受限空间内超声速混合层生长特性

为获得受限空间内激波作用下的超声速混合层生长规律,以支板喷射超燃冲压发动机典型流道为研究对象,开展了2.3Ma氢气射流与2.0Ma空气来流所形成的超声速混合层的生长特性研究.基于OpenFOAM计算平台,采用大涡模拟方法,数值研究了超声速混合层的流场结构和特征,流场结构和组分分布与实验结果吻合较好.通过超声速混合层组分浓度、厚度、可压缩效应及总压损失的分析,获得了超声速混合层的生长特性.研究结果表明:受限空间内超声速混合层的生长过程具有4个典型阶段,支板末端的膨胀波/激波结构会显著减低对流马赫数,从而降低混合层的可压缩性,促进混合层的生长;激波与混合层的相互作用能够增强局部湍流强度,获得涡量增益,加快混合层的生长速率,促进混合效率,但同时会引起较大的总压损失,降低发动机性能.发动机设计时要综合考虑波系结构与混合层相互作用带来的混合增强和总压损失,实现性能优化.

Study on thesupersonic mixing layer growth in confined spacealgorithm

The supersonic mixing layer formed by a planar thin hydrogen jet at 2.3 Ma and a 2.0 Ma surrounding airflow in a scramjet engine model is studied in order to investigate the growth characteristics with consideration of shocks. Flow field structure and features of the supersonic mixing layer are achieved by using large eddy simulation method with the OpenFOAM software. Reasonable agreements are obtained between calculation and experiment in terms of flow field structure and component distribution. The component concentration, the thickness, the compressibility effect and the total pressure loss are analyzed. Results show that four developing regions can be observed for the growth of the mixing layer. The expansion-fan/shock-wave pattern at the injector exit makes the convective mach number decrease dramatically, leading to a reduction in compressibility effects and a contribution to the development of the mixing layer. The interaction of shock/mixing layer results in local amplification of turbulence and gain of vorticity, which is beneficial to the supersonic mixing. However, the increasement in total pressure loss is unavoidable in the presence of shocks because they can bring performance losses of the scramjet. Thus a tradeoff between the enhanced mixing efficiency and the decreased total pressure recovery should be considered in the scramjet optimization design.