Large Flow Research Articles

Numerical simulation of start-up and shutdown transient processes of super large flow and high-power centrifugal pump

Abstract During start-up and shutdown processes, the transient flow of centrifugal pump is complex, which significantly affects the safe and stable operation of the entire pump station. In this paper, considering the effect of the transient process of the pump station, the start-up and shutdown transient processes of a large flow and high-power centrifugal pump was numerically simulated by use of STAR CCM+. The evolution of flow field in the volute and impeller was analyzed. The results show that the flow field of the impeller is filled with complex vortex structures of varying sizes at the beginning of the start-up process of a water pump. As the flow-rate increases, the fluid flow gradually tends to stabilize. During the shutdown process of the water pump, as the flow-rate decreases, the flow field vortices increase progressively, and the flow pattern is unstable. The research results provide a basis for the operation strategy of super large flow and high-power centrifugal pump.

FLOW-Alaiz benchmark for coupled terrain and array interaction flow models. Baseline Results

The FLOW-Alaiz benchmark is established to enhance flow models in complex terrain, building on insights and datasets from previous IEA Task 31 benchmarks around the same test site. The new benchmark aims to create a composite validation dataset by gathering measurements from different periods, notably, the New European Wind Atlas (NEWA) ALEX17 experiment and the Alaiz Site Calibration (SC) campaign. The overall study focuses on wind conditions relevant to siting, power performance, and energy yield prediction. Initial results use industry-standard flow models as baselines such as SiteFlow and PyWAsP/PyWAsP-CFD, all in neutral steady-state conditions. Public datasets, documentation, and evaluation scripts are available in the FLOW-Hub repository to provide transparency on the evaluation methodology while private data is kept on SGRE premises for blind testing. Baseline results focus on cross-predictions and wind profiles for the North and South sectors. Cross-predictions reveal challenges in the NEWA case due to large elevation differences and complex flow interactions in the valley, while SC campaigns show better performance in more realistic siting conditions. Wind profiles for neutral conditions generally align with expectations with main limitations in the wake of flow-separation and forest canopy zones. A comparison with vertical profiles from the ALEX17 Diurnal Cycles benchmark highlights potential improvements from high-fidelity mesoscale-to-microscale modeling, revealing distinct variations in wind shear and profile characteristics when stability is used to categorize the atmospheric conditions.

Energy loss analysis of a double-suction centrifugal pump using in pump mode and turbine mode

As an economical energy recovery device, pump as turbine (PAT) is widely used in micro-hydropower stations and the chemical industry. The inlet and outlet pipelines connected to the double-suction pump are on the same horizontal line. As the pipeline layout is very convenient, in some chemical industries, the way of residual pressure energy utilization is increasing using the double-suction pump as a turbine. Based on numerical simulation, experimental verification, and entropy generation theory, the energy loss rule of each flow component in the pump mode and turbine mode under different flow rates is compared and analyzed. The results show that when the double-suction pump is used as a turbine, the flow rate at the best efficiency point (BEP) in the turbine mode shifts to a large flow rate by 30.89% and the BEP efficiency decreases by 1.30%. In the pump mode and turbine mode, the main energy loss component is the impeller, and the turbulent entropy generation power and the wall entropy generation power are the main sources of energy loss. The energy loss in the suction chamber and impeller increases sharply, and the energy loss is primarily enhanced in the blade trailing edge and the tongue near due to the unsteady flow in the turbine mode. Due to the complex structure, the spiral suction chamber is not suitable for the flow direction of the fluid flow out of the impeller, and the flow state inside the impeller is negatively affected by the suction chamber in the turbine mode. This paper provides a theoretical basis for the design and application of double-suction centrifugal PAT.

