Within the magnetohydrodynamics （MHD） frame, we analyse the effect of viscosity on magneto-Rayleigh Taylor （MRT） instability in a Z-pinch configuration by using an exact method and an approximate method separately...Within the magnetohydrodynamics （MHD） frame, we analyse the effect of viscosity on magneto-Rayleigh Taylor （MRT） instability in a Z-pinch configuration by using an exact method and an approximate method separately. It is demonstrated that the plasma viscosity indeed has a stabilization effect on the MRT mode in the whole wavenumber region, and its influence increases with the perturbation wavenumber increasing. After the characteristics and feasibility of the approximate method have been investigated, we apply it to the stability analysis of viscous plasma where a sheared axial flow （SAF） is involved, and we attain an analytical dispersion relation. It is suggested that the viscosity and the SAF are complemental with each other, and a wide wavenumber range of perturbation is possible to be restrained if the SAF and the viscosity are large enough. Finally, we calculate the possible value of viscosity parameter according to the current experimental conditions, and the results show that since the value of viscosity is much less than the threshold value, its mitigation effect is small enough to be neglected. The role of the viscosity in the stabilization becomes considerable only if special techniques are so developed that the Z-pinch plasma viscosity can be increased greatly.展开更多
The dynamics of an axially accelerating beam subjected to axial flow is studied.Based on the Floquet theory and the Runge-Kutta algorithm,the stability and nonlinear vibration of the beam are analyzed by considering t...The dynamics of an axially accelerating beam subjected to axial flow is studied.Based on the Floquet theory and the Runge-Kutta algorithm,the stability and nonlinear vibration of the beam are analyzed by considering the effects of several system parameters such as the mean speed,flow velocity,axial added mass coefficient,mass ratio,slenderness ratio,tension and viscosity coefficient.Numerical results show that when the pulsation frequency of the axial speed is close to the sum of first-and second-mode frequencies or twice the lowest two natural frequencies,instability with combination or subharmonic resonance would occur.It is found that the beam can undergo the periodic-1 motion under subharmonic resonance and the quasi-periodic motion under combination resonance.With the change of system parameters,the stability boundary may be widened,narrowed or drifted.In addition,the vibration amplitude of the beam under resonance can also be affected by changing the values of system parameters.展开更多
The hydrodynamic instability of the axial flow pump in a loop reactor has long been a troubling issue to be solved in the polyethylene industry due to the lack of a better mechanismic understanding.Generally,the insta...The hydrodynamic instability of the axial flow pump in a loop reactor has long been a troubling issue to be solved in the polyethylene industry due to the lack of a better mechanismic understanding.Generally,the instability of an axial flow pump can be reflected by the fluctuation of the pump head.In this study,the transient computational fluid dynamics(CFD)simulation is adopted to study the hydrodynamic instability of the axial flow pump used in an ethylene polymerization loop reactor.The results show that the pump head under single liquid phase nearly remains constant while the pump head under slurry phase fluctuates due to the variation of solid volume fraction distribution in the pump.Besides,under the combined effect of the maximum solid volume fraction difference in the pump and the turbulence intensity of the liquid phase,the fluctuation of the pump head under slurry phase increases when the solid volume fraction in the loop reactor increases from 0.10 to 0.29,and the fluctuation decreases,when the solid volume fraction increases from 0.29 to 0.35.Furthermore,there is a negative correlation between the pump head and the solid volume fraction in the pump;with the increase of solid volume fraction in the loop reactor,and the correlation coefficient increases as well.Moreover,a‘spiral particulate band’phenomenon is formed in the ascending leg caused by three mechanisms,viz.:the segregation of particles in all bends,the dispersion of particles by the secondary flow in the ascending leg,and the rotational movement of particles in the pump.展开更多
