Convectively unstable processes caused by dense water subsidence are common occurrences in high-latitude oceanic regions,and significantly modulate mass and heat transport and mixing processes in the ocean.An idealize...Convectively unstable processes caused by dense water subsidence are common occurrences in high-latitude oceanic regions,and significantly modulate mass and heat transport and mixing processes in the ocean.An idealized numerical experiment using the large eddy simulation method was conducted to analyze the three-dimensional flow field structure and the mechanism for dense water subsidence.Specifically,a negative salt flux is set at the sea surface,in which salt flux enters the sea surface to simulate the icing and salting-out phenomena that occur at high latitudes.Results show that the mean-state 3D flow field of dense water subsidence exhibits a hollow conical distribution.The horizontal flow field is characterized by a cyclonic vortex that driven primarily by the pressure gradient and influenced by the Coriolis effect.Moreover,the inverse vertical pressure gradient generated by this vortex inhibits the sinking of the plume,leading to its off-axis deflection and the development of an anticyclonic precession.In addition,the impact of rotation on the structure of a sinking plume within a stratified environment is discussed.Both horizontal vortex intensity and cone angle of the hollow cone flow field are increased with increasing rotation rate,resulting in a decrease in the plume’s maximum sinking depth.Variances in rotation direction cause the horizontal vortex and sinking plumes of dense water in the northern and southern hemispheres to rotate in opposite directions.展开更多
An experimental investigation of three-dimensional flow field in a film-cooled turbine model is carried out by using particle image velocimeter （PIV） in a low-speed wind tunnel. The effects of different blowing rati...An experimental investigation of three-dimensional flow field in a film-cooled turbine model is carried out by using particle image velocimeter （PIV） in a low-speed wind tunnel. The effects of different blowing ratios （M=1.5, 2） on the flow field are studied. The experimental results reveal the classical phenomena of the formation of kidney vortex pair and secondary flow in wake region behind the jet hole. And the changes of the kidney vortex pair and the wake at different locations away from the hole on the suction and pressure sides are also studied. Compared with the flow field in stationary cascade, there are centrifugal force and Coriolis force existing in the flow field of rotating turbine, and these forces bring the radial velocity in the jet flow. The effect of rotatien on the flow field of the pressure side is more distinct than that on the suction side from the measured flow fields in Y-Z plane and radial velocity contours. The increase of blowing ratio makes the kidney vortex pair and the secondary flow in the wake region stronger and makes the range of the wake region enlarged.展开更多
Three-dimensional flow field of turbine in torque converter is simulated by numerical calculation in order to improve the performance of torque converter. Calculation model of a torque converter is presented based on ...Three-dimensional flow field of turbine in torque converter is simulated by numerical calculation in order to improve the performance of torque converter. Calculation model of a torque converter is presented based on the mixing-plane technology. In the calculation of flow field, the 3D N-S equations are separated by finite-volume method and solved by semi-implicit method for pressure-linked equations（SIMPLE）. Based on flow field calculation, the flow field of turbine is simulated. The velocity and pressure in the flow field of turbine are analyzed. The external performance of the torque converter is also calculated. Results of flow simulation show that there are secondary flow, off flow and velocity gradient in turbine passage. The validity of numerical simulation is verified by comparing the results of numerical simulation with experiment data.展开更多
Gaseous detonation propagating in a toroidal chamber was numerically studied for hydrogen/oxygen/nitrogen mixtures. The numerical method used is based on the three-dimensional Euler equations with detailed finiterate ...Gaseous detonation propagating in a toroidal chamber was numerically studied for hydrogen/oxygen/nitrogen mixtures. The numerical method used is based on the three-dimensional Euler equations with detailed finiterate chemistry. The results show that the calculated streak picture is in qualitative agreement with the picture recorded by a high speed streak camera from published literature. The three-dimensional flow field induced by a continuously rotating detonation was visualized and distinctive features of the rotating detonations were clearly depicted. Owing to the unconfined character of detonation wavelet, a deficit of detonation parameters was observed. Due to the effects of wall geometries, the strength of the outside detonation front is stronger than that of the inside portion. The detonation thus propagates with a constant circular velocity. Numerical simulation also shows three-dimensional rotating detonation structures, which display specific feature of the detonation- shock combined wave. Discrete burning gas pockets are formed due to instability of the discontinuity. It is believed that the present study could give an insight into the interest- ing properties of the continuously rotating detonation, and is thus beneficial to the design of continuous detonation propulsion systems.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
