非预混连续旋转爆轰发动机流动特性的大涡模拟研究

Study on the detonation propulsion technology, especially Continuously Rotating Detonation Engine (CRDE), is of great significance for China's national defense and military construction. The fuel and oxidizer are usually injected separately into the combustor in a realistic CRDE, and their mixing processes are very complex and have a remarkable impact on the detonation properties. However, most of the numerical simulations on CRDE focused on the ideal premixed injection conditions by solving the Euler governing equations, while the numerical studies on non-premixed CRDE performed recently provided the time-averaged results primarily by solving the Reynolds-Averaged Navier-Stokes equations (RANS), both of which are unable to reveal the unsteady flow phenomenon and the associated physical mechanism in a real CRDE, such as the turbulent mixing, and their interaction with the detonation..This project is to investigate the flow characteristics of non-premixed CRDE using large eddy simulation (LES). A LES-based method for compressible reacting flows will be developed, and the capability of different chemical reaction mechanisms and turbulence combustion models to resolve and predict the flow characteristics of non-premixed CRDE will be examined. Based on the high-resolution LES data, this project will reveal the instantaneous flow structures of non-premixed CRDE, then understand the influence laws of injection conditions and geometries for fuel and oxidizer on the turbulent mixing and detonation properties, and explore the flow physics of non-premixed CRDE with methane and ethylene injection. .The results of this project would promote the understanding of the complex flow physics in a realistic CRDE, and could also provide the theoretical support for its design and engineering application.

研究以连续旋转爆轰发动机(CRDE)为主的爆轰推进技术对我国军事和国防建设具有重要意义。真实CRDE中燃料/氧化剂分开喷注，它们的混合过程极为复杂并会显著影响爆轰特性。但以往研究多基于Euler控制方程围绕预混进气开展，近期以RANS为主的非预混研究主要给出流场时均特征，缺乏对真实CRDE中湍流混合、混合-爆轰相互作用等非定常过程及其物理机理的揭示。.本项目拟采用大涡模拟方法(LES)开展多因素影响下的非预混CRDE流动特性研究。发展可压缩化学反应流动的LES方法，考察不同化学反应机理和湍流燃烧模型对非预混CRDE的刻画和预测能力。根据高时空分辨率的LES数据，揭示非预混CRDE的瞬态流场特征，明确喷注条件和喷注构型对其中湍流混合和爆轰特性的影响机理，探索甲烷、乙烯的非预混CRDE混合和爆轰特性。研究结果可促进对真实CRDE中复杂物理化学过程的认识，更可直接为其研制和设计应用提供理论参考。

真实连续旋转爆轰发动机(CRDE)中混合过程极为复杂并显著影响爆轰性能，已有数值模拟手段对其中非定常过程和物理机理的刻画存在不足。本项目：.(1)建立了以大涡模拟为基础的、基于有限体积离散的、能准确刻画流场瞬时结构特征的可压缩化学反应流动数值模拟方法；.(2)首次对非预混CRDE冷流场中燃料和氧化剂的混合过程及其主要掺混机理开展了定量的深入研究，明确了非预混喷注流场中存在欠膨胀特征、大尺度涡结构，以及回流区等复杂的流动现象。由于K-H不稳定性产生的大尺度湍流涡结构是促进氢/氧混合的主要机制。.(3)考察了氧气喷注位置、氢气喷注角度、平行进气距离等多种因素对流场混合特性的影响。通过定义混合距离、可爆轰范围等定量评估了不同喷注设计的掺混效率。氢/氧在推力墙处分别沿45度靠近内外壁面喷注时掺混效率最高，最有利于两种气体的混合。首次设计了氢/氧分级进气模式，进一步缩短了氢/氧混合距离，增大了可爆轰范围，从而提高了掺混效率。.(4)研究了圆形、椭圆形、方形，以及长方形等喷嘴形状下的流动特性。明确了椭圆射流穿透速率最慢，射流核心区的长度最短，混合面积最大。圆孔和方孔射流的主不稳定性受三维螺旋不稳定模态主导，但椭圆和长方形射流则主要在短轴平面上呈现出二维的不稳定特性。.(5)研究了不同喷压比下高度欠膨胀射流的激波振荡现象。明确了马赫盘的振荡周期对于不同的NPR是相同的，并且在当前喷嘴几何设计下由5.298kHz的轴对称模式支配。径向的冲击振动幅度沿着流动方向增加，而对于较低的NPR，冲击振动幅度较大，这意味着它是尖端振幅的增加函数。.以上工作揭示了非预混CRDE流场的瞬态流动特征，明确了喷注条件、喷注构型及不同燃料对其中湍流混合和爆轰特性的影响机理。研究结果促进了对真实CRDE中复杂物理化学过程的认识，为其研制和设计应用提供了理论参考。