Showing papers by "Sanjoy Banerjee published in 1996"

Direct numerical simulation of near-interface turbulence in coupled gas-liquid flow

Abstract: Turbulence structures near the interface between two flowing fluids have been resolved by direct numerical simulation. As a first step the interface has been kept flat, corresponding closely to the recent gas‐liquid flow experiments of Rashidi and Banerjee [Phys. Fluids A 2, 1827 (1990)], with the fluids coupled through continuity of velocity and shear stress boundary conditions. For density ratios between the fluids typical of air and water, the turbulence characteristics on the gas side are quite similar to that in wall regions. The liquid side shows larger velocity fluctuations close to the interface and ejections originate closer to the interface. The mean velocity distribution, turbulence intensities, Reynolds stress and various other statistical measures are significantly altered compared to those in the wall region of channel flows. Quasi‐streamwise vortices form in the areas between high and low shear stress on both sides of the interface. At any given instant, about a fifth of these appear to be ...

Dynamic slug tracking simulations for gas-liquid flow in pipelines

Abstract: A Lagrangian slug tracking model for dynamic gas-liquid slug flow in pipelines of varying inclinations has been formulated and implemented in C + + using an object-oriented approach. Slugs and bubbles are discrete computational objects which are coupled by exchange of mass and momentum, and organized in linked lists The flow parameters are determined from dynamic integral mass and momentum balances on each slug and bubble. A subgrid is used in bubbles extending over pipe sections with different inclinations Slugs and bubbles are initiated at the pipe inlet, or at low points along a pipeline, and the propagation of individual slugs are tracked dynamically, and without numerical diffusion. Some sample cases demonstrate how the structure of the flow can be followed as it evolves from terrain effects, expansion and wake effects. These are effects that may in some instances cause slugs to disappear and merging of bubbles during simulations. Terrain slugging compulations compare well with some experime...

Direct numerical simulation of stratified gas-liquid flow

Abstract: Interactions through an interface between two turbulent flows play an important role in many environmental and industrial problems, e.g. in determining the coupling fluxes of heat mass and momentum, between the ocean and atmosphere, and in the design of gas-liquid contractors for the chemical industry, as well as in determining interactions between phases in nuclear transients that are accompanied by system voiding e.g. LOCAs. Here, the Direct Numerical Simulation (DNS) of the interaction of two turbulent fluids through a flat interface has been simulated. The flow and the temperature fields are computed using a pseudospectral method. This study shows that shear stress at the interface correlates well with the heat flux. Extensive analysis of the near interface turbulence structure has been performed using quadrant analysis. From this it is clear that gas-side sweeps dominate over the high shear stress regions. This suggests that simple parameterizations based on sweep frequency may be adequate for predictions of scalar transport rates.