The muzzle blast overpressure induces disturbances in the flow field inside the crew compartment(FFICC)of a truck-mounted howitzer during the artillery firing.This overpressure is the primary factor preventing personn...The muzzle blast overpressure induces disturbances in the flow field inside the crew compartment(FFICC)of a truck-mounted howitzer during the artillery firing.This overpressure is the primary factor preventing personnel from firing artillery within the cab.To investigate the overpressure characteristics of the FFICC,a foreign trade equipment model was used as the research object,and a numerical model was established to analyze the propagation of muzzle blast from the muzzle to the interior of the crew compartment under extreme firing condition.For comparative verification,the muzzle blast experiment included overpressure data from both the flow field outside the crew compartment(FFOCC)and the FFICC,as well as the acceleration data of the crew compartment structure(Str-CC).The research findings demonstrate that the overpressure-time curves of the FFICC exhibit multi-peak characteristics,while the pressure wave shows no significant discontinuity.The enclosed nature of the cab hinders the dissipation of pressure wave energy within the FFICC,leading to sustained high-amplitude overpressure.The frameskin structure helps attenuate the impact of muzzle blast on the FFICC.Conversely,local high overpressure caused by the convex or concave features of the cab's exterior significantly amplifies the overpressure amplitude within the FFICC.展开更多
Clarifying the gas ingestion mechanism in the turbine disc cavity of marine gas turbines is crucial for ensuring the normal operation of turbines.However, the ingestion is influenced by factors such as the rotational ...Clarifying the gas ingestion mechanism in the turbine disc cavity of marine gas turbines is crucial for ensuring the normal operation of turbines.However, the ingestion is influenced by factors such as the rotational pumping effect, mainstream pressure asymmetry, rotor–stator interaction,and unsteady flow structures, complicating the flow. To investigate the impact of rotor–stator interaction on ingestion, this paper decouples the model to include only the mainstream. This research employs experiments and numerical simulations to examine the effects of varying the flow coefficient through changes in rotational speed and mainstream flow rate. The main objective is to understand the influence of different rotor–stator interactions on the mainstream pressure field, accompanied by mechanistic explanations. The findings reveal inconsistent effects of the two methods for changing the flow coefficient on the mainstream pressure field. Particularly, the pressure distribution on the vane side primarily depends on the mainstream flow rate, while the pressure on the blade side is influenced by the mainstream flow rate and the attack angle represented by the flow coefficient. A larger angle of attack angle can increase pressure on the blade side, even surpassing the pressure on the vane side. Assessing the degree of mainstream pressure unevenness solely based on the pressure difference on the vane side is insufficient. This research provides a basis for subsequent studies on the influence of coupled real turbine rotor–stator interaction on gas ingestion.展开更多
Artificial intelligence technology is introduced into the simulation of muzzle flow field to improve its simulation efficiency in this paper.A data-physical fusion driven framework is proposed.First,the known flow fie...Artificial intelligence technology is introduced into the simulation of muzzle flow field to improve its simulation efficiency in this paper.A data-physical fusion driven framework is proposed.First,the known flow field data is used to initialize the model parameters,so that the parameters to be trained are close to the optimal value.Then physical prior knowledge is introduced into the training process so that the prediction results not only meet the known flow field information but also meet the physical conservation laws.Through two examples,it is proved that the model under the fusion driven framework can solve the strongly nonlinear flow field problems,and has stronger generalization and expansion.The proposed model is used to solve a muzzle flow field,and the safety clearance behind the barrel side is divided.It is pointed out that the shape of the safety clearance under different launch speeds is roughly the same,and the pressure disturbance in the area within 9.2 m behind the muzzle section exceeds the safety threshold,which is a dangerous area.Comparison with the CFD results shows that the calculation efficiency of the proposed model is greatly improved under the condition of the same calculation accuracy.The proposed model can quickly and accurately simulate the muzzle flow field under various launch conditions.展开更多
Segregated incompressible large eddy simulation and acoustic perturbation equations were used to obtain the flow field and sound field of 1:25 scale trains with three,six and eight coaches in a long tunnel,and the aer...Segregated incompressible large eddy simulation and acoustic perturbation equations were used to obtain the flow field and sound field of 1:25 scale trains with three,six and eight coaches in a long tunnel,and the aerodynamic results were verified by wind tunnel test with the same scale two-coach train model.Time-averaged drag coefficients of the head coach of three trains are similar,but at the tail coach of the multi-group trains it is much larger than that of the three-coach train.The eight-coach train presents the largest increment from the head coach to the tail coach in the standard deviation(STD)of aerodynamic force coefficients:0.0110 for drag coefficient(Cd),0.0198 for lift coefficient(Cl)and 0.0371 for side coef-ficient(Cs).Total sound pressure level at the bottom of multi-group trains presents a significant streamwise increase,which is different from the three-coach train.Tunnel walls affect the acoustic distribution at the bottom,only after the coach number reaches a certain value,and the streamwise increase in the sound pressure fluctuation of multi-group trains is strengthened by coach number.Fourier transform of the turbulent and sound pressures presents that coach number has little influence on the peak frequencies,but increases the sound pressure level values at the tail bogie cavities.Furthermore,different from the turbulent pressure,the first two sound pressure proper orthogonal decomposition(POD)modes in the bogie cavities contain 90%of the total energy,and the spatial distributions indicate that the acoustic distributions in the head and tail bogies are not related to coach number.展开更多
