Study on Mechanism of Vortex Bursting

通过实验研究了火焰沿直涡的发展，阐明了最大周向速度和火焰密度比对火焰发展的影响，并与理论和数值模拟进行了比较。用活塞在火焰密度比为5.1至8.0的氮稀释化学计量氢-氧混合物中产生一对直涡。粒子图像测速（PIV）测量的速度场表明，涡流管的平均最大周向速度为18.0 ~ 35.8 m/s，平均芯径为5 ~ 6 mm。为了不干扰流场，其中一个漩涡在核心处被193纳米的聚焦激光点燃。结果表明，火焰沿直涡轴的传播速度远高于径向和静止混合气的传播速度。当火焰半轴长大于涡流管芯径时，轴向传播速度随时间增加而趋于恒定。稳态时的轴向传播速度大致与最大周向速度和密度比负一成正比。初始阶段轴向传播速度随火焰半轴长度的平方根、最大周向速度和密度比减1而增大。与实验相同构型的数值模拟证明，斜压效应在传播初期产生方位涡量，而对流和拉伸效应在传播后期起主导作用，导致火焰沿涡传播。上述成果已在IUTAM湍流几何与统计研讨会（1999）、第一届计算流体动力学国际会议（2000）、第三届比例建模国际研讨会（2000）和第三十八届全国燃烧研讨会（2000）上发表。少

Flame development along a straight vortex is experimentally studied to elucidate the effects of the maximum circumferential velocity and the density ratio of the flame and to compare with theories and numerical simulations. A pair of straight vortices is produced in nitrogen-diluted stoichiometric hydrogen-oxygen mixtures with density ratios of the flame ranging from 5.1 to 8.0 by a piston. The velocity field measured by the particle image velocimetry (PIV) shows that the vortex tube has a mean maximum circumferential velocity ranging from 18.0 m/s to 35.8 m/s and has a mean core diameter ranging from 5 mm to 6 mm. One of the vortices is ignited at the core by a focused laser light of 193 nm in order not to disturb the flow field. It is found that the flame propagates along the axis of the straight vortex with a speed much higher than that in the radial direction as well as that in the quiescent mixture. The axial propagation velocity increases in time and becomes nearly constant when … More the half-axial length of the flame becomes larger than the core diameter of the vortex tube. The axial propagation velocity at the steady state is roughly proportional to the maximum circumferential velocity and to the density ratio minus unity. The axial propagation velocity at the initial stage increases with the square root of the half-axial length of the flame as well as the maximum circumferential velocity and the density ratio minus unity. Numerical simulation of the same configuration as the experiment proves that the baroclinic effect produces azimuthal vorticity at the early stage of propagation, and that convection and stretch effects dominate the production at the later stage and as a result they provoke the flame to propagate along the vortex. Above results are presented at the IUTAM Symposium on Geometry and Statistics of Turbulence (1999), the First International Conference on Computational Fluid Dynamics (2000), the Third International Symposium on Scale Modeling, (2000), and the Thirty-Eighth Symposium (National) on Combustion (2000). Less