We numerically study the thermodynamic properties of a hard ellipsoid fluid by mainly focusing on its phase transition from an isotropic phase into a nematic phase (i.e. isotropie-nematic phase transition). To impro...We numerically study the thermodynamic properties of a hard ellipsoid fluid by mainly focusing on its phase transition from an isotropic phase into a nematic phase (i.e. isotropie-nematic phase transition). To improve the accuracy, precision, and efficiency of our computations, we attempt to employ the Wang-Landau NPT Monte Carlo algorithm in our simulations to calculate the function p(V) that gives the probability of arriving at the threshold density of the isotropic-nematic transition. Our results directly reveal that the nematic fluid phase, which is characterized by an ordered direction rather than an ordered configuration, appears and coexists with the isotropic phase when the aspect ratio a of the ellipsoid is located in a relatively narrow range of α = 2.0-2.25, and it becomes dominant and is fully established when α≥αcut = 2.25. We find that our estimated αcut is significantly lower than previously reported values of around 2.75. This prediction is further confirmed by the calculations of both the fluid reduced density and pressure of coexistence which show that the pressure grows up as the density increases and the probability function p(V) exhibits double peaks when the pressure enters the coexistence region. Based on these consistent results we are able to conclude that when α≥2.25 an ellipsoid fluid can fully display the nematic behavior. This study will place a useful and tight theoretical constraint on investigations of the isotropic-nematic phase transition in the future.展开更多
Local fluid flow(LFF) at the mesoscopic scale is the main dissipation mechanism of seismic waves in heterogeneous porous media within the seismic frequency band.LFF is easily influenced by the structure and boundary...Local fluid flow(LFF) at the mesoscopic scale is the main dissipation mechanism of seismic waves in heterogeneous porous media within the seismic frequency band.LFF is easily influenced by the structure and boundary conditions of the porous media,which leads to different behaviors of the peak frequency of attenuation.The associated transition frequency can provide detailed information about the trend of LFF;therefore,research on the transition frequency of LFF and its relationship with the peak frequency of the corresponding attenuation(i.e.,inverse of quality factor) facilitates the detailed understanding of the effect of inner structures and boundary conditions in porous media.In this study,we firstly obtain the transition frequency of fluid flux based on Biot's theory of poroelasticity and the fast Fourier transform algorithm in a sample containing one repeating unit cell(RUC).We then analyze changes of these two frequencies in porous media with different porous properties.Finally,we extend our analysis to the influence of the undrained boundary condition on the transition frequency and peak frequency in porous media with multiple RUCs.This setup can facilitate the understanding of the effect from the undrained boundary condition.Results demonstrate that these two frequencies have the same trend at low water saturation,but amplitude variations differ between the frequencies as the amount of saturation increases.However,for cases of high water saturation,both the trend and the amplitude variation of these two frequencies fit well with each other.展开更多
The simultaneous removal of up to 92% of the surfactant template and chemical implantation of transition metal complexes into mesopores has been successfully achieved by treating as-synthesized pure siliceous MCM-41 w...The simultaneous removal of up to 92% of the surfactant template and chemical implantation of transition metal complexes into mesopores has been successfully achieved by treating as-synthesized pure siliceous MCM-41 with supercritical CO2 modified with CH2Cl2/MeOH mixture, resulting in the formation of functionalized material with uniform pore structure.展开更多
Abstract: The physico-chemical conditions under which the pegmatite dyke No. 3 was formed were discussed in the light of fluid-melt inclusion evidence. Our results lend support to the frac-tionation of hydrothermal so...Abstract: The physico-chemical conditions under which the pegmatite dyke No. 3 was formed were discussed in the light of fluid-melt inclusion evidence. Our results lend support to the frac-tionation of hydrothermal solutions from magma. For the pegmatite dike No. 3, the magma-derived hydrothermal solutions are dominated by NaCl + CO2 + H2O.展开更多