In order to clarify the charging characteristics of suspension droplets in ion flow field under different temperatures and humidity,the effective charging factor used to characterize the charging characteristics of su...In order to clarify the charging characteristics of suspension droplets in ion flow field under different temperatures and humidity,the effective charging factor used to characterize the charging characteristics of suspension droplets is introduced in this paper,and a calculation method of charging factor is proposed based on the upstream finite element method(FEM).Then,the charging factor under different temperatures and humidity is calculated,and the analytic expression of the charging factor considering the influence of temperature and humidity is obtained by fitting the calculation results.The influence of suspension droplets on the ion flow field is analyzed.The results show that the charging factor is small and increases little with the relative humidity when the relative humidity is less than 60%,and the charging factor is large and increases rapidly with the relative humidity when the relative humidity is more than 60%.At the same relative humidity,the charging factor increases linearly with the temperature.The influence of charged suspension droplets on the ion flow field can be ignored when the relative humidity is less than 60%and must be considered under high temperature and humidity.The calculation method and analytic expression of the charging factor proposed in this paper can be used to model of ion flow field considering the influence of temperature and humidity and provide technical support for the construction of HVDC transmission lines across high temperature and humidity.展开更多
Due to the inherent working mode of rotating detonation engine(RDE),the detonation flow field has the characteristics of pressure oscillation and axial kinetic energy loss,which makes it difficult to design nozzle and...Due to the inherent working mode of rotating detonation engine(RDE),the detonation flow field has the characteristics of pressure oscillation and axial kinetic energy loss,which makes it difficult to design nozzle and improve propulsion performance.Therefore,in order to improve the characteristics of detonation flow field,the three-dimensional numerical simulation of annular chamber and hollow chamber is carried out with premixed hydrogen/air as fuel in this paper,and then tries to combine the two chambers to weaken the oscillation characteristics of detonation flow field through the interaction of detonation flow field,which is a new method to regulate the detonation flow field.The results show that there are four states of velocity vectors at the outlet of annular chamber and hollow chamber,which makes RDE be affected by rolling moment and results in the loss of axial kinetic energy.In the external flow field of combined chamber,the phenomenon of cyclic reflection of expansion wave and compression wave on the free boundary is observed,which results in Mach disk structure.Moreover,the pressure monitoring points are set at the external flow field.The pressure signal shows that the high-frequency pressure oscillation at the external flow field of the combined chamber has been greatly weakened.Compared to the annular chamber,the relative standard deviation(RSD) has been reduced from 14.6% to5.6%.The results thus demonstrate that this method is feasible to adjust the pressure oscillation characteristics of the detonation flow field,and is of great significance to promote the potential of RDE and nozzle design.展开更多
Based on incompressible viscous fluid Navier-stokes equation and k-ε 2-equations turbulent model, an investigation on 3D turbulent flow field around four kinds of train models has been made by finite element method. ...Based on incompressible viscous fluid Navier-stokes equation and k-ε 2-equations turbulent model, an investigation on 3D turbulent flow field around four kinds of train models has been made by finite element method. From the calculation, the pressure distribution characters of now field around high-speed trains have been obtained. It is significant for strength design of the high-speed train body, for resisting wind design of the facilities beside the high-speed railways and for determining the aerodynamic force of induced air to the human body near the railways.展开更多
Groins are employed to prevent nearshore areas from erosion and to control the direction of flow. However, the groin structure and its associated flow characteristics are the main causes of local erosion. In this stud...Groins are employed to prevent nearshore areas from erosion and to control the direction of flow. However, the groin structure and its associated flow characteristics are the main causes of local erosion. In this study, we investigate the flow patterns around refractive and right-angle groins. In particular, we analytically compare the flow characteristics around a refractive groin and study the degree of accuracy that can be achieved by using a right-angle groin of various projected lengths. To compare the flow characteristics, we replaced the right-angle groin with an approximation of a refractive groin. This replacement had the least effect on the maximum velocity of flow in the channel. Moreover, we investigated the distribution of the density variables of temperature and salinity, and their effects on the flow characteristics around the right-angle groin. A comparison of the flow analysis results in baroclinic and barotropic conditions reveals that the flow characteristic values are very similar for both the refractive and right-angle groins. The geometry of the groin, i.e., right-angle or refractive, has little effect on the maximum speed to relative average speed. Apart from the angular separation, the arm length of the groin in downstream refractive groins has less effect on other flow characteristics than do upstream refractive groins. We also correlated a number of non-dimensional variables with respect to various flow characteristics and groin geometry. These comparisons indicate that the correlation between the thalweg height and width of the channel and groin arm＇s length to projection length have been approximated using linear and nonlinear formulas regardless of inner velocity in the subcritical flow.展开更多
The characteristics of the flowfields of a synthetic jet actuator are experimentally investigated with the slot-nozzle driven by the piezoelectric membrane. The particle image velocimetry （PIV） and the hot-wire anem...The characteristics of the flowfields of a synthetic jet actuator are experimentally investigated with the slot-nozzle driven by the piezoelectric membrane. The particle image velocimetry （PIV） and the hot-wire anemometer are utilized to measure the flowfields and the velocity profiles of the actuator with different actuating factors. Analytical results show that pairs of counter-rotating vortices are generated near the nozzle. With the development of the synthetic ject, the synthetic jet rapidly spreads in the slot-width direction; while in the slot-length direction, it contracts firstly and slowly spreads. The centerline velocity distribution has a up-down tendency varying with axial distances, and accelerates to its maximum at z/b= 10. The transverse velocity profile across the slot-width is centro-symmetric and self-similar. However, the velocity profiles across the slot-length are saddle-like near the nozzle. It shows that there are two resonance frequencies for the actuator. If the actuator works with the resonance frequency, the vorticity and the velocity of the synthetic jet are higher than those of other frequencies. Compared with the continuous jet, the synthetic jet shows special flow characteristics.展开更多
