Internal Flows Research Articles

Application of the fast 3D simplified simulation method for the large CAP1400 nuclear island evaporator based on the coupled source term method

As for the evaporator of the large CAP1400 nuclear power plant, it has a large volume with numerous tubes along with the complex flow heat transfer phenomenon. The traditional direct simulation method usually takes a lot of time and computing resources to obtain the flow heat transfer data. To solve the problem, a fast simulation method established on the porous medium source term was herein proposed. In this simplified simulation method, the complex evaporator model is replaced with the porous medium model, where the derived heat and momentum source terms are added into the governing equation to control the heat flows. Five kinds of simplified evaporator models with different numbers of pipes were set to be the research objects, the internal flows inside the evaporator were studied with the traditional direct simulation method and the newly proposed simplified simulation method. Via comparative analysis, it can be found that: 1) The newly proposed simplified simulation method accurately captures the distribution characteristics of pressure, temperature, and entropy production in the evaporator, serving as a viable alternative to traditional direct simulation methods. Specifically, the average simulation errors for inlet-outlet pressure difference and temperature difference are both less than 5 % and 7 %, respectively. 2) The newly proposed simplified simulation method can capture the mutual interference effects between the evaporator and the nuclear main pump. When the evaporator is connected in series with the main nuclear pump, the average head of the main pump increases by 0.34 m, while the efficiency decreases by an average of 0.34 %. The average simulation errors of the simplified simulation method are 0.06 m and 0.13 %, respectively. 3) The application of the simplified simulation method leads to a significant 85 % decrease in the average computational cost for evaporator calculations and a notable 36 % decrease for combined calculations of the evaporator and main pump. The study here is expected to provide technique support for the simulation and evaluation of the large nuclear island.

Confinement induces internal flows in adherent cell aggregates.

During mesenchymal migration, F-actin protrusion at the leading edge and actomyosin contraction determine the retrograde flow of F-actin within the lamella. The coupling of this flow to integrin-based adhesions determines the force transmitted to the extracellular matrix and the net motion of the cell. In tissues, motion may also arise from convection, driven by gradients in tissue-scale surface tensions and pressures. However, how migration coordinates with convection to determine the net motion of cellular ensembles is unclear. To explore this, we study the spreading of cell aggregates on adhesive micropatterns on compliant substrates. During spreading, a cell monolayer expands from the aggregate towards the adhesive boundary. However, cells are unable to stabilize the protrusion beyond the adhesive boundary, resulting in retraction of the protrusion and detachment of cells from the matrix. Subsequently, the cells move upwards and rearwards, yielding a bulk convective flow towards the centre of the aggregate. The process is cyclic, yielding a steady-state balance between outward (protrusive) migration along the surface, and 'retrograde' (contractile) flows above the surface. Modelling the cell aggregates as confined active droplets, we demonstrate that the interplay between surface tension-driven flows within the aggregate, radially outward monolayer flow and conservation of mass leads to an internal circulation.

Artificial Intelligence for Decision Making in the Supply Chain

Artificial intelligence (AI) is a technology that has the potential to significantly impact organizational decision-making. In supply chain management (SCM), data analysis and organizational decision-mak- ing play a crucial role in providing insights into various aspects of the supply chain, such as relevant goods, inventory levels, order processing times, delivery times, and transportation costs. By analyzing data, companies can identify inefficiencies in their supply chain and take corrective actions to improve performance. The SC system is a customer-oriented and integrated system that determines planning, administration, and management processes for internal and external material and related flows, for- mulating the optimal factor of added value. In this study, we aim to identify hazardous products by analyzing product identification information at customs checkpoints and locations where vendible items are delivered to customers. We have identified several commodity groups and substances that are potentially harmful and dangerous to human health.

