The paper examines the mechanism of the tulip flame formation for the flames propagating in closed tubes of various aspect ratios and in a half-open tube. The formation of tulip flames in 2D channels is studied using high resolution direct numerical simulations of the reactive Navier Stokes equations coupled with a detailed chemical model for a stoichiometric hydrogen/air flame. It is shown that rarefaction waves generated by the flame during the deceleration stage play a key role in the tulip-shaped flame formation. The interaction of the reverse flow created behind the rarefaction wave with previously produced be accelerating flame flow in the unburned gas, results in the decrease of the flow velocity in the near field zone ahead of the flame and in the increase of the boundary layer thickness. The profile of the axial velocity close ahead of the flame takes the form of an inverted tulip. Therefore, the flame front acquires a tulip shape repeating to a large extent the shape of the of the axial velocity profile in the upstream flow.
The Effect of Heat Loss During the Early Stages of Flame Propagation and Tulip Flame Formation
Nordita, KTH Royal Institute of Technology and Stockholm University（诺尔迪塔，皇家理工学院和斯德哥尔摩大学）；Aviation Key Laboratory of Science and Technology on High Speed and High Reynolds Number, Shenyang Key Laboratory of Computational Fluid Dynamics, Aerodynamics Research Institute, AVIC Shenyang（航空高速与高雷诺数科学技术重点实验室，沈阳计算流体力学重点实验室，空气动力学研究所，中航沈飞）