The utilization and storage of CO_(2) emissions from oil production and consumption in the upstream oil industry will contribute to sustainable development.CO_(2) flooding is the key technology for the upstream oil in...The utilization and storage of CO_(2) emissions from oil production and consumption in the upstream oil industry will contribute to sustainable development.CO_(2) flooding is the key technology for the upstream oil industry to transition to sustainable development.However,there is a significant challenge in achieving high recovery and storage efficiency in unconventional reservoirs,particularly in underde-veloped countries.Numerous studies have indicated that the limited sweep range caused by premature gas channeling of CO_(2) is a crucial bottleneck that hinders the enhancement of recovery,storage efficiency and safety.This review provides a comprehensive summary of the research and technical advancements regarding the front sweep characteristics of CO_(2) during migration.It particularly focuses on the char-acteristics,applicable stages,and research progress of different technologies used for regulating CO_(2) flooding sweep.Finally,based on the current application status and development trends,the review offers insights into the future research direction for these technologies.It is concluded that the front migration characteristics of CO_(2) play a crucial role in determining the macroscopic sweep range.The focus of future research lies in achieving cross-scale correlation and information coupling of CO_(2) migration processes.Currently,the influence weight of permeability,injection speed,pressure and other parameters on the characteristics of‘fingering-gas channeling’is still not well clear.There is an urgent need to establish prediction model and early warning mechanism that considers multi-parameters and cross-scale gas channeling degrees,in order to create effective strategies for prevention and control.There are currently three technologies available for sweep regulation:flow field intervention,mobility reduction,and gas channeling plugging.To expand the sweep effectively,it is important to systematically integrate these technologies based on their regulation characteristics and applicable stages.This can be achieved by constructing an intelligent synergistic hierarchical segmented regulation technology known as‘flow field intervention+mobility regulation+channel plugging chemically’.This work is expected to provide valuable insights for achieving conformance control of CO_(2)-EOR and safe storage of CO_(2).展开更多
Based on recent advancements in shale oil exploration within the Ordos Basin,this study presents a comprehensive investigation of the paleoenvironment,lithofacies assemblages and distribution,depositional mechanisms,a...Based on recent advancements in shale oil exploration within the Ordos Basin,this study presents a comprehensive investigation of the paleoenvironment,lithofacies assemblages and distribution,depositional mechanisms,and reservoir characteristics of shale oil of fine-grained sediment deposition in continental freshwater lacustrine basins,with a focus on the Chang 7_(3) sub-member of Triassic Yanchang Formation.The research integrates a variety of exploration data,including field outcrops,drilling,logging,core samples,geochemical analyses,and flume simulation.The study indicates that:(1)The paleoenvironment of the Chang 7_(3) deposition is characterized by a warm and humid climate,frequent monsoon events,and a large water depth of freshwater lacustrine basin.The paleogeomorphology exhibits an asymmetrical pattern,with steep slopes in the southwest and gentle slopes in the northeast,which can be subdivided into microgeomorphological units,including depressions and ridges in lakebed,as well as ancient channels.(2)The Chang 7_(3) sub-member is characterized by a diverse array of fine-grained sediments,including very fine sandstone,siltstone,mudstone and tuff.These sediments are primarily distributed in thin interbedded and laminated arrangements vertically.The overall grain size of the sandstone predominantly falls below 62.5μm,with individual layer thicknesses of 0.05–0.64 m.The deposits contain intact plant fragments and display various sedimentary structure,such as wavy bedding,inverse-to-normal grading sequence,and climbing ripple bedding,which indicating a depositional origin associated with density flows.(3)Flume simulation experiments have successfully replicated the transport processes and sedimentary characteristics associated with density flows.The initial phase is characterized by a density-velocity differential,resulting in a thicker,coarser sediment layer at the flow front,while the upper layers are thinner and finer in grain size.During the mid-phase,sliding water effects cause the fluid front to rise and facilitate rapid forward transport.This process generates multiple“new fronts”,enabling the long-distance transport of fine-grained sandstones,such as siltstone and argillaceous siltstone,into the center of the lake basin.(4)A sedimentary model primarily controlled by hyperpynal flows was established for the southwestern part of the basin,highlighting that the frequent occurrence of flood events and the steep slope topography in this area are primary controlling factors for the development of hyperpynal flows.(5)Sandstone and mudstone in the Chang 7_(3) sub-member exhibit micro-and nano-scale pore-throat systems,shale oil is present in various lithologies,while the content of movable oil varies considerably,with sandstone exhibiting the highest content of movable oil.(6)The fine-grained sediment complexes formed by multiple episodes of sandstones and mudstones associated with density flow in the Chang 7_(3) formation exhibit characteristics of“overall oil-bearing with differential storage capacity”.The combination of mudstone with low total organic carbon content(TOC)and siltstone is identified as the most favorable exploration target at present.展开更多
The relativistic mean-field approach was implemented in the Lanzhou quantum molecular dynamics transport model(LQMD.RMF). Using the LQMD.RMF, the properties of collective flow and pion production were investigated sys...The relativistic mean-field approach was implemented in the Lanzhou quantum molecular dynamics transport model(LQMD.RMF). Using the LQMD.RMF, the properties of collective flow and pion production were investigated systematically for nuclear reactions with various isospin asymmetries. The directed and elliptic flows of the LQMD.RMF are able to describe the experimental data of STAR Collaboration. The directed flow difference between free neutrons and protons was associated with the stiffness of the symmetry energy, that is, a softer symmetry energy led to a larger flow difference. For various collision energies, the ratio between the π^(-) and π^(+) yields increased with a decrease in the slope parameter of the symmetry energy. When the collision energy was 270 MeV/nucleon, the single ratio of the pion transverse momentum spectra also increased with decreasing slope parameter of the symmetry energy in both nearly symmetric and neutron-rich systems.However, it is difficult to constrain the stiffness of the symmetry energy with the double ratio because of the lack of threshold energy correction on the pion production.展开更多