Old but gold: The use of multiregional life tables and the place-of-birth-dependent approach for studying recent internal migration in Italy

There has been a significant shift in migratory behavior within Italy over time. The origins and destinations of the migration flows, which were previously characterized by a clear prevalence of moving from the south to the center-north, are now much more heterogeneous and complex. Despite the important progress achieved in the past 20 years, the measurement of internal migration remains a contentious topic in international research. Using data provided by the Italian National Institute of Statistics, we applied Rogers’ multiregional model place-of-birth-dependent approach to assess the internal migration flows that occurred in Italy in the period 2002 – 2013. This approach provides accurate measurements of internal migration, noting in particular the years of life expectancy for each birth cohort living in each geographical Italian macroregion (northeast, northwest, center, and south). The results indicate that the northwest is the main area of destination for internal migration. The birth cohort in the south is the one that has the greatest number of years of life expectancy in other macroregions. Interestingly, this cohort is the only one characterized by a predominantly male migratory model.

INTERNAL MIGRATION DYNAMICS AND LABOR FORCE CHALLENGES IN KAZAKHSTAN

This study examines the dynamics of internal migration and its impact on labor force challenges in Kazakhstan. Internal migration plays a crucial role in shaping demographic patterns and labor market dynamics in different regions of the country. By analyzing data on internal migration flows and labor force trends, this study aims to shed light on the factors driving internal migration and its implications for the labor market. The findings suggest that internal migration in Kazakhstan is influenced by various factors, including economic opportunities, demographic trends, and government policies. Internal migrants often face challenges in accessing employment, housing, and social services, which can impact their well-being and integration into the labor market. Addressing these challenges requires a comprehensive approach that considers the needs of internal migrants and promotes inclusive growth across regions. By understanding the dynamics of internal migration and its impact on the labor force, policymakers can develop effective strategies to address labor market challenges and promote sustainable development in Kazakhstan.

Uncertainty and cash holdings: the moderating role of political connections

PurposeThis paper aims to investigate the relationship between uncertainty and corporate cash holdings with the moderating role of political connections.Design/methodology/approachWe employ fixed effects estimation on a panel dataset of 669 Vietnamese listed firms over the 2010–2020 period, with one- and two-way standard error clustering. We conduct various robustness tests, including two-stage least squares/instrumental variable and generalized method of moments regressions, alternative cash holding measure, and additional controls for macroeconomic conditions and ownership types.FindingsThe effect of uncertainty on cash holdings is weakened for firms with political connections relative to those without the connections. Although general firms depend on cash flows to adjust their cash holding behavior when uncertainty increases, our findings suggest that politically connected firms do not rely on internal cash flows to accumulate cash when confronted high uncertainty.Practical implicationsOur findings on the role of political connections in moderating the relationship between cash holding and economic policy uncertainty have practical implications for policymaking. Since political connections serve as a buffer for a firm’s liquidity, firms may want to seek those connections, which can, in turn, lead to increasing informal costs and unfair business environment.Originality/valueThis is the first study investigating the role of political connections to the nexus of cash, cash flow and uncertainty, providing novel evidence regarding the less dependence on internal cash flows to save cash by politically connected firms. Second, the paper enriches the literature on the motives of cash holdings by proposing a modified agency view in the context of weak investor protection. Therefore, our findings strengthen the explanation for the positive effect of uncertainty on firms’ cash holdings in emerging markets.

Exhibition Space Circulation in Museums from the Perspective of Pedestrian Simulation

Contemporary studies largely concentrate on the physical aspects of architecture, yet within the sphere of design, the gap between user experience and the designer’s intention is an undeniable fact. This gap, illustrating the contrast between the spatial perception and the actual physical space, to some degree, mirrors preferences in human spatial behavior. It accentuates the complex relationship between human cognitive functions and spatial layout, underlining the critical role of spatial perception in architectural design and planning. This prompts the question of whether perceptions of internal traffic flow within buildings also suffer from spatial distortions. Focusing on museums, and by examining circulation paths and spatial features, a virtual museum model is devised. The research employs a holistic and reductionist approach (complex systems theory) to forge a link between circulation components and the spatial experience of architecture. Utilizing agent-based modeling tools for simulating pedestrian movements, it investigates how different circulation patterns and spatial relationships influence pedestrian behavior. The study proposes a museum circulation optimization strategy, grounded in quantifying spatial experience through Anylogic software analysis. This strategy is aimed at enhancing the design of internal traffic flows in future museum projects, offering fresh insights into museum design research, and probing into new possibilities for using pedestrian simulation software.

