The purpose of this paper is to present a two-phase 3D magnetohydrodynamics （MHD） flow model that combines the volume of fluid （VOF） method with the technique derived from induced-magnetic-field equations for liqu...The purpose of this paper is to present a two-phase 3D magnetohydrodynamics （MHD） flow model that combines the volume of fluid （VOF） method with the technique derived from induced-magnetic-field equations for liquid metal free surface MHD-jet-flow. Analogy between the induced-magnetic-filed equation and the conventional computational fluid dynamics （CFD） equation is made, so that the equation can be conveniently accounted for by CFD. A penalty factor numerical method is introduced in order to force the local divergence-free condition of the magnetic fields and an extension of the void insulating calculation domain is applied to ensure that the induced-magnetic field at its boundaries is null. These simulation results for lithium liquid metal jets under magnetic field configurations of Magnetic Torus （Mtor） and National Spherical Torus Experiment （NSTX） outboard divertor have shown that three dimensional jet can not be annihilated by magnetic braking and its cross-section will deform in such a way that the momentum flux of the jet is conserved. 3D MHD effects from a magnetic field gradient cause return currents to interact with applied magnetic fields and produce unfavorable Lorentz forces. Under 3D applied non-uniform magnetic fields of the divertor, unfavorable Lorentz forces lead to a substantial change in flow pattern and a reduction in flow velocity, with the jet cross-section moving to one side of the jet space. These critical phenomena can not be revealed by 2D models.展开更多
Spray experiments of RP-3 jet fuel at non-evaporating and evaporating environments were studied on a constant volume spray chamber,and diffusive back-imaging technique was used to capture the transient spray developme...Spray experiments of RP-3 jet fuel at non-evaporating and evaporating environments were studied on a constant volume spray chamber,and diffusive back-imaging technique was used to capture the transient spray development processes.Spray tip penetration,projected spray area and cone angle of RP-3 jet fuel were derived from the spray development images,and compared to those of diesel fuel.It is observed that non-evaporating sprays of RP-3 jet fuel and diesel fuel do not exhibit significant differences,as their spray penetration distances,projected spray areas and spray cone angles are consistent at most test conditions.The evaporating sprays of RP-3 jet fuel produce shorter liquid-phase penetration distances and lower projected spray areas than those of diesel fuel,and these differences are particularly pronounced at low ambient temperatures.However,fuel effects on the evaporating spray cone angle are insignificant.Further,increased ambient density or ambient temperature shortens the liquid-phase spray penetration distance and reduces the liquid-phase spray area,and these effects are more pronounced for diesel fuel than RP-3 jet fuel.展开更多
探讨模拟射流雾化的若干典型VOF(Volume of Fluid)界面重构方法,并在开源流体力学计算软件OpenFOAM中运用VOF-LPT(Lagrangian Particle Tracking)耦合算法;该算法兼顾模拟的准确性和计算效率,可较为准确地模拟从连续液体到离散小液滴的...探讨模拟射流雾化的若干典型VOF(Volume of Fluid)界面重构方法,并在开源流体力学计算软件OpenFOAM中运用VOF-LPT(Lagrangian Particle Tracking)耦合算法;该算法兼顾模拟的准确性和计算效率,可较为准确地模拟从连续液体到离散小液滴的射流雾化过程,并为更大尺度的模拟提供了一种可行的高效模拟方案。展开更多
A submerged,vertical turbulent plane water jet impinging onto a free surface will be self-excited into a flapping oscillation when the jet velocity,leaving the jet orifice,exceeds a critical value.The flapping phenome...A submerged,vertical turbulent plane water jet impinging onto a free surface will be self-excited into a flapping oscillation when the jet velocity,leaving the jet orifice,exceeds a critical value.The flapping phenomenon was verified simultaneously in this paper by laser Doppler velocimeter measurement and numerical analyses with volume of fluid approach coupled with a large eddy simulation turbulent model.The general agreement of mean velocities between numerical predictions and experimental results in self-similar region is good for two cases:Reynolds numbers 2090 and 2970,which correspond to the stable impinging jet and flapping jet.Results show that the flapping jet is a new flow pattern for submerged turbulent plane jets with characteristic flapping frequency,and that the decay of the mean velocity along the jet centerline is considerably faster than that of the stable impinging state.展开更多
