颤振诱导不稳定涡对超声速反应混合层的混合增强机理研究

A novel method which employs unstable vortex induced by flutter is brought forward to enhance mixing, based on the characteristics of supersonic reactive mixing-layer. High definition PLIF, PIV, high-speed Schlieren and NPLS will be applied in this project. According to the detailed temporal-spatial structure of the supersonic reactive mixing-layer, self-resemble characteristic of macro-structure and turbulent flame will be extracted. By comparing non-flutter, forced harmonic vibration and flutter, comparing non-reaction and reaction, dynamic couple of flutter/shock-wave/mixing-layer/combustion will be obtained. This will enrich the theory of flutter vortex under the conditions of supersonic, unsymmetrical and reactive flow. Applying both theoretical analysis and LES and optical measurements, several physical topics will be discussed, such as shedding modes of the unstable vortex induced by the flutter, evolution rules of the macro vortex, the effects of combustion and shock wave on the movement and transformation of the vortex, scalar transportation with the vortex and instability characters of the mixing-layer. Based on all of these facts, the mixing enhancement mechanism of unstable vortex induced by flutter in supersonic reactive mixing-layer will finally be disclosed. .This project will be helpful for understanding the supersonic reactive mixing-layer triggered by unstable macro-vortex, and understanding the physical mechanism for mixing enhancement by flutter. This project will also establish the basis of applying the novel method of mixing enhancement.

针对超声速反应混合层的特点，创新性地提出采用颤振诱导不稳定涡进行混合增强。利用高分辨率的PLIF、PIV、高速纹影、NPLS等设备，研究超声速反应混合层的精细时空结构，获得大尺度结构和湍流火焰界面在不同尺度下的自相似特征；通过对比研究无颤振、强迫简谐振动和颤振，无反应和有反应等情况下的流场结构，获得颤振/激波/混合层/燃烧之间的动力学耦合关系，进一步丰富超声速、非对称、反应流下的颤振涡理论；结合理论分析、大涡数值模拟和高分辨率光学观测，明晰颤振诱导不稳定涡的脱落模式、大尺度涡的演化规律、燃烧和激波对涡运动和变形的影响、大尺度涡的标量输运特性、混合层失稳特征等，最终揭示颤振诱导不稳定涡对超声速反应混合层的混合增强机理。.该项研究将加深对大尺度不稳定涡激发下的超声速反应混合层的认识，明确颤振增强混合的物理机制，为拓展这一新型混合增强措施的应用奠定基础。

本项目以超声速反应混合层为研究对象，综合运用试验研究、理论分析和大涡数值模拟方法，深入开展了振动诱导不稳定涡的机制及其增强混合机理的研究工作。.首先开展了超声速反应混合层的流场结构的研究。研究分析了来流马赫数为2.12和3.18，对流马赫数为0.22的平板混合层的流动发展和演化特性，获得了流场的精细结构。通过采用数字图像处理和边缘检测技术获得了混合层增长特性，探讨了混合层非线性增长特征，分析了混合层界面分形维数沿流向的变化以及关联特征。.其次开展了振动诱导不稳定涡的演化规律的研究工作。设计并开展了振动诱导混合增强的试验：设计了用于开展强迫振动的薄平板，采用振动控制系统控制双马赫数喷管尾缘的薄平板的振动，研究了振动频率分别为200Hz，400Hz，2000Hz以及4000Hz，振幅分别为1.5mm和1.5mm条件下混合层流场的非定常特性以及混合增强情况，采用动量厚度、标量混合度以及涡量厚度等指标评估了强迫振动下流场的混合情况，明晰了强迫振动诱导混合增强的机理；设计并开展了平板和二元板在超声速非对称来流下的振动特性研究，明晰了凹腔隔板的自激振动特性。.最后开展了振动诱导不稳定涡来增强混合的研究。采用PIV数据处理获得了不同振动条件下的速度场分布，研究表明高频振动下横向速度的峰值更大，促进了上下高速流动的掺混；高频振动下流动的非定常性显著提高，湍流脉动剧烈程度显著增长；混合层增长速度、动量厚度、标量混合度以及混合层涡量厚度的指标评估结果表明，高频振动诱导的大尺度涡结构的卷吸和夹带作用对混合效率的增强起了主导作用.