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To investigate the effects of cigarette structure parameters on the air flow field inside the cigarette, a computational fluid dynamics (CFD) method was adopted to simulate the air flow process inside a cigarette. The effects of viscous resistance coefficients of cigarette materials and cigarette length on the mouth end pressure drop and the ventilation rates of cigarette paper and filter were analyzed, and the correlation equations, which can quantitatively describe the coupling effect of cigarette structure parameters on the air field inside cigarette, were established. The results showed that: 1) The pressure drop was positively correlated with the viscosity resistance coefficients of cut tobacco, filter, cigarette paper and plug wrapper, the ventilation rate of cigarette paper was positively correlated with the viscosity resistance coefficients of cut tobacco and plug wrapper, and the ventilation rate of filter was positively correlated with the viscosity resistance coefficients of cut tobacco, filter and cigarette paper. 2) As the cigarette length decreased or the cigarette diameter increased, the pressure drop and the ventilation rates of the cigarette paper and filter decreased. 3) As the number of ventilation holes increased, the pressure drop and the ventilation rate of the cigarette paper decreased, while the ventilation rate of the filter increased. As the distance between the ventilation holes and the mouth end increased, the pressure drop and the ventilation rate of the cigarette paper increased, while the ventilation rate of the filter decreased. 4) The correlation coefficients of the established correlation equations were all higher than 0.93, and the relative errors between the predicted and measured values were small, which could accurately describe the coupling effect of cigarette structure parameters on the air flow field inside the cigarette. [ABSTRACT FROM AUTHOR]

A thorough understanding of the reactor core thermal hydraulic behavior is essential for the design and safety analysis of Sodium-cooled Fast Reactors (SFR). Due to the application of hexagonal subassembly, the core thermal hydraulic behavior is significantly affected by the flow field within the subassemblies, the inter-wrapper region and the hot pool. Analysis of the core thermal hydraulic behavior requires a model coupling the three regions mentioned above, which has been identified as one of the thermal hydraulic challenges in SFR. In the present study, a 3D model that covers the three regions was developed for the core of the China Experimental Fast Reactor (CEFR) with the Computational Fluid Dynamic (CFD) code, Fluent. The inter-wrapper region and the hot pool were modeled in detail, while the subassemblies were modeled with a special porous medium model. The core thermal hydraulics behavior under steady state was studied, more specifically, information for the flow field distribution at the core outlet, the inter-wrapper flow and the duct wall temperature distribution was obtained. Under steady state, liquid sodium in the inter-wrapper region is supplied by the inner region of the hot pool. And it enters the inter-wrapper region from the core outer region and returns back to the hot pool inner region from the core central region. The inter-wrapper flow is cooled by non-fuel subassemblies and heated up by fuel subassemblies. For non-fuel subassembly, the ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies could reaches 96%; for fuel subassemblies, the maximum ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies is 2.45%. Significant temperature gradients have been observed on the duct wall, with maximum values of 156.69 K/m in the vertical direction and 2,196.00 K/m in the circumferential direction. The largest temperature gradient appears on the duct of subassemblies adjacent to the transition region of fuel subassemblies and non-fuel subassemblies. [ABSTRACT FROM AUTHOR]

Iliac Vein Compression Syndrome (IVCS) is a common risk factor for deep vein thrombosis in the lower extremities. The objective of this study was to investigate whether employing a porous medium model to simulate the compressed region of an iliac vein could improve the reliability and accuracy of Computational Fluid Dynamics (CFD) analysis outcomes of IVCS. Pre-operative Computed Tomography (CT) scan images of patients with IVCS were utilized to reconstruct models illustrating both the compression and collateral circulation of the iliac vein. A porous medium model was employed to simulate the compressed region of the iliac vein. The agreements of times to peak between discrete phase particles in CFD analysis and contrast agent particles in Digital Subtraction Angiography (DSA) were compared. Furthermore, comparisons were made between the CFD analysis results that incorporated the porous media and those that did not. The results revealed that in the CFD analysis incorporating the porous media model, more than 80% of discrete phase particles reached the inferior vena cava via collateral circulation. Additionally, the concentration variation curve of discrete phase particles demonstrated a high concordance rate of 92.4% compared to that obtained in DSA. In comparison to CFD analysis conducted without the porous medium model, the incorporation of the porous medium model resulted in a substantial decrease in blood flow velocity by 87.5% within the compressed region, a significant increase in pressure gradient of 141 Pa between the inferior vena cava and left iliac vein, and a wider distribution of wall shear stress exceeding 2.0 Pa in collateral vessels rather than in the compressed region. The study suggests that the introduction of a porous medium model improves the hemodynamic analysis of patients with IVCS, resulting in a closer alignment with clinical observations. This provides a novel theoretical framework for the assessment and treatment of patients with IVCS.

