The application of the wavelet method to vortex motion prediction is investigated. First, the wavelet method is used to solve two initial boundary problems so as to verify its abilities of controlling numerical errors...The application of the wavelet method to vortex motion prediction is investigated. First, the wavelet method is used to solve two initial boundary problems so as to verify its abilities of controlling numerical errors and capturing local structures. Then, the adaptive wavelet method is used to simulate the vortex emerging process. The results show that the wavelet method can control numerical errors easily, can capture local structures adaptively, and can predict the vortex fluctuation evolution. Therefore, the application of the wavelet method to turbulence is suggested.展开更多
Gas-liquid two-phase flow in fractal porous media is pivotal for engineering applications,yet it remains challenging to be accurately characterized due to complex microstructure-flow interactions.This study establishe...Gas-liquid two-phase flow in fractal porous media is pivotal for engineering applications,yet it remains challenging to be accurately characterized due to complex microstructure-flow interactions.This study establishes a pore-scale numerical framework integratingMonte Carlo-generated fractal porousmedia with Volume of Fluid(VOF)simulations to unravel the coupling among pore distribution characterized by fractal dimension(Df),flow dynamics,and displacement efficiency.A pore-scale model based on the computed tomography(CT)microstructure of Berea sandstone is established,and the simulation results are compared with experimental data.Good agreement is found in phase distribution,breakthrough behavior,and flow path morphology,confirming the reliability of the numerical simulation method.Ten fractal porous media models with Df ranging from 1.25~1.7 were constructed using a Monte-Carlo approach.The gas-liquid two-phase flow dynamics was characterized using the VOF solver across gas injection rates of 0.05-5m/s,inwhich the time-resolved two-phase distribution patternswere systematically recorded.The results reveal that smaller fractal dimensions(Df=1.25~1.45)accelerate fingering breakthrough(peak velocity is 1.73 m/s at Df=1.45)due to a bimodal pore size distribution dominated by narrow channels.Increasing Df amplifies vorticity generation by about 3 times(eddy viscosity is 0.033 Pa⋅s at Df=1.7)through reduced interfacial curvature,while tortuosity-driven pressure differentials transition from sharp increases(0.4~6.3 Pa at Df=1.25~1.3)to inertial plateaus(4.8 Pa at Df=1.7).A nonlinear increase in equilibrium gas volume fraction(fav=0.692 at Df=1.7)emerges from residual gas saturation and turbulence-enhanced dispersion.This behavior is further modulated by flow velocity,with fav peaking at 0.72 under capillary-dominated conditions(0.05 m/s),but decreasing to 0.65 in the inertial regime(0.5 m/s).The work quantitatively links fractal topology to multiphase flow regimes,demonstrating the critical role of Df in governing preferential pathways,energy dissipation,and phase distribution.展开更多
The improved delayed detached eddy simulation method with shear stress transport model was used to analyze the evolution of vortex structure,velocity and pressure fields of swirling jet.The influence of nozzle pressur...The improved delayed detached eddy simulation method with shear stress transport model was used to analyze the evolution of vortex structure,velocity and pressure fields of swirling jet.The influence of nozzle pressure drop on vortex structure development and turbulence pulsation was investigated.The development of vortex structure could be divided into three stages:Kelvin-Helmholtz(K-H)instability,transition stage and swirling flow instability.Swirling flow could significantly enhance radial turbulence pulsation and increase diffusion angle.At the downstream of the jet flow,turbulence pulsation dissipation was the main reason for jet velocity attenuation.With the increase of pressure drop,the jet velocity,pulsation amplitude and the symmetry of velocity distribution increased correspondingly.Meanwhile the pressure pulsation along with the axis and vortex transport intensity also increased significantly.When the jet distance exceeded about 9 times the dimensionless jet distance,the impact distance of swirling jet could not be improved effectively by increasing the pressure drop.However,it could effectively increase the swirl intensity and jet diffusion angle.The swirling jet is more suitable for radial horizontal drilling with large hole size,coalbed methane horizontal well cavity completion and roadway drilling and pressure relief,etc.展开更多