A centrifugal fan with the high speed and compact dimensions is studied numerically and experimentally. The centrifugal fan consists of a shrouded impeller rotating at 34 000 r/min with a small tip clearance 0.7 mm to...A centrifugal fan with the high speed and compact dimensions is studied numerically and experimentally. The centrifugal fan consists of a shrouded impeller rotating at 34 000 r/min with a small tip clearance 0.7 mm to the fixed outer casing. Computational models with/without the tip clearance are built and the κ-ω shear stress transport （SST） turbulence model and the unstructured mesh are applied to the numerical simulation for unsteady solutions. The overall performance is measured on a standard experimental bench and the major flow feature of each component inside the centrifugal fan is numerically investigated. In the presence of the tip clearance due to the difference of static pressure between leading and trailing edges of the clearance, i. e. , leading and trailing edges of the impeller, a strong return flow exists inside the clearance passage and re-circulates the main stream inside the impeller passage, and produces the strong flow interaction, thus changing the flow field and influencing the overall performance.展开更多
The present study examines the results of the researches related to the gob bulking factor carried out at home and abroad.A mathematical function of a three-dimensional gob bulking factor is described based on a three...The present study examines the results of the researches related to the gob bulking factor carried out at home and abroad.A mathematical function of a three-dimensional gob bulking factor is described based on a three-dimensional gob model.The method of taking value for interstice and permeability ratios is also proposed.The law of air leakage of fully mechanized top coal is researched in this study.The results show that the speed of air flow near the upper and lower crossheadings is higher than that in the central section of the gob at the same distance from the working face.When the amount of air at the working face exceeds a critical amount,the width of the spontaneous combustion zone in the upper and lower crossheadings is also larger than that in the central section.In this situation,the key is preventing the coal left in the upper and lower crossheadings from self-igniting.Reducing the amount of air at the working face can decrease the width of the spontaneous combustion zone,especially the width near the upper and lower crossheadings.This also moves the spontaneous combustion zone in the direction of the working face.It can prevent the coal in the gob from self-igniting by making the coal left in the crossheadings to be inert and by effectively controlling the amount of air at the working face.展开更多
During the electromagnetic railgun launching process,there will be a complex flow field with high temperature in the muzzle area because of the high-speed friction,transition and seco ndary arc-ignition.This paper mod...During the electromagnetic railgun launching process,there will be a complex flow field with high temperature in the muzzle area because of the high-speed friction,transition and seco ndary arc-ignition.This paper models the muzzle area of railgun when the projectile is far away from the muzzle,and the dynamic simulation of the flow field with secondary arc in the muzzle area is carried out based on the magneto hydrodynamic equations.Meanwhile,a multi-component plasma transport model is used to analyze the muzzle arc plasma flow process of the mixed gas of Al vapor and the air.Furthermore,the pressure boundary conditions are fitted by the dynamic mesh simulation results.The current and voltage of the muzzle are obtained through the emission experiment of the railgun experimental prototype.We load the current data into the simulation model and the voltage of experiments and simulations are compared,which proves the accuracy of the simulation.Then the plasma temperature and the composition of Al vapor in the muzzle flow process are analyzed in-depth.展开更多
Rivers are classified into two types.One is the outer river which flows into ocean and the other is the inner river which does not flow into the ocean but into desert or lake.The inner rivers are the erosive rivers th...Rivers are classified into two types.One is the outer river which flows into ocean and the other is the inner river which does not flow into the ocean but into desert or lake.The inner rivers are the erosive rivers that have been seldom studied so far.Based on the field survey data,the analysis on the characteristics of the flow and sediment in the inner rivers' broad-shallow shifting (IRBS) reach.The IRBS reach often bears such the properties as:high gradient bed,usually 10‰or greater;small flow dischar...展开更多
Rotating packing bed(RPB) has a better mixing performance than traditional mixers and shows potential application in the petroleum industry. However, acquisition of information about the mixing process directly throug...Rotating packing bed(RPB) has a better mixing performance than traditional mixers and shows potential application in the petroleum industry. However, acquisition of information about the mixing process directly through experiments is difficult because of the compact structure and complex multiphase flow pattern in RPB. To study the mixing characteristic, Fluent, the computational fluid dynamics(CFD) software, was used to explore the effect of airflow field on droplet diameter. For conducting calculations, the gas-liquid two-phase flow inside the packing was simulated with the RNG k-ε turbulence model and the Lagrange Discrete Phase Model(DPM), respectively. The numerical calculation results showed that coalescence and breakup of droplets can take place in the gas phase flow inside the packing and can be strengthened with increased rotating speed, thereby leading to the enlargement of the average diameter.展开更多
An experimental system based on the background-oriented schlieren（BOS） technique is built to reconstruct the density and temperature distribution of a flame-induced distorted flow field which has a density gradient....An experimental system based on the background-oriented schlieren（BOS） technique is built to reconstruct the density and temperature distribution of a flame-induced distorted flow field which has a density gradient. The cross-correlation algorithm with sub-pixel accuracy is introduced and used to calculate the background-element displacement of a disturbed image and a fourth-order difference scheme is also developed to solve the Poisson equation. An experiment for a disturbed flow field caused by a burning candle is performed to validate the built BOS system and the results indicate that density and temperature distribution of the disturbed flow field can be reconstructed accurately. A notable conclusion is that in order to make the reconstructed results have a satisfactory accuracy, the inquiry step length should be less than the size of the interrogation window.展开更多