The influences of the internal and external outlet angles on separation performance and flow field are compared and analyzed. Two arc functions are employed for controlling the internal and external angles. The separa...The influences of the internal and external outlet angles on separation performance and flow field are compared and analyzed. Two arc functions are employed for controlling the internal and external angles. The separation process in the cyclone tube is calculated by using two-fluid model based on the Eulerian-Eulerian method.The results show that the structure with the internal outlet angle smaller than the external one is more beneficial to the separation performance. It is found that the small internal angle can help increase the swirl number,while the small external angle can help increase the friction coefficient. Several groups of numerical simulations are conducted for the air intake unit of the gas turbine in practice. When the internal outlet angle is 35° and the external outlet angle is 40°,the blade has sufficient cyclone strength and the separation rate of particles with diameters of 10—100 μm is between70%—98%. The small blade angle is more conducive to the separation of fine particles,leading to violent collision of large particles on the outer wall and reduction of separation efficiency. In addition,reducing the external angle is conducive to the discharge of large particles.展开更多
A magnetohydrodynamic (MHD) formulation is derived to investigate and compare the mitigation effects of both the sheared axial flow and finite Larmor radius (FLR) on the Rayleigh-Taylor (RT) instability in Z-pinch imp...A magnetohydrodynamic (MHD) formulation is derived to investigate and compare the mitigation effects of both the sheared axial flow and finite Larmor radius (FLR) on the Rayleigh-Taylor (RT) instability in Z-pinch implosions. The sheared axial flow is introduced into MHD equations in a conventional way and the FLR effect into the equations via /t → -i(w+ik⊥2pi2Ωi,), as proposed in our previous paper [Chin. Phys. Lett. 2002, 19:217] , where k⊥2 pi2 is referred to FLR effect from the general kinetic theory of magnetized plasma. Therefore the linearized continuity and momentum equations for the perturbed mass-density and velocity include both the sheared axial flow and the FLR effect. It is found that the effect of sheared axial flow with a lower peak velocity can mitigate RT instability in the whole wavenumber region and the effect of sheared axial flow with a higher one can mitigate RT instability only in the large wavenumber region (for normalized wavenumber k】2.4); The effect of FLR can mitigate RT instability in the whole wavenumber region and the mitigation effect is stronger than that of the sheared axial flow with a lower peak velocity in the almost whole wavenumber region.展开更多
Airfoil is the element of fan blade design. It is strongly anticipated to design a fan of ave- raged high performance over a wide operation range. Multi-point optimization design of airfoil for axial flow fan was prop...Airfoil is the element of fan blade design. It is strongly anticipated to design a fan of ave- raged high performance over a wide operation range. Multi-point optimization design of airfoil for axial flow fan was proposed over specific operation range. Weighted objective function of airfoil lift-drag ratio was constructed for several operation points around the designing one. Airfoil was defined by parametric B-spline curve of limited shape controlling points. Results show that normal standard airfoils have remained spaces to be optimized under specific operation conditions. Airfoil performance is sensitive to flow′s Reynolds number and cascade solidity. Predicting flow transition along airfoil profile is essential to search for optimized one. Optimized airfoil of wide operation range is possible to obtain with prescribed fitness function. Obtainments of multi-point optimization may be relatively lower at design point, but positive obtainments are achieved at off-design ones. Resulted airfoil is specially suitable for axial flow fans operating frequently at off-design point such as air condition coolers.展开更多
The axial power flow (APF) magnitude and attenuation distributions of ultrasonic longitudinal guided waves in viscous liquid-filled elastic pipes are investigated. The optimal location, optimal mode and its frequency-...The axial power flow (APF) magnitude and attenuation distributions of ultrasonic longitudinal guided waves in viscous liquid-filled elastic pipes are investigated. The optimal location, optimal mode and its frequency-thickness product (fd) for the test of pipes filled with viscous liquid are chosen according to APF and attenuation distributions. The results show that the APF magnitude distribution is an important parameter in choosing the modes and parameters. A particular mode has weak dispersion in ranges of fd values with large group velocity, while other modes with smaller group velocity in the same fd ranges have stronger dispersion. It has been observed that, within these ranges, the chosen mode has a larger APF on the (pipe’s) wall. Therefore, in the region of fd values where a particular mode has a large group velocity, this mode will be effective to be used in testing elastic pipes filled with viscous liquid. The results obtained from both the APF analysis and attenuation distribution are consistent.展开更多
