Forests are experiencing more frequent and intense wildfires in Canada,which pose considerable threats to water quantity and quality,particularly during the summer low-flow period when water demand is high.While the i...Forests are experiencing more frequent and intense wildfires in Canada,which pose considerable threats to water quantity and quality,particularly during the summer low-flow period when water demand is high.While the impacts of wildfire on hydrology have been widely assessed at the watershed scale,the underlying mechanisms of the responses of summer low flows remain poorly understood.In this study,we employed an integrated research framework that combines hydrometric monitoring with geochemical tracing to evaluate how the 2021 White Rock Lake Wildfire affected summer low flows,and to identify the underlying mechanisms governing these responses in the Okanagan Valley,British Columbia(BC),Canada.We found that(1)summer low flows,represented by Q90(flows exceeded at 90%of the time in summer)significantly increased following the wildfire(p<0.05);(2)summer low flows were primarily regulated by snow water in early summer(July),while dominated by groundwater in late summer(August and September);and(3)enhanced snow water contribution and reduced evapotranspiration(ET)were two primary contributors to the increased summer low flows.Our results provide insights for developing sustainable water management strategies for the region in the context of climate change and increasing forest disturbance.This study also demonstrates that the combination of hydrometric monitoring and geochemical tracing is an effective approach towards uncovering mechanisms that drive low-flow responses.展开更多
Climate change will profoundly affect hydrological processes at various temporal and spatial scales.This study is focused on assessing the alteration of water resources availability and low flows frequencies driven by...Climate change will profoundly affect hydrological processes at various temporal and spatial scales.This study is focused on assessing the alteration of water resources availability and low flows frequencies driven by changing climates in different time periods of the 21st century.This study evaluates the adaptability of prevailing Global Circulation Models(GCMs)on a particular watershed through streamflow regimes.This analysis was conducted in the Great Miami River Watershed,Ohio by analyzing historical and future simulated streamflow using 10 climate model outputs and the Soil and Water Assessment Tool(SWAT).The climate change scenarios,consisting of ten downscaled Coupled Model Intercomparision Project Phase 5(CMIP5)climate models in combination with two Representative Concentration Pathways(RCP 4.5 and RCP 8.5)were selected based on the correlation between observed records and model outputs.Streamflow for three future periods,2016-2043,2044-2071 and 2072-2099,were independently analyzed and compared with the baseline period(1988-2015).Results from the average of ten models projected that 7-day low flows in the watershed would increase by 19%in the 21st century under both RCPs.This trend was also consistent for both hydrological(7Q10,1Q10)and biological low flow statistics(4B3,1B3).Similarly,average annual flow and monthly flows would also increase in future periods,especially in the summer.The flows simulated by SWAT in response to the majority of climate model projections showed a consistent increase in low flow patterns.However,the flow estimates using the Max-Planck-Institute Earth System Model(MPI-ESM-LR)climate output resulted in the biological based low flows(4B3,1B3)decreasing by 22.5%and 33.4%under RCP 4.5 and 56.9%and 63.7%under RCP 8.5,respectively,in the future when compared to the baseline period.Regardless,the low flow ensemble from the 10 climate models for the 21st century seemed to be slightly higher than that of historical low flows.展开更多
This study aimed to obtain the production profiles of oil-in-water flow under low flow rate and high water-cut conditions in oil wells.A combination production profile logging composed of an arc-type conductance senso...This study aimed to obtain the production profiles of oil-in-water flow under low flow rate and high water-cut conditions in oil wells.A combination production profile logging composed of an arc-type conductance sensor(ATCS)and a cross-correlation flow meter(CFM)with a center body is proposed and experimentally evaluated.The ATCS is designed for water holdup measurement,whereas the CFM with a center body is proposed to obtain the mixture velocity.Then,a drift-flux model based on flow patterns is established to predict the individual-phase superficial velocity of oil-in-water flows.Results show that the ATCS possesses high resolution in water holdup measurement and that flow pattern information can be deduced from its signal through nonlinear time series analysis.The CFM can enhance the correlation of upstream and downstream signals and simplify the relationship between the cross-correlation velocity and mixture velocity.On the basis of the drift-flux model,individual-phase superficial velocities can be predicted with high accuracy for different flow patterns.展开更多
This paper deals with the numerical solution of inviscid compressible flows.The threedimensional Euler equations describing the mentioned problem are presented and solved numerically with the finite volume method.The ...This paper deals with the numerical solution of inviscid compressible flows.The threedimensional Euler equations describing the mentioned problem are presented and solved numerically with the finite volume method.The evaluation of the numerical flux at the interfaces is performed by using the Toro Vazquez-Harten Lax Leer(TV-HLL)scheme.An essential feature of the proposed scheme is to associate two systems of differential equations,called the advection system and the pressure system.It can be implemented with a very simple manner in the standard finite volume Euler and Navier–Stokes codes as extremely simple task.The scheme is applied to some test problems covering a wide spectrum of Mach numbers,including hypersonic,low speed flow and three-dimensional aerodynamics applications.展开更多
