liquid film flow, which is explained using hydrodynamic lubrication theory.

On The Bifurcation of Laminar Buoyant Jets Discharged Horizontally

Experiments were conducted to determine the trajectory of a high Schmidt number buoyant jet discharged horizontally in a quiescent medium. The range of Reynolds number from 10 to 900 and Froude number from 2 to 40 were covered. The Schmidt number was 740. The flow in the discharge tube was laminar and fully developed in most of the cases. A new phenomenon of bifurcation in buoyant jets was found. Viscous effects prevent bifurcation below certain Gr and Re. When Gr was below 400, no bifurcation was observed for any Re. When Re was below 100, no bifurcation was observed for any Gr. When Fr was above 20 no bifurcation was observed for any Re. This is because transition to turbulence occurs before bifurcation can occur.