Laboratory experiments have been conducted to study the flow field in a cyclone static micro-bubble flotation column. The method of Particle Image Velocimetry (PIV) was used. The flow field velocity distribution in bo...Laboratory experiments have been conducted to study the flow field in a cyclone static micro-bubble flotation column. The method of Particle Image Velocimetry (PIV) was used. The flow field velocity distribution in both cross section and longitudinal section within cyclonic zone was studied for different circulating volumes. The cross sectional vortex was also analyzed. The results show that in cross section as the circulating volume increases from 0.187 to 0.350 m 3 /h, the flow velocity ranges from 0 to 0.68 m/s. The flow field is mainly a non-vortex potential flow that forms a free vortex without outside energy input. In the cyclonic region the vortex deviates from the center of the flotation column because a single tangential opening introduces circulating fluid into the column. The tangential component of the velocity plays a defining role in the cross section. In the longitudinal section the velocity ranges from 0 to 0.08 m/s. The flow velocity increases as does the circulating volume. Advantageous mineral separation conditions arise from the combined effects of cyclonic flow in cross and longitudinal section.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.U2341269)。
文摘The muzzle blast overpressure induces disturbances in the flow field inside the crew compartment(FFICC)of a truck-mounted howitzer during the artillery firing.This overpressure is the primary factor preventing personnel from firing artillery within the cab.To investigate the overpressure characteristics of the FFICC,a foreign trade equipment model was used as the research object,and a numerical model was established to analyze the propagation of muzzle blast from the muzzle to the interior of the crew compartment under extreme firing condition.For comparative verification,the muzzle blast experiment included overpressure data from both the flow field outside the crew compartment(FFOCC)and the FFICC,as well as the acceleration data of the crew compartment structure(Str-CC).The research findings demonstrate that the overpressure-time curves of the FFICC exhibit multi-peak characteristics,while the pressure wave shows no significant discontinuity.The enclosed nature of the cab hinders the dissipation of pressure wave energy within the FFICC,leading to sustained high-amplitude overpressure.The frameskin structure helps attenuate the impact of muzzle blast on the FFICC.Conversely,local high overpressure caused by the convex or concave features of the cab's exterior significantly amplifies the overpressure amplitude within the FFICC.
基金the National Natural Science Foundation Outstanding Youth Foundation (Grant No.52122603)the National Science and Technology Major Project (J2019-Ⅲ-0003–0046)。
文摘Clarifying the gas ingestion mechanism in the turbine disc cavity of marine gas turbines is crucial for ensuring the normal operation of turbines.However, the ingestion is influenced by factors such as the rotational pumping effect, mainstream pressure asymmetry, rotor–stator interaction,and unsteady flow structures, complicating the flow. To investigate the impact of rotor–stator interaction on ingestion, this paper decouples the model to include only the mainstream. This research employs experiments and numerical simulations to examine the effects of varying the flow coefficient through changes in rotational speed and mainstream flow rate. The main objective is to understand the influence of different rotor–stator interactions on the mainstream pressure field, accompanied by mechanistic explanations. The findings reveal inconsistent effects of the two methods for changing the flow coefficient on the mainstream pressure field. Particularly, the pressure distribution on the vane side primarily depends on the mainstream flow rate, while the pressure on the blade side is influenced by the mainstream flow rate and the attack angle represented by the flow coefficient. A larger angle of attack angle can increase pressure on the blade side, even surpassing the pressure on the vane side. Assessing the degree of mainstream pressure unevenness solely based on the pressure difference on the vane side is insufficient. This research provides a basis for subsequent studies on the influence of coupled real turbine rotor–stator interaction on gas ingestion.
基金Supported by the Natural Science Foundation of Jiangsu Province of China(Grant No.BK20210347)Supported by the National Natural Science Foundation of China(Grant No.U2141246).
文摘Artificial intelligence technology is introduced into the simulation of muzzle flow field to improve its simulation efficiency in this paper.A data-physical fusion driven framework is proposed.First,the known flow field data is used to initialize the model parameters,so that the parameters to be trained are close to the optimal value.Then physical prior knowledge is introduced into the training process so that the prediction results not only meet the known flow field information but also meet the physical conservation laws.Through two examples,it is proved that the model under the fusion driven framework can solve the strongly nonlinear flow field problems,and has stronger generalization and expansion.The proposed model is used to solve a muzzle flow field,and the safety clearance behind the barrel side is divided.It is pointed out that the shape of the safety clearance under different launch speeds is roughly the same,and the pressure disturbance in the area within 9.2 m behind the muzzle section exceeds the safety threshold,which is a dangerous area.Comparison with the CFD results shows that the calculation efficiency of the proposed model is greatly improved under the condition of the same calculation accuracy.The proposed model can quickly and accurately simulate the muzzle flow field under various launch conditions.
基金supported by the National Natural Science Foundation of China (Grant No. 52072267)Shanghai Key Lab of Vehicle Aerodynamics and Vehicle Thermal Management Systems (Grant No. 23DZ2229029)
文摘Segregated incompressible large eddy simulation and acoustic perturbation equations were used to obtain the flow field and sound field of 1:25 scale trains with three,six and eight coaches in a long tunnel,and the aerodynamic results were verified by wind tunnel test with the same scale two-coach train model.Time-averaged drag coefficients of the head coach of three trains are similar,but at the tail coach of the multi-group trains it is much larger than that of the three-coach train.The eight-coach train presents the largest increment from the head coach to the tail coach in the standard deviation(STD)of aerodynamic force coefficients:0.0110 for drag coefficient(Cd),0.0198 for lift coefficient(Cl)and 0.0371 for side coef-ficient(Cs).Total sound pressure level at the bottom of multi-group trains presents a significant streamwise increase,which is different from the three-coach train.Tunnel walls affect the acoustic distribution at the bottom,only after the coach number reaches a certain value,and the streamwise increase in the sound pressure fluctuation of multi-group trains is strengthened by coach number.Fourier transform of the turbulent and sound pressures presents that coach number has little influence on the peak frequencies,but increases the sound pressure level values at the tail bogie cavities.Furthermore,different from the turbulent pressure,the first two sound pressure proper orthogonal decomposition(POD)modes in the bogie cavities contain 90%of the total energy,and the spatial distributions indicate that the acoustic distributions in the head and tail bogies are not related to coach number.
