侧面突扩燃烧室冷态流场可视化研究

FLOW VISUALIZATION AND 3-D NUMERICAL STUDY ON COLD FLOW FIELD IN A SIDE DUMP COMBUSTOR

关键词:  冲压喷气发动机  突扩燃烧室  水动力模拟  振荡燃烧  抑制  流场显示

Key words:  Ramjet engine  Dump combustion chamber  Hydrodynamic simulation  Vibrational combustion  Suppression  Flow visualization

摘要:

燃烧室流场中旋涡的不稳定是造成整体式冲压式发动机侧面突扩燃烧室燃烧振荡的重要原因。在透明矩形侧面突扩燃烧室模型上进行了水流模拟显示实验。显示出了燃烧室流场中的振荡涡系和稳定涡系。实验发现：燃烧室头部旋涡非常稳定；进口射流剪切层存在＂马蹄涡＂的周期性脱落；射流在燃烧室通道内卷绕形成涡强较大的二次流螺旋柱状涡对，涡对相撞又使螺旋涡失稳、振荡和破碎。旋涡不稳定性是侧面突扩燃烧室燃烧振荡的流体力学原因。分流的加入挤碎了＂马蹄涡＂，消除了射流势核尾部的旋涡扰动。同时，分流射流横向扩展继续为螺旋柱状旋涡提供足够的涡量，使其稳定旋转。加入分流后的侧面突扩燃烧室在地面热试中燃烧非常稳定。采用Ｓｉｍｐｌｅ方法，通过联立求解定常时均流输运方程和ｋ－ε双方程湍流模型得出了无分流侧面突扩燃烧室和侧面分流突扩燃烧室冷态流场速度分布。除了不稳定流动区域，计算结果与流场显示结果符合良好。

Abstract:

Vortex instablity in combustor flow field is an iynportant reason which leads to combustion oscillation in a side dump combustor. Flow visualization experiments were performed in a transparent rectangular combustion chamber model. Oscillation vortex system and non-oscillating vortex system were found from experiments. A highly stable vortex was found in the head of the combustor. ’Horseshoe’ vortex shedding periodically occur in the shear layer of the inlet jet flow. Asthe jet spread crosswisely through the passage of the combustion chamber, a pair of belieal vortex curlled up with a strong vortex intensity. Owing to the colliding of the vortex-pair, belieal columnar vortex become mis-stability and oscillation, then it smashed. With the injection of the secondary flow, the ’horseshoe’ vortex was smashed, vertex disturbance at the tail of the potential core of the jet flow was eliminated. Next, the belieal columnar vortex get enough the vorticity supplied by the crosswise spread of the secondary jet flow to rotate stably. Meanwhile, the combustion oscillation was removed or decreased. Cold flow field computations based on Simple method to solve the steady state mean flow equations with a two-equation(k-ε) model of turbutence was performed for the side dump combustor and the side dump combustor with secondary flow injection. The results are in good agreement with those of the water tunnel flow visualization results, except the periodic and unstable flow.