Three-dimensional compressible flow simulationswere conducted to develop a Hyperloop pod. Thenovelty is the usage of Gamma transition model, in whichthe transition from laminar to turbulent flow can be predicted.First...Three-dimensional compressible flow simulationswere conducted to develop a Hyperloop pod. Thenovelty is the usage of Gamma transition model, in whichthe transition from laminar to turbulent flow can be predicted.First, a mesh dependency study was undertaken,showing second-order convergence with respect to themesh refinement. Second, an aerodynamic analysis for twodesigns, short and optimized, was conducted with thetraveling speed 125 m/s at the system pressure 0.15 bar.The concept of the short model was to delay the transitionto decrease the frictional drag;meanwhile that of theoptimized design was to minimize the pressure drag bydecreasing the frontal area and introduce the transitionmore toward the front of the pod. The computed resultsshow that the transition of the short model occurred moreon the rear side due to the pod shape, which resulted in 8%smaller frictional drag coefficient than that for the optimizedmodel. The pressure drag for the optimized designwas 24% smaller than that for the short design, half ofwhich is due to the decrease in the frontal area, and theother half is due to the smoothed rear-end shape. The totaldrag for the optimized model was 14% smaller than that forthe short model. Finally, the influence of the systempressure was investigated. As the system pressure and theReynolds number increase, the frictional drag coefficientincreases, and the transition point moves toward the front,which are the typical phenomena observed in the transitionregime.展开更多
Objective Epithelial mesenchymal transition(EMT)plays a very important role in ovarian cancer metastasis,and IL-8 released from mechanosensitive cancer cells may contribute to the EMT process of solid carcinomas.In th...Objective Epithelial mesenchymal transition(EMT)plays a very important role in ovarian cancer metastasis,and IL-8 released from mechanosensitive cancer cells may contribute to the EMT process of solid carcinomas.In this study,we have explored IL-8 and its receptors signal transduction process of human ovarian cancer cells under conditions of FSS,and simultaneously detected the EMT process of ovarian cancer.Methods After the fluid shear stress was loaded,LightCyclerTM system and ELISA were employed to assay the IL-8 mRNA expression and protein production,respectively.Meanwhile,IL-8 reporter gene pEGFP1-IL8USCS was constructed for determining IL-8 gene transcriptional activation through gene transfer and flow cytometric analysis.RT-PCR,Northern blot and immunofluorescence were used to determine the expression of IL-8 receptor CXCR2 at mRNA and protein levels.IL-8 downstream signaling molecule NF-κB nuclear translocation was observed by immunocytofluoresent staining.Western blot was used to examine IκB phosphorylation and EMT-related protein.Results(1)The increase of IL-8 mRNA expression by shear stress was time-dependent.The expression increased when SKOV3 cells exposed to fluid shear stress for 1 h,reached the summits at 2 h,gradually decreased at 3 h and remained at a constant level at 4~12 h.Additionally,IL-8 expression was negatively associated with the intensity of shear stress.After SKOV3 cells were exposed to low fluid shear stress(1.5 dyne/cm2)for 1 h and 2 h,IL-8 mRNA expression increased near 68 and 52 times respectively as that of SKOV3 cells exposed to a high fluid shear stress of 5.0 dyne/cm^2.(2)The productions of IL-8 protein in SKOV3 cells subjected to shear stress were time-dependent.The secretion reached the summit when SKOV3 cells exposed to fluid shear stress for 5 h,then IL-8 secretion gradually decreased at 8 h of stimulation by shear stress.IL-8 secretion increased obviously when fluid shear stress(0.5,1.5,or 2.0 dyne/cm2)was exerted on SKOV3 cells for 1 h.Notablely,the secretion of IL-8 was the highest when SKOV3 cells subjected to fluid shear stress 1.5dyne/cm^2,which was near 6 or 7 times as that of SKOV3 cells subjected to high fluid shear stress(5.0 dyne/cm^2).(3)There was an increase in enhanced green fluorescent protein expression in pEGFPI-IL8USCS-transfected SKOV3 cells subjected to a fluid shear stress of 1.5 dyne/cm2 for 2 h,suggesting a flow shear stress induced IL-8 gene transcriptional activation;(4)CXCR2,which was constitutively present on the surface of SKOV3 cells,increased following exposure to fluid shear stress for 60 min.(5)Following the application of a shear stress of 1.5 dyne/cm^2,NF-κB p65 became detectable in the cell nuclei and Phosphorylated IκB in cell lysates increased significantly;(6)Compared with the control group,critical EMT-related proteins vimentin was upregulated,E-cadherin was downregulated after the application of the 1.5 dyne/cm2shear stress for 2 h,which suggested the EMT of ovarian cancer.Conclusions FSS triggered IL-8/CXCR2 signaling of SK-OV3 cells represents an early gene activation and the activation can be mediated through NF-κB.When the fluid shear stress-induced IL-8/CXCR signaling activated,the expression of EMT-related proteins changed.This observation suggested that fluid shear stress-induced IL-8 activation and the downstream signal pathways may have important contribution to the EMT process of ovarian cancer cells.展开更多
