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

• Applicant: Professor Dr.-Ing. Ronald Mailach
• Subject Area: Hydraulic and Turbo Engines and Piston Engines
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 492295969

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.

• DFG Programme: Research Grants