This paper presents a three-dimensional flow field simulation of the steady flows through diffusers and nozzles with straight or serrated-sided walls to analyze the effect of the channel structure on the flow characte...This paper presents a three-dimensional flow field simulation of the steady flows through diffusers and nozzles with straight or serrated-sided walls to analyze the effect of the channel structure on the flow characteristics.The pressure and velocity profiles in the diffusers and the nozzles as well as the net volumetric flow rate are determined.Our simulation demonstrates that the pressure and velocity profiles in the serrated diffuser/nozzles are more complicated than those with the straight-sided wall,while the net steady flow rate with the straight-sided wall increases monotonically with the increase of the pressure difference,the steady flow rate with serrated sided walls increases gradually to reach a maximum and then decreases with the increase of the pressure difference.The results suggest that the number of the sawteeth plays a significant role in optimizing the design of serrated diffusers and nozzles for improving the transport efficiency of valveless micro-pumps.展开更多
With an application of topological analysis,in this paper the skin-friction line patterns on compressor and turbine cascade surfaces are depicted and the streamline patterns of the secondary flow fields in the cross-s...With an application of topological analysis,in this paper the skin-friction line patterns on compressor and turbine cascade surfaces are depicted and the streamline patterns of the secondary flow fields in the cross-section of a curved pipe and a turbine cascade are drawn under given conditions.In addition the structures of vortices within three-dimensional viscous flow fields in cascades are analysed.展开更多
The hydrodynamic characteristics of a rigid, single, circular cylinder in a three dimensional, incompressible, uniform cross flow were calculated using the large-eddy simulation method of CFX5. Solutions to the three ...The hydrodynamic characteristics of a rigid, single, circular cylinder in a three dimensional, incompressible, uniform cross flow were calculated using the large-eddy simulation method of CFX5. Solutions to the three dimensional N-S equations were obtained by the finite volume method. The focus of this numerical simulation was to research the characteristics of pressure distribution （drag and litt forces） and vortex tubes at high Reynolds numbers. The results of the calculations showed that the forces at every section in the spanwise direction of the cylinder were symmetrical about the middle section and smaller than the forces calculated in two dimensional cases. Moreover, the flow around the cylinder obviously presents three dimensional characteristics.展开更多
This paper presents a numerical study of the flow topologies of three-dimensional （3D） flows in a high pressure compressor stator blade row without and with boundary layer aspiration on the hub wall. The stator blad...This paper presents a numerical study of the flow topologies of three-dimensional （3D） flows in a high pressure compressor stator blade row without and with boundary layer aspiration on the hub wall. The stator blade is representative of the first stage operating under transonic inlet conditions and the blade design encourages development of highly complex 3D flows. The blade has a small tip clearance. The computational fluid dynamics （CFD） studies show progressive increase of hub corner stall with the increase in incidence. Aspiration is implemented on the hub wall via a slot in the comer between the hub wall and the suction surface. The CFD studies show aspiration to be sensitive to the suction flow rate; lower rate leads to very complex flow struc- tures and increased level of losses whereas higher rate renders aspiration effective for control of hub comer separation. The flow topologies are studied by trace of skin friction lines on the walls. The nature of flow can be explained by the topological rules of closed separation. Furthermore, a deeper analysis is done for a particular case with advanced criterion to test the non-degeneracy of critical points in the flow field.展开更多
Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power- ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the de- tailed...Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power- ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the de- tailed two-phase flow inside the columns. The present paper presents a three-dimensional computational fluid dy- namics （CFD） model to simulate the two-phase flow in a representative unit of the column. The unit consists of an CFD calculations on column packed with Flexipak 1Y were implemented within the volume of fluid （VOF） mathe- matical framework. The CFD model was validated by comparing the calculated thickness of liquid film with the available experimental data. Special attention was given to quantitative analysis of the effects of gravity on the hy- drodynamics. Fluctuations in the liquid mass flow rate and the calculated pressure drop loss were found to be quali- tatively in agreement with the experimental observations.展开更多