A new type of two-dimensional self-consistent fluid model that couples an equivalent circuit module is used to in- vestigate the mode transition characteristics and hysteresis in hydrogen inductively coupled plasmas a...A new type of two-dimensional self-consistent fluid model that couples an equivalent circuit module is used to in- vestigate the mode transition characteristics and hysteresis in hydrogen inductively coupled plasmas at different pressures, by varying the series capacitance of the matching box. The variations of the electron density, temperature, and the circuit electrical properties are presented. As cycling the matching capacitance, at high pressure both the discontinuity and hysteresis appear for the plasma parameters and the transferred impedances of both the inductive and capacitive discharge components, while at low pressure only the discontinuity is seen. The simulations predict that the sheath plays a determi- native role on the presence of discontinuity and hysteresis at high pressure, by influencing the inductive coupling efficiency of applied power. Moreover, the values of the plasma transferred impedances at different pressures are compared, and the larger plasma inductance at low pressure due to less collision frequency, as analyzed, is the reason why the hysteresis is not seen at low pressure, even with a wider sheath. Besides, the behaviors of the coil voltage and current parameters during the mode transitions are investigated. They both increase (decrease) at the E to H (H to E) mode transition, indicating an improved (worsened) inductive power coupling efficiency.展开更多
In grassland ecosystems,the aerodynamic roughness(Z0)and frictional wind speed(u*)contribute to the aerodynamic impedance of the grassland canopy.Thus,they are often used in the studies of wind erosion and evapotransp...In grassland ecosystems,the aerodynamic roughness(Z0)and frictional wind speed(u*)contribute to the aerodynamic impedance of the grassland canopy.Thus,they are often used in the studies of wind erosion and evapotranspiration.However,the effect of wind speed and grazing measures on the aerodynamic impedance of the grassland canopy has received less analysis.In this study,we monitored wind speeds at multiple heights in grazed and grazing-prohibited grasslands for 1 month in 2021,determined the transit wind speed at 2.0 m height by comparing wind speed differences at the same height in both grasslands,and divided these transit wind speeds at intervals of 2.0 m/s to analyze the effect of the transit wind speed on the relationship among Z0,u*,and wind speed within the grassland canopy.The results showed that dividing the transit wind speeds into intervals has a positive effect on the logarithmic fit of the wind speed profile.After dividing the transit wind speeds into intervals,the wind speed at 0.1 m height(V0.1)gradually decreased with the increase of Z0,exhibiting three distinct stages:a sharp change zone,a steady change zone,and a flat zone;while the overall trend of u*increased first and then decreased with the increase of V0.1.Dividing the transit wind speeds into intervals improved the fitting relationship between Z0 and V0.1 and changed their fitting functions in grazed and grazing-prohibited grasslands.According to the computational fluid dynamic results,we found that the number of tall-stature plants has a more significant effect on windproof capacity than their height.The results of this study contribute to a better understanding of the relationship between wind speed and the aerodynamic impedance of vegetation in grassland environments.展开更多
The influence of driving frequency on the discharge regime of a homogenous dielectric barrier discharge in argon at atmospheric pressure is studied through a one-dimensional self-consistent fluid model. The simulation...The influence of driving frequency on the discharge regime of a homogenous dielectric barrier discharge in argon at atmospheric pressure is studied through a one-dimensional self-consistent fluid model. The simulation results show that the discharge exhibits five notable discharge modes, namely the Townsend mode, stable glow mode, chaotic mode, asymmetric glow, and multiple period glow mode in a broad frequency range. The transition mechanisms of these modes should be attributed to the competition between the applied voltage and the memory voltage induced by the surface charges.展开更多
