Thermal Barrier Coatings (TBC) have been developed for modern highly loaded turbines to allow their operation at higher temperatures than allowed by substrate blade material. TBC health is critical to blade life and to maintaining the high power output and efficiency achieved with the increased turbine inlet temperatures. However unlike blade material alloys, knowledge of thermal barriers’ deterioration as a result of impacts by suspended particles in the flow field is very limited.
The purpose of this study was to gain better knowledge of turbine blades thermal barrier coatings intensity and pattern of erosion by ingested particles in rotary wing engines. A commercial Computation Fluid Dynamics code, CFX, was used to perform two-phase flow simulations to supply flow and particle trajectory data. The suspended particles tend to deviate from the 3D flow path due to their higher inertia. User Defined Functions (UDF) were developed for restitution coefficients and erosion rate of thermal barrier coated surface based on previous experimentally based empirical models. The UDF was verified to correctly calculate restitution coefficients and erosion rates in a simulated high temperature erosion tunnel.
The models were implemented in ANSYS CFX code which was used to predict the blade surface erosion rates for a gas turbine Auxiliary Power Unit (APU) used in currently operating rotary aircraft. Results are presented for the erosion rates of turbine blade thermal barrier coatings with uniform 36 micron alumina particle ingestion and for non-uniform particle ingestion concentrated in the 5% of the span near the annulus walls. Results for both cases are compared to those obtained from numerical simulations using fixed restitution default models at the blade surface impacts.