Evolution of Surface Deposits on a High-Pressure Turbine Blade—Part II: Convective Heat Transfer

A thermal barrier coating (TBC)-coated turbine blade coupon was exposed to successive deposition in an accelerated deposition facility simulating flow conditions at the inlet to a first stage high pressure turbine (⁠$T=1150°C$⁠, $M=0.31$⁠). The combustor exit flow was seeded with dust particulate that would typically be ingested by a large utility power plant. The turbine coupon was subjected to four successive $2h$ deposition tests. The particulate loading was scaled to simulate 0.02 parts per million weight (ppmw) of particulate over $3months$ of continuous gas turbine operation for each $2h$ laboratory simulation (for a cumulative $1year$ 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, scaled models were produced for testing in a low-speed wind tunnel with a turbulent, zero pressure gradient boundary layer at $Re=750,000$⁠. The average surface heat transfer coefficient was measured using a transient surface temperature measurement technique. Stanton number increases initially with deposition but then levels off as the surface becomes less peaked. Subsequent deposition exposure then produces a second increase in St. Surface maps of St highlight the local influence of deposit peaks with regard to heat transfer.