For the enhancement of heat transfer efficiency,a novel turbulator inspired by the morphology of barchan dunes,called the mimetic barchan dune(MBD)turbulator,is designed and evaluated in the simplified gas turbine tra...For the enhancement of heat transfer efficiency,a novel turbulator inspired by the morphology of barchan dunes,called the mimetic barchan dune(MBD)turbulator,is designed and evaluated in the simplified gas turbine transition section.By using computational fluid dynamics(CFD),the numerical simulations for comparison have been carried out,concluding the smooth thermal surface,a thermal surface with riblet-shaped turbulator and a thermal surface with MBD turbulator.Then,two indicators are investigated for evaluating the coolant performance which are the heat transfer efficiency(η)on the outlet and the pressure loss(ΔP)in the coolant chamber.The numerical results show that the coolant has the best heat transfer efficiency with less pressure loss in the coolant chamber with the MBD turbulator.Then,the effect of the MBD turbulator sizes on heat transfer efficiency is investigated.When the height of the MBD turbulator(h)is set at 8 mm,the maximum amount of heat that could be transfered by the coolant is up to566.2 K and the corresponding heat transfer efficiency is 26.62%.The detail flows have been shown to elucidate the function of the MBD surface which may greatly arouse more design for solving harsh circumstance.展开更多
Nowadays, Autonomous Underwater Vehicles(AUVs) are frequently used for exploring the oceans. The hydrodynamics of AUVs moving in the vicinity of the water surface are significantly different at higher depths. In this ...Nowadays, Autonomous Underwater Vehicles(AUVs) are frequently used for exploring the oceans. The hydrodynamics of AUVs moving in the vicinity of the water surface are significantly different at higher depths. In this paper, the hydrodynamic coefficients of an AUV in non-dimensional depths of 0.75, 1, 1.5, 2, and 4D are obtained for movement close to the free-surface. Reynolds Averaged Navier Stokes Equations(RANS) are discretized using the finite volume approach and the water-surface effects modeled using the Volume of Fraction(VOF) method. As the operating speeds of AUVs are usually low, the boundary layer over them is not fully laminar or fully turbulent, so the effect of boundary layer transition from laminar to turbulent flow was considered in the simulations. Two different turbulence/transition models were used: 1) a full-turbulence model, the k-ε model, and 2) a turbulence/transition model, Menter's Transition-SST model. The results show that the Menter's Transition-SST model has a better consistency with experimental results. In addition, the wave-making effects of these bodies are studied at different immersion depths in the sea-surface vicinity or at finite depths. It is observed that the relevant pitch moments and lift coefficients are non-zero for these axi-symmetric bodies when they move close to the sea-surface. This is not expected for greater depths.展开更多
Experimental techniques for imaging laminar-turbulent transition of boundary layers using IR thermography are presented for both flight and wind tunnel test environments. A brief overview of other transition detection...Experimental techniques for imaging laminar-turbulent transition of boundary layers using IR thermography are presented for both flight and wind tunnel test environments. A brief overview of other transition detection techniques is discussed as motivation. A direct comparison is made between IR thermography and naphthalene flow visualization. A technique for obtaining quantitative transition location is presented.展开更多
Liquid gasification phenomenon was observable in liquid-solid dielectric barrier discharge (DBD) experiments. Starting from classical thermodynamics, this study aimed at finding the reason of liquid gasification in ...Liquid gasification phenomenon was observable in liquid-solid dielectric barrier discharge (DBD) experiments. Starting from classical thermodynamics, this study aimed at finding the reason of liquid gasification in the DBD experiments. Fluid statics and electrohydrodynamics were adopted to analyze the mechanism of phase transition from liquid to gas. The Sumoto effect was also employed to visually explain the change in the pressure of fluid due to the electric field. It was concluded from both theoretical analysis and experiment that the change in liquid pressure was a key factor causing liquid to gasify in DBD conditions.Furthermore, it was stressed that the liquid pressure was affected by many parameters including liquid permittivity, voltage, electric intensity, size of the discharge space and uniformity of the electric field distribution, etc. All of them affected DBD liquid gasification. The related results would provide useful theoretical evidence for multi-phase DBD applications.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 10874111,11304169,and 11174196