Fertilisation strategies and their influence on nutrient flows in organic apple orchards

AbstractIn organic fruit production, permitted fertilisers contain multiple nutrients with stoichiometries differing from the nutrient offtakes of the fruit trees. Furthermore, some pesticides contain nutrients resulting in additional inputs. These conditions may cause unbalanced nutrient supplies and thereby influence the long-term sustainability of the system. An analysis of nutrient management practices in organic apple farms was conducted in three Southern and one Northern German apple-growing region. Data on nutrient inputs (via fertilisers and pesticides) and outputs (via fruit) per orchard were collected along with soil samples from up to five orchards per farm on 19 farms. On average, farmers fertilised 37 kg N and harvested 23 Mg apples per ha and year. Nutrient budgets showed imbalances for N (+ 25 kg ha−1 year−1), P (+ 3 kg), K (− 4 kg), Ca (+ 37 kg), Mg (+ 4 kg), S (+ 53 kg), Na (+ 4 kg) and Cl (+ 3 kg). Base fertilisers like compost or manure contributed to higher nutrient inputs due to a larger P and K-to-N-ratio. Commercial organic fertilisers such as keratins or vinasse contained much lower ratios. The main S input sources were pesticides (46 kg). N inputs by base (p = 0.06) and commercial (p = 0.37) fertilisers had no significant effect on the yield. Balanced nutrition can best be achieved by applying a combination of 20% of the total N demand via base fertilisers, complemented with commercial fertilisers with low element-to-N-ratios (e. g. keratin fertilisers, vinasse or biological N2 fixation). No correlation was found between soil nutrient status and nutrient budgets. Site conditions and internal field nutrient flows (transfer of the inter-row biomass via mulching into the tree row) had a stronger influence on the soil nutrient content than fertilisation strategy. In addition, fruit orchards showed a spatial differentiation of soil nutrient contents. Elevated P and K contents above the recommended range in the tree row were found in 67% of the orchards, while tendencies of depletion were found in the inter-row area. Mulching schemes which transfer biomass from the inter-row area to the tree row need to be adapted to this condition.

Application of a new DES model based on Wray-Agarwal turbulence model in flow simulation of a mixed-flow pump

In recent years, it has been demonstrated for many two- and three-dimensional external and internal turbulent flows that the one-equation Wray-Agarwal turbulence model can compute the complex turbulent flow fields with high computational accuracy, excellent computational convergence and efficiency. In this paper, Wray-Agarwal (WA) turbulence model is employed as part of a detached eddy simulation (DES) method to predict the performance of a mixed-flow pump. By comparing the computations with the experimental results, the differences and similarities between the WA-DES model and the Shear Stress Transfer (SST) k-ω model in predicting the internal and external flow characteristics of the pump are analyzed. The results show that both the SST k-ω model and the WA-DES model can reasonably predict the performance of the pump between 0.6 Q and 1.2 Q, where Q is the design flow rate; however, they have their own merits and deficiencies in predicting head and efficiency of the pump at low and high flow rates. For the velocity field in the rotor-stator interaction region, the WA-DES model shows better prediction accuracy since it can accurately predict the large-scale recirculating vortex structure at the inlet of the guide vane. The SST k-ω model over-predicts the separated flow region, which leads to the emergence of a small vortex structure before the backflow region of the pump. Although the turbulent eddy viscosity predicted by the WA-DES model is higher than that of the SST k-ω model and there is small difference in the results for the scale of the tip leakage vortex (TLV) between the two models, the overall simulation results of the WA-DES model for the high turbulent viscosity region and the pressure increase in the impeller are consistent with the SST k-ω model results. The results of this paper demonstrate the potential of WA-DES model for prediction of flows in pumps.

