Deterioration of Thermal Barrier Coated Turbine Blades by Erosion

A combined experimental and computational study was conducted to investigate the erosion of thermal barrier coated (TBC) blade surfaces by alumina particles ingestion in a single-stage turbine. In the experimental investigation, tests were performed to determine the erosion rates and particle restitution characteristics under different impact conditions. The experimental results show that the erosion rates increase with increased impingement angle, impact velocity, and temperature. In the computational simulations, an Euler-Lagrangian two-stage approach is used in obtaining numerical solutions to the three-dimensional compressible Reynolds-Averaged Navier-Stokes equations and the particles equations of motion in each blade passage reference frame. User defined functions (UDFs) were developed to represent experimentally based correlations for particle surface interaction models and TBC erosion rates models. UDFs were employed in the three-dimensional particle trajectory simulations to determine the particle rebound characteristics and TBC erosion rates on the blade surfaces. Computational results are presented in a commercial turbine and a NASA-designed automotive turbine. The similarities between the erosion patterns in the two turbines are discussed for uniform particle ingestion and for particle ingestion concentrated in the inner and outer 5% of the stator blade span to represent the flow cooling of the combustor liner. 1. Introduction Turbomachinery erosion presents a challenging problem when gas turbine engines operate in dusty environments [1–3]. Some of the mechanisms that cause particle ingestion are (a) the vortex from engine inlet-to-ground during high-power setting with the aircraft standing or moving on the runway; (b) storms transporting sand to several thousand feet altitude; (c) thrust reverser afflux at low airplane speed blowing sand, ice, and other particles into the engine inlets. Erosive solid particles may also be produced during the combustion process, from the burning of different types of heavy oils or synthetic fuels. Helicopter engines are especially susceptible to large amounts of dust and sand ingestion during hover, takeoff, and landing. It is very difficult to remove all solid particles from the gas stream without taxing the performance of gas turbine engines [4, 5]. Even small particles of one to thirty micron sizes have been known to be very damaging to the exposed components of coal burning turbines [6]. In turbomachinery, particle impacts are known to increase tip clearances and blade surface roughness and produce