Experimental study of liquid–liquid dispersion patterns in T-inlet microchannels with different junction angles

Liquid-liquid two-phase flow in T-inlet microchannels with different junction angles (θ = 30°, 60°, 90°, 120° and 150°) was investigated experimentally. Four flow regimes of the dispersed phase were identified, i.e., parallel flow, jetting, dripping and squeezing, and the distribution of flow regimes for the dispersed phase corresponding to variations in the junction angle was plotted. The consequences of varying junction angle and flow conditions in the squeezing regime on the generated droplet size were analyzed. The results indicate that low capillary number and large flow rate ratio are conducive to the formation of large-size droplets. For constant flow conditions, junction angle θ = 90° is detrimental to the formation of squeezing microdroplets. The increase in microchannel junction angle causes the droplet size to decrease until θ > 90°, where the droplet size increases with the junction angle. On the basis of experimental results, the scaling law correlation equations containing the junction angle for predicting the droplet length and droplet volume are proposed, respectively. The predicted values match well with the experimental data. The results of this work contribute to the enhancement of the monodispersity of microdroplets and the precise control over a wide range of the generated droplet size by adjusting the junction angle.

How to Reduce the Number of Inspectors: Operation Mode and Modeling Simulation of Centralized Image Recognition in Railway Passenger Security Inspection

Security inspection is an essential step for passengers entering railway stations in China. Under the existing security inspection operation mode, each X-ray machine needs an image inspector to recognize the X-ray image, which poses the issue of resource optimization for inspectors. Based on the networking of security inspection X-ray machines, an innovative centralized image recognition (CIR) operation mode for railway security inspections is proposed, and it is worth noting that network and device failures are risk factors for this mode. The method for assigning image recognition personnel is designed to reduce labor force needed for security inspection. Using a combination of agent-based modeling method and computer simulation technology, the four elements of passengers, security inspection X-ray machines, X-ray image inspectors, and secondary baggage inspection personnel are modeled, and CIR indicators to study the effectiveness of the operation are designed. Based on the real departing passenger data of the Zhangjiakou section of the Beijing Zhangjiakou Line in China, simulation is conducted in two scenarios: large passenger flow and small passenger flow. The research is conducted from three aspects: operational efficiency, travel experience, and system complexity. Experiments have shown that, with a slight increase in passenger waiting time, the average number of X-ray image inspectors is reduced by more than 70% compared with the existing operation mode. The best pick-up location for passengers is related to passenger flow. The proposed model can analyze the effectiveness of CIR operation mode and provide decisive support for the application of CIR operation mode.

Inner Flow Analysis of Kaplan Turbine under Off-Cam Conditions

Kaplan turbines are widely utilized in low-head and large flow power stations. This paper employs Computational Fluid Dynamics (CFD) to complete numerical calculations of the full flow channel under different blade angles and various guide vane openings, based on 25 off-cam experimental working conditions. The internal flow characteristics of the runner blade and draft tube are analyzed, and a discriminant number for quantitatively assessing the flow uniformity of the draft tube is proposed. The results indicate that low-frequency and high-amplitude pressure pulsations occur on the high- and low-pressure edge of the blade when the opening is small, with pulsations decreasing as the opening increases. The inner flow line of the draft tube is disturbed when both the blade angle and opening are small. Additionally, the secondary frequency of the draft tube inlet is double that of the vane passing frequency. The discriminant number of the flow inhomogeneity approaches 0 under optimal flow conditions. The number increases continuously with the decrease in efficiency, and the flow in the three piers of draft tube becomes more nonuniform. The research results provide a reference for enhancing performance and ensuring the operational stability of Kaplan turbines.

Design, Multi-Point Optimization, and Analysis of Diffusive Stator Vanes to Enable Turbine Integration Into Rotating Detonation Engines

Abstract Pressure gain combustion is considered a possible path toward improved thermal cycle efficiency and reduced carbon emissions. However, ad hoc turbine designs are required to maximize the thermodynamic potential; the new turbomachinery should be suited for the oscillations in flow conditions generated by the detonation combustor, which are very different from conventional gas turbines. This paper investigates the design, optimization, and analysis of diffusive stator vanes operating under large inlet flow angles in the high-subsonic regime. First, the design methodology is outlined, focusing on the geometric requirements to ingest high Mach number flow and the parametric modeling of the endwall and the 3D vane pressure and suction sides. Then, the impact of the inlet flow angle on the flow field and vane design is studied through a multi-point, multi-objective optimization with three different inlet angles, performed using steady Reynolds-averaged Navier–Stokes simulations. Remarkable reductions in pressure loss and stator-induced rotor forcing are attained while maintaining an extensive operating envelope and high flow turning. Moreover, several design guidelines are provided based on the analysis of the optimized geometries. Finally, the effectiveness of the proposed methodology is verified with an unsteady assessment of the baseline and optimized vane designs.