文摘We numerically study the thermodynamic properties of a hard ellipsoid fluid by mainly focusing on its phase transition from an isotropic phase into a nematic phase (i.e. isotropie-nematic phase transition). To improve the accuracy, precision, and efficiency of our computations, we attempt to employ the Wang-Landau NPT Monte Carlo algorithm in our simulations to calculate the function p(V) that gives the probability of arriving at the threshold density of the isotropic-nematic transition. Our results directly reveal that the nematic fluid phase, which is characterized by an ordered direction rather than an ordered configuration, appears and coexists with the isotropic phase when the aspect ratio a of the ellipsoid is located in a relatively narrow range of α = 2.0-2.25, and it becomes dominant and is fully established when α≥αcut = 2.25. We find that our estimated αcut is significantly lower than previously reported values of around 2.75. This prediction is further confirmed by the calculations of both the fluid reduced density and pressure of coexistence which show that the pressure grows up as the density increases and the probability function p(V) exhibits double peaks when the pressure enters the coexistence region. Based on these consistent results we are able to conclude that when α≥2.25 an ellipsoid fluid can fully display the nematic behavior. This study will place a useful and tight theoretical constraint on investigations of the isotropic-nematic phase transition in the future.
基金supported by National Natural Science Foundation of China(Grant No.41374116)the Fundamental Research Funds for Central Universities(Grant No.2014B39014)
文摘Local fluid flow(LFF) at the mesoscopic scale is the main dissipation mechanism of seismic waves in heterogeneous porous media within the seismic frequency band.LFF is easily influenced by the structure and boundary conditions of the porous media,which leads to different behaviors of the peak frequency of attenuation.The associated transition frequency can provide detailed information about the trend of LFF;therefore,research on the transition frequency of LFF and its relationship with the peak frequency of the corresponding attenuation(i.e.,inverse of quality factor) facilitates the detailed understanding of the effect of inner structures and boundary conditions in porous media.In this study,we firstly obtain the transition frequency of fluid flux based on Biot's theory of poroelasticity and the fast Fourier transform algorithm in a sample containing one repeating unit cell(RUC).We then analyze changes of these two frequencies in porous media with different porous properties.Finally,we extend our analysis to the influence of the undrained boundary condition on the transition frequency and peak frequency in porous media with multiple RUCs.This setup can facilitate the understanding of the effect from the undrained boundary condition.Results demonstrate that these two frequencies have the same trend at low water saturation,but amplitude variations differ between the frequencies as the amount of saturation increases.However,for cases of high water saturation,both the trend and the amplitude variation of these two frequencies fit well with each other.
文摘The simultaneous removal of up to 92% of the surfactant template and chemical implantation of transition metal complexes into mesopores has been successfully achieved by treating as-synthesized pure siliceous MCM-41 with supercritical CO2 modified with CH2Cl2/MeOH mixture, resulting in the formation of functionalized material with uniform pore structure.
文摘Abstract: The physico-chemical conditions under which the pegmatite dyke No. 3 was formed were discussed in the light of fluid-melt inclusion evidence. Our results lend support to the frac-tionation of hydrothermal solutions from magma. For the pegmatite dike No. 3, the magma-derived hydrothermal solutions are dominated by NaCl + CO2 + H2O.
基金The authors acknowledge all the members of the Swissloop Team for their great endeavor to compete in the Hyperloop pod Competition and to push the Hyperloop technology forward.The authors gratefully acknowledge Connova AG for their support in manufacturing of the pod.
