高雷诺数超声速湍流混合层标量输运与扩散特性研究

The mixing processes of fuel-rich gas and air in the combustor of combined cycle engine can be viewed as the supersonic mixing layer, and this mixing layer is featured by the high Reynolds number. Moreover, the scalar (temperature and concentration) transport and diffusion processes are important factors for controlling the gas-gas mixing and combustion process. Under high Reynolds number, the turbulence scale, the transport and diffusion of scalar, vortex shape and scalar interfacial area of the mixing flow field reveal more complex physical mechanisms. Herein, the supersonic mixing layer with high Reynolds number is investigated through both the experiment measurement in supersonic wind tunnel and large eddy simulation(LES)/direct numerical simulation (DNS). Then, the goal of this study is to clarify the evolution morphology and the scalar transport and diffusion characteristics of supersonic mixing layer. The high resolution vortical structures, density field, velocity field and concentration field can be captured qualitatively by using the spatiotemporal flow imaging apparatus, and the transport and diffusion quantity of scalar, structure and probability density function (PDF) of scalar are also obtained quantitatively. The more details on the scalar mixing flow field can be obtained by the LES/DNS approaches with the inflow conditions measured in the wind tunnel. Then the influence of Reynolds number and compressibility on the scalar mixing is also discussed. Based on the experimental and numerical data, the growth and mixing mechanism of scalar mixing layer would be clear, and some new mixing models will be built. In addition, the valid methods of mixing enhancement are also proposed.

组合循环发动机内部的富燃燃气与空气的混合过程具有高雷诺数、超声速混合的特点，混合层内的温度、组分浓度等标量输运与扩散过程是制约气气混合与燃烧过程的重要因素。高雷诺数条件下，混合层内的湍流尺度、动量与标量输运和扩散、涡形态、标量界面演化呈现更为复杂的物理机制。本项目拟采用高超声速风洞实验、大涡模拟(LES)/直接数值模拟(DNS)以及理论建模相结合的手段，研究湍流混合层发展形态、标量输运与扩散特性及其影响因素。通过改变来流速度、温度等参数获得高雷诺数湍流来流条件，利用流场精细结构测量方法，定性获得高分辨率的涡结构、标量结构，定量获得速度场、浓度与温度场以及标量PDF分布。针对试验获得的湍流来流，开展混合层的大涡模拟或直接数值模拟研究，得到更为全面的流场数据。探究雷诺数、压缩性等参数对标量输运与扩散的影响，以此为基础建立标量增长与混合模型，并提出有效的混合增强方法。

采用实验、大涡模拟和理论建模相结合的方法研究了超声速混合层增长特性、标量混合特性及其混合增强技术。首先，通过大涡模拟研究了高雷诺数混合层涡结构发展过程，得到了混合层发展各个阶段的增长率，并且通过实验验证了数值仿真的结果。重点研究了特征雷诺数、对流马赫数和隔板厚度等参数对混合层混合特征的影响。然后，研究了超声速混合层各个阶段的标量输运和扩散特性，并且给出了来流雷诺数和对流马赫数的影响。建立了超声速混合层混合率模型。最后，重点研究了超声速混合层的混合增强方法。通过在入口处添加单频或者多频扰动研究了混合层在不同扰动下的增长特性。实验和数值仿真研究了不同的混合器，如波瓣混合器、锯齿型混合器以及等离子体合成射流等对混合层增长率的影响，重点关注了流向涡对混合层的影响。之后，研究了激波和膨胀波对混合层涡量输运、涡结构发展、湍流统计特性以及混合特性的影响。研究结果为组合循环发动机内部燃气与空气的混合过程提供重要参考。