The accuracy of the Earth＇s gravitational field measured from the gravity field and steady-state ocean circulation explorer（GOCE）,up to 250 degrees,influenced by the radial gravity gradient V zz and three-dimension...The accuracy of the Earth＇s gravitational field measured from the gravity field and steady-state ocean circulation explorer（GOCE）,up to 250 degrees,influenced by the radial gravity gradient V zz and three-dimensional gravity gradient V ij from the satellite gravity gradiometry（SGG） are contrastively demonstrated based on the analytical error model and numerical simulation,respectively.Firstly,the new analytical error model of the cumulative geoid height,influenced by the radial gravity gradient V zz and three-dimensional gravity gradient V ij are established,respectively.In 250 degrees,the GOCE cumulative geoid height error measured by the radial gravity gradient V zz is about 2 1/2 times higher than that measured by the three-dimensional gravity gradient V ij.Secondly,the Earth＇s gravitational field from GOCE completely up to 250 degrees is recovered using the radial gravity gradient V zz and three-dimensional gravity gradient V ij by numerical simulation,respectively.The study results show that when the measurement error of the gravity gradient is 3×10 12 /s 2,the cumulative geoid height errors using the radial gravity gradient V zz and three-dimensional gravity gradient V ij are 12.319 cm and 9.295 cm at 250 degrees,respectively.The accuracy of the cumulative geoid height using the three-dimensional gravity gradient V ij is improved by 30%-40% on average compared with that using the radial gravity gradient V zz in 250 degrees.Finally,by mutual verification of the analytical error model and numerical simulation,the orders of magnitude from the accuracies of the Earth＇s gravitational field recovery make no substantial differences based on the radial and three-dimensional gravity gradients,respectively.Therefore,it is feasible to develop in advance a radial cold-atom interferometric gradiometer with a measurement accuracy of 10 13 /s 2-10 15 /s 2 for precisely producing the next-generation GOCE Follow-On Earth gravity field model with a high spatial resolution.展开更多
The present study elaborates three-dimensional flow of Williamson nanoliquid over a nonlinear stretchable surface. Fluid flow obeys Darcy–Forchheimer porous medium. A bidirectional nonlinear stretching surface genera...The present study elaborates three-dimensional flow of Williamson nanoliquid over a nonlinear stretchable surface. Fluid flow obeys Darcy–Forchheimer porous medium. A bidirectional nonlinear stretching surface generates the flow. Convective surface condition of heat transfer is taken into consideration. Further the zero nanoparticles mass flux condition is imposed at the boundary. Effects of thermophoresis and Brownian diffusion are considered. Assumption of boundary layer has been employed in the problem formulation. Convergent series solutions for the nonlinear governing system are established through the optimal homotopy analysis method(OHAM). Graphs have been sketched in order to analyze that how the velocity, temperature and concentration distributions are affected by distinct emerging flow parameters. Skin friction coefficients and local Nusselt number are also computed and discussed.展开更多
In the Jiaoshiba block of the Fuling shale gas field,the employed reserves and recovery factor by primary well pattern are low,no obvious barrier is found in the development layer series,and layered development is dif...In the Jiaoshiba block of the Fuling shale gas field,the employed reserves and recovery factor by primary well pattern are low,no obvious barrier is found in the development layer series,and layered development is difficult.Based on the understanding of the main factors controlling shale gas enrichment and high production,the theory and technology of shale gas three-dimensional development,such as fine description and modeling of shale gas reservoir,optimization of three-dimensional development strategy,highly efficient drilling with dense well pattern,precision fracturing and real-time control,are discussed.Three-dimensional development refers to the application of optimal and fast drilling and volume fracturing technologies,depending upon the sedimentary characteristics,reservoir characteristics and sweet spot distribution of shale gas,to form"artificial gas reservoir"in a multidimensional space,so as to maximize the employed reserves,recovery factor and yield rate of shale gas development.In the research on shale gas three-dimensional development,the geological+engineering sweet spot description is fundamental,the collaborative optimization of natural fractures and artificial fractures is critical,and the improvement of speed and efficiency in drilling and fracturing engineering is the guarantee.Through the implementation of three-dimensional development,the overall recovery factor in the Jiaoshiba block has increased from 12.6%to 23.3%,providing an important support for the continuous and stable production of the Fuling shale gas field.展开更多
This article addresses the three-dimensional stretched flow of the Jeffrey fluid with thermal radiation. The thermal conductivity of the fluid varies linearly with respect to temperature. Computations are performed fo...This article addresses the three-dimensional stretched flow of the Jeffrey fluid with thermal radiation. The thermal conductivity of the fluid varies linearly with respect to temperature. Computations are performed for the velocity and temperature fields. Graphs for the velocity and temperature are plotted to examine the behaviors with different parameters. Numerical values of the local Nusselt number are presented and discussed. The present results are compared with the existing limiting solutions, showing good agreement with each other.展开更多
In this communication a generalized three- dimensional steady flow of a viscous fluid between two infinite parallel plates is considered. The flow is generated due to uniform stretching of the lower plate in x- and y-...In this communication a generalized three- dimensional steady flow of a viscous fluid between two infinite parallel plates is considered. The flow is generated due to uniform stretching of the lower plate in x- and y-directions. It is assumed that the upper plate is uniformly porous and is subjected to constant injection. The governing system is fully coupled and nonlinear in nature. A complete analytic solution which is uniformly valid for all values of the dimensionless parameters β Re and λ is obtained by using a purely analytic technique, namely the homotopy analysis method. Also the effects of the parameters β Re and λ on the velocity field are discussed through graphs.展开更多
