单油滴蒸发燃烧周围流场及火焰结构的数值模拟研究

Numerical study on surrounding gas flow and flame structures of single combusting droplet

采用一步总包有限反应速率模型模拟了不同相对速度、颗粒尺寸、环境温度条件下单个油滴燃烧。对于全包围燃烧模态,火焰半径的模拟结果与文献的理论解析解进行对比,在周向角小于90°范围内和数值模拟结果接近,大于90°,理论解不能精确预测火焰锋面半径;油滴表面局部蒸发率较尾部火焰燃烧模态下的蒸发率小;各个燃烧模态下,局部蒸发率最大的位置发生在前驻点处。燃烧状态下油滴颗粒的阻力系数要比冷态条件下的阻力系数小,不能简单套用Wallis-Kliachko公式计算。阻力系数随着来流速度增大而增大,随着周围环境温度的升高而升高。

A one-step turnkey finite reaction rate model was adopted to simulate different relative velocities,particle sizes,ambient temperature conditions of a single droplet burning.For the full surrounding combustion mode,the simulated results of flame radius was compared with theoretical analytical solution.Theoretical solution is closer to the numerical results for the circumferential angle less than 90°;if the angle is greater than 90°,the theoretical solution cannot accurately predict the flame frontal radius.Under different combustion modes,the maximum local evaporation rate occurs at the front stagnation point.Droplet surface partial evaporation rate is smaller than the rate of evaporation under the tail flame mode.The drag coefficient of a combusting droplet is smaller than that of a cold droplet,hence the formula of Wallis-Kliachk is inaccurate for this case.The drag coefficient increases with an increase in flow velocity, and increases with an increasing ambient temperature.