The evolution of wake structure in a flow around an impulsively stopped sphere in an incompressible viscous fluid is investigated under the influence of a streamwise magnetic field at moderate Reynolds numbers.The res...The evolution of wake structure in a flow around an impulsively stopped sphere in an incompressible viscous fluid is investigated under the influence of a streamwise magnetic field at moderate Reynolds numbers.The research parameter range is 600≤Re≤1400 and 0≤N≤10,where Re and N are the Reynolds number and the interaction parameter,respectively.A vortex ring system is developed,which contains the primary and secondary vortex rings after stopping the sphere.The flow will keep axisymmetric before stopping the sphere for the purpose to investigate the instability of shedding vortex rings.Without the magnetic field,an azimuthal instability will develop on the secondary vortex ring when the Reynolds number is large enough,e.g.,Re=1200.It is caused by the centrifugal movement of the secondary vortex ring and this instability can be suppressed by the streamwise magnetic field.Furthermore,an obvious oscillation caused by the motion of the primary vortex ring on the drag force is found after stopping the sphere.The amplitude of such oscillation increases with enlarging the Reynolds number but decreases with enlarging the magnetic field intensity.展开更多
Immersed boundary method is a crucial method to deal with particle suspension flow.Particle shapes involved in such flow are usually simple geometry,such as sphere and ellipsoid,which can be conveniently represented b...Immersed boundary method is a crucial method to deal with particle suspension flow.Particle shapes involved in such flow are usually simple geometry,such as sphere and ellipsoid,which can be conveniently represented by the triangular surface grid.When the number of particles and resolution of the surface grid increase,calculating the hydrodynamic force on the particle surface through integration can be time-consuming.Hence,the present paper establishes a fast mapping method to evaluate immersed boundary hydrodynamic force.Firstly,the particle surface grid is generated by an initial triangular element grid.Subsequently,the initial surface grid is refined by bisection refinement to the desired resolution.The final step is to find the triangular element index on the particle triangular surface grid,which contains the projective point.Test cases show that the present mapping algorithm has good accuracy and efficiency for calculating hydrodynamic forces of particles.展开更多
基金the National Natural Science Foundation of China(Grant No.52006212)Basic Frontier Science Research Program of Chinese Academy of Sciences(Grant No.ZDBS-LY-JSC033)+1 种基金Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB22040201)China Postdoctoral Science Foundation(Grant No.2019M650815).
文摘The evolution of wake structure in a flow around an impulsively stopped sphere in an incompressible viscous fluid is investigated under the influence of a streamwise magnetic field at moderate Reynolds numbers.The research parameter range is 600≤Re≤1400 and 0≤N≤10,where Re and N are the Reynolds number and the interaction parameter,respectively.A vortex ring system is developed,which contains the primary and secondary vortex rings after stopping the sphere.The flow will keep axisymmetric before stopping the sphere for the purpose to investigate the instability of shedding vortex rings.Without the magnetic field,an azimuthal instability will develop on the secondary vortex ring when the Reynolds number is large enough,e.g.,Re=1200.It is caused by the centrifugal movement of the secondary vortex ring and this instability can be suppressed by the streamwise magnetic field.Furthermore,an obvious oscillation caused by the motion of the primary vortex ring on the drag force is found after stopping the sphere.The amplitude of such oscillation increases with enlarging the Reynolds number but decreases with enlarging the magnetic field intensity.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.51636009 and 52006212)Chinese Academy of Sciences(Grant Nos.ZDBS-LY-JSC033 and XDB22040201).
文摘Immersed boundary method is a crucial method to deal with particle suspension flow.Particle shapes involved in such flow are usually simple geometry,such as sphere and ellipsoid,which can be conveniently represented by the triangular surface grid.When the number of particles and resolution of the surface grid increase,calculating the hydrodynamic force on the particle surface through integration can be time-consuming.Hence,the present paper establishes a fast mapping method to evaluate immersed boundary hydrodynamic force.Firstly,the particle surface grid is generated by an initial triangular element grid.Subsequently,the initial surface grid is refined by bisection refinement to the desired resolution.The final step is to find the triangular element index on the particle triangular surface grid,which contains the projective point.Test cases show that the present mapping algorithm has good accuracy and efficiency for calculating hydrodynamic forces of particles.