The recently introduced real-time three-dimensional color Doppler flow imaging （RT-3D CDFI） technique provides a quick and accurate calculation of regurgitant jet volume （RJV） and fraction. In order to evaluate RT...The recently introduced real-time three-dimensional color Doppler flow imaging （RT-3D CDFI） technique provides a quick and accurate calculation of regurgitant jet volume （RJV） and fraction. In order to evaluate RT-3D CDFI in the noninvasive assessment of aortic RJV and regurgitant jet fraction （RJF） in patients with isolated aortic regurgitation, real-time three-dimensional echocardiographic studies were performed on 23 patients with isolated aortic regurgitation to obtain LV end-diastolic volumes （LVEDV）, end-systolic volumes （LVESV） and RJV, and then RJF could be calculated. The regurgitant volume （RV） and regurgitant fraction （RF） calculated by two-dimensional pulsed Doppler （2D-PD） method served as reference values. The results showed that aortic RJV measured by the RT-3D CDFI method showed a good correlation with the 2D-PD measurements （r= 0.93, Y=0.89X＋ 3.9, SEE= 8.6 mL, P〈0.001 ）; the mean （SD） difference between the two methods was - 1.5 （9.8） mL. % RJF estimated by the RT-3D CDFI method was also correlated well with the values obtained by the 2D-PD method （r=0.88, Y=0.71X＋ 14.8, SEE= 6.4 %, P〈0. 001）; the mean （SD） difference between the two methods was -1.2 （7.9） %. It was suggested that the newly developed RT-3D CDFI technique was feasible in the majority of patients. In patients with eccentric aortic regurgitation, this new modality provides additional information to that obtained from the two-dimensional examination, which overcomes the inherent limitations of two-dimensional echocardiography by depicting the full extent of the jet trajectory. In addition, the RT-3D CDFI method is quick and accurate in calculating RJV and RJF.展开更多
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
Stress raisers such as holes are inevitable in structures at which stress concentration occurs and the static as well as fatigue strength of the structures can be significantly weakened.Therefore,to accurately evaluat...Stress raisers such as holes are inevitable in structures at which stress concentration occurs and the static as well as fatigue strength of the structures can be significantly weakened.Therefore,to accurately evaluate the stress concentration factor and stress fields at holes is of essential importance for structure design and service life prediction.Although stress and strain concentration and fields at holes in finite thickness plates strongly change with and along the thickness,manuals of stress concentration for engineering design are mainly based on twodimensional theory and no explicit formula is available even for circular holes in finite thickness plates.Here we obtain for the first time a complete set of explicit formulae for stress and strain concentration factors and the out-of-plane constraint factor at circular as well as elliptical holes in finite thickness plates by integrating comprehensive three-dimensional finite element analyses and available theoretical solutions.The three-dimensional stress distributions ahead of holes can also be predicted by the obtained formulae.With their accuracy and the corresponding applicable range being analyzed and outlined in detail,the formulae can serve as an important fundamental solution for three-dimensional engineering structure design and guideline for developing threedimensional analytical methods.展开更多
The magnetohydrodynamic(MHD) three-dimensional flow of Jeffrey fluid in the presence of Newtonian heating is investigated. Flow is caused by a bidirectional stretching surface. Series solutions are constructed for the...The magnetohydrodynamic(MHD) three-dimensional flow of Jeffrey fluid in the presence of Newtonian heating is investigated. Flow is caused by a bidirectional stretching surface. Series solutions are constructed for the velocity and temperature fields. Convergence of series solutions is ensured graphically and numerically. The variations of key parameters on the physical quantities are shown and discussed in detail. Constructed series solutions are compared with the existing solutions in the limiting case and an excellent agreement is noticed. Nusselt numbers are computed with and without magnetic fields. It is observed that the Nusselt number decreases in the presence of magnetic field.展开更多
Transonic shocks play a pivotal role in designation of supersonic inlets and ramjets.For the three-dimensional steady non-isentropic compressible Euler system with frictions,we constructe a family of transonic shock s...Transonic shocks play a pivotal role in designation of supersonic inlets and ramjets.For the three-dimensional steady non-isentropic compressible Euler system with frictions,we constructe a family of transonic shock solutions in rectilinear ducts with square cross-sections.In this article,we are devoted to proving rigorously that a large class of these transonic shock solutions are stable,under multidimensional small perturbations of the upcoming supersonic flows and back pressures at the exits of ducts in suitable function spaces.This manifests that frictions have a stabilization effect on transonic shocks in ducts,in consideration of previous works which shown that transonic shocks in purely steady Euler flows are not stable in such ducts.Except its implications to applications,because frictions lead to a stronger coupling between the elliptic and hyperbolic parts of the three-dimensional steady subsonic Euler system,we develop the framework established in previous works to study more complex and interesting Venttsel problems of nonlocal elliptic equations.展开更多
