Riblets reduce friction in turbomachines

Fig. 1: SEM image and 3D illustration of a whitelight confocal measurement of laser-generated riblet structures on a metallic surface

A large part of the loss in turbomachines (turbines, centrifugal pumps, fans, etc.) originates from friction between the fluid or gas and the flowed surfaces. Such loss can be reduced if so-called riblets, ribs arranged in flow direction, are applied to the surface.

In a research project, the Laser Zentrum Hannover e.V. (LZH) and other project partners intend to produce riblets using a laser-assisted and industry-suitable procedure, among others, to create actual flow conditions. The project aims at providing the technological basis for the manufacturing of functional metallic surfaces on flowed blades in turbomachines. In the industrial practice of this field, fundamental examinations are required, since only little knowledge exists both about the shape to be realized and a suitable structuring process.

Due to its high resolution and great flexibility, laser radiation seems to be particularly appropriate to apply the structures with dimensions of up to some 10 µm onto compressor blades with three-dimensional surface geometries. A high potential for this process offer shortpulse lasers with pulse durations in the picosecond range (10-12 s). In process design and strategy development a good balance between the highest structure quality and a low processing time must be considered.

The research tasks at the LZH include, among others, various processing strategies for large-surface microstructuring of metallic materials using picosecond lasers. The focus lies not only on quality, but also on the process speed that can be achieved with regard to the dimensional accuracy and strength of the riblets.

The project is supported by the German Research Foundation (DFG).

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The Laser Zentrum Hannover e.V. (LZH) carries out research and development in the field of laser technology and is supported by the Ministry of Economic Affairs, Labour and Transport of the State of Lower Saxony (Niedersächsisches Ministerium für Wirtschaft, Arbeit und Verkehr).