【作者】 曾军；

【导师】 胡骏；

【作者基本信息】 南京航空航天大学 ， 航空宇航推进理论与工程， 2007， 博士

【摘要】 在提高压气机压比的同时,提升涡轮前温度是改善航空燃气涡轮发动机性能(推重比、耗油率)的有效措施。随着涡轮前温度的不断提高,必须采用气膜冷却等手段来保证其安全工作,而气膜冷却所带来的冷气掺混将直接影响涡轮叶栅流场结构和气动性能。针对目前国内对考虑冷气喷射作用下,叶栅内部流场结构和气动损失研究尚不够深入、气冷涡轮设计基础数据缺乏的现状,本文采用涡轮平面叶栅实验和计算流体动力学(CFD)数值模拟方法,细致地研究了冷气喷射对叶栅流场特征和气动性能的影响。在平面叶栅装置中,采用低堵塞的五孔压力探针和附面层探针,分别对前缘、吸力面、压力面气膜孔以及尾缘劈缝的冷气喷射状态下,叶栅内部流场结构进行了详细的测量。研究了冷气喷射位置、角度和流量对叶栅流场和气动性能的影响;细致分析了叶栅尾迹、涡轮叶片表面附面层内的速度分布;探究了能量损失系数、总压损失系数随冷气喷射位置和流量等参数的变化规律。研究结果表明:冷气在主流方向的分速度量改变了附面层流动速度剖面的形状;当冷气量较大时,压力面和吸力面上的小角度(小于30o)冷气喷射可以降低叶栅流动损失;冷气喷射角度大于60o后,不同冷气量下,压力面和吸力面的冷气喷射均增加了叶栅流动损失;前缘气膜孔的冷气喷射总是增大了叶栅流动损失;而叶栅流动损失随尾缘冷气喷射的变化并非单调,呈现出复杂的规律。同时利用CFD技术,数值模拟了考虑气膜孔冷气喷射情况下的叶栅三维流场,分析了叶栅通道内部的细节流场结构。计算中采用SST(Shear-Stress-Transport)湍流模型,将叶片气膜孔出口做为冷气喷射边界,给定冷气的流量、总温和气流喷射角,冷气的总压和静压则是通过与主流场的耦合迭代计算。研究中发现由于冷气喷射中垂直于主流速度分量的存在,在主流流场中产生一对马蹄涡结构。将一部分主流气流卷入到附面层之中,改变了附面层流动结构。在计算和实验结果比对的基础上,本文对某高负荷高压涡轮导向器扇形叶栅进行了真实工作状态下,叶栅内部流动和损失的数值计算,进一步分析了冷气喷射位置、角度和流量对扇形叶栅流场结构和气动性能的影响。利用Schobeiri模型对尾缘劈缝冷却叶栅流动损失进行了计算,并同实验结果进行了对比,发现该模型预测结果与实验测量结果有明显的差别。综合本文的实验和计算工作显示,通过主流场与冷气射流流场耦合的全三维粘性计算获得的结果与实验结果吻合良好;采用以平面叶栅冷气喷射实验数据为基础,结合主流场与冷气射流流场全三维耦合计算的方法,可很好地研究各种冷气喷射方式对叶栅流场和气动性能的影响。更多还原

【Abstract】 The performance of aero engine (thrust-to-weight ratio, specific fuel consumption) can be improved by increasing the turbine inlet temperature and the compressor pressure ratio. The turbine inlet temperature is now higher than the melting point of turbine material, cooling techniques such as film cooling must be applied to ensure the safety of turbine blade. At the same time, the characteristics of the flow and the aerodynamic performance of turbine cascade are affected greatly by the coolant ejected into turbine cascade from film holes. But there are only a few fundamental researches on this phenomenon in China. In this thesis, experiments and numerical simulations were carried out to investigate the effects of coolant injection on turbine cascade flow fields and the influences on aerodynamic performances.In a plane cascade, five holes pressure probe and boundary layer pressure probe were applied to obtained the detailed characteristics of the flow field when the cool-ant ejected from the film holes at leading edge, suction side and pressure side of tur-bine blade respectively. The velocity profile in boundary layer of blade and trailing flow are measured to study the effect of the coolant ejected positions, angles and mass flow rate. Then the rules of total pressure loss coefficient and energy loss coef-ficient varying with the coolant ejected positions, angles and flow rate were con-cluded.Experimental results show that the velocity profile in boundary layer of blade was changed because of the coolant component velocity in main flow direction. While the flow rate of coolant was larger, the flow loss was decreased when the coolant was ejected in smaller angle (smaller than 30°) from pressure and suction side. The flow loss was increased if coolant was ejected in large angle (larger than 60°) in all flow rate cases. When the coolant was ejected from the film holes in leading edge, the flow loss was always increased in all experimental cases. However, the rule of flow loss varying with the coolant ejected from trailing edge was very complicated.Numerical simulations were carried out additionally to investigate the detailed characteristics of internal flow in the turbine cascade. Shear-Stress-Transport model was used as the turbulence model and the outlet of film hole was set as the coolant inlet boundary in simulations. Mass flow rate, total temperature and ejection direction of coolant were defined in the coolant inlet boundary. Total pressure and static pres-sure of coolant were achieved in the coupled calculations with main flow.Horseshoe vortex induced by the component velocity in the vertical direction of main stream was found in numerical simulations and some part of main stream were transported into boundary layer according to this Horseshoe vortex. Annular turbine cascade was simulated furthermore based on the comparison among experimental and numerical results about the plane turbine cascade.Finally the flow loss according to the coolant ejected from trailing edge was calcu-lated using the Schobeiri model. Significant difference was appeared when comparing this result with experimental result.All the results demonstrate that numerical results gotten by three-dimensional cou-pled calculations agree with experimental results well. The affects of coolant ejection on the flow fields and aerodynamic performances of turbine cascade can be studied very well by the method applied in this study, which analyzes the experimental results achieved in plane turbine cascade together with the three-dimensional coupled nu-merical simulations.更多还原