采用移动粒子法对蒸发管结构优化

采用数值模拟方法研究在驻涡燃烧室试验中出现的部分燃油在外环冷却腔中燃烧的现象,分析导致过低的燃烧效率的原因,并通过优化设计对此现象加以解决.通过移动粒子半隐式方法的计算,结果基本还原了燃油回溅现象,查找出蒸发管结构设计中直段长度过短,并对蒸发管直段结构进行优化加长.在结构优化后的计算中,燃油回溅现象已经得到了很好的抑制,计算溅出的粒子由总数的50%降低至10%左右;试验结果得到的温升法燃烧效率也相应的由50%左右上升至80%～90%,从而验证了优化设计的正确性.     

关于旋涡定义的思考

针对旋涡定义这个长期未解决的难题,在分析历史上提出的几种思路的基础上,本文提出:定义旋涡的总目标,应当体现其管状运动形态,并与其作为流体运动肌腱的动力学功能有机结合;该定义应能以统一的方式覆盖经典涡动力学业已成熟的结果,并且指引对湍流中复杂涡状结构及其相互作用的识别。据此,本文根据涡量场演化的已知规律,提出了旋涡的一个动力学定义,作为继续深化讨论的参考。同时提出,人们针对湍流结构研究构造的各种涡判据,虽然对湍流涡状结构的可视化起了重要作用,但因其难以遵循管式涡量场的因果演化而无法取代完备的涡定义。相比之下,近十年来形成的涡量面理论,有望在未来发展中使旋涡的定义和检验问题回归涡量动力学的自然规律。     

绕三角翼流态中的某些定常与非定常特性研究

利用流动显示及片光技术,对绕三角翼流动中的某些非定常特性进行了研究。首先在涡面剪切层中发现了两种不同的小涡结构。进而对涡破裂点脉动做了系统的观测,发现在破裂点很靠近顶点的迎角下,脉动主频突然增大。此外还对三角翼涡破裂形态做了细致的分析,提出了泡状破裂在一定程度上可以看成螺旋破裂并给出了实验结果,提出了三种特殊的破裂形态。     

圆柱尾流中的二次分离及环量衰减问题

在圆柱绕流的非定常流动中,相应于旋涡的周期性脱落柱后的二次分离是周期性间断发生。二次涡的影响不能忽略。但对长时间流动的模拟还必须考虑尾涡的环量衰减。模拟Bluff Body流动有效的离散涡模型应包括二次分离及尾涡衰减两种机因。本文数值计算结果证明了上述结论。     

Effect of tip geometry and tip clearance on aerodynamic performance of a linear compressor cascade

The tip leakage flow between a blade and a casing wall has a strong impact on compressor pressure rise capability, efficiency, and stability. Consequently, there is a strong motivation to look for means to minimize its impact on performance. This paper presents the potential of passive tip leakage flow control to increase the aerodynamic performance of highly loaded compressor blades. Experimental investigations on a linear compressor cascade equipped with blade winglets mounted to the blade tips have been carried out. Results for a variation of the tip clearance and the winglet geometry are presented. Current results indicate that the use of proper tip winglets in a compressor cascade can positively affect the local aerodynamic field by weakening the tip leakage vortex. Results also show that the suction-side winglets are aerodynamically superior to the pressure-side or combined winglets. The suction-side winglets are capable of reducing the exit total pressure loss associated with the tip leakage flow and the passage secondary flow to a significant degree.     

