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

在不久的将来，诸如选择性激光熔化（SLM）或激光金属沉积（LMD）等增材制造技术将在燃气轮机热气部件的制造和维修中发挥重要作用。在这种情况下，通过新的生产方法，冷却的涡轮机叶片的生产将经历用于冷却系统的设计的显著扩展的参数空间，以便通过更具成本效益的生产和热效率的提高来有助于成本和减排目标。除了导流和冷却空气分配的基本变化之外，内部冷却系统的可能参数空间，包括设置有散热器（肋、销等）的通道，正在改变在这种情况下，增材制造能够实现相对于水力直径（e/Dh≤0.1）的更窄的肋间距（P/e≤5）和更小的肋高度。此外，在增材制造工艺中，内部几何形状与冷却空气孔同时制成。这允许更精确地指定和实现制冷器和冷却空气孔彼此的相对位置。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。拟议项目旨在通过系统参数变化在很大范围内促进对更精细和更窄结构的冷却器的内部冷却及其与冷却空气去除的相互作用的理解。此外，增材制造的部件表现出表面的特征粗糙度，这主要取决于制造工艺的参数（激光功率、速度等）。在该项目范围内，将使用缩放粗糙表面的传热测量来研究肋和高粗糙度的组合是否也会增加传热。拟议项目的目的是探索阻塞比e/Dh、肋间距比P/e和纵横比AR对传热的影响，通过系统地改变肋高度e、肋节距P和冷却通道的高度H，在可由增材制造获得的参数范围内的流场和热性能。重点放在倾斜60°肋上，薄膜冷却孔的位置主要在横向上变化。从第一个肋开始到发展的周期性流动的不同配置的流场和传热将被分析。实验研究将伴随着大涡模拟（LES）的数值。数值计算将首先在实验中得到验证，然后可以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.