Hydraulic valve block is an important part of the hydraulic system.The traditional hydraulic valve block is made by turning and milling,drilling and boring,which leads to many right-angle bending and closed cavity str...Hydraulic valve block is an important part of the hydraulic system.The traditional hydraulic valve block is made by turning and milling,drilling and boring,which leads to many right-angle bending and closed cavity structure of process holes in its internal flow channel,seriously affecting the flow performance of oil.Based on the new design space provided by additive manufacturing technology,the internal hydraulic flow channel of valve block is optimized by using B-spline curve.Computational fluid dynamics analysis is carried out on the hydraulic flow channel to determine the optimal flow channel structure with the smallest pressure drop.The weight reduction of hydraulic valve block is carried out through topology optimization.According to the results of topology optimization,using the method of selective laser melting(SLM),the printing of the hydraulic valve block is completed.The optimized hydraulic channel reduces the pressure loss by 31.4%compared with the traditional hydraulic channel.Compared with the traditional valve block,the hydraulic valve block manufactured by SLM with topology optimization reduces the weight by 33.9%.Therefore,the proposed flow channel optimization and valve block lightweight method provide a new reference for the performance improvement of the internal flow channel of hydraulic valve block and the overall lightweight design of valve block.展开更多
Laminar flow and heat transfer characteristics of jacketed vessel with triangular flow channels were numerically studied under hydrodynamically and thermally fully developed conditions. Constant heat flux at theheated...Laminar flow and heat transfer characteristics of jacketed vessel with triangular flow channels were numerically studied under hydrodynamically and thermally fully developed conditions. Constant heat flux at theheated wall was assumed. The numerical program code interms of vorticity, stream function, axial velocity com ponent and energy equations was written based on a finite volume method. Based on the numerical results, the flow and temperature field were given, and the effects of Dean and Prandtl numbers on flow and heat transfer were ex amined, and the correlations of flow resistance and mean Nusselt number were developed for the jacket. The results show that the structure of secondary flow is steady two vortices in the investigated range of dimensionless curvatureratio and Reynolds number. Two peaks of local Nusselt number increase significantly with Prandtl and Dean num ber increasing, but the local Nusselt numbers near two ends and at the center of the heated wall increase only slightly. The center and two ends of heated wall are the poor positions for heat transfer in the jacket. Compared with the outer half coil jacket at the same area of heated wall, curvature radius, Reynolds number and Prandtl number, e jacket of triangular flow chmnel has lower flow resistance and less mean Nusselt number.展开更多
In order to research how the size of the ink flow channel is affected by the interaction of adjacent ink areas,according to the method of fluid-solid interaction,this paper analyzes the size of the ink flow channel of...In order to research how the size of the ink flow channel is affected by the interaction of adjacent ink areas,according to the method of fluid-solid interaction,this paper analyzes the size of the ink flow channel of two ink rollers' rotation.Firstly,this paper simulates the situation of only one ink area.Secondly,this paper simulates the situation of five adjacent ink areas.Then,through comparing the simulation results of two above situations,it' s obvious that the interaction of adjacent ink areas has big effects on the ink pressure and the size of ink flow channel.At last,this paper gets the main factor that affects the size of ink flow channel in the different situations.展开更多
Through experimental analysis of the liquid flows in a flow channel instrument, prompt evaluation of the physically defined viscosity of non-Newtonian liquid foods was investigated for development into a structurally ...Through experimental analysis of the liquid flows in a flow channel instrument, prompt evaluation of the physically defined viscosity of non-Newtonian liquid foods was investigated for development into a structurally simple and easy-to-use viscometer. For Newtonian and non-Newtonian test liquids, a relation between the friction coefficient and Reynolds number, which was dimensionless as derived from an expression of analysis as a gravity current, indicated a condition under which the flow in the instrument was laminar and under which an average shear rate was on the order of less than 1 s~. Prediction organized based on this empirical relation reproduced practically the flow curve determined for the liquid foods using a rotor type viscometer. Utilization of the channel instrument as a viscometer was formulated in terms of physical meanings of measurements such as the flow length and elapsed time.展开更多