Collision-induced re-laxation process of CH(X^(2)Π,v=0)radical in various bath gases He,Ar,and N_(2)has been investigated ex-perimentally under low-temperature(26-52 K)supersonic flow conditions.The CH radicals were ...Collision-induced re-laxation process of CH(X^(2)Π,v=0)radical in various bath gases He,Ar,and N_(2)has been investigated ex-perimentally under low-temperature(26-52 K)supersonic flow conditions.The CH radicals were generat-ed with internal excitation by multiphoton photolysis of CHBr_(3)at 248 nm,and its rotational temperature was found to relax to the flow temperature in a few microseconds by colliding with bath gas.The relaxation rate coefficients for CH(X^(2)Π,v=0)radical in He,Ar,and N_(2)flow were obtained by time-resolved laser-induced fluorescence measurements,ranging from 10^(-12)cm^(3)·molecule^(-1)·s^(-1)to 10^(-11)cm^(3)·molecule^(-1)·s^(-1).The N_(2)flow exhibits the highest relax-ation rate for CH(X^(2)Π)radical due to its additional rovibrational levels,which allow for more efficient energy dissipation during collisions compared to monoatomic gases.The Ar flow shows a larger relaxation rate than He flow due to its greater polarizability and stronger long-range interaction with the CH(X^(2)Π)radical.展开更多
By analyzing the characteristics of low Mach number perfect gas flows, a novel Slightly Compressible Model (SCM) for low Mach number perect gas flows is derived. In view of numerical calculations, this model is proved...By analyzing the characteristics of low Mach number perfect gas flows, a novel Slightly Compressible Model (SCM) for low Mach number perect gas flows is derived. In view of numerical calculations, this model is proved very efficient, for it is kept within thep-v frame but does not have to satisfy the time consuming divergence-free condition in order to get the incompressible Navier-Stokes equation solution. Writing the equations in the form of conservation laws, we have derived the characteristic systems which are necessary for numerical calculations. A cell-centered finite-volume method with flux difference upwind-biased schemes is used for the equation solutions and a new Exact Newton Relaxation (ENR) implicit method is developed. Various computed results are presented to validate the present model. Laminar flow solutions over a circular cylinder with wake developing and vortex shedding are presented. Results for inviscid flow over a sphere are compared in excellent agreement with the exact analytic incompressible solution. Three-dimensional viscous flow solutions over sphere and prolate spheroid are also calculated and compared well with experiments and other incompressible solutions. Finally, good convergent performances are shown for sphere viscous flows.展开更多
Because of unstable properties of axial mine flow fans working under conditions of low flow rates, the safety and reliability of fans in their operational zone is reduced. At times, serious vibration may bring about t...Because of unstable properties of axial mine flow fans working under conditions of low flow rates, the safety and reliability of fans in their operational zone is reduced. At times, serious vibration may bring about the destruction of equipment or even jeopardize the safety of entire factories. By means of oil flow visualization techniques and numerical simulation, we have investigated the inner-flow of an axial mine flow fan working under low flow rate conditions. The fundamental reasons of complex flow phenomena of the inner-flow of the flow fan under these stated conditions were revealed. At the same time and in order to improve the inner-flow under conditions of low flow rates, a blade separator and air separator were designed. From our tests we found that the blade separator and air separator are two kinds efficient methods to improve the unstable working characteristics of the axial mine flow fan operating under low flow rate conditions. The effect of the improvement of the air separator is stronger than that of the blade separator.展开更多
This study investigate the relationships between geomorphometric properties and the minimum low flow discharge of undisturbed drainage basins in the Taman Bukit Cahaya Seri Alam Forest Reserve, Peninsular Malaysia. Th...This study investigate the relationships between geomorphometric properties and the minimum low flow discharge of undisturbed drainage basins in the Taman Bukit Cahaya Seri Alam Forest Reserve, Peninsular Malaysia. The drainage basins selected were third-order basins so as to facilitate a common base for sampling and performing an unbiased statistical analyses. Three levels of relationships were observed in the study. Significant relationships existed between the geomorphometric properties as shown by the correlation network analysis; secondly, individual geomorphometric properties were observed to influence minimum flow discharge; and finally, the multiple regression model set up showed that minimum flow discharge(Q min) was dependent of basin area(AU), stream length(LS), maximum relief(Hmax), average relief(HAV) and stream frequency(SF). These findings further enforced other studies of this nature that drainage basins were dynamic and functional entities whose operations were governed by complex interrelationships occurring within the basins. Changes to any of the geomorphometric properties would influence their role as basin regulators thus influencing a change in basin response. In the case of the basin's minimum low flow, a change in any of the properties considered in the regression model influenced the “time to peak' of flow. A shorter time period would mean higher discharge, which is generally considered the prerequisite to flooding. This research also conclude that the role of geomorphometric properties to control the water supply within the stream through out the year even though during the drought and less precipitations months. Drainage basins are sensitive entities and any deteriorations involve will generate reciprocals and response to the water supply as well as the habitat within the areas.展开更多
