无源受控扰动下Coanda附壁射流离壁过程研究

The separation process of wall-attached jet is considered to be a crucial part of the Fluidic thrust vectoring technology. Different from free stream, the wall-attached jet is consisted of complex flow structures, including separation bubbles, reattachment structures and vortexes that continuously impinge the wall. Triggered by external turbulence, the attached jet will separate from the wall rapidly, causing incontrollable transition and delay, and significantly affect the deviation performance and dynamic response of the thrust vector apparatus. This project intends to design an experimental device for fluidic thrust vectoring control, the jet separation of which can be triggered through controlled disturbance. In order to measure the thrust vectoring, surface transient pressure and tridimensional transient flow field within the separation process, the Synchronous Measurement Techniques including force, pressure and PIV are adopted. The purpose of this study includes acquiring the transient flow field, vorticity field and developing process of the jet separation, investigating the correlation between primary jet /wall-attached jet and mechanical properties of the thrust vectoring, establishing the flow model of the jet separation process, clarifying the impact mechanism of the uncontrollable separation to the burst of the separation bubbles in attached jet. The problem of separation process of wall-attached jet contains potential fluid mechanical phenomenon with high value of research. Meanwhile, it is highly beneficial for the design of fluidic thrust vector devices, as well as the study of flow vectoring and thrust loss reducing.

附壁射流离壁过程是流体式推力矢量技术中的关键环节。与自由射流不同，附壁射流包含分离泡、再附结构和不断拍击壁面的旋涡等复杂近壁流动结构，受外部气流扰动触发失稳而迅速脱离壁面。常导致射流偏转出现突跳、滞后等非受控问题，进而对推力矢量的偏转性能及动态响应有着重要的影响。本项目拟设计一个可引入受控扰动触发射流离壁的流体推力矢量实验装置，采用测力、动态测压与粒子图像测速（PIV）测试技术对射流瞬态离壁过程中推力矢量、壁面瞬态压力和空间瞬态流场进行同步测量。获得射流离壁过程中瞬态速度场、涡量场及发展演化过程；探讨主射流及近壁流动结构与推力矢量力学特性的相关性；建立射流离壁过程的流动模型，阐明附壁射流分离泡破裂对非受控离壁运动影响的流动机制。附壁射流离壁问题蕴含着新的流体力学现象有待发现，具有重要的基础研究价值。同时对流体推力矢量动力装置的设计、矢量偏转规律的认识、减小推力损失研究等具有重要意义。

附壁射流离壁过程是流体推力矢量技术中的关键环节，而离壁过程中的“突跳”分离现象导致了推力矢量控制的非线性和不受控，不利于该技术的进一步工程应用。本项目针对简化的流体推力矢量实验物理模型，研究了以下内容：1）通过烟流流动显示、染色液流动显示技术和PIV技术分别从定性和定量的角度获得了附壁射流稳态空间流场、近壁分离泡流动结构和动态偏转分离过程中流场结构的发展演化规律，澄清了附壁射流“突然离壁”的物理机制并揭示了突然离壁过程中的流动机理；2）通过矢量力和流场结构同步测量实验获得了射流突然离壁过程中流场结构和矢量推力的相关性；3）通过矢量推力、壁面压力同步测量实验获得了壁面压力和矢量推力的相关性，揭示了推力矢量“突跳”偏转分离的力学机制。结果表明，附壁射流“突跳”分离的根本原因在于：分离泡结构的破裂。而其中的流体物理机制在于：近壁处被动二次流流入和尾缘处流体倒吸共同作用，二次流流入导致分离泡变长，尾缘流体的倒吸导致分离泡突然破裂。其力学机制在于：分离泡破裂后，主射流两侧的压差突然减小，射流无法保持偏转附壁状态，从而迅速离壁，在矢量力控制中表现为突跳和非线性现象。这一结论为未来改善无源流体推力矢量控制非线性、突跳等问题指明了方向。本项目的研究成果可以进一步促进新型流体式推力矢量技术的发展，不仅可应用于航空航天领域，也可应用于船舶、舰艇以及水下航行器。因此，在航空航天航海、国防建设和国民经济方面具有重要应用前景。