Tham khảo tài liệu 'two phase flow phase change and numerical modeling part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 200 Two Phase Flow Phase Change and Numerical Modeling A consequence of the azimuthal rotation is that swirling jets experience swirl decay see Figure 7 . Therefore there is a point beyond which the azimuthal velocity will decay to a degree whereby it no longer significantly impacts the flow field. This factor is crucial in the design of swirling jets and in any applications that employ swirling jets for enhancing heat and mass transfer combustion and flow mixing. 5. Impact of S on the Central Recirculation Zone As the azimuthal velocity increases and exceeds the axial velocity a low pressure region prevails near the jet exit where the azimuthal velocity is the highest. The low pressure causes a reversal in the axial velocity thus producing a region of backflow. Because the azimuthal velocity forms circular planes and the reverse axial velocity superimposes onto it the net result is a pear-shaped central recirculation zone CRZ . From a different point of view for an incompressible swirling jet as S increases the azimuthal momentum increases at the expense of the axial momentum see Equations 6 and 7 . This is consistent with the data in the literature Chigier and Chervinsky 1967 . The CRZ formation results in a region where vortices oscillate similar to vortex shedding for flow around a cylinder. The enhanced mixing associated with the CRZ is attributable to the back flow in the axial direction in particular the back flow acts as a pump that brings back fluid for further mixing. The CRZ vortices tend to recirculate and entrain fluid into the central region of the swirling jet thus enhancing mixing and heat transfer within the CRZ. Fig. 8. Effect of Swirl Angle on the Azimuthal Velocity The Fuego CFD code was used to compute the flow fields shown in Figures 8 through 10 Fuego 2009 . Figure 8 shows the effect of the swirl angle on the azimuthal flow for an unconfined swirling jet. Figure 9 shows the velocity vector azimuthal velocity and the axial velocity for a weak