This paper proposes a new accelerating technique for simulating low speed flows,termed as p Seudo High Speed method(SHS),which uses governing equations and numerical methods of compressible flows.SHS method has advant...This paper proposes a new accelerating technique for simulating low speed flows,termed as p Seudo High Speed method(SHS),which uses governing equations and numerical methods of compressible flows.SHS method has advantages of simple formula,easy manipulation,and only need to modify flux of Euler equations.It can directly employ the existing well-developed schemes of hyperbolic conservation laws.To verify the technique,several numerical experiments are performed,such as:flow past airfoils and flow past a cylinder.Analysis of SHS method and comparisons with some precondition methods are made numerically.All tests show that SHS method can greatly improve the efficiency of compressible method simulating low speed flow fields,which exhibits in accelerating the convergence rate and increasing the accuracy of the numerical results.展开更多
A numerical simulation method is employed to investigate the effects of the unsteady plasma body force over the stalled NACA 0015 airfoil at low Reynolds number flow conditions. The plasma body force created by a diel...A numerical simulation method is employed to investigate the effects of the unsteady plasma body force over the stalled NACA 0015 airfoil at low Reynolds number flow conditions. The plasma body force created by a dielectric barrier discharge actuator is modeled with a phenomenological method for plasma simulation coupled with the compressible Navier-Stokes equations. The governing equations are solved using an efficient implicit finitevolume method. The responses of the separated flow field to the effects of an unsteady body force in various inter- pulses and duty cycles as well as different locations and magnitudes are studied. It is shown that the duty cycle and inter-pulse are key parameters for flow separation control. Additionally, it is concluded that the body force is able to attach the flow and can affect boundary layer grow that Mach number 0.1 and Reynolds number of 45000.展开更多
An attempt was made to extend mild combustion to forward flow furnace, such as the refinery and petrochemical tube furnace. Three dimensional numerical simulation was carried out to study the performance of this furna...An attempt was made to extend mild combustion to forward flow furnace, such as the refinery and petrochemical tube furnace. Three dimensional numerical simulation was carried out to study the performance of this furnace. The Eddy Dissipation Concept(EDC) model coupled with the reaction mechanism DRM-19 was used. The prediction showed a good agreement with the measurement. The effect of air nozzle circle(D), air nozzle diameter(d), air nozzle number(N), and air preheating temperature(Tair) on the flow, temperature and species fields, and the CO and NO emissions was investigated. The results indicate that there are four zones in the furnace, viz.: a central jet zone, an ignition zone, a combustion reaction zone, and a flue gas zone, according to the distribution profiles of H_2 CO and OH. The central jet entrains more flue gas in the furnace upstream with an increasing D while the effect of D is negligible in the downstream. The air jet momentum increases with a decreasing d or an increasing Tair, and entrains more flue gas. The effect of N is mainly identified near the burner exit. More heat is absorbed in the radiant section and less heat is discharged to the atmosphere with a decreasing d and an increasing N as evidenced by the flue gas temperature. The CO and NO emissions are less than 50 μL/L and 10 μL/L, respectively, in most of conditions.展开更多
Considering droplet phenomena at low Mach numbers,large differences in the magnitude of the occurring characteristic waves are presented.As acoustic phenomena often play a minor role in such applications,classical exp...Considering droplet phenomena at low Mach numbers,large differences in the magnitude of the occurring characteristic waves are presented.As acoustic phenomena often play a minor role in such applications,classical explicit schemes which resolve these waves suffer from a very restrictive timestep restriction.In this work,a novel scheme based on a specific level set ghost fluid method and an implicit-explicit(IMEX)flux splitting is proposed to overcome this timestep restriction.A fully implicit narrow band around the sharp phase interface is combined with a splitting of the convective and acoustic phenomena away from the interface.In this part of the domain,the IMEX Runge-Kutta time discretization and the high order discontinuous Galerkin spectral element method are applied to achieve high accuracies in the bulk phases.It is shown that for low Mach numbers a significant gain in computational time can be achieved compared to a fully explicit method.Applica-tions to typical droplet dynamic phenomena validate the proposed method and illustrate its capabilities.展开更多
The qualitative and quantitative assessment of gas flow has become increasingly relevant in the use of everyday systems. The micro flow sensor, developed by Innovative Sensor Technology AG （Switzerland）, is by princ...The qualitative and quantitative assessment of gas flow has become increasingly relevant in the use of everyday systems. The micro flow sensor, developed by Innovative Sensor Technology AG （Switzerland）, is by principle a calorimetric flow sensor produced as a micro system on a glass substrate by means of photolithography and glass etching technology. These structures are arranged as a platinum micro heater and sensor in a Wheatstone bridge. The subsequent etching process produces an exposed area of polyimide membrane that is only a few microns thick and includes the resistive sensor structure as the active area. In addition, the RTD （resistance temperature detector） technology included on the sensor allows for the implementation of a variety of electronic biasing and signal processing modes. Since the sensor can be powered and the bridge can be measured in both CTA （constant temperature anemometer） and calorimetric mode, new possibilities are presented for both low and high flow rates with regard to temperature compensation, self-calibration and self-monitoring.展开更多