Comprehensive comparisons of RANS, LES, and experiments over cross-ventilated building under sheltered conditions

The use of RANS (Reynolds-Averaged Navier-Stokes) simulations to study airflow over cross-ventilated buildings has been widely performed under both isolated and sheltered conditions. For a sheltered environment, great efforts still need to be made as few studies have been conducted on cross-ventilated buildings, located far downstream of the urban morphology. Therefore, in this study, a series of simulations with different turbulence models were conducted to determine the performance in predicting the external and internal airflows of a cross-ventilated building under sheltered conditions and to evaluate the ventilation performance. Two urban building dispositions were considered, namely square (SQ) and staggered (ST) layouts. The evaluation of the velocity profiles was performed in the vertical and horizontal planes of the target building to systematically determine the accuracy of each model. The qualitative results showed that several RANS models are able to generate the main features of the external (in-canyon) and internal flows. In addition, the quantitative evaluations of the internal flow showed that the vertical velocity in the vertical plane and the lateral velocity in the horizontal plane are poorly predicted in the SQ array. Furthermore, the prediction of the streamwise velocity in the horizontal plane of the ST array is not satisfactory. The RANS ventilation rates are comparable to the large-eddy simulation (LES) results for certain models in the SQ array, but the deviations are large for all models in the case of the ST array, with the highest predicted ventilation rate being 40% lower compared to LES.

Noise Generation Mechanisms of Marine Composite Pipelines Excited by the Internal and External Flows

The marine pipeline is an important energy transportation platform today. It can cause underwater noise pollution due to sound radiation caused by pipeline vibration during oil and gas transportation. This study focuses on the noise-generation mechanisms of marine composite pipelines under internal and external flow excitation. We investigated the impact of different materials, diameters, and wall thicknesses on the sound radiation characteristics of the pipeline under internal flow excitation. The relationship between radiated sound power and flow velocity was analysed. Additionally, we discussed the radiated sound field of marine composite pipelines under external flow excitation. Our results show that the radiated sound power under internal flow excitation is over 20 dB higher than that under external flow excitation in the 10 Hz to 2000 Hz frequency range. We conducted an experimental test near Zhoushan city, China, where the internal flow was driven by a pump and the external flow represented ocean currents. The results confirmed that the main noise-generating mechanism of marine composite pipelines is internal flow excitation. The numerical findings were validated by the experimental test. Overall, this paper provides a foundation for future investigations into the sound radiation of marine composite pipelines.

Wall-modeled large eddy simulation in the immersed boundary-lattice Boltzmann method

This work presents the wall-modeled large eddy simulation (WMLES) in the immersed boundary-lattice Boltzmann method (IB-LBM). Here, the wall model with both diffusive- and sharp-interface immersed boundary methods (IBMs) is incorporated into the IB-LBM to handle the turbulent boundary layer in high Reynolds number turbulent flows. To maintain the numerical stability, two collision models, i.e., multiple-relaxation-time (MRT) and recursive regularized (RR), are implemented. The performance of these models in the WMLES is examined and compared in the simulation of internal and external flows by considering four benchmarks, i.e., turbulent flow in a channel, flow around a hull of submarine, flow around an Ahmed car model, and flow around a circular cylinder. It is found that a diffusive-interface IBM with wall model is capable to achieve excellent results for the simulation of external flows around bluff objects but fails in the simulation of internal flows of underestimating the wall shear stress due to its extra dissipation. The sharp-interface IBM with the wall model predicts the internal flow very well but fails in some simulations of external flow around bluff bodies due to the failure in the separation flow modeling. It is also found that the MRT-LBM is less dissipative than the RR-LBM, but it generates spurious nonphysical noise in the turbulent flows and tends to be unstable at high Reynolds numbers. Therefore, the diffusive-interface IBM with the wall model is more suitable for the external turbulent flow modeling, while its sharp-interface counterpart is more suitable for the internal turbulent flow modeling. The RR-LBM outperforms the MRT-LBM for the better stability and less nonphysical noise.

An averaged mass correction scheme for the simulation of high subsonic turbulent internal flows using a lattice Boltzmann method

This paper addresses the simulation of internal high-speed turbulent compressible flows using lattice Boltzmann method (LBM) when it is coupled with the immersed boundary method for non-body-fitted meshes. The focus is made here on the mass leakage issue. The recent LBM pressure-based algorithm [Farag et al. Phys. Fluids 32, 066106 (2020)] has shown its superiority on classical density-based algorithm to simulate high-speed compressible flows. Following our previous theoretical work on incompressible flows [Xu et al. Phys. Fluids 34, 065113 (2022)], we propose an averaged mass correction technique to mitigate mass leakage when simulating high-Mach-number compressible flows. It is adapted to deal here with a density, which is decoupled from the zero-moment definition. The simulations focus on two generic but canonical configurations of more complex industrial devices, the straight channel at different angles of inclination at Mach numbers (Ma) ranging from 0.2 to 0.8, and the National Aeronautics and Space Administration Glenn S-duct at Ma = 0.6. The present results show that mass leakage can be a critical issue for the accuracy of the solution and that the proposed correction technique effectively mitigates it and leads to significant improvements in the prediction of the solution.