低负荷弯叶栅流谱结构与气动性能的实验研究

在一套典型的低负荷矩形涡轮静叶栅中开展弯叶片影响叶栅内部流谱结构与气动性能的实验研究。利用微型5孔探针分别对6套叶栅的进出口流场进行详细测量,并在叶栅表面和端壁进行油流显示实验。从定性和定量的角度考察了叶片弯曲对壁面流谱拓扑结构、出口涡量、出气角及二次流损失分布的影响,总结了弯叶片影响边界层迁移与二次流损失发展的规律。     

涡破裂诱导的垂尾抖振气动弹性分析

通过试验方法分析了三角翼前缘分离涡与垂尾抖振之间的关系,深入研究了尾迹流动对垂尾抖振各阶模态的激励作用。计算得到了垂尾模型固有频率及各阶模态。在风洞试验中,应用激光片光烟流场显示技术,得到了三角翼模型在风速为30 m/s下,各迎角的涡结构;使用加速度传感器测量了垂尾翼根和翼梢的抖振响应;使用热线风速仪测量了垂尾翼根和翼梢位置的脉动速度分量。结果表明:前缘涡破裂后产生的高湍流度的尾迹是垂尾抖振的直接原因,抖振边界与涡破裂的强度和位置有关;涡破裂后尾迹与垂尾产生共振,使得抖振加速度响应频率与垂尾固有频率一致;涡破裂后,在较小迎角下,尾迹对垂尾的高频振动模态的激励较为明显,在较大迎角下,涡破裂流动对垂尾低频振动模态的激励加强了。     

前置隔板对圆柱绕流影响的实验分析

对经典的圆柱绕流模型,运用前置隔板对流场进行控制。利用粒子图像测速(PIV)方法在自循环水槽中研究了雷诺数为1 800时,柔性和刚性2种不同刚度的前置隔板对圆柱绕流的影响。研究发现:柔性隔板自由端的弯曲增加了对流场的额外扰动,并且柔性隔板弯曲变形会诱导产生脱落涡,导致尾迹流场的主频发生变化。在圆柱下游流场,无隔板工况与柔性隔板工况的回流区长度相当,刚性隔板工况的回流区相较之下则更长。结果显示:前置隔板还能在一定程度上减小圆柱绕流的阻力。      

基于流动显示的翼尖涡不稳定频率测量

翼尖涡涡核振荡频率的准确测量是翼尖涡控制技术得以有效实施的重要前提。采用流动显示方法,研究了椭圆机翼翼尖涡在低雷诺数条件下的不稳定特性。分别采用单点谱分析和动力学模态分解技术,从流动显示图像序列中提取了涡核振荡的短波不稳定模态的频率,2种方法得到的频率相对误差最大不超过5%。研究结果表明:涡对的空间运动通常展现出长波与短波模态的耦合,涡核的高频短波振荡耦合在低频长波摆动中,以前者为主要含能模态;短波不稳定性的无量纲振荡频率随雷诺数的增大而增大、随机翼攻角的增大而减小。      

Design and Performance of an Improved Trapped Vortex Combustor

 A trapped vortex combustor (TVC) has been a very promising novel concept for it offers improvements in lean blow out, altitude relight, operating range, as well as a potential to decrease NO_x emissions compared to conventional combustors. The present paper discusses the improved designs of the new combustor over the prior ones of our research group, including that: a) the overall dimensions, both axial and radial, are reduced to those of an actual aero-engine combustor; b) the air flow distribution is optimized, and especially 15% of the air is fed into the liner as cooling air; c) a straight-wall diffuser with divergence angle 9癷s added. A series of experiments (cavity-fueled only, under atmospheric pressure) has been conducted to investigate the performance of the improved TVC. Experimental results show that at the inlet temperature of 523 K, the inlet pressure of 0.1 MPa, stable operation of the TVC test rig is observed for the Mach number 0.15-0.34, indicating good flame stability; the combustion efficiency obtained in this paper falls into the range of 60%-96%; as the total excess air ratio increases, the combustion efficiency decreases, while the increase of the inlet temperature is beneficial to high combustion efficiency; besides, the optimal Mach numbers for high combustion efficiency under different inlet conditions are confirmed. The outlet temperature profiles feature a bottom in the mid-height of the exit. This paper demonstrates the feasibility for the TVC to be applied to a realistic aero-engine preliminarily and provides reference for TVC design.