基金supported by National Natural Science Foundation of China(No.52077074)。
文摘In order to clarify the charging characteristics of suspension droplets in ion flow field under different temperatures and humidity,the effective charging factor used to characterize the charging characteristics of suspension droplets is introduced in this paper,and a calculation method of charging factor is proposed based on the upstream finite element method(FEM).Then,the charging factor under different temperatures and humidity is calculated,and the analytic expression of the charging factor considering the influence of temperature and humidity is obtained by fitting the calculation results.The influence of suspension droplets on the ion flow field is analyzed.The results show that the charging factor is small and increases little with the relative humidity when the relative humidity is less than 60%,and the charging factor is large and increases rapidly with the relative humidity when the relative humidity is more than 60%.At the same relative humidity,the charging factor increases linearly with the temperature.The influence of charged suspension droplets on the ion flow field can be ignored when the relative humidity is less than 60%and must be considered under high temperature and humidity.The calculation method and analytic expression of the charging factor proposed in this paper can be used to model of ion flow field considering the influence of temperature and humidity and provide technical support for the construction of HVDC transmission lines across high temperature and humidity.
文摘Due to the inherent working mode of rotating detonation engine(RDE),the detonation flow field has the characteristics of pressure oscillation and axial kinetic energy loss,which makes it difficult to design nozzle and improve propulsion performance.Therefore,in order to improve the characteristics of detonation flow field,the three-dimensional numerical simulation of annular chamber and hollow chamber is carried out with premixed hydrogen/air as fuel in this paper,and then tries to combine the two chambers to weaken the oscillation characteristics of detonation flow field through the interaction of detonation flow field,which is a new method to regulate the detonation flow field.The results show that there are four states of velocity vectors at the outlet of annular chamber and hollow chamber,which makes RDE be affected by rolling moment and results in the loss of axial kinetic energy.In the external flow field of combined chamber,the phenomenon of cyclic reflection of expansion wave and compression wave on the free boundary is observed,which results in Mach disk structure.Moreover,the pressure monitoring points are set at the external flow field.The pressure signal shows that the high-frequency pressure oscillation at the external flow field of the combined chamber has been greatly weakened.Compared to the annular chamber,the relative standard deviation(RSD) has been reduced from 14.6% to5.6%.The results thus demonstrate that this method is feasible to adjust the pressure oscillation characteristics of the detonation flow field,and is of great significance to promote the potential of RDE and nozzle design.
文摘Based on incompressible viscous fluid Navier-stokes equation and k-ε 2-equations turbulent model, an investigation on 3D turbulent flow field around four kinds of train models has been made by finite element method. From the calculation, the pressure distribution characters of now field around high-speed trains have been obtained. It is significant for strength design of the high-speed train body, for resisting wind design of the facilities beside the high-speed railways and for determining the aerodynamic force of induced air to the human body near the railways.
文摘Groins are employed to prevent nearshore areas from erosion and to control the direction of flow. However, the groin structure and its associated flow characteristics are the main causes of local erosion. In this study, we investigate the flow patterns around refractive and right-angle groins. In particular, we analytically compare the flow characteristics around a refractive groin and study the degree of accuracy that can be achieved by using a right-angle groin of various projected lengths. To compare the flow characteristics, we replaced the right-angle groin with an approximation of a refractive groin. This replacement had the least effect on the maximum velocity of flow in the channel. Moreover, we investigated the distribution of the density variables of temperature and salinity, and their effects on the flow characteristics around the right-angle groin. A comparison of the flow analysis results in baroclinic and barotropic conditions reveals that the flow characteristic values are very similar for both the refractive and right-angle groins. The geometry of the groin, i.e., right-angle or refractive, has little effect on the maximum speed to relative average speed. Apart from the angular separation, the arm length of the groin in downstream refractive groins has less effect on other flow characteristics than do upstream refractive groins. We also correlated a number of non-dimensional variables with respect to various flow characteristics and groin geometry. These comparisons indicate that the correlation between the thalweg height and width of the channel and groin arm＇s length to projection length have been approximated using linear and nonlinear formulas regardless of inner velocity in the subcritical flow.
文摘The characteristics of the flowfields of a synthetic jet actuator are experimentally investigated with the slot-nozzle driven by the piezoelectric membrane. The particle image velocimetry （PIV） and the hot-wire anemometer are utilized to measure the flowfields and the velocity profiles of the actuator with different actuating factors. Analytical results show that pairs of counter-rotating vortices are generated near the nozzle. With the development of the synthetic ject, the synthetic jet rapidly spreads in the slot-width direction; while in the slot-length direction, it contracts firstly and slowly spreads. The centerline velocity distribution has a up-down tendency varying with axial distances, and accelerates to its maximum at z/b= 10. The transverse velocity profile across the slot-width is centro-symmetric and self-similar. However, the velocity profiles across the slot-length are saddle-like near the nozzle. It shows that there are two resonance frequencies for the actuator. If the actuator works with the resonance frequency, the vorticity and the velocity of the synthetic jet are higher than those of other frequencies. Compared with the continuous jet, the synthetic jet shows special flow characteristics.
基金National Key Research and Development Program of China(No.2023YFB4104204)National Natural Science Foundation of China(No.U23B2090).