Background Aortic valve replacement （AVR） improves survival in severe symptomatic aortic stenosis （AS）. Yet, in many patients with severe AS, the timing of AVR remains poorly defined. In particular, it is challeng...Background Aortic valve replacement （AVR） improves survival in severe symptomatic aortic stenosis （AS）. Yet, in many patients with severe AS, the timing of AVR remains poorly defined. In particular, it is challenging in patients with low mean pressure gradient （〈 40 mmHg） and severe AS （aortic valve area （AVA）≤1.0 cm^2） with preserved left ventricular （LV） ejection fraction.展开更多
Rural labor flowing in low marketization level restricts rural production elements of effective allocation, and restricts the development of rural economy, causes the gap between urban and rural areas to continue expa...Rural labor flowing in low marketization level restricts rural production elements of effective allocation, and restricts the development of rural economy, causes the gap between urban and rural areas to continue expanding. This article has analyzed the reasons of phenomenon, and raised some solutions from abolishing the barrier of the household register, improved rural labor＇ s cultural and skills quality, and built a social security system in rural areas improve the marketization level of rural labor flow.展开更多
The retrofit on flow path of low pressure cylinder of domestic made 200 MW steam turbine undertaken by Longwei Power Generation Technology Service Company Ltd by using Westinghouse technology was successful for the fi...The retrofit on flow path of low pressure cylinder of domestic made 200 MW steam turbine undertaken by Longwei Power Generation Technology Service Company Ltd by using Westinghouse technology was successful for the first time on the No. 5 unit of Zhenhai Prover Plant. Zhejiang Province. The test carried out by the Xi’an Thermal Power Research Institute showed that the thermal efficiency after the retrofit展开更多
Some patients with severe aortic stenosis (AS), due to restrictive cardiac physiology, paradoxically have relatively low flow and low gradients across stenotic aortic valves despite preserved left ventricular (LV) sys...Some patients with severe aortic stenosis (AS), due to restrictive cardiac physiology, paradoxically have relatively low flow and low gradients across stenotic aortic valves despite preserved left ventricular (LV) systolic function. It results in symptoms and reduced quality of life and carries a high mortality. Whilst this form of severe AS, termed paradoxical low flow low gradient (pLFLG), is well reported, patients with this diagnosis experience inappropriate barriers to aortic valve replacement (AVR), the only efficacious treatment. We present the case of an 88-year-old female with 12 months of exertional dyspnoea on a background of hypothyroidism and hypercholesterolemia. Transthoracic echocardiogram (TTE) revealed LV hypertrophy, with a small LV cavity size and reduced stroke volume, yet normal systolic function. A heavily calcified aortic valve was identified with severe aortic stenosis, based on valve area, yet with incongruous mean transvalvular gradient of 25 mmHg (severe ≥ 50 mmHg). Following exclusion of other differential diagnoses, her symptoms were attributed to paradoxical LFLG severe AS. She was however declined definitive transcatheter aortic valve implantation (TAVI) due to her paradoxically low mean aortic gradient. Following further deterioration in her symptoms and supportive quantification of poor exercise performance, she was ultimately re-referred, accepted, and underwent TAVI. Following her AVR, the patient experiences significant improvement in both symptoms and quality of life after only one month. Paradoxical LFLG severe AS remains a well-documented yet under recognized disease. It carries high morbidity and mortality if untreated, yet is significantly less likely to be referred and accepted for intervention. With its prevalence expected to rise with an ageing population, this case serves as a timely reminder for clinicians to address the under recognition of important pathology.展开更多
The most controversial river in Thailand is the Yom River.It has not been modified by large dam because of several valuable natural resources.Therefore,the river is flooded in rainy season and very low flow in dry sea...The most controversial river in Thailand is the Yom River.It has not been modified by large dam because of several valuable natural resources.Therefore,the river is flooded in rainy season and very low flow in dry season.The low flow causes drought which is much more serious than flooding.The Yom River Basin management is only way to circumvent the low flow problem by studying base flow index(BFI).Base flow analyses for 8 gauging stations along the river were performed by 2 techniques i.e.graphical and modified U.K.Institute of Hydrology(MIH).The mean BFI results from graphical and MIH are 0.37(0.05)and 0.45(0.12).The result from graphical is more reasonable due to its lower standard deviation.BFI values from MIH vary with watershed area which may result from the using of fixing value of N-day at 10.Solution for this problem is ongoing in this study.展开更多
