NUMERICAL INVESTIGATION OF EFFECT OF DENSITY AND ASPECT RATIO ON BUOYANT OSCILLATORY EXCHANGE FLOW THROUGH CIRCULAR OPENING IN HORIZONTAL PARTITION USING SALT WATER ANALOGY

摘要

An interesting transport phenomenon is observed through openings between two compartments separated by a thin, vented, horizontal partition. A heavier fluid placed on the top of a lighter fluid and separated by a horizontal vent constitutes a gravitationally unstable system and produces a flow that is unstable with irregular oscillatory behavior. Computational fluid dynamics (CFD) simulations have been performed to simulate such type of flow across a circular opening in a horizontal partition using salt water and fresh water as working fluids. The effect of density ratio and opening aspect ratio on the oscillation frequency and flow coefficient through the opening has been investigated. An in-house finite volume method (FVM) based CFD code was developed to solve unsteady, axisymmetric Navier-Stokes equations along with realizable k-ε turbulence model and species transport for salt mass fraction. Higher order convection scheme was used to capture the oscillations correctly. A parametric study was performed with 4 density differences and 5 opening aspect ratios. It was observed that density difference has little influence on flow coefficient and significant influence on pulsation frequency, but aspect ratio has a strong influence on both the flow coefficient, as well as the pulsation frequency. A correlation was developed to predict the frequency of oscillation for a given value of density ratio and opening aspect ratio within a reasonable accuracy.