| Most numerical simulations of granular multiphase flows use spherical particles to approximate the behavior of real particles.Due to the isotropic characteristics of spheres,their translation and rotation are independent of each other.However,for non-isotropic real particles,their translation and rotation are coupled.As the simplest non-isotropic geometric shape,ellipsoids can more accurately approximate the motion and dynamics of real particles.This article employs the Immersed Boundary Method to directly numerically simulate the static and dynamic drag characteristics of elliptical particles with different aspect ratios.In the static simulation,the resistance of stationary elliptical particles under different inflow conditions is considered and compared with empirical formulas.In the dynamic simulation,the free settling problem of single,two,and multiple particles is studied.The research results indicate that:(1)The Reynolds number affects the flow characteristics of ellipsoids by affecting the frictional drag in the flow around the ellipsoid.As the Reynolds number increases,the drag coefficients on the ellipsoid decreases,but when the Reynolds number exceeds a certain range,its influence gradually decreases until it disappears.The aspect ratio changes the shape of the ellipsoid,thereby affecting the drag and wake in the flow around the ellipsoid.The larger the drag,the more chaotic the wake state,and the larger the downstream influence range of the ellipsoid with different aspect ratios.(2)The settling of ellipsoidal particles is relatively stable at low Reynolds numbers,and the orientation of the ellipsoid hardly changes during the settling process.The settling of ellipsoids also exhibits the same phenomenon of DKT(Drafting,Kissing,Tumbling)as spherical particles,i.e.,acceleration traction and deceleration separation,but it does not repeat during the settling process.Instead,each ellipsoid continues to settle after separation in the horizontal plane.When the number of ellipsoids increases,the influence of the wake of the lower ellipsoids will change the stable settling state,but the orientation of the ellipsoid only oscillates within a certain range and does not flip over. |