The head-flow rate curve with double humps brings greater challenges to the stable operation of a pump-turbine in pump mode,and the present investigation aims to reveal the formation mechanisms behind it.We performed ...The head-flow rate curve with double humps brings greater challenges to the stable operation of a pump-turbine in pump mode,and the present investigation aims to reveal the formation mechanisms behind it.We performed unsteady simulations by applying a modified partially averaged Navier-Stokes(PANS)model and the double hump phenomenon was satisfactorily captured with relative errors within 3.87%by comparing the head with the experimental data.The results showed that the rotating stall occurred in the guide vane during both the first and second hump regions and induced the dominant pressure pulsation component with an oscillating frequency 11.7%times the runner rotation frequency.The reverse flow was observed due to the propagation of rotating stall cells in the guide vane,and the first hump was attributed to the vortex in the vaneless region,with a reduction in the runner's capacity for doing work as the reverse flow reached the blade trailing edge.The second hump was attributed to the flow separation near the leading edge of the runner blades,which extended to the runner outlet and interacted with the rotating stall cell,leading to a rapid extension of the reverse flow into the runner.This not only reduces the runner's capacity for doing work but also significantly increases the energy loss in the blade-to-blade flow passage near the runner exit.This study enhances the understanding of the flow mechanism in the hump region,which can provide insights into the suppression of unstable flows and runner optimization.展开更多
This research utilizes theΩvortex identification method to address the turbulent flows in a single-stage side channel pump,to comprehensively characterize the three types of dynamic vortex structures classified based...This research utilizes theΩvortex identification method to address the turbulent flows in a single-stage side channel pump,to comprehensively characterize the three types of dynamic vortex structures classified based on directions.Premised on the Galilean invariance,the work employs coordinate rotation and transformation.Thus,the indistinguishable 3-D vortex can be simplified to 2-D vortex on typical research planes.When juxtaposing the overall performance,it was revealed that a diversity of areas with high values yielded enhanced reflection of the vortex intensity,as measured by velocity distribution.The axial vortex structure with high intensity exists at the outer radius under all conditions largely.While the longitudinal vortex usually shows high intensity between the middle and outer radius.Simultaneously,the radial vortex is more likely to be at the inner radius near the suction face.Finally,this paper introduces a specific valueξ,which represents the ratio of decomposition to the total of the manifestation of the fluid rotational pattern.From the fluctuation and mean value,it can be realized that the development of the specific vortex in three directions at different positions.For example,the specific valueξ2 refers to the typical longitudinal vortex as dynamic vortex are almost from 20%to 50%,which illustrates that the longitudinal vortex only occupies a minor percentage in the total vortex.This phenomenon is one of the main reasons for the low efficiency.The present work could provide some suggestions and references for in-depth studies in fluid engineering with intense swirling flows.展开更多
In order to comprehensively analyze the operation instability of the pump turbine S-shaped region,this paper uses DDES turbulence model to calculate the model pump turbine from the perspective of the evolution law of ...In order to comprehensively analyze the operation instability of the pump turbine S-shaped region,this paper uses DDES turbulence model to calculate the model pump turbine from the perspective of the evolution law of runner vortex and draft tube vortex rope and entropy production rate,combined with experiments.The results show that the numerical simulation is in good agreement with the experiment.Omega vortex analysis method is more accurate than other vortex recognition methods because it is not affected by the threshold value.The vortices at the runner region under the runaway condition and the turbine brake condition develop towards the vaneless space and the blade pressure surface respectively,which will cause the flow obstruction and blade separation.The overall vorticity of the reverse pump condition is the largest.The vortex rope of the draft tube under runaway and turbine brake conditions is columnar in shape and has very high rotational strength.The vortex rope under reverse pump conditions is prone to fracture and form scattered vortices,impeding the normal movement of the fluid.The entropy production rate of the spanwise surface near the upper ring and the lower crown is greater than the middle spanwise surface due to the boundary layer effect.And the energy dissipation in the runner under reverse pump conditions is characterized by high at both ends of the runner and low in the middle.The energy dissipation near the wall of the straight cone section of the draft tube is large due to the squeezing effect of the vortex rope on the flow.展开更多
基金Project supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(No.50921001)the National Program on the Key Basic Research Project of China(973 Program)(No.2010CB832700)
文摘The application of the wavelet method to vortex motion prediction is investigated. First, the wavelet method is used to solve two initial boundary problems so as to verify its abilities of controlling numerical errors and capturing local structures. Then, the adaptive wavelet method is used to simulate the vortex emerging process. The results show that the wavelet method can control numerical errors easily, can capture local structures adaptively, and can predict the vortex fluctuation evolution. Therefore, the application of the wavelet method to turbulence is suggested.
