Cooling of additively manufactured turbine blades - Influence of roughness and reduced dimensions of turbulators on heat transfer in internal cooling channels

选择性激光熔化(SLM)或激光金属沉积(LMD)等附加制造技术将在不久的将来在燃气轮机热气部件的制造和修复中发挥重要作用。在这种背景下，通过新的生产方式，冷却涡轮叶片的生产将经历冷却系统设计的参数空间的显著扩展，以通过更具成本效益的生产和提高热效率来为实现成本和减排目标做出贡献。除了流动导向和冷却空气分配方面的根本变化外，内部冷却系统的可能参数空间也在变化，该系统由配备有扰流板(肋骨、销钉等)的通道组成。在这种情况下，添加制造可以实现更窄的肋节距(P/e≤5)和相对于液压直径的更小的肋高度(e/dh≤0.1)。此外，在添加制造工艺中，内部几何形状与冷却空气孔同时制造。这使得搅拌器和冷却空气孔彼此之间的相对位置可以更精确地指定和实施。系统地考虑内部流动和气膜冷却之间的相互作用对叶片热负荷的影响，需要对这种相互作用有一个基本的了解。该项目旨在通过大范围的系统参数变化，帮助理解湍流细小结构的内部冷却以及它们与冷却空气的相互作用。此外，添加制造的部件表现出表面的特征粗糙度，这主要取决于制造过程的参数(激光功率、速度等)。在本项目的范围内，将通过测量有比例的粗糙表面的换热来研究肋条和高粗糙度的组合是否也会导致换热增加。本项目的目的是通过系统地改变肋条高度e、肋条间距P和冷却通道H的高度，在附加制造可获得的参数范围内，探索堵塞比e/dh、肋条间距比P/e和高宽比AR对换热、流场和热性能的影响。分析了从第一肋到发展周期流的不同构型的流场和换热情况。实验研究将伴随着大涡模拟(LES)。这些数值将首先在实验中得到验证，然后才能更好地分析和理解物理原理。高质量的数值模拟可以用来扩展研究的参数空间。

Additive manufacturing techniques such as Selective Laser Melting (SLM) or Laser Metal Deposition (LMD) will play an important role in the manufacture and repair of hot gas components in gas turbines in the near future. In this context, the production of cooled turbine blades will experience a significantly extended parameter space for the design of the cooling system through the new production methods, in order to contribute to the cost and emission reduction targets through more cost-effective production and improvement of the thermal efficiency. In addition to fundamental changes in the flow guidance and cooling air distribution, the possible parameter space for the internal cooling system, consisting of channels provided with turbulators (ribs, pins etc.), is changing. In this case, additive manufacturing enables a narrower rib pitch (P/e≤5) and a smaller rib height in relation to the hydraulic diameter (e/Dh≤0.1). Furthermore, in additive manufacturing processes, the internal geometry is made simultaneously with the cooling air holes. This allows a more precise specification and implementation of the relative position of turbulator and cooling air hole to each other. The systematic consideration of the interaction between internal flow and film cooling on the thermal load of the blade requires a fundamental understanding of this interaction. The proposed project aims to contribute to the understanding of the internal cooling of finer and narrower structures of the turbulators and their interaction with the removal of cooling air through systematic parameter variation over a wide range. In addition, additively manufactured components exhibit a characteristic roughness of the surfaces, which depends primarily on the parameters of the manufacturing process (laser power, speed, etc.). Within the scope of the project, heat transfer measurements of a scaled rough surface will be used to investigate whether an increase in heat transfer also occurs with a combination of ribs and high roughness.The aim of the proposed project is to explore the influence of blockage ratio e/Dh, rib pitch ratio P/e and aspect ratio AR on heat transfer, flow field and thermal performance in the parameter range accessible by additive manufacturing by systematically varying the rib height e, the rib pitch P and the height of the cooling channel H. The focus is on oblique 60° ribs and the position of the film cooling hole will be varied primarily in the lateral direction. Flow field and heat transfer will be analyzed for the different configurations starting from the first rib to the developed periodic flow. The experimental investigations will be numerically accompanied by Large Eddy Simulations (LES). The numerics will first be validated on the experiments to then allow a better analysis and understanding of the physical principles. The high quality numerical simulations can be used to extend the parameter space of the investigation.