基金Supported by the National Natural Science Foundation of China(Nos.42250710152,42192562)the Southern Laboratory of Ocean Science and Engineering(Guangdong Zhuhai)(No.SML 2020 SP 007)。
文摘Convectively unstable processes caused by dense water subsidence are common occurrences in high-latitude oceanic regions,and significantly modulate mass and heat transport and mixing processes in the ocean.An idealized numerical experiment using the large eddy simulation method was conducted to analyze the three-dimensional flow field structure and the mechanism for dense water subsidence.Specifically,a negative salt flux is set at the sea surface,in which salt flux enters the sea surface to simulate the icing and salting-out phenomena that occur at high latitudes.Results show that the mean-state 3D flow field of dense water subsidence exhibits a hollow conical distribution.The horizontal flow field is characterized by a cyclonic vortex that driven primarily by the pressure gradient and influenced by the Coriolis effect.Moreover,the inverse vertical pressure gradient generated by this vortex inhibits the sinking of the plume,leading to its off-axis deflection and the development of an anticyclonic precession.In addition,the impact of rotation on the structure of a sinking plume within a stratified environment is discussed.Both horizontal vortex intensity and cone angle of the hollow cone flow field are increased with increasing rotation rate,resulting in a decrease in the plume’s maximum sinking depth.Variances in rotation direction cause the horizontal vortex and sinking plumes of dense water in the northern and southern hemispheres to rotate in opposite directions.
基金This project is supported by National Natural Science Foundation ofChina(No. 50406017)
文摘An experimental investigation of three-dimensional flow field in a film-cooled turbine model is carried out by using particle image velocimeter （PIV） in a low-speed wind tunnel. The effects of different blowing ratios （M=1.5, 2） on the flow field are studied. The experimental results reveal the classical phenomena of the formation of kidney vortex pair and secondary flow in wake region behind the jet hole. And the changes of the kidney vortex pair and the wake at different locations away from the hole on the suction and pressure sides are also studied. Compared with the flow field in stationary cascade, there are centrifugal force and Coriolis force existing in the flow field of rotating turbine, and these forces bring the radial velocity in the jet flow. The effect of rotatien on the flow field of the pressure side is more distinct than that on the suction side from the measured flow fields in Y-Z plane and radial velocity contours. The increase of blowing ratio makes the kidney vortex pair and the secondary flow in the wake region stronger and makes the range of the wake region enlarged.
基金This project is supported by National Natural Science Foundation of China (No. 50175042).
文摘Three-dimensional flow field of turbine in torque converter is simulated by numerical calculation in order to improve the performance of torque converter. Calculation model of a torque converter is presented based on the mixing-plane technology. In the calculation of flow field, the 3D N-S equations are separated by finite-volume method and solved by semi-implicit method for pressure-linked equations（SIMPLE）. Based on flow field calculation, the flow field of turbine is simulated. The velocity and pressure in the flow field of turbine are analyzed. The external performance of the torque converter is also calculated. Results of flow simulation show that there are secondary flow, off flow and velocity gradient in turbine passage. The validity of numerical simulation is verified by comparing the results of numerical simulation with experiment data.
基金supported by the National Natural Science Foundation of China (10872096)the Open Fund of State Key Laboratory of Explosion Science and Technology, Beijing University of Science and Technology (KFJJ09-13)
文摘Gaseous detonation propagating in a toroidal chamber was numerically studied for hydrogen/oxygen/nitrogen mixtures. The numerical method used is based on the three-dimensional Euler equations with detailed finiterate chemistry. The results show that the calculated streak picture is in qualitative agreement with the picture recorded by a high speed streak camera from published literature. The three-dimensional flow field induced by a continuously rotating detonation was visualized and distinctive features of the rotating detonations were clearly depicted. Owing to the unconfined character of detonation wavelet, a deficit of detonation parameters was observed. Due to the effects of wall geometries, the strength of the outside detonation front is stronger than that of the inside portion. The detonation thus propagates with a constant circular velocity. Numerical simulation also shows three-dimensional rotating detonation structures, which display specific feature of the detonation- shock combined wave. Discrete burning gas pockets are formed due to instability of the discontinuity. It is believed that the present study could give an insight into the interest- ing properties of the continuously rotating detonation, and is thus beneficial to the design of continuous detonation propulsion systems.
