High Temperature Oxidation Stability of Aerodynamically Optimised Riblets for Blades of Aero-engine Applications
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The mechanism of nature’s way of friction reduction and aerodynamical optimisation is applied worldwide. There is ample literature on investigations and measurement of skin friction reduction in the boundary layer over flat plates and on turbo machinery type blades. When using a surface with riblet structures, the turbulent momentum transfer at the wall which is responsible for the skin friction is hampered. This paper deals with the oxidation and characterisation of riblets with micrometer dimensions for aerodynamically optimised high temperature turbine applications. Riblets were fabricated on EB-PVD NiCoCrAlY coatings by using a pico-second laser. The high temperature oxidation stability of the riblets was tested by conducting cyclic oxidation tests. The temperatures were selected as 900 and 1100 °C and the time of oxidation was varied between 1 and 1,000 cycles. The thermocyclic tests at 900 °C proved that the riblets are stable even after 1,000 cycles and at 1,100 °C the stability is permitted to until only 100 cycles. With few modifications in the structuring process this stability can be further improved.
KeywordsNiCoCrAlY coating Oxidation Riblets Yttria formation EB-PVD
The authors would like to express their gratitude to A. Handwerk for thermal cycling tests and D. Peters for EB-PVD experiments. The authors would like to thank the DFG under SPP1299 for financial support.
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