A centrifugal fan with the high speed and compact dimensions is studied numerically and experimentally. The centrifugal fan consists of a shrouded impeller rotating at 34 000 r/min with a small tip clearance 0.7 mm to...A centrifugal fan with the high speed and compact dimensions is studied numerically and experimentally. The centrifugal fan consists of a shrouded impeller rotating at 34 000 r/min with a small tip clearance 0.7 mm to the fixed outer casing. Computational models with/without the tip clearance are built and the κ-ω shear stress transport （SST） turbulence model and the unstructured mesh are applied to the numerical simulation for unsteady solutions. The overall performance is measured on a standard experimental bench and the major flow feature of each component inside the centrifugal fan is numerically investigated. In the presence of the tip clearance due to the difference of static pressure between leading and trailing edges of the clearance, i. e. , leading and trailing edges of the impeller, a strong return flow exists inside the clearance passage and re-circulates the main stream inside the impeller passage, and produces the strong flow interaction, thus changing the flow field and influencing the overall performance.展开更多
There is a relatively complex flow state inside the high speed on-off valve,which often produces low pressure area and oil reflux in the high-speed opening and closing process of the spool,causing cavitation and vorte...There is a relatively complex flow state inside the high speed on-off valve,which often produces low pressure area and oil reflux in the high-speed opening and closing process of the spool,causing cavitation and vortex and other phenomena.These phenomena will affect the stability of the internal flow field of the plate valve and the flow characteristics of the high speed on-off valve.Aiming at the problems of small flow rate and instability of internal flow field,a new spool structure was designed.The flow field models of two-hole and three-hole plate spools with different openings were established,and software ANSYS Workbench was chosen to mesh the model.The standard k−εturbulence model was selected for numerical simulation using FLUENT software.The pressure distribution and velocity distribution under the same pressure and different opening degree were obtained.The structure and parameters of the optimization model were also obtained.The stability analysis of flow field under different pressure was carried out.The results demonstrate that the three-hole spool has a similar flow field change with the two-hole spool,but it does not create a low pressure zone,and the three-hole spool can work stably at 2 MPa or less.This method improves the appearance of low pressure area and oil backflow in the process of high speed opening and closing of spool.The stability of flow field and the flow rate of high speed switch valve are improved.Finally,the products designed in this paper are compared with existing hydraulic valve products.The results show that the three-hole plate type high speed on-off valve designed in this paper maintains the stability of the internal flow field under the condition of 200 Hz and large opening degree,and realizes the increase of flow rate.展开更多
In this paper,multi_quadric equations interpolation is used to establish a widely covered and valuable speed field model,with which the crustal movement image is obtained.
A series of experimental results of field-reversed configurations(FRCs) on a KMAX(Keda Mirror with AXisymmetricity) tandem mirror machine are reported.Single-side FRC translation processes with three different gas spe...A series of experimental results of field-reversed configurations(FRCs) on a KMAX(Keda Mirror with AXisymmetricity) tandem mirror machine are reported.Single-side FRC translation processes with three different gas species were measured by avalanche photodiodes.Consistent with the theoretical prediction, the measured FRC speeds were inversely proportional to the square root of the ion mass.However, the speeds of the hydrogen FRC increased even in a uniform magnetic field region while the speeds of the helium and argon FRCs decreased.Possible mechanisms are discussed.The speed of the second pass due to the reflection of the mirror fields was found to be ~1/3 of the first pass speed.The internal magnetic fields were measured for a colliding-merging argon FRC, and the results show that, even for very slowmoving FRCs, merging can occur.展开更多
During high-speed gas metal arc welding （GMAW）, the backward flowing molten jet with high momentum in the weld pool is considered to be responsible for the occurrence of humping bead. To suppress humping bead, an el...During high-speed gas metal arc welding （GMAW）, the backward flowing molten jet with high momentum in the weld pool is considered to be responsible for the occurrence of humping bead. To suppress humping bead, an electromagnetic device is developed and coupled with the welding system. By adjusting the conditions of external magnetic field, forward electromagnetic force is obtained to reduce the momentum of the backward flow of molten metal in weld pool. Consequently, the humping bead can be suppressed by adjusting the external magnetic field. Bead-on-plate welding experiment was conducted on mild steel plates, and the influence of magnetic flux density on the arc deflection angle and weld bead quality is investigated. It is found that external magnetic field can remarkably adjust the momentum of backward flow jet and significantly improve the quality of weld bead.展开更多