Jet fuel is widely used in air transportation,and sometimes for special vehicles in ground transportation.In the latter case,fuel spray auto-ignition behavior is an important index for engine operation reliability.Sur...Jet fuel is widely used in air transportation,and sometimes for special vehicles in ground transportation.In the latter case,fuel spray auto-ignition behavior is an important index for engine operation reliability.Surrogate fuel is usually used for fundamental combustion study due to the complex composition of practical fuels.As for jet fuels,two-component or three-component surrogate is usually selected to emulate practical fuels.The spray auto-ignition characteristics of RP-3 jet fuel and its three surrogates,the 70%mol n-decane/30%mol 1,2,4-trimethylbenzene blend(Surrogate 1),the 51%mol n-decane/49%mol 1,2,4-trimethylbenzene blend(Surrogate 2),and the 49.8%mol n-dodecane/21.6%mol iso-cetane/28.6%mol toluene blend(Surrogate 3)were studied in a heated constant volume combustion chamber.Surrogate 1 and Surrogate 2 possess the same components,but their blending percentages are different,as the two surrogates were designed to capture the H/C ratio(Surrogate 1)and DCN(Surrogate 2)of RP-3 jet fuel,respectively.Surrogate 3 could emulate more physiochemical properties of RP-3 jet fuel,including molecular weight,H/C ratio and DCN.Experimental results indicate that Surrogate 1 overestimates the auto-ignition propensity of RP-3 jet fuel,whereas Surrogates 2 and 3 show quite similar auto-ignition propensity with RP-3 jet fuel.Therefore,to capture the spray auto-ignition behaviors,DCN is the most important parameter to match when designing the surrogate formulation.However,as the ambient temperature changes,the surrogates matching DCN may still show some differences from the RP-3 jet fuel,e.g.,the first-stage heat release influenced by low-temperature chemistry.展开更多
In the present work, we propose to numerically study a combined turbulent wall and offset jet flow(this combination will be denoted WOJ). Several turbulence models were tested in this study: the standard k-w, SST k-w,...In the present work, we propose to numerically study a combined turbulent wall and offset jet flow(this combination will be denoted WOJ). Several turbulence models were tested in this study: the standard k-w, SST k-w, standard k-ε, RNG, and realizable k-ε model. A parametric study was performed to determine the effect of offset ratio H and the velocity ratio r on the longitudinal and transverse positions of the merge point(MP), the combined point(CP), the upper vortex center(UVC) and the lower vortex center(LVC). Correlations that predict the position of these characteristic points of the WOJ flow as a function of H and r have been provided. Results show that any increase in the velocity ratio causes a displacement of the MP, CP, UVC and LVC further upstream along the longitudinal direction. Concerning the transverse positions, the increase of velocity ratio results in a deviation of the merge point(MP) and the lower vortex center(LVC) toward the strong jet(LWJ) whereas the transverse position of combined point(CP) and the upper vortex center(UVC) is almost independent of the velocity ratio.展开更多
This paper applies numerical methods to investigate the non-spherical bubble collapse near a rigid boundary. A three-dimensional model, with the mass conservation equation reformulated for considering the compressibil...This paper applies numerical methods to investigate the non-spherical bubble collapse near a rigid boundary. A three-dimensional model, with the mass conservation equation reformulated for considering the compressibility effect, is built to deal with the coupling between the pressure and the flow velocity in the momentum and energy equations and to simulate the temporal evolution of the single bubble oscillation and its surrounding flow structure. The investigations focus on the global bubble patterns and its schlieren contours, as well as the high-speed jet accompanied when the bubble collapses and the counter jet is generated in the rebound stage. The results show that the robust pressure waves emitted due to the bubble collapse lead to substantial changes of the flow structures around the bubble, especially the formation of the counter jet generated in the rebound stage. Furthermore, compared with the high-speed jet when the bubble collapses, the counter jet in the rebound stage emits the momentum several times greater in the magnitude and in diametrically opposite direction at the monitoring point.展开更多
