Evolution of Surface Deposits on a High Pressure Turbine Blade: Part I — Physical Characteristics

Abstract

Turbine blade coupons with three different surface treatments were exposed to deposition conditions in an accelerated deposition facility. The facility simulates the flow conditions at the inlet to a first stage high pressure turbine (T = 1150°C, M = 0.31). The combustor exit flow is seeded with dust particulate that would typically be ingested by a large utility power plant. The three coupon surface treatments included: (1) bare polished metal, (2) polished thermal barrier coating with bondcoat, and (3) unpolished oxidation resistant bondcoat. Each coupon was subjected to four successive 2 hour deposition tests. The particulate loading was scaled to simulate 0.02 ppmw (parts per million weight) of particulate over three months of continuous gas turbine operation for each 2 hour laboratory simulation (for a cumulative one year of operation). Three-dimensional maps of the deposit-roughened surfaces were created between each test, representing a total of four measurements evenly spaced through the lifecycle of a turbine blade surface. From these measurements the surface topology and roughness statistics were determined. Despite the different surface treatments, all three surfaces exhibited similar non-monotonic changes in roughness with repeated exposure. In each case, an initial build-up of isolated roughness peaks was followed by a period when valleys between peaks were filled with subsequent deposition. This trend is well documented using the average forward facing roughness angle in combination with the average roughness height as characteristic roughness metrics. Deposition-related mechanisms leading to spallation of the thermal barrier coated coupons are identified and documented.

Experimental Investigation of Particulate Deposition on a Simulated Film-Cooled Turbine Vane Pressure Surface in a High Pressure Combustion Facility

“…However, at the highest blowing ratio of 1.0 there was no evidence of deposition in the holes. These results appear to agree with the work of ( [16], [17]) that the cooling jets both deflect smaller particles away and lower the surface temperature of the component to reduce the overall amount of deposition.…”

“…The Sra or average roughness increased by 365% while the RMS averaged roughness increased by 240%. The increase in Sra was much larger than the increase reported in Wammack et al [17] which reported an increase of approximately 50%. In the current study the Sra value increased from 17 to 79 m while in [17] the increase was from 10 to 15 m.…”

“…affect the evolution of deposits. As discussed earlier, the TADF, developed at BYU, has been employed to perform numerous studies of the factors affecting deposition ([6], [10], [14], [15], [16], [17], [18], and [19]). Bons et al [6] performed a study examining the deposition from four different materials: straw, sawdust, coal and petroleum coke (petcoke).…”

“…Wammack et al [17] performed a study using the TADF to examine the evolution of Lawson and Thole [12] found that deposition decreased with an increase in coolant mass flow because coolant jets diverted particle trajectories and cooled particles preventing them from sticking upon impacting the surface. Albert and Bogard [13] examined an isothermal vane and an internally cooled vane.…”

Adhesion of Volcanic Ash Particles under Controlled Conditions and Implications for Their Deposition in Gas Turbines

“…The particle temperature on impact is clearly a key parameter, although the substrate temperature, roughness and motion can also be important. Lower deposition rates are observed on cooler [19] and smoother [20] surfaces. It has also been noted [4,21] that deposition rates are much higher on static surfaces, such as platforms and guide vanes, than on rotating components, such as blades.…”