Abstract:
In order to alleviate particle ingestion problems during mission flights in sandy desert regions, most of the rotorcraft gas turbine engines are fitted with inlet particle separators. However, these particle separators, which are typically vortex cyclone flow type separators, are not 100% efficient in filtering fine sand particles of size 75 microns or below. These fine sand particles are in a molten state as they exit the combustor and deposit on to and clog the first stage turbine nozzle vanes and rotor blades badly. This sand deposition causes sudden engine power loss as well as eventual blade damages that include blade coating wear, sand glazing, Calcia-Magnesia-Alumina-Silicates (CMAS) attack, oxidation, and plugged cooling holes. Rapid engine performance deterioration has caused loss of aircraft and loss of life incidents during military missions in degraded particle laden environment. The objective of this research is to prevent molten fine particle interactions with typical turbine blade ceramic coatings at the microstructure level. A set of multi-layered and composite coating materials and processes were selected and tested in this round robin experimental evaluation to study their ability to prevent molten sand (CMAS) attack on Yttria Stabilized Zirconia (YSZ) based thermal barrier coatings (TBCs), used in current rotorcraft gas turbine engines. The test evaluations were conducted at the coupon level using a Jet Burner Rig with particulate ingestion facility available at the U.S Army Research Laboratory, Aberdeen Proving Ground, Maryland. The engineered coatings evaluated at the coupon level were down-selected and applied to the first stage turbine nozzle ring of a typical rotorcraft gas turbine engine. The full-scale engine level sand ingestion tests were conducted at the NAVAIR facility, Patuxent River, Maryland. The CMAS infiltration into the coatings and the glassified sand deposition characteristics of the various tailored coatings are compared in this paper. The promising coating candidates from the engine level sand ingestion tests are summarized and future recommendations are presented in this paper. A summary of the ongoing simulations work to understand the interactions of sand particulates with TBCs of turbine blades is also presented in this paper.