基金Project supported by the National Science Foundation of China (Grant Nos 10575014 and 10635050)
文摘Within the magnetohydrodynamics （MHD） frame, we analyse the effect of viscosity on magneto-Rayleigh Taylor （MRT） instability in a Z-pinch configuration by using an exact method and an approximate method separately. It is demonstrated that the plasma viscosity indeed has a stabilization effect on the MRT mode in the whole wavenumber region, and its influence increases with the perturbation wavenumber increasing. After the characteristics and feasibility of the approximate method have been investigated, we apply it to the stability analysis of viscous plasma where a sheared axial flow （SAF） is involved, and we attain an analytical dispersion relation. It is suggested that the viscosity and the SAF are complemental with each other, and a wide wavenumber range of perturbation is possible to be restrained if the SAF and the viscosity are large enough. Finally, we calculate the possible value of viscosity parameter according to the current experimental conditions, and the results show that since the value of viscosity is much less than the threshold value, its mitigation effect is small enough to be neglected. The role of the viscosity in the stabilization becomes considerable only if special techniques are so developed that the Z-pinch plasma viscosity can be increased greatly.
基金supported by the National Natural Science Foundation of China(Nos.11972167,12072119,12102139).
文摘The dynamics of an axially accelerating beam subjected to axial flow is studied.Based on the Floquet theory and the Runge-Kutta algorithm,the stability and nonlinear vibration of the beam are analyzed by considering the effects of several system parameters such as the mean speed,flow velocity,axial added mass coefficient,mass ratio,slenderness ratio,tension and viscosity coefficient.Numerical results show that when the pulsation frequency of the axial speed is close to the sum of first-and second-mode frequencies or twice the lowest two natural frequencies,instability with combination or subharmonic resonance would occur.It is found that the beam can undergo the periodic-1 motion under subharmonic resonance and the quasi-periodic motion under combination resonance.With the change of system parameters,the stability boundary may be widened,narrowed or drifted.In addition,the vibration amplitude of the beam under resonance can also be affected by changing the values of system parameters.
基金financial supports from Projects of the National Natural Science Foundation of China for Young (No.21808198)the Major Research Project of National Natural Science Foundation of China (No.91834303)the Science Fund for Creative Research Groups of National Natural Science Foundation of China (No.61621002)
文摘The hydrodynamic instability of the axial flow pump in a loop reactor has long been a troubling issue to be solved in the polyethylene industry due to the lack of a better mechanismic understanding.Generally,the instability of an axial flow pump can be reflected by the fluctuation of the pump head.In this study,the transient computational fluid dynamics(CFD)simulation is adopted to study the hydrodynamic instability of the axial flow pump used in an ethylene polymerization loop reactor.The results show that the pump head under single liquid phase nearly remains constant while the pump head under slurry phase fluctuates due to the variation of solid volume fraction distribution in the pump.Besides,under the combined effect of the maximum solid volume fraction difference in the pump and the turbulence intensity of the liquid phase,the fluctuation of the pump head under slurry phase increases when the solid volume fraction in the loop reactor increases from 0.10 to 0.29,and the fluctuation decreases,when the solid volume fraction increases from 0.29 to 0.35.Furthermore,there is a negative correlation between the pump head and the solid volume fraction in the pump;with the increase of solid volume fraction in the loop reactor,and the correlation coefficient increases as well.Moreover,a‘spiral particulate band’phenomenon is formed in the ascending leg caused by three mechanisms,viz.:the segregation of particles in all bends,the dispersion of particles by the secondary flow in the ascending leg,and the rotational movement of particles in the pump.
