Direct Numerical Simulation Of Three-dimensional Gas-Solid Two-Phase Wake Of A Circular Cylinder

The main object is to study three-dimensional physical character of gas-solid flow past a circular cylinder by using direct numerical simulation method. And after study the mechanism of vortexes shed off cylinder, find that motion of characteristic of cylinder tail field have closely relation with Reynolds number of gas field. With Reynolds number increase, large-scale structure of the cylinder wake is stretched at higher amplitudes, the frequency of the vortexes shed off the wake fast. For the transition process of flow field of a circular cylinder, recognize that it is evoked by the instability of ellipses in the vortex kernel, and this instability cause the motion of the vortex along spanwise, and streamwise coherent structures, and spanwise large-scale vortex broken up the small-scale vortex structures.And after investigation the flow field, particle dispersion characteristic in the field of wake of a circular cylinder also studied. The Stokes number is the main factor of settlement particle dispersion. For a circular cylinder wake, two symmetrically vortexes with opposite sign are separately and alternately generate. They are convected and diffused away from the cylinder but no vortex pairing interactions happens. The mechanism for the particle dispersion in the wake mainly depends on the suction force effect associated with the vortex sheet region between adjacent two vortex structures. The force not only draws the small particles (St=0.01,0.1) firmly to approach backward cylinder even collide with its back face but causes particles burst out from the high concentration area and finally develop a mushroom shaped distribution. Obviously, it is different from the mixing layer, which involves a well-known vortex pairing process to cause an important physical mechanism for particles dispersion folding process.As to the turbulence modulation by the effects of the particles on the gas-solid wake of a circular cylinder, the study of the two-way coupling DNS shows that the particles at the different Stokes number promote the evolving of the coherent structures in the flow field and make the turbulence intensity power; and the particles make velocity vector of different direction in the flow field augment. At the two-way coupling, characteristics of diffusion statistics accord with its at the one-way coupling, but the function number of its is a little lower. And it declares that the particles dispersion is more evenly than at the one-way coupling.Because there is a blunt body in the flow field, when gas-solid flow runs around the...