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Flow entrained with permeable particles is frequently encountered in natural and engineering applications. However, the lack of knowledge about the drag on the porous spheres and the corresponding complex flow structures has been a hindrance for better understanding of these flow systems In this work, we perform a comprehensive numerical simulation of flow past a porous particle with a wide range of Reynolds number (5 ≤ Re ≤ 200) and porosity (0.1 ≤ ɛ ≤ 0.95). Furthermore, considering that few studies has reported the flows with moving porous spheres, the simulation of both a single and two porous spheres settling in an enclosure is conducted for further evaluating the effect of moving porous media on the fluid–solid flows. The lattice Boltzmann method (LBM) is applied to the fluid flow, and particularly, the immersed moving boundary (IMB) scheme describes the interaction between the fluid and porous solid body. The accuracy of that the hybrid IMB-LBM for modeling porous sphere flows, to our knowledge, is first explored and established by the present study. The results suggest that both Re and ɛ have a significant influence on the drag and recirculation flow of porous particles. At Re ≤ 75, the porous particle experiences a lower resistance than that of the impermeable counterpart. When Re exceeds 75, the drag ratio is higher than unity for ɛ ≤ 0.85. With increasing porosity, the recirculation wake penetrates the particle, then detaches from the particle, and eventually disappears in the particle rear. Based on the simulated results, a new drag correlation for porous spheres is developed. As for the moving porous spheres, they fall slower than the solid counterparts, and their drafting, kissing and tumbling (DKT) process can also be slowed down. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to numerically solve fully developed laminar flow in trapezoidal ducts with rounded corners which result following forming processes. Design/methodology/approach: A two-dimensional model for a trapezoidal duct with rounded corners is developed and conservation of momentum equation is solved. The flow is assumed to be steady, fully developed, laminar, isothermal and incompressible. The key flow characteristics including the Poiseuille number and the incremental pressure drop have been computed and tabulated for a wide range of: sidewall angle (θ); the ratio of the height of the duct to its smaller base (α); and the ratio of the fillet radius of the duct to its smaller base (β). Findings: The results show that Poiseuille number decreases, and all the other dimensionless numbers increase with increasing the radii of the fillets of the duct; these effects were found to amplify with decreasing duct heights or increasing sidewall angles. The maximum axial velocity was shown to increase with increasing the radii of the fillets of the duct. For normally used ducts in hydrogen fuel cells, the impact of rounded corners cannot be overlooked for very low channel heights or very high sidewall angles. Practical implications: The data generated in this study are highly valuable for engineers interested in estimating pressure drops in rounded trapezoidal ducts; these ducts have been increasingly used in hydrogen fuel cells where flow channels are stamped on thin metallic sheets. Originality/value: Fully developed laminar flow in trapezoidal ducts with four rounded corners has been solved for the first time, allowing for more accurate estimation of pressure drop. [ABSTRACT FROM AUTHOR]

Explicit consideration of in-stream flow requirement (IFR) has now become almost mandatory in many rivers before irrigation withdrawal is made. Thereby, the primary objective was to evaluate the IFR through hydrological approaches and compare the condition with current flow variability and trends. Flow records were collected from five discharge stations for IFR estimation. Performance of the river was also judged with respect to nine hydraulic cross-sectional data and stage data of ten water-level monitoring stations of BangladeshWater Development Board (BWDB). Results showthat since 2000, the upper Karatoawas able to meet IFR, but the lowest part of the river experienced severe deterioration in addressing its dry season functionality. Also, the decreasing trend in off-stream availability is recognized as a threat to the Singra site resulting from severe aggradations of the river beds.Attention to the less off-stream availability at Singra raises concerns over sustaining the river from drying out. It is now evident that a hydrological approach of IFR is more than just an initial rough estimate. Such a precautionary method works well to provide quick technical support and decision reference for a complex system, in particular, to find specific drying out parts of a river of concern. [ABSTRACT FROM AUTHOR]