| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1990: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1989: ¥1,600,000 (Direct Cost: ¥1,600,000)
|
|---|
| Research Abstract |
1) The mean and turbulent properties, notably the Reynolds shear stress and turbulent heat fluxes of turbulent plane jets and plumes are measured. The results show that buoyancy increases the turbulence levels in plumes when compared with jets. For example, the maximum Reynolds shear stress is nearly 60 % higher in plumes. The constant eddy viscosity model is found to be applicable to describe the turbulence structure in both flows. Furthermore, the differences in turbulent kinetic energy balance between both flows are examined. The buoyant production of turbulent energy is about 30 % of the shear production in plumes.
2) Coherent structures' dynamics in plane forced plumes is investigated experimentally by using a flow visualization and two-points measurement of velocity fluctuations and temperature fluctuations. Ensemble averages are conditioned on the occurrence of temperature fronts. The averages show that large scale coherent structures appear alternately on both sides of the cente
… More
rline, which consist of vortex roll of opposite circulation each other. A flapping motion of discharged fluid is likely attributed to the asymmetric arrangement of the structures. From topological consideration, entrainment of ambient fluid proceeds by engulfment along the converging separatrix towards the saddle point connecting adjacent, samesigned vortical structures on each side.
3) A numerical simulation of the vortex-street model for the coherent structures in a turbulent plane jet and plume is described. Attention is focussed on the topological features of the coherent structures detected experimentally. The model formulation includes the streamwise development of von karman-type vortex street pattern in terms of the similarity-scaling relationships. The model was found to predict the lateral profiles of mean flow and turbulence quantities including the Reynolds stress, in particular, the differences of their quantities in a jet and a plume reasonably well. The non-symmetric arrangement of coherent structures is the essential mechanism for the production of the Reynolds stress and the entrainment. Less
|
