High temperature oxidation stability of aerodynamically optimised riblets for blades of aero-engine applications

Abstract

The mechanism of nature’s way of friction reduction and aerodynamical optimisation is applied worldwide. There is ample literature on investigation 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 to 1000 h. The thermocyclic tests at 900°C proved that the riblets are stable even after 1000 h and at 1100°C the stability is permitted to until only 100 h. With few modifications in the structuring process this stability can be further improved.