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A detailed and systematic assessment of the plastic collapse load of 90° shape imperfect pipe bends subjected to in-plane opening bending was conducted by implementing three-dimensional non-linear finite element analyses. The material considered in the analysis is the elastic-perfectly plastic type with a large change geometry option. Shape distortions in the pipe's cross-section and through-wall circumferential crack at the intrados region were the defects analyzed in this study. Ovality (C o) and thinning (C t) were varied from 0% to 20% with a 5% incrementation, and crack angles of 45°, 60°, and 90° were considered at the intrados. The twice-elastic slope method effectively evaluates the plastic collapse moment as mandated by the ASME B&PV code NB-3213.25, section III. The reaction moment and angular rotation curves were generated for all pipe bend models. The outcomes of the analysis revealed that the plastic collapse moment load of pipe bends was affected by through-wall circumferential crack and C o , while thinning produced negligible effect, which was subsequently excluded from the analysis. The combined effect of through-wall circumferential crack and C o produces a consequential influence on the pipe bend at 45° angle, which is severe at 60°, and even more critical at 90°. In the analysis, the plastic collapse moment for short bend radius was reduced, while that of thin-walled pipe bends increased with an increase in thickness and bend radius. The plastic collapse moment of the present analysis was validated using experimental data acquired from open literature. An enhanced structural correlation assessment was proposed for through-wall circumferential crack shape-distorted 90° pipe bends. [ABSTRACT FROM AUTHOR]

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.

Numerical simulations of evolution characteristics of slug flow across a 90° pipe bend have been carried out to study the fluid—structure interaction response induced by internal slug flow. The two-phase flow patterns and turbulence were modelled by using the volume of fluid (VOF) model and the Realizable k−ε turbulence model respectively. Firstly, validation of the CFD model was carried out and the desirable results were obtained. The different flow patterns and the time-average mean void fraction was coincident with the reported experimental data. Simulations of different cases of slug flow have been carried out to show the effects of superficial gas and liquid velocity on the evolution characteristics of slug flow. Then, a one-way coupled fluid—structure interaction framework was established to investigate the slug flow interaction with a 90° pipe bend under various superficial liquid and gas velocities. It was found that the maximum total deformation and equivalent stress increased with the increasing superficial gas velocity, while decreased with the increasing superficial liquid velocity. In addition, the total deformation and equivalent stress has obvious periodic fluctuation. Furthermore, the distribution position of maximum deformation and stress was related to the evolution of slug flow. With the increasing superficial gas velocity, the maximum total deformation was mainly located at the 90° pipe bend. But as the superficial liquid velocity increases, the maximum total deformation was mainly located in the horizontal pipe section. Consequently, the slug flow with higher superficial gas velocity will induce more serious cyclical impact on the 90° pipe bend. [ABSTRACT FROM AUTHOR]

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.

A single phase, incompressible turbulent flow through a 90° pipe bend with/without guide vane conditions has been studied here. The present work deals with the numerical simulation to investigate the change in flow separation and velocity distribution at the downstream section due to the effect of the guide vane. The k-ε turbulence model has been adopted for simulation purposes to obtain the results. After the validation of existing experimental and numerical results, a detailed study has been performed for three different Reynolds number and four different positions of the guide vane. The value of the Curvature ratio (Rc/D) has been considered as one factor for the present study. The curvature ratio can be defined as the ratio between the bend curvature radius and hydraulic diameter of the pipe. The results obtained from the present study have been presented in graphical form. A flow separation region has been found at the bend outlet for flow through 90° pipe bend without the guide vane. This flow separation region was absent for the cases which dealt with the flow through 90° pipe bend with the guide vane. Velocity distribution at four different downstream positions for different cases and different Reynolds numbers have been compared and reported in the present study. [ABSTRACT FROM AUTHOR]

Present paper makes an effort to study the flow separation and velocity distribution for incompressible turbulent flow through 90o pipe bend due to the effect of guide vane installed in the bend portion. It has been observed here how the normalized velocity distribution profile changes if the guide vane is provided. k - ε turbulence model has been adopted for simulation purpose. After validating with existing experimental results, a detailed study has been performed for a particular Reynolds number and four different positions of guide vane. The value of Curvature ratio (Rc/D) has been considered as 1 for present study. The results obtained from the present study have been presented in terms of graphical form. A flow separation region was found at bend outlet for flow through 90o pipe bend without guide vane. This secondary flow separation region was absent for the cases which deals with the flow through 90o pipe bend with guide vane. Velocity distribution at seven different downstream positions have been presented in graphical form. Position to get a fully developed velocity distribution profile for each cases has been estimated on the basis of presented results. [ABSTRACT FROM AUTHOR]

Curved pipes are very often used in hydraulic systems facilitating compact, lightweight designs. But they can also be the cause of complex secondary flows as the curvature brings change of velocity profile, generation of vortices and production of hydraulic losses. In the present study, turbulent single phase flows through circular 90° curved bend for different curvature ratio (Rc/D = 1 to 5), defined as the bend mean curvature radius (Rc) to pipe diameter (D) is investigated numerically for different Reynolds number (Rc) ranging from 1 × 105 to 10 × 105. The purpose of this study is to simulate numerically the flow pattern and characterize the swirling secondary flow in 90° bends. Flow simulation using CFD techniques are performed to understand these phenomena. The k -- ε model with SIMPLE method is used for present study. After validation of present model with published experimental data, a detail study has been performed to characterize the flow separation and the dependency of swirl intensity on Reynolds number and curvature ratio in 90° pipe bend for single phase turbulent flow. [ABSTRACT FROM AUTHOR]