Design and performance analysis of high-speed on/off valve based on energy-coupled actuator

The development digital hydraulics demands higher performance on high-speed on/off valves. In order to fully exploit the energy saving advantages of digital hydraulics, advanced high-speed valves are expected to possess a fast response and a large nominal flow rate simultaneously. Energy-coupled-actuator (ECA) utilizes the shear working mode of magnetic rheological fluid to achieve reciprocating motion of the valve spool through the coupling/decoupling of a pair of disks and a translational piece and its driving force is not affected by the valve spool’s position. The reported advantages of ECA meets the design requirements of actuators for high-speed on/off valve. This study gives the detailed design proposal of high-speed valve based on ECA (ECAV). The work also established a multi-physics coupled model for ECAV, calculated the key parameters of the valve driving system, and predicted the switching performance of ECAV. Finally, a prototype of ECAV with updated sealing solution between the actuator and valve block was fabricated and experimental tested. The results indicate that for current ECAV prototype successfully established 40 l min−1@5 bar (1.5 mm stroke) using response time less than 7 ms. Moreover, the prototype only consumed 14 ms to reach a long stroke of 5 mm with a significantly increased ratio of stroke over response time.

Внедрение технологии виртуальной реальности в образовательный процесс системы высшего образования

The purpose of the study is to identify modern technology – virtual reality (VR technology) in order to define positive and negative pedagogical aspects, analyze the current situation of using VR technologies in some universities of the country. The article examines the domestic and foreign literature on the current situation, which is characterized by turbulence, uncertainty and the rapidly changing role of a man in society. The Fourth Industrial Revolution or Industry 4.0 is of great interest, as it changes the landscape of many professions and dictates requirements regarding the quality of education. A large flow of information, close human interaction with digital technologies contribute to the development of clip thinking. The education system is designed to take into account current trends, as well as to provide students with a set of competencies, hard and soft skills, systemic thinking and fundamental knowledge. The scientific novelty of the study lies in the fact that the authors identified the need for the development of systemic thinking and the possibility of its formation through the use of VR technologies, described ways of using virtual reality, contributing to the improvement of professional skills, as well as imagination, memory, cognitive abilities, allowing to produce non-standard solutions. As a result of the study, it was found that the education system can no longer fully rely on traditional teaching methods, it must look for more effective and modern ways of interacting with students. One of these methods is virtual reality. The article considers examples of the use of VR technologies in the educational process of higher education in the medical, transport and engineering fields, shows the influence of virtual reality on the development of professional and personal competencies.

Preoperative embolization of brain arteriovenous malformation and efficacy in intraoperative blood loss reduction: a quantitative study

BackgroundEmbolization of brain arteriovenous malformations (bAVMs) is often used as adjuvant therapy to microsurgical resection to reduce the high-risk features of bAVMs such as large size and high flow. However,...

3D printing of poly(ethyleneimine)-functionalized Mg-Al mixed metal oxide monoliths for direct air capture of CO2

Direct air capture (DAC) of CO2 plays an indispensable role in achieving carbon-neutral goals as one of the key negative emission technologies. Since large air flows are required to capture the ultradilute CO2 from the air, lab-synthesized adsorbents in powder form may cause unacceptable gas pressure drops and poor heat and mass transfer efficiencies. A structured adsorbent is essential for the implementation of gas-solid contactors for cost- and energy-efficient DAC systems. In this study, efficient adsorbent poly(ethyleneimine) (PEI)-functionalized Mg-Al-CO3 layered double hydroxide (LDH)-derived mixed metal oxides (MMOs) are three-dimensional (3D) printed into monoliths for the first time with more than 90% adsorbent loadings. The printing process has been optimized by initially printing the LDH powder into monoliths followed by calcination into MMO monoliths. This structure exhibits a 32.7% higher specific surface area and a 46.1% higher pore volume, as compared to the direct printing of the MMO powder into a monolith. After impregnation of PEI, the monolith demonstrates a large adsorption capacity (1.82 mmol/g) and fast kinetics (0.7 mmol/g/h) using a CO2 feed gas at 400 ppm at 25 °C, one of the highest values among the shaped DAC adsorbents. Smearing of the amino-polymers during the post-printing process affects the diffusion of CO2, resulting in slower adsorption kinetics of pre-impregnation monoliths compared to post-impregnation monoliths. The optimal PEI/MeOH ratio for the post-impregnation solution prevents pores clogging that would affect both adsorption capacity and kinetics.