Based on well test interpretation,production performance analysis,overburden permeability and porosity test,gas-water core flooding test and high-pressure mercury injection,a quantitative correlation has been built of...Based on well test interpretation,production performance analysis,overburden permeability and porosity test,gas-water core flooding test and high-pressure mercury injection,a quantitative correlation has been built of in-situ effective permeability with routine permeability and water saturation,and the ranges of Main Flow Channel Index(MFCI)are determined for different permeability levels in porous sand gas reservoirs.A new method to evaluate the in-situ effective permeability of porous sand reservoir and a correlation chart of reserves producing degree and main flow channel index are established.The results reveal that the main flow channel index of porous sand gas reservoirs has close correlation with routine matrix permeability and water saturation.The lower the routine matrix permeability and the higher the water saturation,the lower the MFCI is.If the routine matrix permeability is greater than 5.0×10-3,the MFCI is generally greater than 0.5.When the routine matrix permeability is from 1.0×10-3 to 5.0×10-3,the MFCI is mainly between 0.2 and 0.5.When the routine matrix permeability is less than 1.0×10-3,the MFCI is less than 0.2.The evaluation method of in-situ effective permeability can be used to evaluate newly discovered or not tested porous sand gas reservoirs quickly and identify whether there is tight sand gas.The correlation chart of reserves producing degree and main flow channel index can provide basis for recoverable reserves evaluation and well infilling,and provide technical support for formulation of reasonable technical policy of gas reservoir.展开更多
The permeability of coal ahead of the working face obviously changes dues to changes in abutment pressure.The formation and evolution of gas flow channels within the abutment pressure area was studied by analyzing the...The permeability of coal ahead of the working face obviously changes dues to changes in abutment pressure.The formation and evolution of gas flow channels within the abutment pressure area was studied by analyzing the fracture extension mechanism and fracture development in different zones of the abutment pressure area.Fracture and damage mechanics theory is used to understand the observations.The following two techniques were used to understand the evolution of gas flow channels:field observation of the characteristic fractures at different positions relative to the working face and fluorescence micrographs of prepared coal samples.Bending tensile fractures develop along an approximately vertical direction that forms a microscopic network of channels in areas of stress concentration.The abutment pressure affects the local stress and,hence,the local gas conduction.The fractures induced by large deformation and plastic flow form macroscopically networked channels in the reduced stress area.Closer to the working face the gas flow channels evolve from microscopic to macroscopic and from isolated to network.Gas permeability continuously increases during this time.This is corroborated by field observations of the displacement of top coal and the gas flow from gas extraction drillings.展开更多
To identify the type of main flow channels of complex porous media in oil and gas reservoirs,the"main flow channel index"is defined as the ratio of comprehensive permeability obtained from well test to matri...To identify the type of main flow channels of complex porous media in oil and gas reservoirs,the"main flow channel index"is defined as the ratio of comprehensive permeability obtained from well test to matrix permeability obtained from core analysis or well logging.Meanwhile,a mathematical model is established based on equivalent flow assumption,the classification method for main flow channels is put forward,and quantitative characterization of main flow channels is realized.The method has been verified by analysis of typical gas reservoirs.The study results show that the"main flow channel index"can quantitatively classify types of flow channels.If the index is less than 3,the matrix pore is the main flow channel;if the index is between 3 and 20,the fracture is the main flow channel and the matrix pore acts as the supplement one;if the index is more than 20,the fracture is the only seepage channel.The dynamic analysis of typical gas reservoirs shows that the"main flow channel index"can be used to identify the type of flow channel in complex porous media,guiding the classified development of gas reservoirs,and avoiding development risk.展开更多
Reactant gas and liquid water transport phenomena in the flow channels are complex and critical to the performance and durability of polymer electrolyte membrane fuel cells.The polymer membrane needs water at an optim...Reactant gas and liquid water transport phenomena in the flow channels are complex and critical to the performance and durability of polymer electrolyte membrane fuel cells.The polymer membrane needs water at an optimum level for proton conductivity.Water management involves the prevention of dehydration,waterlogging,and the cell’s subsequent performance decline and degradation.This process requires the study and understanding of internal two-phase flows.Different experimental visualization techniques are used to study two-phase flows in polymer electrolyte membrane fuel cells.However,the experiments have limitations in in situ measurements;they are also expensive and time exhaustive.In contrast,numerical modeling is cheaper and faster,providing insights into the complex multiscale processes occurring across the components of the polymer electrolyte membrane fuel cells.This paper introduces the recent design of flow channels.It reviews the numerical modeling techniques adopted for the transport phenomena therein:the two-fluid,multiphase mixture,volume of fluid,lattice Boltzmann,and pressure drop models.Furthermore,this work describes,compares,and analyses the models’approaches and reviews the representative results of some selected aspects.Finally,the paper summarizes the modeling perspectives,emphasizing future directions with some recommendations.展开更多