文摘The influences of the internal and external outlet angles on separation performance and flow field are compared and analyzed. Two arc functions are employed for controlling the internal and external angles. The separation process in the cyclone tube is calculated by using two-fluid model based on the Eulerian-Eulerian method.The results show that the structure with the internal outlet angle smaller than the external one is more beneficial to the separation performance. It is found that the small internal angle can help increase the swirl number,while the small external angle can help increase the friction coefficient. Several groups of numerical simulations are conducted for the air intake unit of the gas turbine in practice. When the internal outlet angle is 35° and the external outlet angle is 40°,the blade has sufficient cyclone strength and the separation rate of particles with diameters of 10—100 μm is between70%—98%. The small blade angle is more conducive to the separation of fine particles,leading to violent collision of large particles on the outer wall and reduction of separation efficiency. In addition,reducing the external angle is conducive to the discharge of large particles.
基金This work was supported by the National Natural Science Foundation of China No.10035020.
文摘A magnetohydrodynamic (MHD) formulation is derived to investigate and compare the mitigation effects of both the sheared axial flow and finite Larmor radius (FLR) on the Rayleigh-Taylor (RT) instability in Z-pinch implosions. The sheared axial flow is introduced into MHD equations in a conventional way and the FLR effect into the equations via /t → -i(w+ik⊥2pi2Ωi,), as proposed in our previous paper [Chin. Phys. Lett. 2002, 19:217] , where k⊥2 pi2 is referred to FLR effect from the general kinetic theory of magnetized plasma. Therefore the linearized continuity and momentum equations for the perturbed mass-density and velocity include both the sheared axial flow and the FLR effect. It is found that the effect of sheared axial flow with a lower peak velocity can mitigate RT instability in the whole wavenumber region and the effect of sheared axial flow with a higher one can mitigate RT instability only in the large wavenumber region (for normalized wavenumber k】2.4); The effect of FLR can mitigate RT instability in the whole wavenumber region and the mitigation effect is stronger than that of the sheared axial flow with a lower peak velocity in the almost whole wavenumber region.
基金Strategic Leading Project of Shanghai Municipal Science Committee(16DZ1121202)
文摘Airfoil is the element of fan blade design. It is strongly anticipated to design a fan of ave- raged high performance over a wide operation range. Multi-point optimization design of airfoil for axial flow fan was proposed over specific operation range. Weighted objective function of airfoil lift-drag ratio was constructed for several operation points around the designing one. Airfoil was defined by parametric B-spline curve of limited shape controlling points. Results show that normal standard airfoils have remained spaces to be optimized under specific operation conditions. Airfoil performance is sensitive to flow′s Reynolds number and cascade solidity. Predicting flow transition along airfoil profile is essential to search for optimized one. Optimized airfoil of wide operation range is possible to obtain with prescribed fitness function. Obtainments of multi-point optimization may be relatively lower at design point, but positive obtainments are achieved at off-design ones. Resulted airfoil is specially suitable for axial flow fans operating frequently at off-design point such as air condition coolers.
文摘The axial power flow (APF) magnitude and attenuation distributions of ultrasonic longitudinal guided waves in viscous liquid-filled elastic pipes are investigated. The optimal location, optimal mode and its frequency-thickness product (fd) for the test of pipes filled with viscous liquid are chosen according to APF and attenuation distributions. The results show that the APF magnitude distribution is an important parameter in choosing the modes and parameters. A particular mode has weak dispersion in ranges of fd values with large group velocity, while other modes with smaller group velocity in the same fd ranges have stronger dispersion. It has been observed that, within these ranges, the chosen mode has a larger APF on the (pipe’s) wall. Therefore, in the region of fd values where a particular mode has a large group velocity, this mode will be effective to be used in testing elastic pipes filled with viscous liquid. The results obtained from both the APF analysis and attenuation distribution are consistent.
