01. Experimental/Computational Fluid Dynamics

Jets have been utilized as a blower method for air conditioners because of their high mixing and diffusion characteristics. Recently, a new air conditioning method that reduces the power consumption and improves the comfort has been proposed, in which only a local area of the target is intensively conditioned, and this method requires a technique to inhibit mixing and diffusion of the thermal fluid during transport. In this research, the effects of the velocity ratio γ1 between the circular and annular jets of the coaxial jet and the velocity ratio γ2 between the inner circular jet and the added swirl velocity on the vortex structure and mixing / diffusion characteristics of the circular jet were investigated experimentally in order to establish a diffusion inhibition method for the coaxial jet. The results indicate the following. As the velocity ratio γ1 closer to 1, the jet width becomes narrower and the diffusion of the jet is inhibited. Meanwhile, for velocity ratio γ2, the jet width decreased with decreasing velocity ratio γ2 above 0.5, but the jet width hardly changed at velocity ratios γ2 below 0.5. The diffusion behavior of the jets started initially in the annular jets, followed slightly later by the diffusion in the circular jets. A negative pressure region was generated in the center of the circular jet due to the effect of the swirling flow, and this region was expected to inhibit diffusion, whereas instability was observed in the jet due to vortex breakdown caused by the reverse pressure gradient in the direction of flow. Regarding the vortex structure, the addition of swirl velocity delayed the generation of vortex rings, however, the generated vortex rings broke down quickly, resulting in a shorter diffusion inhibition effect than in the case without swirling.