The transient friction in channel mean flows is the sum of two contributions,i.e.,the underlying laminar flow(ULF)and the purely turbulent component(PTC),and the contributions are analyzed separately by theoretical ex...The transient friction in channel mean flows is the sum of two contributions,i.e.,the underlying laminar flow(ULF)and the purely turbulent component(PTC),and the contributions are analyzed separately by theoretical experiments.It is found that,the transient friction may be higher or remarkably lower than that in equal-Reynolds number steady-state flows.The universal time constant for plane-parallel laminar flows is reported,and the role of the time constant in a turbulent mean flow is examined.It is shown that the time constant is related to the turbulence's frozen time.Finally,a study of the logarithmic layer during the transient flow is accomplished,which shows that the logarithmic layer is destroyed.展开更多
This study presents a numerical analysis of three-dimensional steady laminar flow in a rectangular channel with a 180-degree sharp turn. The Navier-Stokes equations are solved by using finite difference method for Re ...This study presents a numerical analysis of three-dimensional steady laminar flow in a rectangular channel with a 180-degree sharp turn. The Navier-Stokes equations are solved by using finite difference method for Re = 900. Three-dimensional streamlines and limiting streamlines on wall surface are used to analyze the three-dimensional flow characteristics. Topological theory is applied to limiting streamlines on inner walls of the channel and two-dimensional streamlines at several cross sections. It is also shown that the flow impinges on the end wall of turn and the secondary flow is induced by the curvature in the sharp turn.展开更多
Flow channels with a variable cross-section are important components of piping system and are widely used in variousfields of engineering.Using afinite element method and modal analysis theory,flow-induced noise,mode ...Flow channels with a variable cross-section are important components of piping system and are widely used in variousfields of engineering.Using afinite element method and modal analysis theory,flow-induced noise,mode shapes,and structure-borne noise in such systems are investigated in this study.The results demonstrate that the maximum displacement and equivalent stress are located in the part with variable cross-sectional area.The aver-age excitation force on theflow channel wall increases with theflow velocity.The maximum excitation force occurs in the range of 0–20 Hz,and then it decreases gradually in the range of 20–1000 Hz.Additionally,as theflow velocity rises from 1 to 3 m/s,the overall sound pressure level associated with theflow-induced noise grows from 49.37 to 66.37 dB.Similarly,the overall sound pressure level associated with the structure-borne noise rises from 40.27 to 72.20 dB.When theflow velocity is increased,the increment of the structure-borne noise is higher than that of theflow-induced noise.展开更多
Fully connected neural networks(FCNNs)have been developed for the closure of subgrid-scale(SGS)stress and SGS heat flux in large-eddy simulations of compressible turbulent channel flow.The FCNNbased SGS model trained ...Fully connected neural networks(FCNNs)have been developed for the closure of subgrid-scale(SGS)stress and SGS heat flux in large-eddy simulations of compressible turbulent channel flow.The FCNNbased SGS model trained using data with Mach number Ma=3.0 and Reynolds number Re=3000 was applied to situations with different Mach numbers and Reynolds numbers.The input variables of the neural network model were the filtered velocity gradients and temperature gradients at a single spatial grid point.The a priori test showed that the FCNN model had a correlation coefficient larger than 0.91 and a relative error smaller than 0.43,with much better reconstructions of SGS unclosed terms than the dynamic Smagorinsky model(DSM).In a posteriori test,the behavior of the FCNN model was marginally better than that of the DSM in predicting the mean velocity profiles,mean temperature profiles,turbulent intensities,total Reynolds stress,total Reynolds heat flux,and mean SGS flux of kinetic energy,and outperformed the Smagorinsky model.展开更多
The interaction between free fast-moving bodies(or particles)and the fluid surrounding them is studied,motivated by applications in different branches of industry,biomedicine,the environment and science such as flying...The interaction between free fast-moving bodies(or particles)and the fluid surrounding them is studied,motivated by applications in different branches of industry,biomedicine,the environment and science such as flying droplets,ice growth,dust,impacts,food grains,sport,complexity and storms.New inviscid-based modelling and results on the behaviour of two interacting bodies inside a channel flow are described.This is followed by discussion of the more-bodies extension with a view to treating arrays of bodies in a rational manner.Significant dependences on initial conditions and on the comparative body masses and moments of inertia are found for the occurrence of body-body impacts as opposed to wall-body impacts and for the associated impact times.展开更多
In this letter,the effect of slip boundary on the origin of subcritical transition in two-dimensional chan-nel flows is studied numerically and theoretically.It is shown that both the positive and the negative slip le...In this letter,the effect of slip boundary on the origin of subcritical transition in two-dimensional chan-nel flows is studied numerically and theoretically.It is shown that both the positive and the negative slip lengths will increase the critical Reynolds number of localized wave packet and hence postpone the transition.By applying a variable transformation and expanding the variables about a small slip length,it is illustrated that the slip boundary effect only exists in the second and higher order modulations of the no-slip solution,and hence explains the power law found in simulations,i.e.the relative increment of the critical Reynolds number due to the slip boundary is proportional to the square of the slip length.展开更多