A submerged turbulent plane jet in shallow water impinging vertically onto the free surface will produce a large-scale flapping motion when the jet exit velocity is larger than a critical one.The flapping phenomenon i...A submerged turbulent plane jet in shallow water impinging vertically onto the free surface will produce a large-scale flapping motion when the jet exit velocity is larger than a critical one.The flapping phenomenon is verified in this paper through a large eddy simulation where the free surface is modeled by volume of fluid approach.The quantitative results for flapping jet are found to be in good agreement with available experimental data in terms of mean velocity,flapping-induced velocity and turbulence intensity.Results show that the flapping motion is a new flow pattern with characteristic flapping frequency for submerged turbulent plane jets,the mean centerline velocity decay is considerably faster than that of the stable impinging jet without flapping motion,and the flapping-induced velocities are as important as the turbulent fluctuations.展开更多
In this article,laminar convective heat transfer of a confined slot impinging jet with nanofluid has been numerically investigated over Reynolds number ranges of 200e1000.Two circular ribs are mounted on the lower-tar...In this article,laminar convective heat transfer of a confined slot impinging jet with nanofluid has been numerically investigated over Reynolds number ranges of 200e1000.Two circular ribs are mounted on the lower-target surface:one rib located right the stagnation point and another one located on the left of the stagnation point.SiO2-water nanofluid with nanoparticles volume fraction ranging from 0 to 4%and nanoparticles diameters of 30 nm has been examined.The two-dimensional governing continuity,momentum and energy equations have been solved using finite volume method based on SIMPLE algorithm.The effect of Reynolds number,nanoparticles volume fraction,rib height and rib location on the flow and thermal characteristics are presented and discussed.Results showed that the average Nusselt number,performance factor,total entropy generation as well as friction factor increase with increasing nanoparticles volume fraction.In addition,it is found that the best thermal-hydraulic performance factor is around 1.89 which is obtained at Reynolds number of 1000,nanoparticles volume fraction of 4%,the rib height of 0.1 and the rib location of 2.展开更多
基金National Natural Science Foundation of China (No. 503006006) and by the Scientific Research Foun-dation for the Returned Overseas Chinese Scholars, State Education Ministry
文摘The purpose of this paper is to present a two-phase 3D magnetohydrodynamics （MHD） flow model that combines the volume of fluid （VOF） method with the technique derived from induced-magnetic-field equations for liquid metal free surface MHD-jet-flow. Analogy between the induced-magnetic-filed equation and the conventional computational fluid dynamics （CFD） equation is made, so that the equation can be conveniently accounted for by CFD. A penalty factor numerical method is introduced in order to force the local divergence-free condition of the magnetic fields and an extension of the void insulating calculation domain is applied to ensure that the induced-magnetic field at its boundaries is null. These simulation results for lithium liquid metal jets under magnetic field configurations of Magnetic Torus （Mtor） and National Spherical Torus Experiment （NSTX） outboard divertor have shown that three dimensional jet can not be annihilated by magnetic braking and its cross-section will deform in such a way that the momentum flux of the jet is conserved. 3D MHD effects from a magnetic field gradient cause return currents to interact with applied magnetic fields and produce unfavorable Lorentz forces. Under 3D applied non-uniform magnetic fields of the divertor, unfavorable Lorentz forces lead to a substantial change in flow pattern and a reduction in flow velocity, with the jet cross-section moving to one side of the jet space. These critical phenomena can not be revealed by 2D models.
