The formation of air-core vortex is a common phenomenon during the draining process. However, there is an upward flow which is called as 'reverse jet' attempts during the air-core vortex formation. These phenomena if not properly controlled may reduce the efficiency and lifespan of liquid draining tank. Nevertheless, there is still no numerical research directed on the relation between air-core vortex and reverse jet, which might be very beneficial for the future study. Hence, the objective of this paper is to re revisits the fundamental physics flow of the reverse jet during the generation of air-core vortex.OpenFOAM®, an open source CFD package is used to simulate the flow inside the draining tank and the existence of reverse jet has been proved through the wake momentum thickness and Power-Spectral Density function (PSD).
In this article, a numerical approach is applied to study the flow regimes surround a generic train model travelling on different bridge configurations under the influence of crosswind. The bridge is varies based on the different geometry of the bridge girder. The crosswind flow angle (Ψ) is varied from 0° to 90°. The incompressible flow around the train was resolved by utilizing the Reynolds-averaged Navier-Stokes (RANS) equations combined with the SST k-ω turbulence model. The Reynolds number used, based on the height of the train and the freestream velocity, is 3.7 × 105. In the results, it was found that variations of the crosswind flow angles produced different flow regimes. Two unique flow regimes appear, representing (i) slender body flow behaviour at a smaller range of Ψ (i.e. Ψ ≤ 45°) and (ii) bluff body flow behaviour at a higher range of Ψ (i.e. Ψ ≥ 60°). As the geometries of the bridge girder were varied, the bridge with the wedge girder showed the worst aerodynamic properties with both important aerodynamic loads (i.e. side force and rolling moment), followed by the triangular girder and the rectangular girder. This was due to the flow separation on the windward side and flow structure formation on the leeward side, both of which are majorly influenced by the flow that moved from the top and below of the bridge structures.
Accurate numerical simulation of liquid draining is important to study the physics fluid flow. However, liquid draining involves multiphase and rotational flows, where numerical simulation is expensive to accurately recreate these flow behaviors. The accuracy of numerical results has been also debatable and it is mainly affected by the computational modeling approaches. Therefore, this study evaluates different computational modelling approaches such as DNS, RANS k-ε, RANS k-ω and LES turbulence models. The results for the draining time and flow visualization of the generation of an air-core are in a good agreement with the available published data. The Direct Numerical Simulation (DNS) seems most reasonably satisfactory for VOF studies relating air-core compared to other different turbulence modeling approaches.
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