The background to this research was a flooding incident that occurred in Bridgend, Co. Donegal, Ireland in August 2017. While several properties were flooded, a flooding case study of a single dwelling house adjacent ...The background to this research was a flooding incident that occurred in Bridgend, Co. Donegal, Ireland in August 2017. While several properties were flooded, a flooding case study of a single dwelling house adjacent to the Bridgend River at Riverdale, Bunamayne, Co. Donegal, Ireland is used herein. For this study the flooded site shall be referred to as the “Hegarty property”. A structure in the form of a stone arched culvert is located directly adjacent to the two-storey detached dwelling house on the Hegarty Property. While the culvert is referred to locally as a bridge, within this research the word culvert will be used in connection with the structure. The culvert has a concrete surrounded utility (watermain) crossing at a gradient below the culvert soffit on the upstream face of the structure. The utility obstructed flow through the culvert and contributed to the flooding event. Given the implication of climate change and the increased probability of more extreme flooding events, it was decided to explore the case study to ascertain the factors that contribute to flooding events when utilities are positioned at culvert or bridge structures. This work was completed to assist undergraduate students, researchers, and local authorities in a relatively unknown area of flood causation.展开更多
Vegetation of different heights commonly grows in natural rivers, canals and wetlands and affects the biodiversity and morphological process. The role of vegetation has drawn great attention in river ecosystems and en...Vegetation of different heights commonly grows in natural rivers, canals and wetlands and affects the biodiversity and morphological process. The role of vegetation has drawn great attention in river ecosystems and environmental management. Due to the complexity of the vegetated flow, most previous research focuses on the effect of uniformed one-layered vegetation on the flow structure and morphological process. However, less attention was paid to the impact of the mixing vegetation of different heights, which is more realistic and often occurs in natural riverine environments. This paper aims to investigate the effect of mixing three-layered vegetation on flow characteristics, particularly the velocity distrbution, via a novel experiment. Experiments were performed in a titling water flume fully covered with vegetation of three heights (10, 15 and 20 cm) arranged in a staggered pattern, which is partially submerged. Velocities at different positions along a half cross-section were measured using a mini propeller velocimeter. Observed results showed that the velocity has a distinct profile directly behind vegetation and behind the vegetation gap. The overall profile has two distinct reflections about ? below or near the top of short vegetation (h): the velocity remains almost constant in the bottom layer ( h) the velocities directly behind the middle after short vegetation increase much faster than those directly behind the short after tall vegetation. The finding in this study would help river riparian and ecosystem management. .展开更多
An improved divided channel method has been proposed by modelling a parameter using the function of depth ratio for a multi-stage compound channel. Experimental data suggest that as the flow depth increases over the s...An improved divided channel method has been proposed by modelling a parameter using the function of depth ratio for a multi-stage compound channel. Experimental data suggest that as the flow depth increases over the second stage floodplain, fractional contribution of the main channel and first stage floodplain under bankfull height plays a pivotal role in shear layer and momentum distribution. Therefore, a new mathematical model has been suggested for estimating the stage-discharge relationship for staged channels of more than one floodplain using the 1D technique of overall roughness correction. .展开更多
This study performs a numerical analysis of three-dimensional liquid metal(LM) magnetohydrodynamic(MHD) flows in a square duct with an FCI in a non-uniform magnetic field. The current study predicts detailed informati...This study performs a numerical analysis of three-dimensional liquid metal(LM) magnetohydrodynamic(MHD) flows in a square duct with an FCI in a non-uniform magnetic field. The current study predicts detailed information on flow velocity, Lorentz force, pressure, current and electric potential of MHD duct flows for different Hartmann numbers. Also, the effect of the electric conductivity of FCI on the pressure drop along the main flow direction in a non-uniform magnetic field is examined. The present study investigates the features of LM MHD flows in consideration of the interdependency among the flow variables.展开更多
