竖通道内液体燃料燃烧形成的旋转火焰特性

Characteristics of fire whirls induced by liquid fuel in a vertical shaft

为了掌握有侧开缝的竖通道内液体燃料燃烧所形成的旋转火焰特性,分别利用实验与基于液体火源的LES数值模拟技术对以正庚烷液体为燃料,在200 cm高的竖通道内所形成的旋转火焰热流场进行了研究.在确定了数值模拟有效性的基础上得知:在各个高度处,通道内边侧的切向速度绝对值保持在100 cm/s左右;在60 cm高度时,由火焰中心向通道壁面方向,切向速度先迅速增大再逐渐降低至100 cm/s,而在120 cm高度以上时,切向速度仅有逐渐上升过程;由火焰中心向通道两侧方向,旋转科氏力与浮力之比值的变化规律均是先逐渐增大,而后又逐渐降低,最大比值发生在火焰外侧位置;相比浮力,旋转科氏力对通道下半部分流场的影响较大,影响程度随着高度的增加而减弱;通道内旋转火焰热流场的最大轴向速度约为最大切向速度的2倍.

To understand the characteristics of fire whirls in a vertical shaft with corner gaps, experiments of fire whirls induced by n-heptanes and numerical modeling for liquid fuel which is based on large-eddy simulation were performed in a vertical shaft with the height of 200 cm. Model validation was verified. Absolute values of tangential velocity at typical height are around 100 cm/s on the edge of shaft. When the height is 60 era, from the fire to the walls of the shaft, firstly, the tangential velocity immediately increases to the maximum value, and then, decreases to 100 cm/s. However, once the height is greater than 120 cm, the tangential velocity increases only. From the fire to the walls of the shaft, the ratio of Coriolis force and buoyancy is almost symmetrical. The ratio first increases, then decreases and the position where the ratio of Coriolis force and buoyancy achieves its maximum value is outside the fire. In contrast with buoyancy effect, the Coriolis force has great effect on lower part of the shaft, and the effect drops as the altitude rises. The maximal axial velocity is almost two times of the maximal tangential velocity for the thermal flow field of fire whirls in a vertical shaft.