Clearance Nonlinear Control Method of Electro-Hydraulic Servo System Based on Hopfield Neural Network

The electro-hydraulic servo system has advantages such as high pressure, large flow, and high power, etc., which can also realize stepless regulation, so it is widely used in many engineering machineries. A linear model is sometimes only a simple approximation of an idealized model, but in an actual system, there may be nonlinear and transient variation characteristics in the systems. Coupling is reflected in the fact that the components or functional structures implemented by each system used for the design of hydraulic systems are not completely or independently related to each other, but affect each other. The nonlinear clearance between the actuator and the load reduces the control accuracy of the system and increases the impact, thus losing stable working conditions. In the paper, based on the nonlinear clearance problem of the electro-hydraulic servo system, a mathematical transfer model with clearance is established, and on this basis, a clearance compensation method based on the Hopfield neural network is proposed. In this way, clearance compensation can be realized by adjusting the parameters of neural network nodes, through simple and convenient operation. Finally, by setting different clearance values, the results of the step response and sine response curve before and after clearance compensation of the hydraulic system are compared, and the effectiveness of Hopfield neural network compensation clearance control is verified based on the comparison simulation results.

Research on the Energy Consumption Influence Mechanism and Prediction for the Early Design Stage of University Public Teaching Buildings in Beijing

The public teaching buildings of universities have a large flow of people, high lighting requirements, and large energy consumption, which present significant potential for energy saving. The greatest opportunity for integrating “green” architectural design strategies lies in the design phase, especially the early stage of architectural design. However, current designers often rely on experience or qualitative judgment for decision-making. Thus, there is a pressing need for rational and quantitative green architectural design theories and techniques to guide and support decision-making for the design parameters of teaching buildings. This study, based on field surveys of 40 teaching buildings, constructs building archetypes regarding energy consumption including 28 typical values. Based on the “Rectangle”, “L”, “U”, and “Courtyard” archetypes, through batch energy consumption simulation and multiple regression methods, the influence mechanisms of nine energy consumption influencing factors on four types of building energy consumptions were explored, and energy consumption prediction models were derived. The findings of this research can serve as factor evaluation and selection in the early stage of architectural design for public teaching buildings at universities, and the prediction model can assist in the early estimation of energy consumption. This aims to enrich and supplement green architectural design methods by supporting the design of green public teaching buildings and providing reference and application for relevant engineering practices.

LES of the upper plenum of the liquid metal fast reactor under the forced flow conditions

A Large Eddy Simulation (LES) of the upper plenum of the E-SCAPE (European SCAled Pool Experiment) facility under the normal operations has been conducted to gain deeper insights into the thermal hydraulics phenomena in liquid metal fast reactors (LMFRs). The results unravel the overall flow features in the upper plenum, the thermal instability in the above core structure region and the impact of the jets from the barrel holes on the large flow circulation and thermal mixing.The above core structure region is represented using a homogeneous porous model. It is shown that during the normal operations, most of the hot stream of the lead bismuth eutectic (LBE) from the core center rises to the top and disperses from the upper barrel holes. Conversely, the cold LBE spread out from the lower barrel holes. Mixing between the two streams only affect the fluids leaving from the middle heights demonstrating limited mixing. These jets help to create a large circulation in the upper plenum region which prevents any thermal stratification. At the interface between the hotter and colder streams, there are unsteady large-scale structures resulting in a mixing layer in the thermal field. This strong mixing is not conventional turbulence and potentially cannot be captured by Reynolds Averaged Navier Stokes average (RANS) modelling.The flow in the upper plenum is dominated by the influences of the different types of jets, which include some free jets issued horizontally or angled upwards and some jets impinging onto the structures in the plenum. The jets overall behave similar to ‘standard’ jets, though significant interactions between the top and bottom jets and the background circulations have strong influences at later stages of the jets, typically after four jet diameters leading to the jets not reaching self-similarity. In addition, the turbulence that is observed in the upper plenum is largely generated by the jet flows and hence the distribution of turbulence is very non-uniform. Away from the jets, turbulence is minimal with the mixing largely driven by the large-scale circulation.