文摘Three-dimensional compressible flow simulationswere conducted to develop a Hyperloop pod. Thenovelty is the usage of Gamma transition model, in whichthe transition from laminar to turbulent flow can be predicted.First, a mesh dependency study was undertaken,showing second-order convergence with respect to themesh refinement. Second, an aerodynamic analysis for twodesigns, short and optimized, was conducted with thetraveling speed 125 m/s at the system pressure 0.15 bar.The concept of the short model was to delay the transitionto decrease the frictional drag;meanwhile that of theoptimized design was to minimize the pressure drag bydecreasing the frontal area and introduce the transitionmore toward the front of the pod. The computed resultsshow that the transition of the short model occurred moreon the rear side due to the pod shape, which resulted in 8%smaller frictional drag coefficient than that for the optimizedmodel. The pressure drag for the optimized designwas 24% smaller than that for the short design, half ofwhich is due to the decrease in the frontal area, and theother half is due to the smoothed rear-end shape. The totaldrag for the optimized model was 14% smaller than that forthe short model. Finally, the influence of the systempressure was investigated. As the system pressure and theReynolds number increase, the frictional drag coefficientincreases, and the transition point moves toward the front,which are the typical phenomena observed in the transitionregime.
基金supported by Foundation of Sichuan Provincial Science and Technology Program ( 2019YFH0147,2019YFH0158)1. 3. 5 Project for Disciplines of Excellence,West China Hospital,Sichuan University ( ZYJC18016)
文摘Objective Epithelial mesenchymal transition(EMT)plays a very important role in ovarian cancer metastasis,and IL-8 released from mechanosensitive cancer cells may contribute to the EMT process of solid carcinomas.In this study,we have explored IL-8 and its receptors signal transduction process of human ovarian cancer cells under conditions of FSS,and simultaneously detected the EMT process of ovarian cancer.Methods After the fluid shear stress was loaded,LightCyclerTM system and ELISA were employed to assay the IL-8 mRNA expression and protein production,respectively.Meanwhile,IL-8 reporter gene pEGFP1-IL8USCS was constructed for determining IL-8 gene transcriptional activation through gene transfer and flow cytometric analysis.RT-PCR,Northern blot and immunofluorescence were used to determine the expression of IL-8 receptor CXCR2 at mRNA and protein levels.IL-8 downstream signaling molecule NF-κB nuclear translocation was observed by immunocytofluoresent staining.Western blot was used to examine IκB phosphorylation and EMT-related protein.Results(1)The increase of IL-8 mRNA expression by shear stress was time-dependent.The expression increased when SKOV3 cells exposed to fluid shear stress for 1 h,reached the summits at 2 h,gradually decreased at 3 h and remained at a constant level at 4~12 h.Additionally,IL-8 expression was negatively associated with the intensity of shear stress.After SKOV3 cells were exposed to low fluid shear stress(1.5 dyne/cm2)for 1 h and 2 h,IL-8 mRNA expression increased near 68 and 52 times respectively as that of SKOV3 cells exposed to a high fluid shear stress of 5.0 dyne/cm^2.(2)The productions of IL-8 protein in SKOV3 cells subjected to shear stress were time-dependent.The secretion reached the summit when SKOV3 cells exposed to fluid shear stress for 5 h,then IL-8 secretion gradually decreased at 8 h of stimulation by shear stress.IL-8 secretion increased obviously when fluid shear stress(0.5,1.5,or 2.0 dyne/cm2)was exerted on SKOV3 cells for 1 h.Notablely,the secretion of IL-8 was the highest when SKOV3 cells subjected to fluid shear stress 1.5dyne/cm^2,which was near 6 or 7 times as that of SKOV3 cells subjected to high fluid shear stress(5.0 dyne/cm^2).(3)There was an increase in enhanced green fluorescent protein expression in pEGFPI-IL8USCS-transfected SKOV3 cells subjected to a fluid shear stress of 1.5 dyne/cm2 for 2 h,suggesting a flow shear stress induced IL-8 gene transcriptional activation;(4)CXCR2,which was constitutively present on the surface of SKOV3 cells,increased following exposure to fluid shear stress for 60 min.(5)Following the application of a shear stress of 1.5 dyne/cm^2,NF-κB p65 became detectable in the cell nuclei and Phosphorylated IκB in cell lysates increased significantly;(6)Compared with the control group,critical EMT-related proteins vimentin was upregulated,E-cadherin was downregulated after the application of the 1.5 dyne/cm2shear stress for 2 h,which suggested the EMT of ovarian cancer.Conclusions FSS triggered IL-8/CXCR2 signaling of SK-OV3 cells represents an early gene activation and the activation can be mediated through NF-κB.When the fluid shear stress-induced IL-8/CXCR signaling activated,the expression of EMT-related proteins changed.This observation suggested that fluid shear stress-induced IL-8 activation and the downstream signal pathways may have important contribution to the EMT process of ovarian cancer cells.
