超声速单边扩张燃烧室分离区振荡现象及其解耦分析

Decoupling Analysis on Oscillation of Separated Region in a Supersonic Combustor with Single-Side Expansion

关键词:  超声速燃烧  反压  分离区  激波边界层干扰  解耦分析

Key words:  Supersonic combustion  Backpressure  Separated region  Shockwave/boundary layer interaction  Decoupling analysis

摘要:

为了揭示超声速燃烧中非定常现象的主导机制，通过解耦分析系统研究了单边扩张燃烧室中一种以分离区不稳定为特征的非稳态燃烧。采用控制变量的方法，对Ma=6条件(隔离段来流马赫数3.46，总温1430K)下燃烧不稳定的可能影响因素进行了解耦分析，并对典型工况在直连式实验台上开展了验证。研究表明，火焰不是本文中燃烧不稳定现象的主要影响因素，释热形成的反压才是该现象的主因。低当量比工况下反压较小，流场的非稳态机制由射流和凹腔共同主导；中高当量比工况下反压较大，非稳态机制由反压主导。射流与凹腔相互作用能形成周期性极强的非稳态过程，其压力振荡频率约为200Hz。在较高反压的驱动下，超声速燃烧室内会发生复杂的非定常现象，具体表现为激波串轴向大幅振荡，并伴有非对称分离区的间歇性切换。由反压主导的流场振荡周期性不强、频率以中低频为主(100～500Hz)。非稳态过程可能源于激波边界层干扰中的低频不稳定性，其被燃烧释热所形成的分离区放大，在下游反压的影响下形成了流场中复杂的非定常过程。

Abstract:

For the purpose of uncovering the key physics of unsteady phenomena in supersonic combustion， a decoupling analysis is implemented to study the unsteady combustion induced by separation in a single-expanded supersonic combustor. The control variate method is applied to discover the key impact factor of the unsteady combustion under Mach 6 flight condition (isolator entrance Mach number of 3.46， and air stagnation temperature of 1430K). Experiments have been implemented on a direct connect facility to verify the main viewpoints of typical operating conditions. The systematic researches indicate that flame does not have much impact on the unsteady behaviors of combustion， and the backpressure induced by heat release is what really matters. The jet together with cavity account for the periodic oscillation at low equivalence ratio (the backpressure is relatively low)， and the frequency of static pressure oscillation is about 200Hz. The backpressure (high enough) caused by heat release results in the complicated dynamic combustion under higher equivalence ratios. During the dynamic process， the shock train travels along the length of the combustor with high amplitude， and the asymmetric separated region switches intermittently between both sides of walls. The oscillation induced by backpressure is broadband， and the main component of oscillation is low frequency (100～500Hz). The low frequency unsteady process may be related to the low frequency unsteadiness in shockwave/boundary layer interaction (SWBLI). Such an unsteadiness is amplified by the large separated region and promoted by the backpressure from downstream， which forms a complex unsteady process.