Abstract This paper presents a topology optimization approach for the surface flows on variable design domains. Via this approach, the matching between the pattern of a surface flow and the 2-manifold used to define the pattern can be optimized, where the 2-manifold is implicitly defined on another fixed 2-manifold named as the base manifold. The fiber bundle topology optimization approach is developed based on the description of the topological structure of the surface flow by using the differential geometry concept of the fiber bundle. The material distribution method is used to achieve the evolution of the pattern of the surface flow. The evolution of the implicit 2-manifold is realized via a homeomorphous map. The design variable of the pattern of the surface flow and that of the implicit 2-manifold are regularized by two sequentially implemented surface-PDE filters. The two surface-PDE filters are coupled, because they are defined on the implicit 2-manifold and base manifold, respectively. The surface Navier-Stokes equations, defined on the implicit 2-manifold, are used to describe the surface flow. The fiber bundle topology optimization problem is analyzed using the continuous adjoint method implemented on the first-order Sobolev space. Several numerical examples have been provided to demonstrate this approach, where the combination of the viscous dissipation and pressure drop is used as the design objective.

This paper presents a topology optimization approach for the surface flows on variable design domains. Via this approach, the matching between the pattern of a surface flow and the 2-manifold used to define the pattern can be optimized, where the 2-manifold is implicitly defined on another fixed 2-manifold named as the base manifold. The fiber bundle topology optimization approach is developed based on the description of the topological structure of the surface flow by using the differential geometry concept of the fiber bundle. The material distribution method is used to achieve the evolution of the pattern of the surface flow. The evolution of the implicit 2-manifold is realized via a homeomorphous map. The design variable of the pattern of the surface flow and that of the implicit 2-manifold are regularized by two sequentially implemented surface-PDE filters. The two surface-PDE filters are coupled, because they are defined on the implicit 2-manifold and base manifold, respectively. The surface Navier-Stokes equations, defined on the implicit 2-manifold, are used to describe the surface flow. The fiber bundle topology optimization problem is analyzed using the continuous adjoint method implemented on the first-order Sobolev space. Several numerical examples have been provided to demonstrate this approach, where the combination of the viscous dissipation and pressure drop is used as the design objective. [ABSTRACT FROM AUTHOR]

A thorough understanding of the reactor core thermal hydraulic behavior is essential for the design and safety analysis of Sodium-cooled Fast Reactors (SFR). Due to the application of hexagonal subassembly, the core thermal hydraulic behavior is significantly affected by the flow field within the subassemblies, the inter-wrapper region and the hot pool. Analysis of the core thermal hydraulic behavior requires a model coupling the three regions mentioned above, which has been identified as one of the thermal hydraulic challenges in SFR. In the present study, a 3D model that covers the three regions was developed for the core of the China Experimental Fast Reactor (CEFR) with the Computational Fluid Dynamic (CFD) code, Fluent. The inter-wrapper region and the hot pool were modeled in detail, while the subassemblies were modeled with a special porous medium model. The core thermal hydraulics behavior under steady state was studied, more specifically, information for the flow field distribution at the core outlet, the inter-wrapper flow and the duct wall temperature distribution was obtained. Under steady state, liquid sodium in the inter-wrapper region is supplied by the inner region of the hot pool. And it enters the inter-wrapper region from the core outer region and returns back to the hot pool inner region from the core central region. The inter-wrapper flow is cooled by non-fuel subassemblies and heated up by fuel subassemblies. For non-fuel subassembly, the ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies could reaches 96%; for fuel subassemblies, the maximum ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies is 2.45%. Significant temperature gradients have been observed on the duct wall, with maximum values of 156.69 K/m in the vertical direction and 2,196.00 K/m in the circumferential direction. The largest temperature gradient appears on the duct of subassemblies adjacent to the transition region of fuel subassemblies and non-fuel subassemblies.