文摘The utilization and storage of CO_(2) emissions from oil production and consumption in the upstream oil industry will contribute to sustainable development.CO_(2) flooding is the key technology for the upstream oil industry to transition to sustainable development.However,there is a significant challenge in achieving high recovery and storage efficiency in unconventional reservoirs,particularly in underde-veloped countries.Numerous studies have indicated that the limited sweep range caused by premature gas channeling of CO_(2) is a crucial bottleneck that hinders the enhancement of recovery,storage efficiency and safety.This review provides a comprehensive summary of the research and technical advancements regarding the front sweep characteristics of CO_(2) during migration.It particularly focuses on the char-acteristics,applicable stages,and research progress of different technologies used for regulating CO_(2) flooding sweep.Finally,based on the current application status and development trends,the review offers insights into the future research direction for these technologies.It is concluded that the front migration characteristics of CO_(2) play a crucial role in determining the macroscopic sweep range.The focus of future research lies in achieving cross-scale correlation and information coupling of CO_(2) migration processes.Currently,the influence weight of permeability,injection speed,pressure and other parameters on the characteristics of‘fingering-gas channeling’is still not well clear.There is an urgent need to establish prediction model and early warning mechanism that considers multi-parameters and cross-scale gas channeling degrees,in order to create effective strategies for prevention and control.There are currently three technologies available for sweep regulation:flow field intervention,mobility reduction,and gas channeling plugging.To expand the sweep effectively,it is important to systematically integrate these technologies based on their regulation characteristics and applicable stages.This can be achieved by constructing an intelligent synergistic hierarchical segmented regulation technology known as‘flow field intervention+mobility regulation+channel plugging chemically’.This work is expected to provide valuable insights for achieving conformance control of CO_(2)-EOR and safe storage of CO_(2).
基金Supported by the CNPC Major Science and Technology Project(2021DJ1806).
文摘Based on recent advancements in shale oil exploration within the Ordos Basin,this study presents a comprehensive investigation of the paleoenvironment,lithofacies assemblages and distribution,depositional mechanisms,and reservoir characteristics of shale oil of fine-grained sediment deposition in continental freshwater lacustrine basins,with a focus on the Chang 7_(3) sub-member of Triassic Yanchang Formation.The research integrates a variety of exploration data,including field outcrops,drilling,logging,core samples,geochemical analyses,and flume simulation.The study indicates that:(1)The paleoenvironment of the Chang 7_(3) deposition is characterized by a warm and humid climate,frequent monsoon events,and a large water depth of freshwater lacustrine basin.The paleogeomorphology exhibits an asymmetrical pattern,with steep slopes in the southwest and gentle slopes in the northeast,which can be subdivided into microgeomorphological units,including depressions and ridges in lakebed,as well as ancient channels.(2)The Chang 7_(3) sub-member is characterized by a diverse array of fine-grained sediments,including very fine sandstone,siltstone,mudstone and tuff.These sediments are primarily distributed in thin interbedded and laminated arrangements vertically.The overall grain size of the sandstone predominantly falls below 62.5μm,with individual layer thicknesses of 0.05–0.64 m.The deposits contain intact plant fragments and display various sedimentary structure,such as wavy bedding,inverse-to-normal grading sequence,and climbing ripple bedding,which indicating a depositional origin associated with density flows.(3)Flume simulation experiments have successfully replicated the transport processes and sedimentary characteristics associated with density flows.The initial phase is characterized by a density-velocity differential,resulting in a thicker,coarser sediment layer at the flow front,while the upper layers are thinner and finer in grain size.During the mid-phase,sliding water effects cause the fluid front to rise and facilitate rapid forward transport.This process generates multiple“new fronts”,enabling the long-distance transport of fine-grained sandstones,such as siltstone and argillaceous siltstone,into the center of the lake basin.(4)A sedimentary model primarily controlled by hyperpynal flows was established for the southwestern part of the basin,highlighting that the frequent occurrence of flood events and the steep slope topography in this area are primary controlling factors for the development of hyperpynal flows.(5)Sandstone and mudstone in the Chang 7_(3) sub-member exhibit micro-and nano-scale pore-throat systems,shale oil is present in various lithologies,while the content of movable oil varies considerably,with sandstone exhibiting the highest content of movable oil.(6)The fine-grained sediment complexes formed by multiple episodes of sandstones and mudstones associated with density flow in the Chang 7_(3) formation exhibit characteristics of“overall oil-bearing with differential storage capacity”.The combination of mudstone with low total organic carbon content(TOC)and siltstone is identified as the most favorable exploration target at present.
基金This study was supported by the National Natural Science Foundation ofChina(Nos.12147106,12175072,and 11722546)the Talent Programof South China University of Technology(No.20210115).
文摘The relativistic mean-field approach was implemented in the Lanzhou quantum molecular dynamics transport model(LQMD.RMF). Using the LQMD.RMF, the properties of collective flow and pion production were investigated systematically for nuclear reactions with various isospin asymmetries. The directed and elliptic flows of the LQMD.RMF are able to describe the experimental data of STAR Collaboration. The directed flow difference between free neutrons and protons was associated with the stiffness of the symmetry energy, that is, a softer symmetry energy led to a larger flow difference. For various collision energies, the ratio between the π^(-) and π^(+) yields increased with a decrease in the slope parameter of the symmetry energy. When the collision energy was 270 MeV/nucleon, the single ratio of the pion transverse momentum spectra also increased with decreasing slope parameter of the symmetry energy in both nearly symmetric and neutron-rich systems.However, it is difficult to constrain the stiffness of the symmetry energy with the double ratio because of the lack of threshold energy correction on the pion production.