基金supported by National Natural Science Foundation of China(Grant Nos.52022058 and 51776124)by Ministry of Education of China(Grant No.6141A020335)。
文摘Spray experiments of RP-3 jet fuel at non-evaporating and evaporating environments were studied on a constant volume spray chamber,and diffusive back-imaging technique was used to capture the transient spray development processes.Spray tip penetration,projected spray area and cone angle of RP-3 jet fuel were derived from the spray development images,and compared to those of diesel fuel.It is observed that non-evaporating sprays of RP-3 jet fuel and diesel fuel do not exhibit significant differences,as their spray penetration distances,projected spray areas and spray cone angles are consistent at most test conditions.The evaporating sprays of RP-3 jet fuel produce shorter liquid-phase penetration distances and lower projected spray areas than those of diesel fuel,and these differences are particularly pronounced at low ambient temperatures.However,fuel effects on the evaporating spray cone angle are insignificant.Further,increased ambient density or ambient temperature shortens the liquid-phase spray penetration distance and reduces the liquid-phase spray area,and these effects are more pronounced for diesel fuel than RP-3 jet fuel.
文摘探讨模拟射流雾化的若干典型VOF(Volume of Fluid)界面重构方法,并在开源流体力学计算软件OpenFOAM中运用VOF-LPT(Lagrangian Particle Tracking)耦合算法;该算法兼顾模拟的准确性和计算效率,可较为准确地模拟从连续液体到离散小液滴的射流雾化过程,并为更大尺度的模拟提供了一种可行的高效模拟方案。
基金supported by the National Natural Science Foundation of China(Grant No.10472046)the Priority Academic Program Development of Jiangsu Higher Education Institutions,grants from the Postgraduate Research and Innovation Project of Jiangsu Province(Grant No.CX08B_035Z)PhD Thesis Innovation and Excellence Fund of Nanjing University of Aeronautics&Astronautics(Grant No.BCXJ08-01)
文摘A submerged,vertical turbulent plane water jet impinging onto a free surface will be self-excited into a flapping oscillation when the jet velocity,leaving the jet orifice,exceeds a critical value.The flapping phenomenon was verified simultaneously in this paper by laser Doppler velocimeter measurement and numerical analyses with volume of fluid approach coupled with a large eddy simulation turbulent model.The general agreement of mean velocities between numerical predictions and experimental results in self-similar region is good for two cases:Reynolds numbers 2090 and 2970,which correspond to the stable impinging jet and flapping jet.Results show that the flapping jet is a new flow pattern for submerged turbulent plane jets with characteristic flapping frequency,and that the decay of the mean velocity along the jet centerline is considerably faster than that of the stable impinging state.
基金This research work was supported by the National Natural Science Foundation of China(Grant Nos.51776124 and 51861135303)the Belt and Road International Collaboration Program by Shanghai Science and Technology Committee(Grant No.19160745400).
文摘Jet fuel is widely used in air transportation,and sometimes for special vehicles in ground transportation.In the latter case,fuel spray auto-ignition behavior is an important index for engine operation reliability.Surrogate fuel is usually used for fundamental combustion study due to the complex composition of practical fuels.As for jet fuels,two-component or three-component surrogate is usually selected to emulate practical fuels.The spray auto-ignition characteristics of RP-3 jet fuel and its three surrogates,the 70%mol n-decane/30%mol 1,2,4-trimethylbenzene blend(Surrogate 1),the 51%mol n-decane/49%mol 1,2,4-trimethylbenzene blend(Surrogate 2),and the 49.8%mol n-dodecane/21.6%mol iso-cetane/28.6%mol toluene blend(Surrogate 3)were studied in a heated constant volume combustion chamber.Surrogate 1 and Surrogate 2 possess the same components,but their blending percentages are different,as the two surrogates were designed to capture the H/C ratio(Surrogate 1)and DCN(Surrogate 2)of RP-3 jet fuel,respectively.Surrogate 3 could emulate more physiochemical properties of RP-3 jet fuel,including molecular weight,H/C ratio and DCN.Experimental results indicate that Surrogate 1 overestimates the auto-ignition propensity of RP-3 jet fuel,whereas Surrogates 2 and 3 show quite similar auto-ignition propensity with RP-3 jet fuel.Therefore,to capture the spray auto-ignition behaviors,DCN is the most important parameter to match when designing the surrogate formulation.However,as the ambient temperature changes,the surrogates matching DCN may still show some differences from the RP-3 jet fuel,e.g.,the first-stage heat release influenced by low-temperature chemistry.
