Effects of Trailing Edge Thickness and Blade Loading Distribution on the Aerodynamic Performance of Simulated CMC Turbine Blades

Aerodynamic loss levels were measured experimentally for three simulated Ceramic Matrix Composite (CMC) blade sets in a large-scale transonic turbine blade cascade.  Due to potential manufacturing restrictions, the trailing edge thicknesses of CMC blades are anticipated to be significantly larger than those of current metallic blades.  The blades tested in the current study had trailing edge thicknesses of 5%, 7%, and 9% relative to the blade axial chord.  The blades were designed with uniform throat dimensions for all the three blade sets, so the blade loading distributions were varied to retain similar overall loading levels.  The 9% blade was significantly front-loaded, with loading distributions shifting aft for the lower trailing edge thicknesses.  Data were acquired at four Reynolds numbers, covering a factor of six variation.  All data were acquired nominally at the design isentropic exit Mach number of 0.74.  Measurements include blade loading and five-hole probe surveys at two downstream stations.  The effects of inlet turbulence intensity were also examined.  Total pressure loss data were integrated to determine overall loss levels for each of the three measured blade passages.  Excellent periodicity was noted for all passages.  For low inlet turbulence levels, losses were surprisingly lower for the thickest trailing edge at low Reynolds numbers, but were highest at the highest Reynolds number. In general, losses were found to scale well with Reynolds number, although front loading was found to significantly reduce the loss sensitivity to Reynolds number.  For high inlet turbulence intensity, losses were found to scale with trailing edge thickness as expected, and Reynolds number sensitivity was reduced for all three blade sets.  Loss levels at the highest Reynolds number were comparable at low and high inlet turbulence intensity levels.