The orientation and concentration distributions of fibres in laminar and turbulent channel flows are investigated numerically. The obtained results are in good agreement with the experimental data. In the laminar flow...The orientation and concentration distributions of fibres in laminar and turbulent channel flows are investigated numerically. The obtained results are in good agreement with the experimental data. In the laminar flow regime, more fibres orient to the flow direction as the Reynolds number increases. The shear rate of fluid around a fibre plays an important role in determining the orientation distribution of fibres, while the fibre density and the fibre aspect-ratio have marginal influence on the orientation distribution. In the turbulent regime, the orientation distribution of fibres becomes more homogeneous with the increase of Reynolds number, and the concentration profile is flatter than that in the laminar regime. The fluctuating intensity of fibre velocity in the downstream direction is larger than that in the lateral directions.展开更多
The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influ...The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.展开更多
基金supported by the National Natural Science Foundation of China(No.51775273)the Jiangsu Province Science and Technology Support Plan Project(No.BE2018010-2)+2 种基金the National Defence Basic Scientific Research Program of China(No.JCKY2018605C010)the Frontiers of Science and Technology Program of China (No.1816312ZT00406301)the Aeronautical Science Foundation of China(No.2020Z049052002)
文摘Hydraulic valve block is an important part of the hydraulic system.The traditional hydraulic valve block is made by turning and milling,drilling and boring,which leads to many right-angle bending and closed cavity structure of process holes in its internal flow channel,seriously affecting the flow performance of oil.Based on the new design space provided by additive manufacturing technology,the internal hydraulic flow channel of valve block is optimized by using B-spline curve.Computational fluid dynamics analysis is carried out on the hydraulic flow channel to determine the optimal flow channel structure with the smallest pressure drop.The weight reduction of hydraulic valve block is carried out through topology optimization.According to the results of topology optimization,using the method of selective laser melting(SLM),the printing of the hydraulic valve block is completed.The optimized hydraulic channel reduces the pressure loss by 31.4%compared with the traditional hydraulic channel.Compared with the traditional valve block,the hydraulic valve block manufactured by SLM with topology optimization reduces the weight by 33.9%.Therefore,the proposed flow channel optimization and valve block lightweight method provide a new reference for the performance improvement of the internal flow channel of hydraulic valve block and the overall lightweight design of valve block.
基金Supported by the Speciai Pogram forLocal Universities Development of Central Finance of China （2050205）, the National Natural Science Foundation of China （21106086）, and the Program for Liaoning Excellent Talents in University （LJQ2012035）.
文摘Laminar flow and heat transfer characteristics of jacketed vessel with triangular flow channels were numerically studied under hydrodynamically and thermally fully developed conditions. Constant heat flux at theheated wall was assumed. The numerical program code interms of vorticity, stream function, axial velocity com ponent and energy equations was written based on a finite volume method. Based on the numerical results, the flow and temperature field were given, and the effects of Dean and Prandtl numbers on flow and heat transfer were ex amined, and the correlations of flow resistance and mean Nusselt number were developed for the jacket. The results show that the structure of secondary flow is steady two vortices in the investigated range of dimensionless curvatureratio and Reynolds number. Two peaks of local Nusselt number increase significantly with Prandtl and Dean num ber increasing, but the local Nusselt numbers near two ends and at the center of the heated wall increase only slightly. The center and two ends of heated wall are the poor positions for heat transfer in the jacket. Compared with the outer half coil jacket at the same area of heated wall, curvature radius, Reynolds number and Prandtl number, e jacket of triangular flow chmnel has lower flow resistance and less mean Nusselt number.
基金Supported by the National Natural Science Foundation of China(No.51105009)the National Science and Technology Support Program(No.2012BAF13B05)
文摘In order to research how the size of the ink flow channel is affected by the interaction of adjacent ink areas,according to the method of fluid-solid interaction,this paper analyzes the size of the ink flow channel of two ink rollers' rotation.Firstly,this paper simulates the situation of only one ink area.Secondly,this paper simulates the situation of five adjacent ink areas.Then,through comparing the simulation results of two above situations,it' s obvious that the interaction of adjacent ink areas has big effects on the ink pressure and the size of ink flow channel.At last,this paper gets the main factor that affects the size of ink flow channel in the different situations.
文摘Through experimental analysis of the liquid flows in a flow channel instrument, prompt evaluation of the physically defined viscosity of non-Newtonian liquid foods was investigated for development into a structurally simple and easy-to-use viscometer. For Newtonian and non-Newtonian test liquids, a relation between the friction coefficient and Reynolds number, which was dimensionless as derived from an expression of analysis as a gravity current, indicated a condition under which the flow in the instrument was laminar and under which an average shear rate was on the order of less than 1 s~. Prediction organized based on this empirical relation reproduced practically the flow curve determined for the liquid foods using a rotor type viscometer. Utilization of the channel instrument as a viscometer was formulated in terms of physical meanings of measurements such as the flow length and elapsed time.