AIM： To investigate the role of second-look laparoscopy in patients with acute mesenteric ischemia （AMI）. METHODS： Between January 2000 and November 2005, 71 patients were operated for the treatment of AMI. The in...AIM： To investigate the role of second-look laparoscopy in patients with acute mesenteric ischemia （AMI）. METHODS： Between January 2000 and November 2005, 71 patients were operated for the treatment of AMI. The indications for a second-look were low flow state, bowel resection and anastomosis or mesenteric thromboembolectomy performed during the first operation. Regardless of the clinical course of patients, the second-look laparoscopic examination was performed 72 h post-operatively at the bed side in the ICU or operating room. RESULTS： The average time of admission to the hospital after the initation of syrnptoms was 3 d （range, 5 h-9 d）. In 14 patients, laparotomy was performed. In 11 patients, small and/or large bowel necrosis was detected and initial resection and anastomosis were conducted. A low flow state was observed in two patients and superior mesenteric artery thromboembolectomy with small bowel resection was performed in one patient. In 13 patients, a second-look laparoscopic examination revealed normal bowel viability, but in one patient, intestinal necrosis was detected. In two of the patients, a third operation was necessary to correct anastomotic leakage. The overall complication rate was 42.8%, and in-hospital mortality rate was 57.1% （n = 6）. CONCLUSION： Second-look laparoscopy is a minimally invasive, technically simple procedure that is performed for diagnostic as well as therapeutic purposes. The simplicity and ease of this method may encourage wider application to benefit more patients. However, the timing of a second-look procedure is unclear particularly in a patient with anastomosis.展开更多
基金the China Scholarship Council(CSC)the Uplifting Reciprocal Research Scholarship Program for sponsoring Shixuan Lyu+1 种基金supported by MITACS Accelerate(No.IT39116)the Okanagan Basin Water Board water conservation and quality improvement grant program。
文摘Forests are experiencing more frequent and intense wildfires in Canada,which pose considerable threats to water quantity and quality,particularly during the summer low-flow period when water demand is high.While the impacts of wildfire on hydrology have been widely assessed at the watershed scale,the underlying mechanisms of the responses of summer low flows remain poorly understood.In this study,we employed an integrated research framework that combines hydrometric monitoring with geochemical tracing to evaluate how the 2021 White Rock Lake Wildfire affected summer low flows,and to identify the underlying mechanisms governing these responses in the Okanagan Valley,British Columbia(BC),Canada.We found that(1)summer low flows,represented by Q90(flows exceeded at 90%of the time in summer)significantly increased following the wildfire(p<0.05);(2)summer low flows were primarily regulated by snow water in early summer(July),while dominated by groundwater in late summer(August and September);and(3)enhanced snow water contribution and reduced evapotranspiration(ET)were two primary contributors to the increased summer low flows.Our results provide insights for developing sustainable water management strategies for the region in the context of climate change and increasing forest disturbance.This study also demonstrates that the combination of hydrometric monitoring and geochemical tracing is an effective approach towards uncovering mechanisms that drive low-flow responses.
文摘Climate change will profoundly affect hydrological processes at various temporal and spatial scales.This study is focused on assessing the alteration of water resources availability and low flows frequencies driven by changing climates in different time periods of the 21st century.This study evaluates the adaptability of prevailing Global Circulation Models(GCMs)on a particular watershed through streamflow regimes.This analysis was conducted in the Great Miami River Watershed,Ohio by analyzing historical and future simulated streamflow using 10 climate model outputs and the Soil and Water Assessment Tool(SWAT).The climate change scenarios,consisting of ten downscaled Coupled Model Intercomparision Project Phase 5(CMIP5)climate models in combination with two Representative Concentration Pathways(RCP 4.5 and RCP 8.5)were selected based on the correlation between observed records and model outputs.Streamflow for three future periods,2016-2043,2044-2071 and 2072-2099,were independently analyzed and compared with the baseline period(1988-2015).Results from the average of ten models projected that 7-day low flows in the watershed would increase by 19%in the 21st century under both RCPs.This trend was also consistent for both hydrological(7Q10,1Q10)and biological low flow statistics(4B3,1B3).Similarly,average annual flow and monthly flows would also increase in future periods,especially in the summer.The flows simulated by SWAT in response to the majority of climate model projections showed a consistent increase in low flow patterns.However,the flow estimates using the Max-Planck-Institute Earth System Model(MPI-ESM-LR)climate output resulted in the biological based low flows(4B3,1B3)decreasing by 22.5%and 33.4%under RCP 4.5 and 56.9%and 63.7%under RCP 8.5,respectively,in the future when compared to the baseline period.Regardless,the low flow ensemble from the 10 climate models for the 21st century seemed to be slightly higher than that of historical low flows.
基金supported by the National Natural Science Foundation of China(Nos.51527805 and 11572220)
文摘This study aimed to obtain the production profiles of oil-in-water flow under low flow rate and high water-cut conditions in oil wells.A combination production profile logging composed of an arc-type conductance sensor(ATCS)and a cross-correlation flow meter(CFM)with a center body is proposed and experimentally evaluated.The ATCS is designed for water holdup measurement,whereas the CFM with a center body is proposed to obtain the mixture velocity.Then,a drift-flux model based on flow patterns is established to predict the individual-phase superficial velocity of oil-in-water flows.Results show that the ATCS possesses high resolution in water holdup measurement and that flow pattern information can be deduced from its signal through nonlinear time series analysis.The CFM can enhance the correlation of upstream and downstream signals and simplify the relationship between the cross-correlation velocity and mixture velocity.On the basis of the drift-flux model,individual-phase superficial velocities can be predicted with high accuracy for different flow patterns.