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.
基金the National Natural Science Foundation of China(Grant Nos.61376115,11672065).
文摘This paper presents a three-dimensional flow field simulation of the steady flows through diffusers and nozzles with straight or serrated-sided walls to analyze the effect of the channel structure on the flow characteristics.The pressure and velocity profiles in the diffusers and the nozzles as well as the net volumetric flow rate are determined.Our simulation demonstrates that the pressure and velocity profiles in the serrated diffuser/nozzles are more complicated than those with the straight-sided wall,while the net steady flow rate with the straight-sided wall increases monotonically with the increase of the pressure difference,the steady flow rate with serrated sided walls increases gradually to reach a maximum and then decreases with the increase of the pressure difference.The results suggest that the number of the sawteeth plays a significant role in optimizing the design of serrated diffusers and nozzles for improving the transport efficiency of valveless micro-pumps.
文摘With an application of topological analysis,in this paper the skin-friction line patterns on compressor and turbine cascade surfaces are depicted and the streamline patterns of the secondary flow fields in the cross-section of a curved pipe and a turbine cascade are drawn under given conditions.In addition the structures of vortices within three-dimensional viscous flow fields in cascades are analysed.
文摘The hydrodynamic characteristics of a rigid, single, circular cylinder in a three dimensional, incompressible, uniform cross flow were calculated using the large-eddy simulation method of CFX5. Solutions to the three dimensional N-S equations were obtained by the finite volume method. The focus of this numerical simulation was to research the characteristics of pressure distribution （drag and litt forces） and vortex tubes at high Reynolds numbers. The results of the calculations showed that the forces at every section in the spanwise direction of the cylinder were symmetrical about the middle section and smaller than the forces calculated in two dimensional cases. Moreover, the flow around the cylinder obviously presents three dimensional characteristics.
文摘This paper presents a numerical study of the flow topologies of three-dimensional （3D） flows in a high pressure compressor stator blade row without and with boundary layer aspiration on the hub wall. The stator blade is representative of the first stage operating under transonic inlet conditions and the blade design encourages development of highly complex 3D flows. The blade has a small tip clearance. The computational fluid dynamics （CFD） studies show progressive increase of hub corner stall with the increase in incidence. Aspiration is implemented on the hub wall via a slot in the comer between the hub wall and the suction surface. The CFD studies show aspiration to be sensitive to the suction flow rate; lower rate leads to very complex flow struc- tures and increased level of losses whereas higher rate renders aspiration effective for control of hub comer separation. The flow topologies are studied by trace of skin friction lines on the walls. The nature of flow can be explained by the topological rules of closed separation. Furthermore, a deeper analysis is done for a particular case with advanced criterion to test the non-degeneracy of critical points in the flow field.
基金Supported by the Major State Basic Research Development Program of China(2011CB706501)the National Natural Science Foundation of China(51276157)
文摘Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power- ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the de- tailed two-phase flow inside the columns. The present paper presents a three-dimensional computational fluid dy- namics （CFD） model to simulate the two-phase flow in a representative unit of the column. The unit consists of an CFD calculations on column packed with Flexipak 1Y were implemented within the volume of fluid （VOF） mathe- matical framework. The CFD model was validated by comparing the calculated thickness of liquid film with the available experimental data. Special attention was given to quantitative analysis of the effects of gravity on the hy- drodynamics. Fluctuations in the liquid mass flow rate and the calculated pressure drop loss were found to be quali- tatively in agreement with the experimental observations.