Internal Migration in Pakistan: Some Socio-Economic Determinants and Significances

ABSTRACT: Since early years, humans are migrating to ensure their survival or to improve their socio-economic position in society. In Pakistan, internal migration has not been given proper attention in policy making. Consequently, government is facing problems in managing the challenges and opportunities posed by internal migration. The present study attempted to analyse socio-economic factors that play crucial role in a household's decision to migrate internally by using data of Labour Force Survey 2020-21. In the questionnaire of labour force survey, there is a specific section related to migration. The migration is defined as 'households that has moved from one district to another district or to different country', it excludes the migration within district. The logit regression has been used to estimate the model. It has been found that more educated people particularly having professional and technical education tends to migrate. The internal migration increases with age, but after certain level it tends to start declining. It has also concluded that employment in public sector (due to job security or provision of housing facilities) motivate people to internally migrate. People belonging to middle income families are more likely to migrate in comparison to rich or very poor. Study confirms that search of better job opportunities and family compulsions are major factors in internal voluntary migration. However, law and order situations emerge as a significant factor in forced migration. As the internal migration are much higher than international migration so there is need that role of internal migration may be recognised in reducing poverty, employment and socio-economic development. Unfortunately, there exists lack of policy on internal labour flows. Most the labour force is not even registered at migration destinations. It is very crucial to calculate value of domestic remittances. It will be helpful in devising the policy to improve the status of internal migrants by providing them targeted technical and vocational education training so that they can get better job opportunities in destination places.

Research and Development of Recommendations for Building a Computational Grid for Numerical Simulation of Typical Internal and External Flows in Relation to Aeronautical Engineering Problems

Research and Development of Recommendations for Building a Computational Grid for Numerical Simulation of Typical Internal and External Flows in Relation to Aeronautical Engineering Problems

Surface Nanodroplet‐Confined Engineering of Gold (I) ‐Thiolate Nanostructures

AbstractGold(I)‐thiolate complexes have served as primary building blocks for diverse Au nanostructure synthesis strategies. A delicate approach to characterize and control Au(I)‐thiolate motif formation and assembly on the surface is needed as it can potentially solve challenges associated with utilizing gold nanomaterials in many applications. Here, the controllable generation of flower‐shaped surface gold nanostructures (FSGNs) is demonstrated by manipulating the formation‐assembly process of Au(I)‐dodecanethiolate motifs within nanoscale surface droplets. The morphology and structure of the resulting Au nanostructures are governed by internal convection flows and interfacial energy, modulated by the nanodroplet composition and substrate wettability. The obtained FSGNs are proven to act as versatile scaffolds for the selective generation of Au spiky nanostars. These FSGNs can also be utilized to functionalize nanodroplet‐based reactors, boosting the fluorescent intensity of Nile red (NR) fluorophores and decomposing NR via catalytic reaction. Remarkably, with FSGN functionalized droplets smaller than a radius of 500 nm, the decomposition rate of NR can reach ≈0.01 s−1. These results highlight a miniaturized, controllable, and automated method for the in situ production of 3D gold nanostructures on substrates, offering prospects for fast surface nanostructure fabrication and efficient environmental pollutant treatment.