文摘This paper deals with the numerical solution of inviscid compressible flows.The threedimensional Euler equations describing the mentioned problem are presented and solved numerically with the finite volume method.The evaluation of the numerical flux at the interfaces is performed by using the Toro Vazquez-Harten Lax Leer(TV-HLL)scheme.An essential feature of the proposed scheme is to associate two systems of differential equations,called the advection system and the pressure system.It can be implemented with a very simple manner in the standard finite volume Euler and Navier–Stokes codes as extremely simple task.The scheme is applied to some test problems covering a wide spectrum of Mach numbers,including hypersonic,low speed flow and three-dimensional aerodynamics applications.
基金supported by the National Natural Science Foundation of China(No.22273103)the National Natural Science Foundation of China(NSFC Center for Chemical Dynamics)(No.22288201)+1 种基金Dalian Institute of Chemical Physics(DICP I202230)the Scientific Instrument Developing Project of the Chinese Academy of Sciences(grant GJJSTD20220001)。
文摘Collision-induced re-laxation process of CH(X^(2)Π,v=0)radical in various bath gases He,Ar,and N_(2)has been investigated ex-perimentally under low-temperature(26-52 K)supersonic flow conditions.The CH radicals were generat-ed with internal excitation by multiphoton photolysis of CHBr_(3)at 248 nm,and its rotational temperature was found to relax to the flow temperature in a few microseconds by colliding with bath gas.The relaxation rate coefficients for CH(X^(2)Π,v=0)radical in He,Ar,and N_(2)flow were obtained by time-resolved laser-induced fluorescence measurements,ranging from 10^(-12)cm^(3)·molecule^(-1)·s^(-1)to 10^(-11)cm^(3)·molecule^(-1)·s^(-1).The N_(2)flow exhibits the highest relax-ation rate for CH(X^(2)Π)radical due to its additional rovibrational levels,which allow for more efficient energy dissipation during collisions compared to monoatomic gases.The Ar flow shows a larger relaxation rate than He flow due to its greater polarizability and stronger long-range interaction with the CH(X^(2)Π)radical.
基金The project supported by the Basic Research on Frontier Problems in Fluid and Aerodynamics in Chinathe National Natural Science Foundation of China (19772069)
文摘By analyzing the characteristics of low Mach number perfect gas flows, a novel Slightly Compressible Model (SCM) for low Mach number perect gas flows is derived. In view of numerical calculations, this model is proved very efficient, for it is kept within thep-v frame but does not have to satisfy the time consuming divergence-free condition in order to get the incompressible Navier-Stokes equation solution. Writing the equations in the form of conservation laws, we have derived the characteristic systems which are necessary for numerical calculations. A cell-centered finite-volume method with flux difference upwind-biased schemes is used for the equation solutions and a new Exact Newton Relaxation (ENR) implicit method is developed. Various computed results are presented to validate the present model. Laminar flow solutions over a circular cylinder with wake developing and vortex shedding are presented. Results for inviscid flow over a sphere are compared in excellent agreement with the exact analytic incompressible solution. Three-dimensional viscous flow solutions over sphere and prolate spheroid are also calculated and compared well with experiments and other incompressible solutions. Finally, good convergent performances are shown for sphere viscous flows.
文摘Because of unstable properties of axial mine flow fans working under conditions of low flow rates, the safety and reliability of fans in their operational zone is reduced. At times, serious vibration may bring about the destruction of equipment or even jeopardize the safety of entire factories. By means of oil flow visualization techniques and numerical simulation, we have investigated the inner-flow of an axial mine flow fan working under low flow rate conditions. The fundamental reasons of complex flow phenomena of the inner-flow of the flow fan under these stated conditions were revealed. At the same time and in order to improve the inner-flow under conditions of low flow rates, a blade separator and air separator were designed. From our tests we found that the blade separator and air separator are two kinds efficient methods to improve the unstable working characteristics of the axial mine flow fan operating under low flow rate conditions. The effect of the improvement of the air separator is stronger than that of the blade separator.
文摘This study investigate the relationships between geomorphometric properties and the minimum low flow discharge of undisturbed drainage basins in the Taman Bukit Cahaya Seri Alam Forest Reserve, Peninsular Malaysia. The drainage basins selected were third-order basins so as to facilitate a common base for sampling and performing an unbiased statistical analyses. Three levels of relationships were observed in the study. Significant relationships existed between the geomorphometric properties as shown by the correlation network analysis; secondly, individual geomorphometric properties were observed to influence minimum flow discharge; and finally, the multiple regression model set up showed that minimum flow discharge(Q min) was dependent of basin area(AU), stream length(LS), maximum relief(Hmax), average relief(HAV) and stream frequency(SF). These findings further enforced other studies of this nature that drainage basins were dynamic and functional entities whose operations were governed by complex interrelationships occurring within the basins. Changes to any of the geomorphometric properties would influence their role as basin regulators thus influencing a change in basin response. In the case of the basin's minimum low flow, a change in any of the properties considered in the regression model influenced the “time to peak' of flow. A shorter time period would mean higher discharge, which is generally considered the prerequisite to flooding. This research also conclude that the role of geomorphometric properties to control the water supply within the stream through out the year even though during the drought and less precipitations months. Drainage basins are sensitive entities and any deteriorations involve will generate reciprocals and response to the water supply as well as the habitat within the areas.