Featured Application: The developed topology optimization approach may give a potential design idea for body shape drag reduction of micro underwater vehicles and other underwater equipment worked in low speed. This paper presents a variable density topology optimization method to numerically investigate the optimal drag-reduction shape of objects in the two-dimensional and three-dimensional flows with steady incompressible external flow conditions, taking into account material volume constraints. By introducing the porous media model, the artificial Darcy friction is added to the Navier-Stokes equation to characterize the influence of materials on the fluid. Material density is applied to implement material interpolation. By transforming the boundary integral form of viscous dissipative expression of drag into the volume integral of artificial Darcy friction and convection term, we solve the problem of drag expression on the implicit interface corresponding to the structure. The continuous adjoint method is used to analyze gradient information for iteratively solving topology optimization problems. We obtain the relevant topology optimization structures of the minimum drag shapes, investigate the effect of the low Reynolds number on the drag force corresponding to two objective functions and discuss the mechanism of drag reduction by a hydrodynamic body shape. [ABSTRACT FROM AUTHOR]

The perforated plates are commonly used for gas flow control in the wide-angle diffusers of electrostatic precipitators of large power plants. Many studies dealt with the investigation of the effects of the perforated plate's geometry on flow parameters in the cases where incoming flow is perpendicular to the plate and the plate is covering the whole cross-section of the flowing channel. These results are partially applicable in cases where flow is inclined on the plate or when the plate is not occupying the whole cross-section of the channel. The subject of this work is a numerical investigation of flow through the rectangular channel with a perforated plate in various positions in the cross-section of the channel. The aim was to investigate the effect of the plate position on the flow. The perforated plates were modeled as thin porous media of finite thickness by using the directional loss model. Numerical experiments are carried out by using CFD software ANSYS CFX. Results of pressure drop and velocity distribution behind the plate are compared to the results of CFD simulation of the full 3-D plate model. In order to obtain a reasonable agreement both of the pressure drop and velocity distribution behind the plate when using a simplified thin porous plate model, the value of streamwise permeability of the plate had to be adjusted. The level of adjustments has determined iteratively and it depends on the plate position in the channel's cross-section. [ABSTRACT FROM AUTHOR]

Chronic obstructive pulmonary disease (COPD) is a primary chronic respiratory disease associated with pulmonary congestion that restricts airflow and thereby affects the exchange of gases between the alveoli and the blood capillaries in the lungs. Dual scale-global and local-porous medium models have been developed and reported in this work, to study the effects of air-side congestion on the blood-oxygen content in the alveolar region of the human lung. The human lung is model as a global, equivalent, heterogeneous porous medium comprising three zones with distinct permeabilities related to their progressively complex branching structure. Airflow for each breathing cycle is determined by solving mass and momentum transfer equations across the three porous medium zones. The congestion is introduced by appropriate modification of the porous medium properties of the zones considered. The congestion-affected air velocity reaching Zone 3 is given as input to a separate "local model" employed at several locations of the alveoli of Zone 3. The local model determines the oxygen content in the blood flow in the capillaries of the alveoli by solving suitable mass, momentum and species transport equations. The transient simulation results performed for a long duration of multiple breathing cycles, demonstrate that a normal, healthy human lung is functional for up to 40% volume congestion or when 50% of the lung is congested to about 23.5%. Increasing congestion beyond this value, quickly-within a few hours-depletes the oxygen exchange in the blood flow of the alveolar region (of Zone 3), leading to hypoxemia. The effects of congestion progression on oxygen exchange dynamics determined through the dual-scale porous medium modelling approach provide researchers and medical professionals with in silico predictive estimates to generate treatment strategies for chronic respiratory diseases., (© 2024 John Wiley & Sons Ltd.)