基金Project supported by the Main Direction Program of Knowledge Innovation of the Chinese Academy of Sciences for Distinguished Young Scholars (Grant No. KZCX2-EW-QN114)the National Natural Science Foundation of China for Young Scholars (GrantNos. 41004006,41131067,and 11173049)+3 种基金the Merit-Based Scientific Research Foundation of the State Ministry of Human Resources and Social Security of China for Returned Overseas Chinese Scholars (Grant No. 2011)the Open Research Fund Programof the Key Laboratory of Computational Geodynamics of the Chinese Academy of Sciences (Grant No. 2011-04)the Frontier Field Program of Knowledge Innovation of Institute of Geodesy and Geophysics of the Chinese Academy of Sciencesthe Open Fund of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Grant No. PLN1113)
文摘The accuracy of the Earth＇s gravitational field measured from the gravity field and steady-state ocean circulation explorer（GOCE）,up to 250 degrees,influenced by the radial gravity gradient V zz and three-dimensional gravity gradient V ij from the satellite gravity gradiometry（SGG） are contrastively demonstrated based on the analytical error model and numerical simulation,respectively.Firstly,the new analytical error model of the cumulative geoid height,influenced by the radial gravity gradient V zz and three-dimensional gravity gradient V ij are established,respectively.In 250 degrees,the GOCE cumulative geoid height error measured by the radial gravity gradient V zz is about 2 1/2 times higher than that measured by the three-dimensional gravity gradient V ij.Secondly,the Earth＇s gravitational field from GOCE completely up to 250 degrees is recovered using the radial gravity gradient V zz and three-dimensional gravity gradient V ij by numerical simulation,respectively.The study results show that when the measurement error of the gravity gradient is 3×10 12 /s 2,the cumulative geoid height errors using the radial gravity gradient V zz and three-dimensional gravity gradient V ij are 12.319 cm and 9.295 cm at 250 degrees,respectively.The accuracy of the cumulative geoid height using the three-dimensional gravity gradient V ij is improved by 30%-40% on average compared with that using the radial gravity gradient V zz in 250 degrees.Finally,by mutual verification of the analytical error model and numerical simulation,the orders of magnitude from the accuracies of the Earth＇s gravitational field recovery make no substantial differences based on the radial and three-dimensional gravity gradients,respectively.Therefore,it is feasible to develop in advance a radial cold-atom interferometric gradiometer with a measurement accuracy of 10 13 /s 2-10 15 /s 2 for precisely producing the next-generation GOCE Follow-On Earth gravity field model with a high spatial resolution.
文摘The present study elaborates three-dimensional flow of Williamson nanoliquid over a nonlinear stretchable surface. Fluid flow obeys Darcy–Forchheimer porous medium. A bidirectional nonlinear stretching surface generates the flow. Convective surface condition of heat transfer is taken into consideration. Further the zero nanoparticles mass flux condition is imposed at the boundary. Effects of thermophoresis and Brownian diffusion are considered. Assumption of boundary layer has been employed in the problem formulation. Convergent series solutions for the nonlinear governing system are established through the optimal homotopy analysis method(OHAM). Graphs have been sketched in order to analyze that how the velocity, temperature and concentration distributions are affected by distinct emerging flow parameters. Skin friction coefficients and local Nusselt number are also computed and discussed.
基金Supported by the Sinopec Science and Technology Project(P22183).
文摘In the Jiaoshiba block of the Fuling shale gas field,the employed reserves and recovery factor by primary well pattern are low,no obvious barrier is found in the development layer series,and layered development is difficult.Based on the understanding of the main factors controlling shale gas enrichment and high production,the theory and technology of shale gas three-dimensional development,such as fine description and modeling of shale gas reservoir,optimization of three-dimensional development strategy,highly efficient drilling with dense well pattern,precision fracturing and real-time control,are discussed.Three-dimensional development refers to the application of optimal and fast drilling and volume fracturing technologies,depending upon the sedimentary characteristics,reservoir characteristics and sweet spot distribution of shale gas,to form"artificial gas reservoir"in a multidimensional space,so as to maximize the employed reserves,recovery factor and yield rate of shale gas development.In the research on shale gas three-dimensional development,the geological+engineering sweet spot description is fundamental,the collaborative optimization of natural fractures and artificial fractures is critical,and the improvement of speed and efficiency in drilling and fracturing engineering is the guarantee.Through the implementation of three-dimensional development,the overall recovery factor in the Jiaoshiba block has increased from 12.6%to 23.3%,providing an important support for the continuous and stable production of the Fuling shale gas field.
基金supported by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah,Saudi Arabia (No. 2-135/HiCi)
文摘This article addresses the three-dimensional stretched flow of the Jeffrey fluid with thermal radiation. The thermal conductivity of the fluid varies linearly with respect to temperature. Computations are performed for the velocity and temperature fields. Graphs for the velocity and temperature are plotted to examine the behaviors with different parameters. Numerical values of the local Nusselt number are presented and discussed. The present results are compared with the existing limiting solutions, showing good agreement with each other.
文摘In this communication a generalized three- dimensional steady flow of a viscous fluid between two infinite parallel plates is considered. The flow is generated due to uniform stretching of the lower plate in x- and y-directions. It is assumed that the upper plate is uniformly porous and is subjected to constant injection. The governing system is fully coupled and nonlinear in nature. A complete analytic solution which is uniformly valid for all values of the dimensionless parameters β Re and λ is obtained by using a purely analytic technique, namely the homotopy analysis method. Also the effects of the parameters β Re and λ on the velocity field are discussed through graphs.