文摘Based on well test interpretation,production performance analysis,overburden permeability and porosity test,gas-water core flooding test and high-pressure mercury injection,a quantitative correlation has been built of in-situ effective permeability with routine permeability and water saturation,and the ranges of Main Flow Channel Index(MFCI)are determined for different permeability levels in porous sand gas reservoirs.A new method to evaluate the in-situ effective permeability of porous sand reservoir and a correlation chart of reserves producing degree and main flow channel index are established.The results reveal that the main flow channel index of porous sand gas reservoirs has close correlation with routine matrix permeability and water saturation.The lower the routine matrix permeability and the higher the water saturation,the lower the MFCI is.If the routine matrix permeability is greater than 5.0×10-3,the MFCI is generally greater than 0.5.When the routine matrix permeability is from 1.0×10-3 to 5.0×10-3,the MFCI is mainly between 0.2 and 0.5.When the routine matrix permeability is less than 1.0×10-3,the MFCI is less than 0.2.The evaluation method of in-situ effective permeability can be used to evaluate newly discovered or not tested porous sand gas reservoirs quickly and identify whether there is tight sand gas.The correlation chart of reserves producing degree and main flow channel index can provide basis for recoverable reserves evaluation and well infilling,and provide technical support for formulation of reasonable technical policy of gas reservoir.
基金supported by a Grant from the State Key Basic Research Program of China(No.2011CB201204)the Central University Basic Scientific Research Business Expenses(No.2011ZY05)
文摘The permeability of coal ahead of the working face obviously changes dues to changes in abutment pressure.The formation and evolution of gas flow channels within the abutment pressure area was studied by analyzing the fracture extension mechanism and fracture development in different zones of the abutment pressure area.Fracture and damage mechanics theory is used to understand the observations.The following two techniques were used to understand the evolution of gas flow channels:field observation of the characteristic fractures at different positions relative to the working face and fluorescence micrographs of prepared coal samples.Bending tensile fractures develop along an approximately vertical direction that forms a microscopic network of channels in areas of stress concentration.The abutment pressure affects the local stress and,hence,the local gas conduction.The fractures induced by large deformation and plastic flow form macroscopically networked channels in the reduced stress area.Closer to the working face the gas flow channels evolve from microscopic to macroscopic and from isolated to network.Gas permeability continuously increases during this time.This is corroborated by field observations of the displacement of top coal and the gas flow from gas extraction drillings.
文摘To identify the type of main flow channels of complex porous media in oil and gas reservoirs,the"main flow channel index"is defined as the ratio of comprehensive permeability obtained from well test to matrix permeability obtained from core analysis or well logging.Meanwhile,a mathematical model is established based on equivalent flow assumption,the classification method for main flow channels is put forward,and quantitative characterization of main flow channels is realized.The method has been verified by analysis of typical gas reservoirs.The study results show that the"main flow channel index"can quantitatively classify types of flow channels.If the index is less than 3,the matrix pore is the main flow channel;if the index is between 3 and 20,the fracture is the main flow channel and the matrix pore acts as the supplement one;if the index is more than 20,the fracture is the only seepage channel.The dynamic analysis of typical gas reservoirs shows that the"main flow channel index"can be used to identify the type of flow channel in complex porous media,guiding the classified development of gas reservoirs,and avoiding development risk.
基金supported under the program of the top project unveiled by the Inner Mongolia Autonomous Region(Grant No.22JBGS0027).
文摘Reactant gas and liquid water transport phenomena in the flow channels are complex and critical to the performance and durability of polymer electrolyte membrane fuel cells.The polymer membrane needs water at an optimum level for proton conductivity.Water management involves the prevention of dehydration,waterlogging,and the cell’s subsequent performance decline and degradation.This process requires the study and understanding of internal two-phase flows.Different experimental visualization techniques are used to study two-phase flows in polymer electrolyte membrane fuel cells.However,the experiments have limitations in in situ measurements;they are also expensive and time exhaustive.In contrast,numerical modeling is cheaper and faster,providing insights into the complex multiscale processes occurring across the components of the polymer electrolyte membrane fuel cells.This paper introduces the recent design of flow channels.It reviews the numerical modeling techniques adopted for the transport phenomena therein:the two-fluid,multiphase mixture,volume of fluid,lattice Boltzmann,and pressure drop models.Furthermore,this work describes,compares,and analyses the models’approaches and reviews the representative results of some selected aspects.Finally,the paper summarizes the modeling perspectives,emphasizing future directions with some recommendations.
