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In order to investigate the evolution characteristics of gas-liquid two-phase flow passing through a 90° pipe bend, the volume of fluid (VOF) multiphase flow model and the Realizable k-ε turbulence model are used to conduct numerical simulations. The evolution of velocity, pressure distribution, gas void fraction, and flow pattern passing through a 90° pipe bend is studied in detail. The results show that different gas-liquid two-phase flow patterns will produce different degrees of secondary flow phenomenon after passing through the 90° pipe bend, and the tangential velocity presents a bimodal distribution, which eventually dissipates into a unimodal distribution in the horizontal pipe. The pressure on the outer wall of the pipe bend increases as the inlet velocity increases. The change of gas void fraction is related to the transformation of the flow pattern, the bubbly flow evolves into a slender slug flow in the horizontal pipe after passing through the 90° pipe bend, and the gas void fraction will decrease. The slug flow, the churn flow, and the annular flow evolve into the stratified-wave flow in the horizontal pipe after passing through the pipe bend, and the variation of the gas void fraction is relatively low. The research results can provide certain theoretical support for the design and development of gas-liquid two-phase flow conveying elbows and the prediction of induced stress.

The present study expresses the turbulent flow characteristics through a 90° pipe bend using a numerical method by determining the solutions for Reynolds Averaged Navier-Stokes (RANS) expression using the k-ω (SST) turbulence model. For that purpose, numerical analysis has been carried out by solving RANS equations using ANSYS FLUENT 16.2, considering incompressible fluid in turbulent flow conditions. Simulations have been carried out for three different Reynolds number ranging from 1×105 to 10×105 at three different bend curvature ratios (Rc/D = 1, 1.5, and 2). Pipe bends with guide vane are generally used where flow separation and space problem makes an issue in mechanical design. The presence of guide vane inside the bend positively suppressed the flow separation and presence of cross-flow which can cause the engine to run off design, thus reducing the engine efficiency. So, to observe the effect of guide vane and its position on turbulence characteristics, four different positions of guide vane inside the bend are considered in the present study. At first, an analysis was led to make sure that the results obtained from the present numerical model are reliable and in line with previous results obtained from similar published experiments and numerical work. Research has been conducted to find out the impact of Reynolds number, bend curvature ratio and position of guide vane on different turbulence characteristics namely; turbulent kinetic energy, turbulent intensity, and wall shear stress at bend outlet position. In general, the turbulent intensity is found larger for the lower bend curvature ratio at the inner wall curvature side. Results for turbulent kinetic energy have similarities in results with turbulent intensity. Significantly, the wall shear stress represented a strong dependency on the circumferential angle at the bend outlet cross-section, and curvature ratio rather than Reynolds number and guide vane positions. [ABSTRACT FROM AUTHOR]

The present paper makes an effort to find the flow separation characteristics under high Reynolds number in pipe bends. Single phase turbulent flow through pipe bends is investigated using k-ε turbulence model. After the validation of present model against existing experimental results, a detailed study has been performed to study the influence of Reynolds number on flow separation and reattachment. The separation region and the velocity field of the primary and the secondary flows in different sections have been illustrated. Numerical results show that flow separation can be clearly visualized for bend with low curvature ratio. Distributions of the velocity vector show the secondary motion clearly induced by the movement of fluid from inner to outer wall of the bend leading to flow separation. This paper provides numerical results to understand the flow characteristics of fluid flow in 90° bend pipe.