• POM can reproduce the hemodynamic changes of coiled aneurysm. • Neck, pre- and postoperative inflow areas were related with aneurysm recurrence. • A large postoperative inflow area independently predicts the recurrence of coiled PAs. This study aims to investigate recurrence risk factors of simply coiled unruptured paraclinoid aneurysms based on a porous medium model (POM). Twenty unruptured coiled paraclinoid aneurysms with digital subtract angiography (DSA) follow-up were enrolled to analyze morphological and hemodynamic variables to predict recurrence. Recurrent aneurysms have larger neck areas than stable aneurysms (34.43 ± 21.46 mm2 vs. 16.12 ± 7.10 mm2; p = 0.048). For hemodynamic variables, recurrent aneurysms had larger preoperative (16.40 ± 11.38 mm2 vs. 7.87 ± 3.75 mm2; p = 0.048) and postoperative inflow areas (14.07 ± 6.80 mm2 versus 6.73 ± 4.20 mm2; p = 0.021) than the stable group. Only the postoperative inflow area (p = 0.031, OR = 1.289; 95% CI 1.024–1.624) was an independent predictor of recurrence after multivariate regression analysis. The receiver operating characteristic (ROC) curve analysis efficiently predicted recurrence (AUC = 0.833, p = 0.021) with an inflow area cutoff value (9.15 mm2; sensitivity, 0.833; specificity, 0.857). Neck area along with pre- and postoperative inflow areas were associated with aneurysm recurrence. These findings suggest that a large postoperative inflow area independently predicts the recurrence of coiled paraclinoid aneurysms. [ABSTRACT FROM AUTHOR]

This paper presents a variable density topology optimization method to numerically investigate the optimal drag-reduction shape of objects in the two-dimensional and three-dimensional flows with steady incompressible external flow conditions, taking into account material volume constraints. By introducing the porous media model, the artificial Darcy friction is added to the Navier-Stokes equation to characterize the influence of materials on the fluid. Material density is applied to implement material interpolation. By transforming the boundary integral form of viscous dissipative expression of drag into the volume integral of artificial Darcy friction and convection term, we solve the problem of drag expression on the implicit interface corresponding to the structure. The continuous adjoint method is used to analyze gradient information for iteratively solving topology optimization problems. We obtain the relevant topology optimization structures of the minimum drag shapes, investigate the effect of the low Reynolds number on the drag force corresponding to two objective functions and discuss the mechanism of drag reduction by a hydrodynamic body shape.

Desulphurization is the key to the upgrading of oil products, and the high pressure hydrogenation reactor is a key device for desulfurization. The catalyst bed is one of the most core components of the hydrogenation reactor, and the flow characteristics of the internal multiphase fluid directly affect the reaction efficiency and product quality of the hydrogenation reactor. The multiphase flow process and the lumped reaction law of hydrodesulfurization in the catalyst bed are studied by adding the porous medium model and the laminar finite rate model in this paper. Combined the porous medium model and the laminar finite rate model, the mass fraction of hydrogen sulfide formation and Arrhenius reaction rate of desulfurization reaction with different porosity, different material inlet velocity and different hydrogen-oil ratio are studied. The result can provide theoretical basis for the optimization of the hydrogenation reaction parameters. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combining global simplified and local turbulence models to calculate flow details. • Analysis of the low-pressure heater pipe failure causes. • Simulate the low-pressure heater with the porous medium model. • Obtained flow information in the damaged local area. Low-pressure heaters are critical heat exchange equipment in thermal and nuclear power generation. The high-speed steam flow in the low-pressure heaters induces pipe vibration, causing pipe failure. The large size and complex flow make it hard to calculate directly. This paper employs a combined method of the porous medium and local models by substituting the boundary to calculate and prove steam flow trajectory and velocity are consistent with the actual situation. The analysis of the turbulent kinetic energy exhibits that the primary causes of pipe vibration are the periodic vortex shedding and the impact of the impingement plate on the pipes. The stress analysis indicates that the loosening of the pipes leads to a 368 times amplification of the shear stress by 0.1 MPa. The most crucial step in solving such a problem is to strengthen the fixation of the pipes, especially near the shell region. [ABSTRACT FROM AUTHOR]

