Problem Statement:
A 3D tank is filled with liquid water (multiphase flow [air-water]).
CFD:
Computational Fluid Dynamics (CFD) is the process of mathematically modelling a physical phenomenon involving fluid flow and solving it numerically using the computational process.
In a CFD software analysis, the examination of fluid flow by its physical properties such as velocity, pressure, temperature, density, and viscosity. To generate an accurate solution for a physical phenomenon associated with fluid flow, those properties must be considered simultaneously.
A mathematical model of the physical case and a numerical method are used in a CFD software tool to analyze the fluid flow. For instance, the Navier-Stokes (N-S) equations are specified as the mathematical model of the physical case. This describes changes in all those physical properties for both fluid flow and heat transfer. A mathematical model varies by the content of the problem such as heat transfer, mass transfer, phase change, chemical reaction, etc. Moreover, the reliability of a CFD analysis highly depends on the whole structure of the process.
Theory:
The main feature of flow through a bend is the presence of a radial pressure gradient created by the centrifugal force acting on the fluid. Because of this, the fluid at the centre of the pipe moves towards the outer side and comes back along the wall towards the inner side. This creates a double spiral flow field shown schematically. If the bend curvature is strong enough, the adverse pressure gradient near the outer wall in the bend and near the inner wall just after the bend may lead to flow separation at these points, giving rise to a large increase in pressure losses. Even for fairly large-radius bends, the flow field in the bend will be severely distorted.
The pressure losses suffered in a bend are caused by both friction and momentum exchanges resulting from a change in the direction of flow. Both these factors depend on the bend angle, the curvature ratio and the Reynolds Number. The overall pressure drop can be expressed as the sum of two components: 1) that resulting from friction in a straight pipe of equivalent length which depends mainly on the Reynolds number (and the pipe roughness); and 2) that resulting from losses due to change of direction, normally expressed in terms of a bend-loss coefficient, which depends mainly on the curvature ratio and the bend angle. The pressure loss in a bend can thus be calculated as:
Geometry:
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