【作者】 刘捷；

【导师】 蒋洪德； 刘建军；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 工程热物理， 2008， 博士

【摘要】 随着燃气轮机透平前燃气温度的不断提高,气膜冷却技术已经成为透平叶片冷却的重要手段之一。作为叶片上热负荷最高的区域,叶片前缘,尤其是滞止线附近的流动极为复杂,受主流滞止、叶片曲率、射流孔排之间的相互作用等多种因素的影响,必须对气膜冷却以及叶片前缘的流动和换热特性进行深入分析,才能为开展有针对性的高温透平气膜冷却设计和改进提供依据。针对这一问题,本论文首先建立了平板气膜冷却实验台,应用热敏液晶测量技术测量射流孔下游的壁面温度分布,进而得到绝热气膜冷却效率和换热系数。文中讨论了不同吹风比、不同射流孔长径比、不同射流注入角等因素对射流孔下游冷却特性的影响,绝热气膜冷却效率被作为衡量不同条件下气膜冷却性能优劣的重要参数;为了补充和验证实验数据,采用CFD软件CFX数值模拟了平板气膜冷却的流动和换热特性;在实验测量和数值模拟结果基础上,深入研究了某重型燃气轮机透平静叶的气膜冷却,分析了静叶前缘及滞止线附近的气膜冷却效果、传热及冷气喷射对气动性能的影响等问题,发现了静叶前缘气膜冷却设计中存在的问题和不足;在此基础上,提出了对静叶前缘气膜冷却结构的五个改进设计方案,并进一步采用CFX对改进设计后的前缘气膜冷却进行数值模拟,分析比较了不同改进设计方案的优劣,探索了提高前缘气膜冷却效果的方法。本文的主要研究结论如下:对于平板气膜冷却,在低吹风比条件下,与主流相比,射流动量较低,受主流影响,射流容易贴附在射流孔下游表面,射流孔近孔区域取得良好的冷却效果;高吹风比条件下,由于射流动量较高,在冷却孔下游容易发生“吹离”和“再附”现象。在低射流孔长径比条件下(L/D=2),射流流动未能在孔内允分发展,射流孔下游的平均冷却效率相对较低;通过设置不同的射流注入角条件来考察不同垂直方向速度分量对射流孔下游冷却特性的影响,极限情况下,即当射流注入角为90°时,低吹风条件下冷却孔下游近孔区域等值线依然呈现锥形分布的特点。对于透平静叶气膜冷却,当冷却孔的出口恰好位于滞止线上时,在压力面侧冷却射流的径向速度分量起主导作用,而在吸力面一侧由于主流的加速作用,射流的径向速度分量相对较弱;当冷却孔的出口位于滞止线一侧时,此时射流的周向速度分量起主导作用。要想获得滞止线及两侧壁面更好的冷却效果,应当沿着滞止线方向定位两排孔,这两排孔分别位于滞止线的各一侧并且交错排列,同时保证滞止线穿过每一个孔的出口边缘,同时要调整这两排孔的径向喷射角,避免径向逆主流喷射。分离结点附近的壁面很难被完全气膜覆盖,通过降低吹风比和增加射流孔出口与分离结点的距离可以获得相对较好的冷却效果。本文的5种改进方案中,方案Ⅴ的改进结果是最好的。更多还原

【Abstract】 Film cooling, as one of the cooling types, has been used in gas turbines for many years and proved to be an efficient method protecting blade or vane, especially the vicinity of the stagnation line, is a critical region because thermal load is at its highest in this area and particular protection and cooling design are required. The flow around the leading edge is always associated with mainstream stagnation, strong pressure gradient, variable curvature, and interaction between rows of showerhead holes. It is necessary to understand flow and heat transfer characteristics of the leading edge film cooling for achieving a reliable film cooling design improvement for gas turbines.In this dissertation, the experimental setup of film cooling on flat plates is configured firstly, and thermo-chromic liquid crystal is utilized to measure the temperature distributions downstream of the injection holes. Then we discuss the influences on film cooling brought by different blowing ratio, different injection hole length to diameter ratios and different injection angles, etc. The adiabatic film cooling effectiveness is regarded as an important parameter to weigh the cooling performance at different experimental conditions. Numerical simulations for film cooling characteristics on flat plat were also performed. Based on the experimental and numerical results, the investigations on the leading-edge film cooling of an inlet guide vane have been done. The original design is simulated to obtain flow mechanism and heat transfer characteristics of the leading edge film cooling. The film cooling characteristics and interactions between jets and mainstream around the leading edge, especially near the stagnation line, are analyzed in detail. To provide better coolant coverage on the leading edge, the cooling configuration is modified based upon the analysis and understanding of the 3D prediction for the original design. The modified designs are compared with the original design and provide better coolant coverage on the leading edge. The main conclusions of the dissertation are as follows:At a low blowing ratio, the secondary injection flow has low momentum compared to the mainstream, so it is easily suppressed by the mainstream to a region near the cooper plate surface. Better cooling performance can be achieved in the region immediately out of the injection holes. When the blowing ratio increases, the phenomenon of "blowing off" and "re-attachment" happen downstream of the film holes. At a low hole length to diameter ratio (L/D=2), the air flow cannot fully develop in the hole and the adiabatic film cooling effectiveness of are lower. The effect on the cooling performance due to different vertical velocity component is considered in connection with different injection angles downstream the injection hole. The results show that the contours still appear in a taper shape in the nearby region of the film hole at a low blowing ratio when only vertical velocity existsWhen the holes just locate on the stagnation line, the radial movement of the coolant is dominating only at the pressure side close to the holes. At the suction side close to the holes, the radial movements is weakened by mainstream accelerating. When the holes locate alongside the stagnation line, the circumferential movement of the coolant dominates. Better cooling effects at the stagnation line and both sides of the line can be obtained two intercross rows of holes at both sides of stagnation line and assuring that the stagnation line traverses the exit of each hole. It is necessary to avoid opposite jets occurring in the radial direction by changing the radial angles. It is difficult to obtain full coverage near the attachment node. Adopting lower blowing ratio and adding the circumferential distance to the attachment node can obtain better cooling better cooling effects. The modified design V is the best in the five designs.更多还原