Experimental and Numerical Investigation of Environmental Barrier Coated CMC Turbine Airfoil Erosion

Abstract

Ceramic matrix composite (CMC) have higher temperature durability and lower density property compared to nickel-based super-alloys which so far have been widely applied to hot section components of aero-engines / gas turbines. One of promising CMC systems, SiC-SiC CMC is able to sustain its mechanical property at higher temperature, though it inherently needs environmental barrier coating (EBC) to avoid oxidation. There are several requirements for EBC. One of such critical requirements is its resistance to particle erosion, whereas this subject hasn’t been well investigated in the past. The present work presents the results of a combined experimental and numerical research to evaluate the erosion characteristics of CMC+EBC material developed by IHI. First, experiments were carried out in an erosion test facility using 50 micron diameter silica as erosion media under typical engine conditions with velocity of 225 m/s, temperature of 1311 K, and impingement angles of 30, 60, and 80deg. The data displayed brittle erosion mode in that the erosion rate increased with impact angles. Next, multi-phase flow simulations were carried out for the experimental setup and the predicted erosion rates were compared with the measured data, and consequently, the applied numerical method was verified. The validated numerical method was then applied to compute three dimensional flow field, particle trajectories, and erosion profile around a generic turbine airfoil to assess the erosion characteristics of the proposed CMC+EBC material when applied to airfoil. The trajectories indicated that the particles primarily impacted the airfoil leading edge and the pressure surface. Surface erosion patterns were predicted based on the calculated trajectories and the experimentally-based erosion characteristics.

Prediction of erosion in an axial turbine with initial position of blade

“…The other regions of moderate and low erosion rates are attributed to impacts by small particles of lower impingement angle. These results are also supported by Metwally et al (1995) who have revealed that the erosion of rotor blade is limited to one-third of blade pressure surface with the maximum of erosion seen at the trailing edge tip corner and one fourth of suction surface from leading edge. The rotor shroud of this model of HPT is heavily eroded, where erosion patterns are visible from the blade leading edge and spreading around both sides.…”

“…The particle dynamics and impacts and the particle size distribution has the significant influence on erosion intensity and pattern. Metwally et al (1995) provided a detailed description of particle trajectories and erosion in a power turbine, and showed that the maximum erosion is at the trailing edges of guide vane and stator and the outermost radial part of rotor blade. Hamed et al (2005) investigated both experimentally and numerically the deterioration of vane and blade surfaces of a low-pressure gas turbine.…”

“…Also, Chen et al (2016) by using particle trajectory calculations showed that the particles do not accelerate at same speed as steam, but travel much slower when they hit the moving blade leading edge and are thrown back to hit the trailing edge of fixed blade. Due to strong centrifugal forces, particles are thrown outwards and damage both outer extension ring and tip seals Recently, Okita et al (2018) combined experimental and numerical investigation to evaluate the erosive damage of coated turbine airfoil by sand particles. The experimental data of surface erosion rate was used to calibrate correlation factors in an erosion prediction model used to simulate of the three-dimensional multi-phase field.…”