Based on incompressible viscous fluid Navier-stokes equation and k-ε 2-equations turbulent model, an investigation on 3D turbulent flow field around four kinds of train models has been made by finite element method. ...Based on incompressible viscous fluid Navier-stokes equation and k-ε 2-equations turbulent model, an investigation on 3D turbulent flow field around four kinds of train models has been made by finite element method. From the calculation, the pressure distribution characters of now field around high-speed trains have been obtained. It is significant for strength design of the high-speed train body, for resisting wind design of the facilities beside the high-speed railways and for determining the aerodynamic force of induced air to the human body near the railways.展开更多
The hydrodynamic performance of a high forward-speed ship in obliquely propagating waves is numerically examined to assess both free motions and wave field in comparison with a low forward-speed ship.This numerical mo...The hydrodynamic performance of a high forward-speed ship in obliquely propagating waves is numerically examined to assess both free motions and wave field in comparison with a low forward-speed ship.This numerical model is based on the time-domain potential flow theory and higher-order boundary element method,where an analytical expression is completely expanded to determine the base-unsteady coupling flow imposed on the moving condition of the ship.The ship in the numerical model may possess different advancing speeds,i.e.stationary,low speed,and high speed.The role of the water depth,wave height,wave period,and incident wave angle is analyzed by means of the accurate numerical model.It is found that the resonant motions of the high forward-speed ship are triggered by comparison with the stationary one.More specifically,a higher forward speed generates a V-shaped wave region with a larger elevation,which induces stronger resonant motions corresponding to larger wave periods.The shoaling effect is adverse to the motion of the low-speed ship,but is beneficial to the resonant motion of the high-speed ship.When waves obliquely propagate toward the ship,the V-shaped wave region would be broken due to the coupling effect between roll and pitch motions.It is also demonstrated that the maximum heave motion occurs in beam seas for stationary cases but occurs in head waves for high speeds.However,the variation of the pitch motion with period is hardly affected by wave incident angles.展开更多
文摘A centrifugal fan with the high speed and compact dimensions is studied numerically and experimentally. The centrifugal fan consists of a shrouded impeller rotating at 34 000 r/min with a small tip clearance 0.7 mm to the fixed outer casing. Computational models with/without the tip clearance are built and the κ-ω shear stress transport （SST） turbulence model and the unstructured mesh are applied to the numerical simulation for unsteady solutions. The overall performance is measured on a standard experimental bench and the major flow feature of each component inside the centrifugal fan is numerically investigated. In the presence of the tip clearance due to the difference of static pressure between leading and trailing edges of the clearance, i. e. , leading and trailing edges of the impeller, a strong return flow exists inside the clearance passage and re-circulates the main stream inside the impeller passage, and produces the strong flow interaction, thus changing the flow field and influencing the overall performance.
基金Project(51975164)supported by the National Natural Science Foundation of ChinaProject(201908230358)supported by the China Scholarship CouncilProject supported by the Fundamental Research Foundation for Universities of Heilongjiang Province,China。
文摘There is a relatively complex flow state inside the high speed on-off valve,which often produces low pressure area and oil reflux in the high-speed opening and closing process of the spool,causing cavitation and vortex and other phenomena.These phenomena will affect the stability of the internal flow field of the plate valve and the flow characteristics of the high speed on-off valve.Aiming at the problems of small flow rate and instability of internal flow field,a new spool structure was designed.The flow field models of two-hole and three-hole plate spools with different openings were established,and software ANSYS Workbench was chosen to mesh the model.The standard k−εturbulence model was selected for numerical simulation using FLUENT software.The pressure distribution and velocity distribution under the same pressure and different opening degree were obtained.The structure and parameters of the optimization model were also obtained.The stability analysis of flow field under different pressure was carried out.The results demonstrate that the three-hole spool has a similar flow field change with the two-hole spool,but it does not create a low pressure zone,and the three-hole spool can work stably at 2 MPa or less.This method improves the appearance of low pressure area and oil backflow in the process of high speed opening and closing of spool.The stability of flow field and the flow rate of high speed switch valve are improved.Finally,the products designed in this paper are compared with existing hydraulic valve products.The results show that the three-hole plate type high speed on-off valve designed in this paper maintains the stability of the internal flow field under the condition of 200 Hz and large opening degree,and realizes the increase of flow rate.
