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

A 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 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, 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.