Large-eddy simulation of a buoyant plume past a bluff body: Effects of flow structures on entrainment characteristics

摘要

A large-eddy simulation of a buoyant plume past a bluff body (BB) is performed. The modified Rayleigh number based on the total heat input and the diameter of a BB is set at 1.2×1010. Distributions of basic statistics showed that the existence of a BB greatly varies the spatial structures of momentum and energy transport, although they gradually approached distributions corresponding to the similarity law for a fully developed plume when z/D > 2.5 (z: vertical position from a heat source, D: BB diameter) since the influence of a BB becomes weaker there. Then, the relationship between entrainment and flow structures was investigated and the entrainment coefficient was found to be locally large right above a BB owing to stationary horizontal flows and azimuthal vortices. Moreover, in the case of an insulated BB, some azimuthal vortices were formed in the process of developing a plume, 1.0 < z/D < 2.0, owing to both weak buoyancy and BB effects, and it is suggested that they are linked to the increase of entrainment there.