文摘In this paper,multi_quadric equations interpolation is used to establish a widely covered and valuable speed field model,with which the crustal movement image is obtained.
基金supported by the National Key R&D Program of China (Nos.2017YFA0402500 and 2017YFE0301802)National Natural Science Foundation (No.11475172)the Key Research Program of Frontier Sciences, CAS (No.QYZDJ-SSW-DQC010)
文摘A series of experimental results of field-reversed configurations(FRCs) on a KMAX(Keda Mirror with AXisymmetricity) tandem mirror machine are reported.Single-side FRC translation processes with three different gas species were measured by avalanche photodiodes.Consistent with the theoretical prediction, the measured FRC speeds were inversely proportional to the square root of the ion mass.However, the speeds of the hydrogen FRC increased even in a uniform magnetic field region while the speeds of the helium and argon FRCs decreased.Possible mechanisms are discussed.The speed of the second pass due to the reflection of the mirror fields was found to be ~1/3 of the first pass speed.The internal magnetic fields were measured for a colliding-merging argon FRC, and the results show that, even for very slowmoving FRCs, merging can occur.
基金The authors are grateful to the financial support for this research from the National Natural Science Foundation of China，the Research Fund for the Doctoral Program of Higher Education of China
文摘During high-speed gas metal arc welding （GMAW）, the backward flowing molten jet with high momentum in the weld pool is considered to be responsible for the occurrence of humping bead. To suppress humping bead, an electromagnetic device is developed and coupled with the welding system. By adjusting the conditions of external magnetic field, forward electromagnetic force is obtained to reduce the momentum of the backward flow of molten metal in weld pool. Consequently, the humping bead can be suppressed by adjusting the external magnetic field. Bead-on-plate welding experiment was conducted on mild steel plates, and the influence of magnetic flux density on the arc deflection angle and weld bead quality is investigated. It is found that external magnetic field can remarkably adjust the momentum of backward flow jet and significantly improve the quality of weld bead.
文摘Based on incompressible viscous fluid Navier-stokes equation and k-ε 2-equations turbulent model, an investigation on 3D turbulent flow field around four kinds of train models has been made by finite element method. From the calculation, the pressure distribution characters of now field around high-speed trains have been obtained. It is significant for strength design of the high-speed train body, for resisting wind design of the facilities beside the high-speed railways and for determining the aerodynamic force of induced air to the human body near the railways.
基金supported by the National Natural Science Foundation of China(Grant Nos.52271278 and 52111530137)the Natural Science Foundation of Jiangsu Province(Grant No.SBK2022020579)the Newton Advanced Fellowships by the Royal Society(Grant No.NAF\R1\180304).
文摘The hydrodynamic performance of a high forward-speed ship in obliquely propagating waves is numerically examined to assess both free motions and wave field in comparison with a low forward-speed ship.This numerical model is based on the time-domain potential flow theory and higher-order boundary element method,where an analytical expression is completely expanded to determine the base-unsteady coupling flow imposed on the moving condition of the ship.The ship in the numerical model may possess different advancing speeds,i.e.stationary,low speed,and high speed.The role of the water depth,wave height,wave period,and incident wave angle is analyzed by means of the accurate numerical model.It is found that the resonant motions of the high forward-speed ship are triggered by comparison with the stationary one.More specifically,a higher forward speed generates a V-shaped wave region with a larger elevation,which induces stronger resonant motions corresponding to larger wave periods.The shoaling effect is adverse to the motion of the low-speed ship,but is beneficial to the resonant motion of the high-speed ship.When waves obliquely propagate toward the ship,the V-shaped wave region would be broken due to the coupling effect between roll and pitch motions.It is also demonstrated that the maximum heave motion occurs in beam seas for stationary cases but occurs in head waves for high speeds.However,the variation of the pitch motion with period is hardly affected by wave incident angles.