文摘The transient friction in channel mean flows is the sum of two contributions,i.e.,the underlying laminar flow(ULF)and the purely turbulent component(PTC),and the contributions are analyzed separately by theoretical experiments.It is found that,the transient friction may be higher or remarkably lower than that in equal-Reynolds number steady-state flows.The universal time constant for plane-parallel laminar flows is reported,and the role of the time constant in a turbulent mean flow is examined.It is shown that the time constant is related to the turbulence's frozen time.Finally,a study of the logarithmic layer during the transient flow is accomplished,which shows that the logarithmic layer is destroyed.
文摘This study presents a numerical analysis of three-dimensional steady laminar flow in a rectangular channel with a 180-degree sharp turn. The Navier-Stokes equations are solved by using finite difference method for Re = 900. Three-dimensional streamlines and limiting streamlines on wall surface are used to analyze the three-dimensional flow characteristics. Topological theory is applied to limiting streamlines on inner walls of the channel and two-dimensional streamlines at several cross sections. It is also shown that the flow impinges on the end wall of turn and the secondary flow is induced by the curvature in the sharp turn.
基金supported by the Key Research and Development Project of Shandong Province[2019GSF109084]the National Natural Science Foundation of China[51776111]Young Scholars Program of Shandong University[2018WLJH73].
文摘Flow channels with a variable cross-section are important components of piping system and are widely used in variousfields of engineering.Using afinite element method and modal analysis theory,flow-induced noise,mode shapes,and structure-borne noise in such systems are investigated in this study.The results demonstrate that the maximum displacement and equivalent stress are located in the part with variable cross-sectional area.The aver-age excitation force on theflow channel wall increases with theflow velocity.The maximum excitation force occurs in the range of 0–20 Hz,and then it decreases gradually in the range of 20–1000 Hz.Additionally,as theflow velocity rises from 1 to 3 m/s,the overall sound pressure level associated with theflow-induced noise grows from 49.37 to 66.37 dB.Similarly,the overall sound pressure level associated with the structure-borne noise rises from 40.27 to 72.20 dB.When theflow velocity is increased,the increment of the structure-borne noise is higher than that of theflow-induced noise.
基金Financial support provided by the National Natural Science Foundation of China(Grant Nos.11702042 and 91952104)。
文摘Fully connected neural networks(FCNNs)have been developed for the closure of subgrid-scale(SGS)stress and SGS heat flux in large-eddy simulations of compressible turbulent channel flow.The FCNNbased SGS model trained using data with Mach number Ma=3.0 and Reynolds number Re=3000 was applied to situations with different Mach numbers and Reynolds numbers.The input variables of the neural network model were the filtered velocity gradients and temperature gradients at a single spatial grid point.The a priori test showed that the FCNN model had a correlation coefficient larger than 0.91 and a relative error smaller than 0.43,with much better reconstructions of SGS unclosed terms than the dynamic Smagorinsky model(DSM).In a posteriori test,the behavior of the FCNN model was marginally better than that of the DSM in predicting the mean velocity profiles,mean temperature profiles,turbulent intensities,total Reynolds stress,total Reynolds heat flux,and mean SGS flux of kinetic energy,and outperformed the Smagorinsky model.
文摘The interaction between free fast-moving bodies(or particles)and the fluid surrounding them is studied,motivated by applications in different branches of industry,biomedicine,the environment and science such as flying droplets,ice growth,dust,impacts,food grains,sport,complexity and storms.New inviscid-based modelling and results on the behaviour of two interacting bodies inside a channel flow are described.This is followed by discussion of the more-bodies extension with a view to treating arrays of bodies in a rational manner.Significant dependences on initial conditions and on the comparative body masses and moments of inertia are found for the occurrence of body-body impacts as opposed to wall-body impacts and for the associated impact times.
基金The present research is financially supported by the National Natural Science Foundation of China(Grants No.91752203).
文摘In this letter,the effect of slip boundary on the origin of subcritical transition in two-dimensional chan-nel flows is studied numerically and theoretically.It is shown that both the positive and the negative slip lengths will increase the critical Reynolds number of localized wave packet and hence postpone the transition.By applying a variable transformation and expanding the variables about a small slip length,it is illustrated that the slip boundary effect only exists in the second and higher order modulations of the no-slip solution,and hence explains the power law found in simulations,i.e.the relative increment of the critical Reynolds number due to the slip boundary is proportional to the square of the slip length.
