Product Code: ICA11_M603

Large-Area Production of Dynamically Scaled Microstructures Using Diffractive Optical Elements
Authors:
Bodo Wojakowski, Laser Zentrum Hannover e.V.; Hannover Germany
Ulrich Klug, Laser Zentrum Hannover e.V.; Hannover Germany
Rainer Kling, Laser Zentrum Hannover e.V.; Hannover Germany
Presented at ICALEO 2011

Drag-reduction of turbine-compressor-blades has been successfully demonstrated by using single-spot picosecond-laser-ablation. To accomplish this goal, small periodic riblets have been scribed into the blades surface parallel to the flow direction to reduce the turbulent airflow within the turbine. This approach is successful but lacks an industry-compatible process-speed. Therefore beam-splitting Diffractive Optical Elements (DOEs) are used to parallelize the machining and to exploit the full power of modern picosecond-laser systems without side effects on the quality.
Until now using a DOE only structures bearing a fixed riblet-pitch could be engraved into the blades surface, but to further optimize the drag-reduction dynamic changes of these pitches along the direction of the air-flow are necessary. Since dynamically changing the DOE is not an acceptable solution, this limitation is overcome by rotating the DOE to tilt the spot-array and thus change the resulting spot distances.
In this paper we show ablation results of multi-spot DOE laser-machining as well as a mathematical approach to optimize the structure fill-factor, to minimize necessary DOE rotation-angles, and to minimize the number of dead-end riblets on the compressor-blades surface thus further reducing the number of turbulence-seeds.