Asymmetric jet shapes with two-dimensional jet tomography

Two-dimensional (2D) jet tomography is a promising tool to study jet medium modification in high-energy heavy-ion collisions. It combines gradient (transverse) and longitudinal jet tomography for selection of events with localized initial jet production positions. It exploits the transverse asymmetry and energy loss that depend, respectively, on the transverse gradient and jet path length inside the quark-gluon plasma (QGP). In this study, we employ 2D jet tomography to study medium modification of the jet shape of γ-triggered jets within the linear Boltzmann transport (LBT) model for jet propagation in heavy-ion collisions. Our results show that jets with small transverse asymmetry (ANn⃗) or small γ-jet asymmetry (xJγ=pTjet/pTγ) exhibit a broader jet shape than those with larger ANn⃗ or xJγ, since the former are produced at the center and go through longer path lengths while the later are off center and close to the surface of the QGP fireball. In events with finite values of ANn⃗, jet shapes are asymmetric with respect to the event plane. Hard partons at the core of the jet are deflected away from the denser region while soft partons from the medium response at large angles flow toward the denser part of QGP. Future experimental measurements of these asymmetric features of the jet shape can be used to study the transport properties of jets and medium responses. Published by the American Physical Society 2024

Strengthening Understanding of Customer Services and Practical Instructions for Hospital Financial Management

Increasing competition in the health industry at the national level makes the hospital management always tidy up in improving the quality of service to patients and improving the quality of medical infrastructure facilities according to the standard HNAC (Hospital National Accreditation Committee). Armed with the success of the value chain strategy concept training agenda at Elizabeth Semarang Hospital on May 16, 2018, I submitted the same training proposal to the Miriam Pratama Clinic, Kudus. The underlying factor is the urgency of the MIRIAM Pratama Clinic to raise the level of its business to become an C accredited hospital so that it can continue to survive and from the results of their communication with one of my relatives in Kudus who has heard me conduct training on the topic of value chain strategy at Elizabeth Hospital Semarang. So then I made a communication with the MIRIAM Pratama Clinic to get approval for the implementation of the training activities on March 18, 2019. Seeing the urgency of increasing the status of this business level, then I added aspects of financial management with the basis of considerations to raise the level of business and build a system of value chain strategies from Swayne, et.al. (2006) a large cash flow is needed. And this will be fulfilled with the right budgeting model. Finally, the activity was successfully carried out on March 18, 2019 with a very good response from participants who asked about how to regulate social and business motives in managing clinical businesses in the midst of a lack of cash flow and a budgeting model that does not have to be a month to month approach from Berger (2008). So the short answer is to raise the level of business, business motives should be a priority because improving the quality of services will require large costs and to fulfill them is not necessary with a month to month budgeting approach from Berger (2008) but can be from budget flexibility according to the clinical work calendar. In the mentoring activities on April 18, 2019 there were more positive results from the training activities on March 18, 2019 namely the more enthusiastic doctors, nurses and non-nursing staff working and more positive testimonials from key patients, mothers giving birth and their families. This has had a positive impact on status of the clinic as a C accreditation.

The rights of Venezuelan Indigenous women in Brazil

The large flow of indigenous refugees/migrants in Brazil represents a range of challenges in the context of social protection. Indigenous women face various forms of historical discrimination, and the situation is aggravated with the migrant and refugee population. This fact results in the exposure of this population to human rights violations in all everyday contexts, impacting civil, political, economic, social, cultural rights, access to justice, as well as the right to a life without violence. The study has as general objective to identify the rights of indigenous Venezuelan women in Brazil. A qualitative descriptive methodology was used, through a bibliographical review through the reading of literary works, articles, theses, and monographs that cover the object of study, as well as IOM Reports in Brazil. It is concluded that there is still much to be done, but, in the context of social assistance, in the analyzed location, the rights of Venezuelan indigenous women are being observed and the implemented actions are being improved.

