Application of Photoluminescent Measurement Techniques for Quantitative Assessment of Turbine Film Cooling
Application of Photoluminescent Measurement Techniques for Quantitative Assessment of Turbine Film Cooling
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光致发光测量技术在涡轮气膜冷却定量评估中的应用
DOI：
10.5075/epfl-thesis-4650
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
M. Jonsson
中科院分区：
文献类型：
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作者：
M. Jonsson
通过最大限度地提高燃气轮机进口温度，可以实现燃气轮机比油耗的降低。然而，这需要详细了解发动机的冷却性能，以确保发动机安全经济地运行。这是因为在叶片壁上产生的温度分布决定了发动机热段的热应力和寿命。气膜冷却性能依赖于包括湍流在内的大量参数，这使得数值预测变得复杂。此外，在燃烧室正下游的涡轮机中发现了恶劣的流动条件，因此很难获得相关数量的高分辨率测量。因此，为了通过匹配最重要的流动相似参数来模拟发动机的情况，采用简化的实验。更具体地说，热气体和冷却空气之间的巨大温差导致了气膜冷却射流和热气体之间的密度差异很大。这可以在环境温度下通过向密度较低的主气流中注入一种重的外来气体来模拟。本论文旨在论证光致发光涂料作为敏感元件在气膜冷却测量中的适用性。当这种类型的传感器被紫外光激发时，光致发光过程导致红移光的发射。发光不仅依赖于涂层表面的温度，还依赖于氧气压力。选用一种商用压敏涂料(PSP)对气膜冷却的两个基本量：绝热气膜冷却效率、换热系数进行了实验表征。绝热气膜冷却效率是冷却剂和主流之间混合程度的量度。根据传热和传质的类比，这个量对应于气体物种的浓度。无氧冷却剂在稀释主流的氧气时起到示踪气体的作用，允许使用PSP对冷却气体浓度进行详细测量。通过施加热流密度的阶跃变化和跟踪壁面的瞬时温度响应来测量相应的对流换热系数。为此，利用该技术固有的温度敏感度，将相同的PSP传感器用于热像测量。一个发动机真实的测试案例说明了该技术在复杂流动条件下的能力。它可以证明，高空间分辨率的测量可以在很短的时间内在大部分表面上获得。结果表明，氧压和温度传感器的组合，以发光涂料的形式，在壁面有适度换热的可压缩流动实验中特别有利。该技术的另一个重要优点是可以将绝热气膜冷却效果与壁面换热效果分开，而不需要为单独的实验应用另一种涂层。这确保了实验模型的小尺寸冷却孔的高几何公差。然而，这项技术受到光致发光系统最高适用温度的限制，这使得它首先适合于冷流测量。虽然压力和温度敏感涂料以前都被用于气膜冷却研究，但提出的这两种技术的组合是独特的，因为它允许同时测量气膜冷却中的两个基本量，但不存在耦合。本文的研究结果表明，该技术的应用可以验证数值流动模型的有效性。此外，可以将结论以技术趋势的形式转移到真实发动机的建模上。最终，这可以优化气膜冷却性能并降低燃气轮机的燃料消耗。
Reduction of the specific fuel consumption of gas turbines can be achieved by maximizing the turbine inlet temperature. However, this requires a detailed understanding of the cooling performance in order to ensure safe and economical operation of the engine. This is because the resulting temperature distributions in the blade walls dictate the thermal stresses and life-time of the hot section of the engine. Film cooling performance depends on a large number of parameters including turbulence making it complex to predict numerically. Moreover, the harsh flow conditions found in turbines situated directly downstream of the combustion chamber makes it difficult to obtain high resolution measurements of the relevant quantities. Therefore, simplified experiments are employed in order to simulate the engine situation by matching the most important flow similarity parameters. More specifically, the large difference in temperature between hot-gas and cooling air leads to considerable difference in density between the film cooling jets and hot-gas. This can be simulated at ambient temperatures by injecting a heavy foreign gas into a less dense main-flow of air. This thesis aims at demonstrating the applicability of photoluminescent paints as sensing element for film cooling measurements. When this type of sensor is excited by ultraviolet light, the photoluminescent process leads to the emission of red-shifted light. The luminescence depends on oxygen pressure as well as temperature at the coating surface. A commercially available Pressure Sensitive Paint (PSP) is chosen for experimental characterization of the two fundamental quantities of film cooling: Adiabatic film cooling effectiveness Heat transfer coefficients The adiabatic film cooling effectiveness is a measure of the mixing between coolant and mainflow. This quantity corresponds to concentration of gas species according to the analogy between heat and mass transfer. An oxygen-free coolant acts as tracer gas as it dilutes the oxygen of the main-flow, allowing for detailed measurements of the cooling gas concentration with PSP. The corresponding convective heat transfer coefficient is measured by imposing step changes in heat flux and tracing the transient temperature response of the wall. For this purpose, the same PSP-sensor is employed for thermography measurements by taking advantage of the inherent temperature sensitivity of this technology. An engine-realistic test case illustrates the capability of the technique under complex flow conditions. It allows to demonstrate that measurements with high spatial resolution can be obtained over large portions of the surface within a short period of time. It turns out that the combination of oxygen pressure and temperature sensors, in the form of photoluminescent paint, is particularly advantageous in compressible flow experiments with moderate heat transfer at the wall. Another important advantage of the technique is the possibility to separate the adiabatic film cooling effectiveness from the wall heat transfer effects, without applying another coating for separate experiments. This ensures high geometrical tolerance of the small-scale cooling holes of the experimental models. However, the technique is limited by the maximum applicable temperature of the photoluminescent system making it first of all suitable for cold-flow measurements. While both pressure and temperature sensitive paints have previously been employed in film cooling studies, the proposed combination of those techniques is unique in that it allows for simultaneous, yet decoupled measurement of the two fundamental quantities in film cooling. In the present thesis, it is shown that the application of the presented technique allows to validate numerical flow models. Furthermore, conclusions can be transferred to the modelling of real engines in the form of technology trends. Ultimately, this allows to optimize film cooling performance and reduce the fuel consumption of gas turbines.
DOI：
10.2495/1-84564-095-0
发表时间：
2006
期刊：
--
影响因子：
--
作者：
R. Liebe
通讯作者：
R. Liebe