热诱导浮力羽流涡旋结构直接数值模拟

Direct numerical simulation of the large vortical structures in heat-induced buoyant plumes

涡旋结构是湍流流场重要的研究内容之一,也是影响特殊火行为的重要因素之一,如涡旋在飞火传播中起着非常重要的作用。火羽流涡旋结构的详细分析对火灾蔓延特性的研究有重要指导意义。该文对轴对称热羽流和平面热羽流进行了直接数值模拟,分别基于涡旋动力学及涡旋稳定性角度对计算结果进行详细分析。研究表明平面热羽流的涡量值明显高于轴对称热羽流,平面热羽流具有较低的脉动频率。从涡量输运方程出发,分析得出拉伸项的存在降低了轴对称热羽流的混合强度。

Vortical structure is not only an important component of turbulence flow,but also an important factor in special fire behaviors.Detailed analysis of vortical structure in fire plume has an important significance in the research of the spread of fire.Direct numerical simulation is presented for axisymmetric thermal plume and planar thermal plume.The vorticity transport equation was analyzed to examine the mechanisms leading to the difference between them.Fourier spectra were also studied.Vorticity is found to be stronger in the planar thermal plume than in the axisymmetric thermal plume.Meanwhile,puffing frequency of planar thermal plumes is lower than the axisymmetric thermal plumes.The stretching term in the vorticity transport equation is found to be the major mechanism to reduce the degree of mixing in axisymmetric plume.