Distribution pattern of large old Ginkgo biloba in China under climate change scenarios.

Large old Ginkgo biloba trees (LOGTs), with profound ecological and cultural significance in China, face increasing threats from climate change and human activities. We employed the BIOCLIM and DOMAIN species distribution models to predict their spatial patterns under the present climate and doubled-CO2 climate change scenario in 2100. We collected 604 validated LOGT occurrence records and data on 19 bioclimate factors for the analysis. Our study yielded a LOGT geographic distribution pattern covering a wide latitudinal belt extending from south subtropical to temperate zones in central and eastern China, concentrating in low elevations and coastal regions. The principal component analysis identified the dominant bioclimatic factors shaping their distribution, namely annual precipitation and low winter temperatures. BIOCLIM and DOMAIN generated predicted suitable habitats that match the present distribution range well. However, under the future climate scenario, the models indicated habitat retentions mainly in the core distribution areas and habitat losses mainly in the southern edge of the present range and scattered pockets elsewhere. Some retained habitats, including excellent ones, will suffer from fragmentation. The predicted new habitats may permit some range expansion and migration but are beset by small patch size and large interpatch distance, bringing fragmentation and gene flow restrictions. The anticipated projected range decline highlights considerable threats climate change poses to the long-term survival of the precious natural-cum-cultural resource. Understanding the distribution patterns and underlying drivers and distillation of practical conservation measures can foster sustainable management vis-a-vis the looming global change.

Intrinsically Episodic Antarctic Shelf Intrusions of Circumpolar Deep Water via Canyons

Abstract The structure of the Antarctic Slope Current at the continental shelf is crucial in governing the poleward transport of warm water. Canyons on the continental slope may provide a pathway for warm water to cross the slope current and intrude onto the continental shelf underneath ice shelves, which can increase rates of ice shelf melting, leading to reduced buttressing of ice shelves, accelerating glacial flow and hence increased sea level rise. Observations and modeling studies of the Antarctic Slope Current and cross-shelf warm water intrusions are limited, particularly in the East Antarctica region. To explore this topic, an idealized configuration of the Antarctic Slope Current is developed, using an eddy-resolving isopycnal model that emulates the dynamics and topography of the East Antarctic sector. Warm water intrusions via canyons are found to occur in discrete episodes of large onshore flow induced by eddies, even in the absence of any temporal variability in external forcings, demonstrating the intrinsic nature of these intrusions to the slope current system. Canyon width is found to play a key role in modulating cross-shelf exchanges; warm water transport through narrower canyons is more irregular than transport through wider canyons. The intrinsically episodic cross-shelf transport is found to be driven by feedbacks between wind energy input and eddy generation in the Antarctic Slope Current. Improved understanding of the intrinsic variability of warm water intrusions can help guide future observational and modeling studies in the analysis of eddy impacts on Antarctic shelf circulation.

The Bow Shock and Magnetosheath Responses to Density Depletion Structures

AbstractHot flow anomalies (HFAs) are typical and important foreshock transients characterized by large flow deflection and plasma heating. HFAs can deform the Earth's bow shock by dynamic pressure perturbation resulting in disturbance in the magnetosphere and ionosphere. Traditionally, HFAs are believed to be associated with discontinuities. But recently, HFA‐like structures were simulated by a magnetohydrodynamics (MHD) model without the discontinuity prerequisite. In this study, three HFA‐like structures are shown to present the MHD formation mechanism. Multi‐points observation by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission tracks the formation of an HFA from a density depletion upstream. HFAs with high‐ or low‐ density cores are observed by the Magnetospheric Multiscale mission in the flank region. The comparisons of the observation and their simulation show general agreement, particularly in the presence of a core with strong heating and velocity deflection, and two compression regions (shocks) with clear maxima in the ram pressure with a strongly inclined normal boundary at the leading edge and moderately inclined at the trailing edge. Agreement is better when the MHD simulations used a transient change to quasi‐parallel solar wind magnetic field during the events.