基金funded by the National Key R&D Program of China,China(Grant No.2023YFB4005500)National Natural Science Foundation of China,China(Grant Nos.52379113 and 52379114).
文摘Gas-liquid two-phase flow in fractal porous media is pivotal for engineering applications,yet it remains challenging to be accurately characterized due to complex microstructure-flow interactions.This study establishes a pore-scale numerical framework integratingMonte Carlo-generated fractal porousmedia with Volume of Fluid(VOF)simulations to unravel the coupling among pore distribution characterized by fractal dimension(Df),flow dynamics,and displacement efficiency.A pore-scale model based on the computed tomography(CT)microstructure of Berea sandstone is established,and the simulation results are compared with experimental data.Good agreement is found in phase distribution,breakthrough behavior,and flow path morphology,confirming the reliability of the numerical simulation method.Ten fractal porous media models with Df ranging from 1.25~1.7 were constructed using a Monte-Carlo approach.The gas-liquid two-phase flow dynamics was characterized using the VOF solver across gas injection rates of 0.05-5m/s,inwhich the time-resolved two-phase distribution patternswere systematically recorded.The results reveal that smaller fractal dimensions(Df=1.25~1.45)accelerate fingering breakthrough(peak velocity is 1.73 m/s at Df=1.45)due to a bimodal pore size distribution dominated by narrow channels.Increasing Df amplifies vorticity generation by about 3 times(eddy viscosity is 0.033 Pa⋅s at Df=1.7)through reduced interfacial curvature,while tortuosity-driven pressure differentials transition from sharp increases(0.4~6.3 Pa at Df=1.25~1.3)to inertial plateaus(4.8 Pa at Df=1.7).A nonlinear increase in equilibrium gas volume fraction(fav=0.692 at Df=1.7)emerges from residual gas saturation and turbulence-enhanced dispersion.This behavior is further modulated by flow velocity,with fav peaking at 0.72 under capillary-dominated conditions(0.05 m/s),but decreasing to 0.65 in the inertial regime(0.5 m/s).The work quantitatively links fractal topology to multiphase flow regimes,demonstrating the critical role of Df in governing preferential pathways,energy dissipation,and phase distribution.
基金Supported by the Beijing Natural Science Foundation Project(3222039)National Natural Science Foundation of China(51827804).
文摘The improved delayed detached eddy simulation method with shear stress transport model was used to analyze the evolution of vortex structure,velocity and pressure fields of swirling jet.The influence of nozzle pressure drop on vortex structure development and turbulence pulsation was investigated.The development of vortex structure could be divided into three stages:Kelvin-Helmholtz(K-H)instability,transition stage and swirling flow instability.Swirling flow could significantly enhance radial turbulence pulsation and increase diffusion angle.At the downstream of the jet flow,turbulence pulsation dissipation was the main reason for jet velocity attenuation.With the increase of pressure drop,the jet velocity,pulsation amplitude and the symmetry of velocity distribution increased correspondingly.Meanwhile the pressure pulsation along with the axis and vortex transport intensity also increased significantly.When the jet distance exceeded about 9 times the dimensionless jet distance,the impact distance of swirling jet could not be improved effectively by increasing the pressure drop.However,it could effectively increase the swirl intensity and jet diffusion angle.The swirling jet is more suitable for radial horizontal drilling with large hole size,coalbed methane horizontal well cavity completion and roadway drilling and pressure relief,etc.