文摘The background to this research was a flooding incident that occurred in Bridgend, Co. Donegal, Ireland in August 2017. While several properties were flooded, a flooding case study of a single dwelling house adjacent to the Bridgend River at Riverdale, Bunamayne, Co. Donegal, Ireland is used herein. For this study the flooded site shall be referred to as the “Hegarty property”. A structure in the form of a stone arched culvert is located directly adjacent to the two-storey detached dwelling house on the Hegarty Property. While the culvert is referred to locally as a bridge, within this research the word culvert will be used in connection with the structure. The culvert has a concrete surrounded utility (watermain) crossing at a gradient below the culvert soffit on the upstream face of the structure. The utility obstructed flow through the culvert and contributed to the flooding event. Given the implication of climate change and the increased probability of more extreme flooding events, it was decided to explore the case study to ascertain the factors that contribute to flooding events when utilities are positioned at culvert or bridge structures. This work was completed to assist undergraduate students, researchers, and local authorities in a relatively unknown area of flood causation.
文摘Vegetation of different heights commonly grows in natural rivers, canals and wetlands and affects the biodiversity and morphological process. The role of vegetation has drawn great attention in river ecosystems and environmental management. Due to the complexity of the vegetated flow, most previous research focuses on the effect of uniformed one-layered vegetation on the flow structure and morphological process. However, less attention was paid to the impact of the mixing vegetation of different heights, which is more realistic and often occurs in natural riverine environments. This paper aims to investigate the effect of mixing three-layered vegetation on flow characteristics, particularly the velocity distrbution, via a novel experiment. Experiments were performed in a titling water flume fully covered with vegetation of three heights (10, 15 and 20 cm) arranged in a staggered pattern, which is partially submerged. Velocities at different positions along a half cross-section were measured using a mini propeller velocimeter. Observed results showed that the velocity has a distinct profile directly behind vegetation and behind the vegetation gap. The overall profile has two distinct reflections about ? below or near the top of short vegetation (h): the velocity remains almost constant in the bottom layer ( h) the velocities directly behind the middle after short vegetation increase much faster than those directly behind the short after tall vegetation. The finding in this study would help river riparian and ecosystem management. .
文摘An improved divided channel method has been proposed by modelling a parameter using the function of depth ratio for a multi-stage compound channel. Experimental data suggest that as the flow depth increases over the second stage floodplain, fractional contribution of the main channel and first stage floodplain under bankfull height plays a pivotal role in shear layer and momentum distribution. Therefore, a new mathematical model has been suggested for estimating the stage-discharge relationship for staged channels of more than one floodplain using the 1D technique of overall roughness correction. .
基金supported by the National R&D Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology & Ministry of knowledge Economy (Grant No. 2015M1A7A1A02050613)
文摘This study performs a numerical analysis of three-dimensional liquid metal(LM) magnetohydrodynamic(MHD) flows in a square duct with an FCI in a non-uniform magnetic field. The current study predicts detailed information on flow velocity, Lorentz force, pressure, current and electric potential of MHD duct flows for different Hartmann numbers. Also, the effect of the electric conductivity of FCI on the pressure drop along the main flow direction in a non-uniform magnetic field is examined. The present study investigates the features of LM MHD flows in consideration of the interdependency among the flow variables.
基金Project supported by the National Natural Science Foundation （Grant No 10372090） and the Doctorate Program of Higher Education of China （Grant No 20030335001）.
文摘The orientation and concentration distributions of fibres in laminar and turbulent channel flows are investigated numerically. The obtained results are in good agreement with the experimental data. In the laminar flow regime, more fibres orient to the flow direction as the Reynolds number increases. The shear rate of fluid around a fibre plays an important role in determining the orientation distribution of fibres, while the fibre density and the fibre aspect-ratio have marginal influence on the orientation distribution. In the turbulent regime, the orientation distribution of fibres becomes more homogeneous with the increase of Reynolds number, and the concentration profile is flatter than that in the laminar regime. The fluctuating intensity of fibre velocity in the downstream direction is larger than that in the lateral directions.
基金supported by the National Natural Science Foundation of China (Grants No.50879019,50909036,and 50879020)the Research Fund for the Doctoral Program of Higher Education (Grants No.200802940001 and 200802941028)+3 种基金the Fundamental Research Funds for the Central Universities (Grants No.2010B02214,2009B08014,and 2010B14214)the Natural Science Foundation of Hohai University(Grant No. 2008426411)the Jiangsu "333" Program for High Level Talents (Grant No. 2017-B08038)the National Undergraduate Innovation Training Plan (Grant No.G20101106)
文摘The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.