基金supported by the National Natural Science Foundation of China(Grant Nos.11175034,11205025,11305023,and 11075029)
文摘A new type of two-dimensional self-consistent fluid model that couples an equivalent circuit module is used to in- vestigate the mode transition characteristics and hysteresis in hydrogen inductively coupled plasmas at different pressures, by varying the series capacitance of the matching box. The variations of the electron density, temperature, and the circuit electrical properties are presented. As cycling the matching capacitance, at high pressure both the discontinuity and hysteresis appear for the plasma parameters and the transferred impedances of both the inductive and capacitive discharge components, while at low pressure only the discontinuity is seen. The simulations predict that the sheath plays a determi- native role on the presence of discontinuity and hysteresis at high pressure, by influencing the inductive coupling efficiency of applied power. Moreover, the values of the plasma transferred impedances at different pressures are compared, and the larger plasma inductance at low pressure due to less collision frequency, as analyzed, is the reason why the hysteresis is not seen at low pressure, even with a wider sheath. Besides, the behaviors of the coil voltage and current parameters during the mode transitions are investigated. They both increase (decrease) at the E to H (H to E) mode transition, indicating an improved (worsened) inductive power coupling efficiency.
基金funded by the National Natural Science Foundation of China(52279017 and 52079063)Technological Achievements of Inner Mongolia Autonomous Region of China(2020CG0054 and 2022YFDZ0050)+1 种基金the Graduate Education Innovation Program of Inner Mongolia Autonomous Region of China(B20210188Z)the Program for Innovative Research Team in Universities of Inner Mongolia Autonomous Region,China(NMGIRT2313).
文摘In grassland ecosystems,the aerodynamic roughness(Z0)and frictional wind speed(u*)contribute to the aerodynamic impedance of the grassland canopy.Thus,they are often used in the studies of wind erosion and evapotranspiration.However,the effect of wind speed and grazing measures on the aerodynamic impedance of the grassland canopy has received less analysis.In this study,we monitored wind speeds at multiple heights in grazed and grazing-prohibited grasslands for 1 month in 2021,determined the transit wind speed at 2.0 m height by comparing wind speed differences at the same height in both grasslands,and divided these transit wind speeds at intervals of 2.0 m/s to analyze the effect of the transit wind speed on the relationship among Z0,u*,and wind speed within the grassland canopy.The results showed that dividing the transit wind speeds into intervals has a positive effect on the logarithmic fit of the wind speed profile.After dividing the transit wind speeds into intervals,the wind speed at 0.1 m height(V0.1)gradually decreased with the increase of Z0,exhibiting three distinct stages:a sharp change zone,a steady change zone,and a flat zone;while the overall trend of u*increased first and then decreased with the increase of V0.1.Dividing the transit wind speeds into intervals improved the fitting relationship between Z0 and V0.1 and changed their fitting functions in grazed and grazing-prohibited grasslands.According to the computational fluid dynamic results,we found that the number of tall-stature plants has a more significant effect on windproof capacity than their height.The results of this study contribute to a better understanding of the relationship between wind speed and the aerodynamic impedance of vegetation in grassland environments.
基金supported by the National Natural Science Foundation of China(Grant No.11205044)the Hebei Natural Science Fund,China(GrantNos.A2012201015 and A2011201006)+1 种基金the Research Foundation of Education Bureau of Hebei Province,China(Grant No.Y2012009)the Postdoctoral Science Foundation and Foundation of Hebei University,China(Grant No.2010Q30)
文摘The influence of driving frequency on the discharge regime of a homogenous dielectric barrier discharge in argon at atmospheric pressure is studied through a one-dimensional self-consistent fluid model. The simulation results show that the discharge exhibits five notable discharge modes, namely the Townsend mode, stable glow mode, chaotic mode, asymmetric glow, and multiple period glow mode in a broad frequency range. The transition mechanisms of these modes should be attributed to the competition between the applied voltage and the memory voltage induced by the surface charges.