The strategy of particle-resolved computational fluid dynamics (CFD) has been widely used to study the hydrodynamic properties of fluid flow in small-sized pebble bed, but generally suffers from the tedious creation of body-fitted grids. Previously, we proposed a novel particle-resolved CFD strategy, p-IBM, which combines mesh-adaption and the immersed boundary method. The primary objective of this work is to test different mesh-adaption strategies and evaluate the quantitative accuracy degree of p-IBM simulations. For this purpose, two packed bed systems reported in the literature are simulated based on the p-IBM strategy. The flow behavior and heat transfer properties of the interstitial gas are analyzed and compared with published experimental results. Comparisons show that the simulation results are in quantitative agreement with the experimental data. This work thus lays a solid foundation for future detailed investigations of the flow and transfer performance of fluid in a small-sized pebble bed. [Display omitted] • The quantitative accuracy of a novel particle-resolved CFD strategy is evaluated. • A mesh adaption strategy reducing the grid number by several times is proposed. • The predicted results are in quantitative agreement with experimental data. [ABSTRACT FROM AUTHOR]

In this study, a semi-analytical solution is developed to investigate the wave interference and corresponding dynamic responses of an array of submersible flexible fish cages. The net chamber is modelled as a perforated cylindrical shell, and the penetration flow through the cage interface is described by a porous medium model. Based on the potential flow theory, the solution to this physical problem is expanded as a series of eigenfunctions in the local coordinate system of each cage, and the scattered wave potentials generated by all cages are superimposed wherein Graf's addition theorem is employed for the coordinate transformation. The mean wave drift effect is also explored, which is a nonlinear phenomenon derivable from the first-order solution. The results indicate that the interference of waves is determined by wavenumbers, cage spacings or net porosities, and significant wave responses are manifested near the top part of the cage. Additionally, the first-order wave force vanishes at a ratio of cage diameter to wavelength = 0.59, and, along the direction of wave incidence, the rear cages experience opposite mean wave drift loads relative to those on the front cages. These studies provide benchmark results for understanding the hydroelastic characteristics of multi-cage systems. • The shell-membrane theory introduced in the semi-analytical solution of waves and an array of fish cages interactions. • Prediction of the mean wave drift loads on fish cages based on the first-order solutions of the wavefield. • The total wave force acting on all cages is zero if the ratio of cage diameter to wavelength is approximately 0.59. • Wave interference in a cage array depends on the ratio of cage spacing or size to wavelength and the net porosity. [ABSTRACT FROM AUTHOR]

Surface flows can represent the motions of the viscous and incompressible fluid at the solid/fluid interfaces. This paper presents a topology optimization approach for surface flows and extends the design space of topology optimization of fluidic structures onto the curved surfaces in the forms of 2-manifolds corresponding to the geometrical configurations of the solid/fluid interfaces. The presented approach is implemented by filling a porous medium onto the 2-manifolds. An artificial Darcy friction is correspondingly added to the area force term of the surface Navier-Stokes equations used to describe the surface flows and the physical area forces are penalized to eliminate their existence in the fluidic regions and to avoid the invalidity of the porous medium based topology optimization model. Topology optimization for the steady and unsteady surface flows has been executed by iteratively evolving the impermeability of the porous medium, where the impermeability is interpolated by the material density derived from a design variable. The related partial differential equations are solved by using the surface finite element method. Numerical examples have been provided to demonstrate this topology optimization approach for the surface flows, including the boundary velocity driven flows, the area force driven flows and the convection-diffusion flows. [ABSTRACT FROM AUTHOR]