单边扩张燃烧室燃烧非对称及非稳态现象研究

Investigation of Asymmetric and Unsteady Combustion in a Supersonic Combustor with Single-Side Expansion

为了探究单边扩张超声速燃烧室在不同当量比下出现的多种模态及其内在机理,通过实验和数值模拟,对该构型燃烧室在并联凹腔对称喷注的工况下进行了系统研究。实验中,隔离段来流入口马赫数为3.46,来流总温为1486K;采用乙烯作为燃料,当量比范围从0.26到0.51。结果表明:燃烧室工况随着当量比的上升而改变,且可分为三个模态。当量比较低时(0.26),形成只有剪切层内有火焰的对称燃烧。当量比较高时(0.51),形成上凹腔为凹腔内燃烧、下凹腔为剪切层燃烧的非对称燃烧。当量比适中时(0.4),火焰在上下凹腔间来回震荡。在非稳态过程中,预燃激波串沿燃烧室轴向做周期性往复运动,定量分析表明火焰震荡的频率约为170Hz。燃烧震荡来源于分离区喷注与燃烧的耦合效应,震荡机制与涡无关,可能是由声振机制引起的凹腔自激震荡。

In order to explore the mechanism of different operating conditions under various equivalence ratios in a supersonic combustor with single-side expansion,experimental and computational investigations of the flow field associated with parallel cavity-based flame holder were carried out. Experiments were conducted with isolator entrance Mach number of 3.46,and air stagnation temperature of 1486 K. Ethylene was used to fuel the combustor over an equivalence ratio range 0.26φ0.51. Results indicated that the combustion characteristics varied from different equivalence ratios,which formed three operating modes. A symmetric combustion was held in shear layers of both cavities under low equivalence ratio（0.26）,while asymmetric combustion appeared at high equivalence ratio（0.51）. In that case,flame stabilized inside the top cavity and the shear layer at bottom.For a moderate range of φ=0.4,the flame oscillated between dual cavities. Shock train travelled periodically along the axis of combustor during the unsteady process. Quantitative analysis showed that the average frequency of flame oscillation is about 170 Hz. The cause of self sustained oscillation is found to be related to the coupling of injection and combustion in separated region along with the acoustic characteristic of cavity,which has nothing to do with eddy.