摘要:
基于不可压Navier-Stokes方程,采用计算流体力学方法,数值模拟与分析了层流圆管潜射流在密度均匀黏性流体中的演化机理及其表现特征,定量研究了蘑菇形涡结构无量纲射流长度L?、螺旋形涡环半径R?及其包络外形长度d?等几何特征参数随无量纲时间t?的变化规律.数值结果表明,蘑菇形涡结构的形成与演化过程可分为三个不同的阶段:启动阶段、发展阶段和衰退阶段.在启动阶段, L?和d?随t?线性变化,而R?则近似为一个常数;在发展阶段,蘑菇形涡结构的演化具有自相似性, L?, R?和d?与t?1/2均为同一正比关系,而且雷诺数和无量纲射流时间不影响该正比关系;在衰退阶段, L?和R?正比于t?1/5,而d?则近似为一个常数.此外,还对蘑菇形涡结构二次回流点、动量源作用中心及其几何中心的速度变化规律、垂向涡量分布特征和涡量-流函数关系进行了分析.
Abstract:
A numerical investigation on the evolution mechanism and characteristics of the submerged laminar round jet in a viscous homoge-nous fluid is conducted by using the computational fluid dynamics method based on the incompressible Navier-Stokes equation. Three non-dimensional parameters for the mushroom-like vortex structure, including the length of the jet L?, the radius of the mushroom-like vortex R? and the length of vortex circulation d?, are introduced and the variation characteristics of these parameters with the non-dimensional time t?are quantitatively analyzed. Results show that there exist three distinct stages in the formation and evolution procedures of the mushroom-like vortex structure, including the starting, developing and decaying stages. In the starting stage, L?and d? increase linearly with t?, while R? approximately remains to be a constant;in the developing stage, a considerable self-similarity is confirmed, and L?, R?, d? display the same proportional relationship to t?1/2 regardless of the variations of Reynolds number and injection duration; in the decaying stage, L? and R?are approximately proportional to t?1/5, while d? nearly levels off as a constant. Moreover, velocity characteristics at the secondary backflow point and the momentum and geometry centers, the distribution features of the vertical vorticity, as well as the vorticity-stream function relationship are analyzed for the mushroom-like vortex structure.
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