基金supported by the National Key R&D Program of China (No.2018YFB1105100)the National Natural Science Foundation of China (No.51975246)+2 种基金the Advanced Manufacturing Project of Provincial School Construction of Jilin Province (No. SXGJSF2017-2)the Program for JLU Science and Technology Innovative Research Team (2019TD-34)the China Postdoctoral Science Foundation Funded Project (No. 2016M590256)
文摘For the enhancement of heat transfer efficiency,a novel turbulator inspired by the morphology of barchan dunes,called the mimetic barchan dune(MBD)turbulator,is designed and evaluated in the simplified gas turbine transition section.By using computational fluid dynamics(CFD),the numerical simulations for comparison have been carried out,concluding the smooth thermal surface,a thermal surface with riblet-shaped turbulator and a thermal surface with MBD turbulator.Then,two indicators are investigated for evaluating the coolant performance which are the heat transfer efficiency(η)on the outlet and the pressure loss(ΔP)in the coolant chamber.The numerical results show that the coolant has the best heat transfer efficiency with less pressure loss in the coolant chamber with the MBD turbulator.Then,the effect of the MBD turbulator sizes on heat transfer efficiency is investigated.When the height of the MBD turbulator(h)is set at 8 mm,the maximum amount of heat that could be transfered by the coolant is up to566.2 K and the corresponding heat transfer efficiency is 26.62%.The detail flows have been shown to elucidate the function of the MBD surface which may greatly arouse more design for solving harsh circumstance.
文摘Nowadays, Autonomous Underwater Vehicles(AUVs) are frequently used for exploring the oceans. The hydrodynamics of AUVs moving in the vicinity of the water surface are significantly different at higher depths. In this paper, the hydrodynamic coefficients of an AUV in non-dimensional depths of 0.75, 1, 1.5, 2, and 4D are obtained for movement close to the free-surface. Reynolds Averaged Navier Stokes Equations(RANS) are discretized using the finite volume approach and the water-surface effects modeled using the Volume of Fraction(VOF) method. As the operating speeds of AUVs are usually low, the boundary layer over them is not fully laminar or fully turbulent, so the effect of boundary layer transition from laminar to turbulent flow was considered in the simulations. Two different turbulence/transition models were used: 1) a full-turbulence model, the k-ε model, and 2) a turbulence/transition model, Menter's Transition-SST model. The results show that the Menter's Transition-SST model has a better consistency with experimental results. In addition, the wave-making effects of these bodies are studied at different immersion depths in the sea-surface vicinity or at finite depths. It is observed that the relevant pitch moments and lift coefficients are non-zero for these axi-symmetric bodies when they move close to the sea-surface. This is not expected for greater depths.
文摘Experimental techniques for imaging laminar-turbulent transition of boundary layers using IR thermography are presented for both flight and wind tunnel test environments. A brief overview of other transition detection techniques is discussed as motivation. A direct comparison is made between IR thermography and naphthalene flow visualization. A technique for obtaining quantitative transition location is presented.
基金supported by the Doctoral Research Fund of Higher Education of China (No.20070286099)
文摘Liquid gasification phenomenon was observable in liquid-solid dielectric barrier discharge (DBD) experiments. Starting from classical thermodynamics, this study aimed at finding the reason of liquid gasification in the DBD experiments. Fluid statics and electrohydrodynamics were adopted to analyze the mechanism of phase transition from liquid to gas. The Sumoto effect was also employed to visually explain the change in the pressure of fluid due to the electric field. It was concluded from both theoretical analysis and experiment that the change in liquid pressure was a key factor causing liquid to gasify in DBD conditions.Furthermore, it was stressed that the liquid pressure was affected by many parameters including liquid permittivity, voltage, electric intensity, size of the discharge space and uniformity of the electric field distribution, etc. All of them affected DBD liquid gasification. The related results would provide useful theoretical evidence for multi-phase DBD applications.