Effect of LULC Changes on Annual Water Yield in the Urban Section of the Chili River, Arequipa, Using the InVEST Model

Arequipa is a semi-desert city located in southern Peru which depends on the Chili River as its only water source. During recent years, this city has increased its number of inhabitants significantly as a result of internal migratory flows and population growth. Because of this, the city has undergone a rapid urbanization process which has increased the urban areas near the river and caused the destruction of agricultural areas, as well as their native vegetation. This change in land use can be quantified through satellite image analysis across many years, but as noted, there are no studies on its impact on water yield (WY) in the urban section of the river. Now, by using the Integrated Valuation of Ecosystem Services and Compensation (InVEST) model, which allows the WY of the study area to be evaluated in millimeters and cubic meters by introducing a series of variables, such as precipitation, reference evapotranspiration and types of land use classes, among others, it is possible to determine that the WY from the study area was 1,743,414 m3 in 1984 and 1,323,792 m3 in 2022; the urban area is the type of land use with the highest increase with respect to its percentage contribution to the WY, going from 30.43% to 49.62% between 1984 and 2022, respectively. The increase in urban area mitigated the loss of total WY, explained by a higher percentage runoff rate, surface flow and drainage problems in the study area.

An Experimental and Numerical Study on the Cavitation and Spray Characteristics of Micro-Orifice Injectors under Low-Pressure Conditions

A fuel injector plays a crucial role in an internal combustion engine, and the occurrence of cavitation inside the injector may affect the engine’s spray, atomization, and combustion efficiency. In this study, a micro-turbojet engine equipped with a micro-orifice fuel injector was developed that operated under low injection pressure (Pinj), that is, at a low Reynolds number (Re). Given the paucity of cavitation studies conducted under such conditions, the current study experimentally and numerically investigated the cavitation and spray characteristics of water and kerosene in a micro-orifice injector with a diameter of 0.3 mm. The results indicated that the water and kerosene exhibited no cavitation, cavitation, supercavitation, and hydraulic flip. However, the discharged jet was unaffected by internal flows, and the jet angles remained nearly constant, indicating that the cavitation in micro-orifice injectors at a low Re is less important than that at a high Re. Because cavitation in micro-orifice injectors under a low Re has no positive effects on the atomization and spray, determining the geometry of a micro-injector is essential. The injector with a length-to-diameter (L/D) ratio of 3 exhibited an approximately 25% higher discharge coefficient (Cd) than those of injectors with L/D ratios of 6 and 8 and, thus, is recommended for injectors in micro-turbojet engines.

Filling fraction measurement around a drying drop onto nanoporous silicon using digital holographic microscopy

In this work, we implemented an off-axis digital holographic microscopy (DHM) setup to study the behavior of liquid drops on nanostructured porous silicon (PS) membranes. When a liquid comes into contact with the PS structure, capillary action and surface tension give rise to imbibition of the liquid into the intricate volume of the pores. At the same time, the vapor field developed around the drop enhances liquid condensation and evaporation into and from the pores. The complex interplay between these phenomena (capillary driven internal flows, condensation, and evaporation) is not yet fully understood but the methods we propose can provide new insights. We demonstrate how DHM allows determining the filling fraction of the porous membrane around drying drops of water and isobutyl alcohol. The phase information obtained from registered holograms provides quantitative information that permits to reconstruct the filling fraction along the porous membrane and its evolution during the drying process. Additionally, relevant parameters such as speed and contact angle during retraction of the drops can be measured. These methods can be further extended to other porous materials, such as porous alumina, micro- and macro-PS, to develop better fluid-dynamic models for describing fluid behavior in highly confined structures.

Transformations of the transverse Poynting vector distribution upon diffraction of a circularly polarized paraxial beam.

Usually, the structure of paraxial light beams is characterized by the intensity associated with distribution of the longitudinal energy flow density (Poynting momentum) across the transverse plane. In this work, special attention is paid to the distribution of internal energy flows described by the transverse Poynting momentum (TPM) components. This approach discloses additional polarization-dependent features of the vector beam transformations; in application to the edge diffraction of a circularly polarized (CP) Gaussian beam, it reveals the helicity-dependent asymmetry of the diffracted-field TPM profile characterized by the shifts of the TPM singularity, maximum, etc. These phenomena are confirmed experimentally and interpreted in terms of the spin-orbit interaction (SOI) and spin Hall effect of light. In contrast to the known SOI manifestations in the CP beams' diffraction originating from the small longitudinal component of a paraxial field, the new TPM-related effects stem from the transverse field components and are thus much higher in magnitude.