文摘In the present work, we propose to numerically study a combined turbulent wall and offset jet flow(this combination will be denoted WOJ). Several turbulence models were tested in this study: the standard k-w, SST k-w, standard k-ε, RNG, and realizable k-ε model. A parametric study was performed to determine the effect of offset ratio H and the velocity ratio r on the longitudinal and transverse positions of the merge point(MP), the combined point(CP), the upper vortex center(UVC) and the lower vortex center(LVC). Correlations that predict the position of these characteristic points of the WOJ flow as a function of H and r have been provided. Results show that any increase in the velocity ratio causes a displacement of the MP, CP, UVC and LVC further upstream along the longitudinal direction. Concerning the transverse positions, the increase of velocity ratio results in a deviation of the merge point(MP) and the lower vortex center(LVC) toward the strong jet(LWJ) whereas the transverse position of combined point(CP) and the upper vortex center(UVC) is almost independent of the velocity ratio.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.41776194,91752105 and 51679005).
文摘This paper applies numerical methods to investigate the non-spherical bubble collapse near a rigid boundary. A three-dimensional model, with the mass conservation equation reformulated for considering the compressibility effect, is built to deal with the coupling between the pressure and the flow velocity in the momentum and energy equations and to simulate the temporal evolution of the single bubble oscillation and its surrounding flow structure. The investigations focus on the global bubble patterns and its schlieren contours, as well as the high-speed jet accompanied when the bubble collapses and the counter jet is generated in the rebound stage. The results show that the robust pressure waves emitted due to the bubble collapse lead to substantial changes of the flow structures around the bubble, especially the formation of the counter jet generated in the rebound stage. Furthermore, compared with the high-speed jet when the bubble collapses, the counter jet in the rebound stage emits the momentum several times greater in the magnitude and in diametrically opposite direction at the monitoring point.
基金The work was supported by National Natural Science Foundation of China(Grant No.10472046)the Priority Academic Program Development of Jiangsu Higher Education Institutions,grants from the Postgraduate Research and Innovation Project of Jiangsu Province(GrantNo.CX08B 035)PhD Thesis Innovation and Excellence Fund of NUAA(Grant No.BCXJ08-01).
文摘A submerged turbulent plane jet in shallow water impinging vertically onto the free surface will produce a large-scale flapping motion when the jet exit velocity is larger than a critical one.The flapping phenomenon is verified in this paper through a large eddy simulation where the free surface is modeled by volume of fluid approach.The quantitative results for flapping jet are found to be in good agreement with available experimental data in terms of mean velocity,flapping-induced velocity and turbulence intensity.Results show that the flapping motion is a new flow pattern with characteristic flapping frequency for submerged turbulent plane jets,the mean centerline velocity decay is considerably faster than that of the stable impinging jet without flapping motion,and the flapping-induced velocities are as important as the turbulent fluctuations.
文摘In this article,laminar convective heat transfer of a confined slot impinging jet with nanofluid has been numerically investigated over Reynolds number ranges of 200e1000.Two circular ribs are mounted on the lower-target surface:one rib located right the stagnation point and another one located on the left of the stagnation point.SiO2-water nanofluid with nanoparticles volume fraction ranging from 0 to 4%and nanoparticles diameters of 30 nm has been examined.The two-dimensional governing continuity,momentum and energy equations have been solved using finite volume method based on SIMPLE algorithm.The effect of Reynolds number,nanoparticles volume fraction,rib height and rib location on the flow and thermal characteristics are presented and discussed.Results showed that the average Nusselt number,performance factor,total entropy generation as well as friction factor increase with increasing nanoparticles volume fraction.In addition,it is found that the best thermal-hydraulic performance factor is around 1.89 which is obtained at Reynolds number of 1000,nanoparticles volume fraction of 4%,the rib height of 0.1 and the rib location of 2.