文摘This paper proposes a new accelerating technique for simulating low speed flows,termed as p Seudo High Speed method(SHS),which uses governing equations and numerical methods of compressible flows.SHS method has advantages of simple formula,easy manipulation,and only need to modify flux of Euler equations.It can directly employ the existing well-developed schemes of hyperbolic conservation laws.To verify the technique,several numerical experiments are performed,such as:flow past airfoils and flow past a cylinder.Analysis of SHS method and comparisons with some precondition methods are made numerically.All tests show that SHS method can greatly improve the efficiency of compressible method simulating low speed flow fields,which exhibits in accelerating the convergence rate and increasing the accuracy of the numerical results.
文摘A numerical simulation method is employed to investigate the effects of the unsteady plasma body force over the stalled NACA 0015 airfoil at low Reynolds number flow conditions. The plasma body force created by a dielectric barrier discharge actuator is modeled with a phenomenological method for plasma simulation coupled with the compressible Navier-Stokes equations. The governing equations are solved using an efficient implicit finitevolume method. The responses of the separated flow field to the effects of an unsteady body force in various inter- pulses and duty cycles as well as different locations and magnitudes are studied. It is shown that the duty cycle and inter-pulse are key parameters for flow separation control. Additionally, it is concluded that the body force is able to attach the flow and can affect boundary layer grow that Mach number 0.1 and Reynolds number of 45000.
基金supported by the technology development fund of China Petroleum & Chemical Corporation (Sinopec 312016 and 314054)
文摘An attempt was made to extend mild combustion to forward flow furnace, such as the refinery and petrochemical tube furnace. Three dimensional numerical simulation was carried out to study the performance of this furnace. The Eddy Dissipation Concept(EDC) model coupled with the reaction mechanism DRM-19 was used. The prediction showed a good agreement with the measurement. The effect of air nozzle circle(D), air nozzle diameter(d), air nozzle number(N), and air preheating temperature(Tair) on the flow, temperature and species fields, and the CO and NO emissions was investigated. The results indicate that there are four zones in the furnace, viz.: a central jet zone, an ignition zone, a combustion reaction zone, and a flue gas zone, according to the distribution profiles of H_2 CO and OH. The central jet entrains more flue gas in the furnace upstream with an increasing D while the effect of D is negligible in the downstream. The air jet momentum increases with a decreasing d or an increasing Tair, and entrains more flue gas. The effect of N is mainly identified near the burner exit. More heat is absorbed in the radiant section and less heat is discharged to the atmosphere with a decreasing d and an increasing N as evidenced by the flue gas temperature. The CO and NO emissions are less than 50 μL/L and 10 μL/L, respectively, in most of conditions.
基金support provided by the Deutsche Forschun-gsgemeinschaft(DFG,German Research Foundation)through the project GRK 2160/1“Droplet Interaction Technologies”and through the project no.457811052
文摘Considering droplet phenomena at low Mach numbers,large differences in the magnitude of the occurring characteristic waves are presented.As acoustic phenomena often play a minor role in such applications,classical explicit schemes which resolve these waves suffer from a very restrictive timestep restriction.In this work,a novel scheme based on a specific level set ghost fluid method and an implicit-explicit(IMEX)flux splitting is proposed to overcome this timestep restriction.A fully implicit narrow band around the sharp phase interface is combined with a splitting of the convective and acoustic phenomena away from the interface.In this part of the domain,the IMEX Runge-Kutta time discretization and the high order discontinuous Galerkin spectral element method are applied to achieve high accuracies in the bulk phases.It is shown that for low Mach numbers a significant gain in computational time can be achieved compared to a fully explicit method.Applica-tions to typical droplet dynamic phenomena validate the proposed method and illustrate its capabilities.
文摘The qualitative and quantitative assessment of gas flow has become increasingly relevant in the use of everyday systems. The micro flow sensor, developed by Innovative Sensor Technology AG （Switzerland）, is by principle a calorimetric flow sensor produced as a micro system on a glass substrate by means of photolithography and glass etching technology. These structures are arranged as a platinum micro heater and sensor in a Wheatstone bridge. The subsequent etching process produces an exposed area of polyimide membrane that is only a few microns thick and includes the resistive sensor structure as the active area. In addition, the RTD （resistance temperature detector） technology included on the sensor allows for the implementation of a variety of electronic biasing and signal processing modes. Since the sensor can be powered and the bridge can be measured in both CTA （constant temperature anemometer） and calorimetric mode, new possibilities are presented for both low and high flow rates with regard to temperature compensation, self-calibration and self-monitoring.
