Testing of a Low Cooled Ceramic Nozzle Vane Under Transient Conditions

At the Institut fu¨r Thermische Stro¨mungsmaschinen, University of Karlsruhe (ITS), a design technology has been introduced to reduce the mechanically and especially the thermally induced stresses in ceramic components. The concept is based on a three-layered construction (outer ceramic shell, heat insulating layer, and metallic core) and an optimization of the thicknesses of the single layers, in order to obtain a homogenous temperature distribution in the ceramic structure. The optimization is performed by finite element analyses in combination with failure probability calculations. This methodology has been applied to increase the reliability of a first stage Sintered Silicon Carbide (SSiC) ceramic nozzle vane of a stationary gas turbine (70 MW/1400°C). As a result it was found that the mechanically and thermally induced loads have been reduced considerably and do not exceed 100 MPa, thus achieving adequate life based upon failure probability calculations. Even in a trip situation (fuel cutoff), when the highest loads do occur, the calculations demonstrate a significantly reduced failure probability. The results of the finite element analyses were verified by simulating the typical operating conditions after fuel cutoff in a test rig.