动叶顶部离散式隔板迷宫间隙流动传热机理及准则方程构建

The decreasing leakage rate can improve efficiency of turbine. The advanced cooling can prolong lifespan of turbine. There is a very complex three dimensional flow in the micro gap of the blade tip. It is difficult to understand the phenomena of convective heat transfer. The very few theory model can guide the design of cool performance on the blade tip. The feasilibility of both sealing and cooling of the labrinth tip has been approved by numerical simulation. In this project, the detailed performance of flow, the performance of convective heat transfer, the performance of film cooling in the micro scale tip gap will be studied by numerical simulation, analysis of theory and measurement. The synergistic analysis of pressure and veolicity, veolicity and temperature, velocity and concentration will be conducted. The mechanics of decreasing leakage rate, reducing capability of heat transfer and increasing the utilization of coolant will be explained. The regular of flow and heat transfer on the labrinth tip will be disclosed. The influence of micro scale on the flow and heat transfer will be analysed. The models of the leakage rate, the convective heat transfer and the film cooling effectiveness will be established. The code programm will be developed to calculate the flow and heat transfer in the labyrinth gap. The correlation formulations between the flow and heat transfer will be conducted. The optimal structure will be obtained by overrall consideration of sealing and cooling. The studied results will enrich the theory of heat transfer about micro scale and provide a novel method of design about the sealing and cooling on the blade tip.

减少叶顶间隙泄漏量会提高涡轮效率。有效冷却能够延长涡轮部件寿命。叶顶间隙尺度处于微米量级，三维流动非常复杂，对流换热机理尚不明了，缺少基础理论指导叶顶间隙密封和冷却设计。数值模拟初步证明了隔板迷宫间隙具有改善密封和冷却的双重作用。本项目采用数值模拟、理论分析和实验测量相结合方法，进一步研究微尺度隔板迷宫间隙燃气节流特性、冷气绕流特性、对流换热特性和气膜冷却特性。对压力梯度和速度矢量协同分析阐明泄漏量减少机理；对速度矢量和温度梯度协同分析阐明燃气传热能力降低机理；对掺混流体速度矢量和冷气浓度梯度协同分析阐明冷气热容利用率提高机理。揭示隔板式迷宫间隙流动传热规律，分析尺度效应对流动传热影响。建立泄漏量、对流换热和气膜冷却模型。编制一套计算迷宫间隙流动传热的程序。推导衡量密封冷却综合特性的准则数及相应准则方程，确定最优迷宫结构。该研究将丰富微尺度流动传热理论，为叶顶间隙密封冷却设计提供新思路。

涡轮部件受工作时热应变、离心力等因素影响，叶顶和机匣之间必须预留一定的间隙。燃气在压力面与吸力面压差作用下流过间隙，不仅会降低涡轮工作效率，叶顶区域的高热流密度还会造成叶片氧化寿命缩短。离散式隔板迷宫叶顶是在凹槽叶顶开设气膜孔并在气膜孔下游离散排布小隔板。具有改善间隙密封和叶顶冷却效果双重作用。.本项目通过实验和数值计算研究了间隙高度、隔板排布形式、吹风比对叶顶间隙流场和气膜冷却效率影响，并对密封冷却综合效果进行理论分析。.（1）迷宫间隙流动和泄漏量减少机理。研究了叶片静止和转动两种情况叶顶间隙泄漏流场，结果表明：叶片静止时，靠近压力面侧前缘产生的泄漏涡是凹槽内泄漏旋涡主要成因，泄漏旋涡形成后会在腔内逐渐向吸力面和叶片尾缘同时发展，影响范围逐渐变大，有一部分泄漏涡在发展过程中，随着涡尺度的加大而流出凹槽。前缘靠近吸力面侧，一部分气体进入凹槽内后又在吸力面肩壁流出。压力面尾缘形成的泄漏流动受凹槽内泄漏涡作用直接由吸力面侧流出间隙，形成泄漏流动，阻塞主流通道。.（2）迷宫间隙对流换热能力降低和冷气热熔利用率提高机理。在对流换热能力降低机理方面，研究了叶栅进气攻角和叶片转动对叶顶传热特性影响。结果表明：静止叶片的叶顶换热系数沿着叶型中弧线方向减小。叶片转动虽然降低了间隙泄漏流速度，但是叶顶平均换热系数略有增大。叶片转动使三种攻角叶顶最高换热系数分别降低了7.5%、8.1%、19.2%。攻角从-5°变化到5°，叶片有无转动的叶顶最高换热系数分别降低了14.9%和22.4%。在冷气热熔利用率提高机理方面，搭建了叶顶气膜冷却效率实验台，采用稳态液晶测温技术测得凹槽和迷宫间隙叶顶冷却效率分布。结果表明：间隙高度增加，隔板迷宫间隙叶顶冷却效率降低较为缓慢。随吹风比增加两种叶顶冷却效率都是先增加后减小，隔板迷宫间隙叶顶冷却效率变化波动较小。迷宫间隙叶顶能够明显改善叶顶冷却效率分布。.（3）迷宫间隙密封冷却理论模型建立及准则数构建。为了评估带气膜冷却涡轮叶顶间隙密封冷却综合特性，在强化传热综合因子中引入气膜冷却效率，推导出了密封冷却综合因子表达式。利用该因子对密封冷却综合特性进行了评估。结果表明: 迷宫结构冷却效果相比于平叶顶间隙有所改进， 随着吹风比减小， 改进程度先增加后减小; 密封效果只有在高吹风比时有所改进。密封冷却综合特性都得到了改进， 吹风比越小， 密封冷却综合特性越显著。

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