文摘The recently introduced real-time three-dimensional color Doppler flow imaging （RT-3D CDFI） technique provides a quick and accurate calculation of regurgitant jet volume （RJV） and fraction. In order to evaluate RT-3D CDFI in the noninvasive assessment of aortic RJV and regurgitant jet fraction （RJF） in patients with isolated aortic regurgitation, real-time three-dimensional echocardiographic studies were performed on 23 patients with isolated aortic regurgitation to obtain LV end-diastolic volumes （LVEDV）, end-systolic volumes （LVESV） and RJV, and then RJF could be calculated. The regurgitant volume （RV） and regurgitant fraction （RF） calculated by two-dimensional pulsed Doppler （2D-PD） method served as reference values. The results showed that aortic RJV measured by the RT-3D CDFI method showed a good correlation with the 2D-PD measurements （r= 0.93, Y=0.89X＋ 3.9, SEE= 8.6 mL, P〈0.001 ）; the mean （SD） difference between the two methods was - 1.5 （9.8） mL. % RJF estimated by the RT-3D CDFI method was also correlated well with the values obtained by the 2D-PD method （r=0.88, Y=0.71X＋ 14.8, SEE= 6.4 %, P〈0. 001）; the mean （SD） difference between the two methods was -1.2 （7.9） %. It was suggested that the newly developed RT-3D CDFI technique was feasible in the majority of patients. In patients with eccentric aortic regurgitation, this new modality provides additional information to that obtained from the two-dimensional examination, which overcomes the inherent limitations of two-dimensional echocardiography by depicting the full extent of the jet trajectory. In addition, the RT-3D CDFI method is quick and accurate in calculating RJV and RJF.
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supported by the National Natural Science Foundation of China(51535005,51472117)the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(MCMS-I-0418K01,MCMS-I-0418Y01,MCMS-0417G02,MCMS-0417G03)+1 种基金the Fundamental Research Funds for the Central Universities(NP2017101,NC2018001)a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.The authors would like to thank Dr.Chongmin She for helpful discussions.
文摘Stress raisers such as holes are inevitable in structures at which stress concentration occurs and the static as well as fatigue strength of the structures can be significantly weakened.Therefore,to accurately evaluate the stress concentration factor and stress fields at holes is of essential importance for structure design and service life prediction.Although stress and strain concentration and fields at holes in finite thickness plates strongly change with and along the thickness,manuals of stress concentration for engineering design are mainly based on twodimensional theory and no explicit formula is available even for circular holes in finite thickness plates.Here we obtain for the first time a complete set of explicit formulae for stress and strain concentration factors and the out-of-plane constraint factor at circular as well as elliptical holes in finite thickness plates by integrating comprehensive three-dimensional finite element analyses and available theoretical solutions.The three-dimensional stress distributions ahead of holes can also be predicted by the obtained formulae.With their accuracy and the corresponding applicable range being analyzed and outlined in detail,the formulae can serve as an important fundamental solution for three-dimensional engineering structure design and guideline for developing threedimensional analytical methods.
文摘The magnetohydrodynamic(MHD) three-dimensional flow of Jeffrey fluid in the presence of Newtonian heating is investigated. Flow is caused by a bidirectional stretching surface. Series solutions are constructed for the velocity and temperature fields. Convergence of series solutions is ensured graphically and numerically. The variations of key parameters on the physical quantities are shown and discussed in detail. Constructed series solutions are compared with the existing solutions in the limiting case and an excellent agreement is noticed. Nusselt numbers are computed with and without magnetic fields. It is observed that the Nusselt number decreases in the presence of magnetic field.
基金This work was supported in part by National Nature Science Foundation of China(11371141 and 11871218)by Science and Technology Commission of Shanghai Municipality(18dz2271000).
文摘Transonic shocks play a pivotal role in designation of supersonic inlets and ramjets.For the three-dimensional steady non-isentropic compressible Euler system with frictions,we constructe a family of transonic shock solutions in rectilinear ducts with square cross-sections.In this article,we are devoted to proving rigorously that a large class of these transonic shock solutions are stable,under multidimensional small perturbations of the upcoming supersonic flows and back pressures at the exits of ducts in suitable function spaces.This manifests that frictions have a stabilization effect on transonic shocks in ducts,in consideration of previous works which shown that transonic shocks in purely steady Euler flows are not stable in such ducts.Except its implications to applications,because frictions lead to a stronger coupling between the elliptic and hyperbolic parts of the three-dimensional steady subsonic Euler system,we develop the framework established in previous works to study more complex and interesting Venttsel problems of nonlocal elliptic equations.
