A New Approach for a Low-Cooled Ceramic Nozzle Vane

Abstract

At the Institute for Thermal Turbomachinery, University of Karlsruhe (ITS) a new methodology for designing thermally loaded ceramic components based on numerical analyses of the thermal and structural behaviour is developed. Major issues are an effective optimization of the geometry and an aqw-csment of the load.

Systematic Reduction of Stress Levels for a Thermally High Loaded Ceramic Nozzle Vane With Trailing Edge Ejection

“…1700 and 6000 W/m2K. The gas path flow temperature varies with the radial position due to the specific combustor outlet conditions [2].…”

“…The dominant stresses in ceramic vane profiles are induced by temperature gradients in the ceramic component [2,3,4]. The reliability of ceramic parts can be improved in reducing the thermal stresses for continuous operation and for transients as well.…”

“…The flat wall model of the ceramic shell component is given in Figure 1. Concentrating on steady state conditions the local heat flux can be described as : linG 2liter (2) The local thermal boundary conditions are fixed due to the local hot gas flow (lbia,THa) and the local cooling gas Temperature (Tao) respectively. Furthermore the thermal conductivity A cer is a fixed material constant and can not be included to adjust the thermal behavior of the ceramic structure.…”

“…SSiC is considered to be the most promising material for operating temperatures up to 1673K since it shows no significant drop in strength with increased temperatures [1]. Promising approaches to introduce ceramic components into gas turbines were carried out through development of a convectively cooled multi-layered hybrid design [2,3]. The intention was to obtain homogenous temperature distributions in the ceramic structure, i.e.…”

“…Therefore, the temperature distribution can be kept homogenous if the temperature gradients 8/8t T cer(t) are forced to be constant for the whole ceramic component. Taking Equation 11 the local temperature gradients can be adjusted by carefully varying the local wall thicknesses do,, which is known to be a powerful approach to reduce temperature gradients during transient operation [2,3,8]: For a given temperature gradient 6/6t T ur(t) the local wall thicknesses de, have to be chosen according to the following equation: This differential equation is not be solved for different instants in time since d ce, can not be a function of time. To overcome this problem the optimum thickness of the ceramic shell is adjusted for thermal boundary conditions occuring 2.5 seconds after fuel-cutoff which is found to lead to the most favorable results.…”