Numerical Investigations on Multiple Structures of Confined Swirling Flows

• Main Authors: Chih-Hung Shen, 沈志鴻
• Other Authors: Tsang-Leo Jiang
• Format: Others
• Language: zh-TW
• Published: 1993
• Online Access: http://ndltd.ncl.edu.tw/handle/54068485304178358089

碩士 === 國立成功大學 === 航空太空工程學系 === 81 === Turbulent swirling flow has drawn considerable attention in the past decades since it possesses wide-range applications in many practical combustion devices. It promotes mixing of fuel and air, reducing flame lengths and pollutant emission. It also provides good flame stabilization such that the flame holding mechanisms installed in the combustor can be eliminated. However, due to its complexity associated with the coupling of turbulence and swirling, it is still a challenging subject for numerical studies. Turbulent swirling flow calculations can be inaccurate due to at least three major reasons: limitations of the turbulence modeling used, incorrect or inadequate specifications of inlet boundary conditions, and error introduced through the numerical diffusion. Furthermore, multiple flow structures for confined swirling flows were found at certain flow conditions by our group recently. This finding has significant impacts on the swirling flow study and is further investigated in this thesis. The numerical results obtained in the present study reveal that, when the sizes of internal and external recirculation zones are exhibited to be comparable, multiple flow structures result. The internal and external recirculation zone sizes, however, depend upon not only the flow conditions but also the employed numerical scheme, grid system, and physical models. It is found that the previous arguments regarding k-.epsilon. model's performance should be reexamined since some previous computational results, which deviated significantly from the experimental results, just fell into the other branch than the one for the experimental conditions.