文摘A centrifugal fan with the high speed and compact dimensions is studied numerically and experimentally. The centrifugal fan consists of a shrouded impeller rotating at 34 000 r/min with a small tip clearance 0.7 mm to the fixed outer casing. Computational models with/without the tip clearance are built and the κ-ω shear stress transport （SST） turbulence model and the unstructured mesh are applied to the numerical simulation for unsteady solutions. The overall performance is measured on a standard experimental bench and the major flow feature of each component inside the centrifugal fan is numerically investigated. In the presence of the tip clearance due to the difference of static pressure between leading and trailing edges of the clearance, i. e. , leading and trailing edges of the impeller, a strong return flow exists inside the clearance passage and re-circulates the main stream inside the impeller passage, and produces the strong flow interaction, thus changing the flow field and influencing the overall performance.
基金Financial support for this work was obtained from the National Natural Science Foundation of China(No.51074059)
文摘The present study examines the results of the researches related to the gob bulking factor carried out at home and abroad.A mathematical function of a three-dimensional gob bulking factor is described based on a three-dimensional gob model.The method of taking value for interstice and permeability ratios is also proposed.The law of air leakage of fully mechanized top coal is researched in this study.The results show that the speed of air flow near the upper and lower crossheadings is higher than that in the central section of the gob at the same distance from the working face.When the amount of air at the working face exceeds a critical amount,the width of the spontaneous combustion zone in the upper and lower crossheadings is also larger than that in the central section.In this situation,the key is preventing the coal left in the upper and lower crossheadings from self-igniting.Reducing the amount of air at the working face can decrease the width of the spontaneous combustion zone,especially the width near the upper and lower crossheadings.This also moves the spontaneous combustion zone in the direction of the working face.It can prevent the coal in the gob from self-igniting by making the coal left in the crossheadings to be inert and by effectively controlling the amount of air at the working face.
文摘During the electromagnetic railgun launching process,there will be a complex flow field with high temperature in the muzzle area because of the high-speed friction,transition and seco ndary arc-ignition.This paper models the muzzle area of railgun when the projectile is far away from the muzzle,and the dynamic simulation of the flow field with secondary arc in the muzzle area is carried out based on the magneto hydrodynamic equations.Meanwhile,a multi-component plasma transport model is used to analyze the muzzle arc plasma flow process of the mixed gas of Al vapor and the air.Furthermore,the pressure boundary conditions are fitted by the dynamic mesh simulation results.The current and voltage of the muzzle are obtained through the emission experiment of the railgun experimental prototype.We load the current data into the simulation model and the voltage of experiments and simulations are compared,which proves the accuracy of the simulation.Then the plasma temperature and the composition of Al vapor in the muzzle flow process are analyzed in-depth.
文摘Rivers are classified into two types.One is the outer river which flows into ocean and the other is the inner river which does not flow into the ocean but into desert or lake.The inner rivers are the erosive rivers that have been seldom studied so far.Based on the field survey data,the analysis on the characteristics of the flow and sediment in the inner rivers' broad-shallow shifting (IRBS) reach.The IRBS reach often bears such the properties as:high gradient bed,usually 10‰or greater;small flow dischar...
基金financially supported by the Natural Science Foundations of China(No.21206153,21376229)the Excellent Youth Science and Technology Foundation of Province Shanxi of China(No.2014021007)+1 种基金the Natural Science Foundation of Shanxi Province(Grant No.2011021012,2012011008-2)the Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi(201316)
文摘Rotating packing bed(RPB) has a better mixing performance than traditional mixers and shows potential application in the petroleum industry. However, acquisition of information about the mixing process directly through experiments is difficult because of the compact structure and complex multiphase flow pattern in RPB. To study the mixing characteristic, Fluent, the computational fluid dynamics(CFD) software, was used to explore the effect of airflow field on droplet diameter. For conducting calculations, the gas-liquid two-phase flow inside the packing was simulated with the RNG k-ε turbulence model and the Lagrange Discrete Phase Model(DPM), respectively. The numerical calculation results showed that coalescence and breakup of droplets can take place in the gas phase flow inside the packing and can be strengthened with increased rotating speed, thereby leading to the enlargement of the average diameter.
基金supported by the Key Program of the National Natural Science Foundation of China(Grant No.NSFC 91441205)
文摘An experimental system based on the background-oriented schlieren（BOS） technique is built to reconstruct the density and temperature distribution of a flame-induced distorted flow field which has a density gradient. The cross-correlation algorithm with sub-pixel accuracy is introduced and used to calculate the background-element displacement of a disturbed image and a fourth-order difference scheme is also developed to solve the Poisson equation. An experiment for a disturbed flow field caused by a burning candle is performed to validate the built BOS system and the results indicate that density and temperature distribution of the disturbed flow field can be reconstructed accurately. A notable conclusion is that in order to make the reconstructed results have a satisfactory accuracy, the inquiry step length should be less than the size of the interrogation window.
基金the State Key Basic Research Program of China (No. 2012CB214905)Key Program of National Natural Science Foundation of China (No. 500834006)the National Natural Science Foundation of China (No. 50974119) for financial support
文摘Laboratory experiments have been conducted to study the flow field in a cyclone static micro-bubble flotation column. The method of Particle Image Velocimetry (PIV) was used. The flow field velocity distribution in both cross section and longitudinal section within cyclonic zone was studied for different circulating volumes. The cross sectional vortex was also analyzed. The results show that in cross section as the circulating volume increases from 0.187 to 0.350 m 3 /h, the flow velocity ranges from 0 to 0.68 m/s. The flow field is mainly a non-vortex potential flow that forms a free vortex without outside energy input. In the cyclonic region the vortex deviates from the center of the flotation column because a single tangential opening introduces circulating fluid into the column. The tangential component of the velocity plays a defining role in the cross section. In the longitudinal section the velocity ranges from 0 to 0.08 m/s. The flow velocity increases as does the circulating volume. Advantageous mineral separation conditions arise from the combined effects of cyclonic flow in cross and longitudinal section.