基金supported by the National Natural Science Foundation of China(Grant No.52336001)the China Postdoctoral Science Foundation(Grant Nos.2022TQ0168,2023M731895)。
文摘The head-flow rate curve with double humps brings greater challenges to the stable operation of a pump-turbine in pump mode,and the present investigation aims to reveal the formation mechanisms behind it.We performed unsteady simulations by applying a modified partially averaged Navier-Stokes(PANS)model and the double hump phenomenon was satisfactorily captured with relative errors within 3.87%by comparing the head with the experimental data.The results showed that the rotating stall occurred in the guide vane during both the first and second hump regions and induced the dominant pressure pulsation component with an oscillating frequency 11.7%times the runner rotation frequency.The reverse flow was observed due to the propagation of rotating stall cells in the guide vane,and the first hump was attributed to the vortex in the vaneless region,with a reduction in the runner's capacity for doing work as the reverse flow reached the blade trailing edge.The second hump was attributed to the flow separation near the leading edge of the runner blades,which extended to the runner outlet and interacted with the rotating stall cell,leading to a rapid extension of the reverse flow into the runner.This not only reduces the runner's capacity for doing work but also significantly increases the energy loss in the blade-to-blade flow passage near the runner exit.This study enhances the understanding of the flow mechanism in the hump region,which can provide insights into the suppression of unstable flows and runner optimization.
基金supported by the Ranking the Top of the List for Science and Technology Projects of Yunnan Province(Grant No.202204BW050001)the Taizhou Science and Technology Project(Grant Nos.21gyb05,21gyb08)+2 种基金the Research Innovation Program for College Graduates of Jiangsu Province(Grant No.KYCX22_3641)gratefully acknowledge financial support from China Scholarship CouncilProject supported by the National Natural Science Foundation of China(Grant Nos.52279086,52150410397).
文摘This research utilizes theΩvortex identification method to address the turbulent flows in a single-stage side channel pump,to comprehensively characterize the three types of dynamic vortex structures classified based on directions.Premised on the Galilean invariance,the work employs coordinate rotation and transformation.Thus,the indistinguishable 3-D vortex can be simplified to 2-D vortex on typical research planes.When juxtaposing the overall performance,it was revealed that a diversity of areas with high values yielded enhanced reflection of the vortex intensity,as measured by velocity distribution.The axial vortex structure with high intensity exists at the outer radius under all conditions largely.While the longitudinal vortex usually shows high intensity between the middle and outer radius.Simultaneously,the radial vortex is more likely to be at the inner radius near the suction face.Finally,this paper introduces a specific valueξ,which represents the ratio of decomposition to the total of the manifestation of the fluid rotational pattern.From the fluctuation and mean value,it can be realized that the development of the specific vortex in three directions at different positions.For example,the specific valueξ2 refers to the typical longitudinal vortex as dynamic vortex are almost from 20%to 50%,which illustrates that the longitudinal vortex only occupies a minor percentage in the total vortex.This phenomenon is one of the main reasons for the low efficiency.The present work could provide some suggestions and references for in-depth studies in fluid engineering with intense swirling flows.
基金The authors acknowledge that this work was financially supported by the National Natural Science Foundation of China(Grant No.52079118)Sichuan Provincial Department of Science and Technology Project(Grant No.2023YFQ0021).
文摘In order to comprehensively analyze the operation instability of the pump turbine S-shaped region,this paper uses DDES turbulence model to calculate the model pump turbine from the perspective of the evolution law of runner vortex and draft tube vortex rope and entropy production rate,combined with experiments.The results show that the numerical simulation is in good agreement with the experiment.Omega vortex analysis method is more accurate than other vortex recognition methods because it is not affected by the threshold value.The vortices at the runner region under the runaway condition and the turbine brake condition develop towards the vaneless space and the blade pressure surface respectively,which will cause the flow obstruction and blade separation.The overall vorticity of the reverse pump condition is the largest.The vortex rope of the draft tube under runaway and turbine brake conditions is columnar in shape and has very high rotational strength.The vortex rope under reverse pump conditions is prone to fracture and form scattered vortices,impeding the normal movement of the fluid.The entropy production rate of the spanwise surface near the upper ring and the lower crown is greater than the middle spanwise surface due to the boundary layer effect.And the energy dissipation in the runner under reverse pump conditions is characterized by high at both ends of the runner and low in the middle.The energy dissipation near the wall of the straight cone section of the draft tube is large due to the squeezing effect of the vortex rope on the flow.