文摘Background Aortic valve replacement （AVR） improves survival in severe symptomatic aortic stenosis （AS）. Yet, in many patients with severe AS, the timing of AVR remains poorly defined. In particular, it is challenging in patients with low mean pressure gradient （〈 40 mmHg） and severe AS （aortic valve area （AVA）≤1.0 cm^2） with preserved left ventricular （LV） ejection fraction.
文摘Rural labor flowing in low marketization level restricts rural production elements of effective allocation, and restricts the development of rural economy, causes the gap between urban and rural areas to continue expanding. This article has analyzed the reasons of phenomenon, and raised some solutions from abolishing the barrier of the household register, improved rural labor＇ s cultural and skills quality, and built a social security system in rural areas improve the marketization level of rural labor flow.
文摘The retrofit on flow path of low pressure cylinder of domestic made 200 MW steam turbine undertaken by Longwei Power Generation Technology Service Company Ltd by using Westinghouse technology was successful for the first time on the No. 5 unit of Zhenhai Prover Plant. Zhejiang Province. The test carried out by the Xi’an Thermal Power Research Institute showed that the thermal efficiency after the retrofit
文摘Some patients with severe aortic stenosis (AS), due to restrictive cardiac physiology, paradoxically have relatively low flow and low gradients across stenotic aortic valves despite preserved left ventricular (LV) systolic function. It results in symptoms and reduced quality of life and carries a high mortality. Whilst this form of severe AS, termed paradoxical low flow low gradient (pLFLG), is well reported, patients with this diagnosis experience inappropriate barriers to aortic valve replacement (AVR), the only efficacious treatment. We present the case of an 88-year-old female with 12 months of exertional dyspnoea on a background of hypothyroidism and hypercholesterolemia. Transthoracic echocardiogram (TTE) revealed LV hypertrophy, with a small LV cavity size and reduced stroke volume, yet normal systolic function. A heavily calcified aortic valve was identified with severe aortic stenosis, based on valve area, yet with incongruous mean transvalvular gradient of 25 mmHg (severe ≥ 50 mmHg). Following exclusion of other differential diagnoses, her symptoms were attributed to paradoxical LFLG severe AS. She was however declined definitive transcatheter aortic valve implantation (TAVI) due to her paradoxically low mean aortic gradient. Following further deterioration in her symptoms and supportive quantification of poor exercise performance, she was ultimately re-referred, accepted, and underwent TAVI. Following her AVR, the patient experiences significant improvement in both symptoms and quality of life after only one month. Paradoxical LFLG severe AS remains a well-documented yet under recognized disease. It carries high morbidity and mortality if untreated, yet is significantly less likely to be referred and accepted for intervention. With its prevalence expected to rise with an ageing population, this case serves as a timely reminder for clinicians to address the under recognition of important pathology.
文摘The most controversial river in Thailand is the Yom River.It has not been modified by large dam because of several valuable natural resources.Therefore,the river is flooded in rainy season and very low flow in dry season.The low flow causes drought which is much more serious than flooding.The Yom River Basin management is only way to circumvent the low flow problem by studying base flow index(BFI).Base flow analyses for 8 gauging stations along the river were performed by 2 techniques i.e.graphical and modified U.K.Institute of Hydrology(MIH).The mean BFI results from graphical and MIH are 0.37(0.05)and 0.45(0.12).The result from graphical is more reasonable due to its lower standard deviation.BFI values from MIH vary with watershed area which may result from the using of fixing value of N-day at 10.Solution for this problem is ongoing in this study.
文摘AIM： To investigate the role of second-look laparoscopy in patients with acute mesenteric ischemia （AMI）. METHODS： Between January 2000 and November 2005, 71 patients were operated for the treatment of AMI. The indications for a second-look were low flow state, bowel resection and anastomosis or mesenteric thromboembolectomy performed during the first operation. Regardless of the clinical course of patients, the second-look laparoscopic examination was performed 72 h post-operatively at the bed side in the ICU or operating room. RESULTS： The average time of admission to the hospital after the initation of syrnptoms was 3 d （range, 5 h-9 d）. In 14 patients, laparotomy was performed. In 11 patients, small and/or large bowel necrosis was detected and initial resection and anastomosis were conducted. A low flow state was observed in two patients and superior mesenteric artery thromboembolectomy with small bowel resection was performed in one patient. In 13 patients, a second-look laparoscopic examination revealed normal bowel viability, but in one patient, intestinal necrosis was detected. In two of the patients, a third operation was necessary to correct anastomotic leakage. The overall complication rate was 42.8%, and in-hospital mortality rate was 57.1% （n = 6）. CONCLUSION： Second-look laparoscopy is a minimally invasive, technically simple procedure that is performed for diagnostic as well as therapeutic purposes. The simplicity and ease of this method may encourage wider application to benefit more patients. However, the timing of a second-look procedure is unclear particularly in a patient with anastomosis.
