1 数値シミュレーションによる二次元噴流に見られる巻上がり渦列の合体

Abstract

A vortex growth in two-dimensional jet flow is numerically analysed by solving full Navier-Stokes equations. For the symmetrical disturbance induced by computational errors, the flow field takes unique vortex passage frequency which is dominantly amplified disturbance frequency. Several asymmetrical disturbances with this frequency and different amplitudes are applied at IN-boundary to get asymmetrical vortex array. In the case of disturbance with maximum amplitude 1 percent of the inlet velocity, the array of vortices shows the asymmetry in early stage and persists in the computational domain. For 0.5 percent amplitude, the coalesced vortices are simulated after a large time elapses. This phenomenum may be triggered by lateral displacements of vortices. which imply that each vortex travels downstream with different speed. In the coalescing process, two vortices rotate each other, and one of vortices is outer vortex downstream of the other which is inner vortex. The traveling speed of outer vortex becomes low, so two vortices draw near and coalesce.