Development of an Inside-Out Ceramic Turbine

Abstract

Ceramic turbines could substantially increase operating temperatures of turbomachinery without the need of blade cooling, leading to higher conversion efficiency and power density. However, the inherent brittleness and low tensile strength of ceramic materials limits the use of hub-based ceramic turbines. This paper presents a novel inside-out turbine architecture, permitting the use of monolithic ceramic blades. The proposed architecture uses a carbon-polymer composite rim which converts the rotor radial loads to tangential hoop stress. The blades mainly support compressive loads, minimizing tensile stresses within the blade and thus crack propagation. This allows the use of low tensile strength ceramics which cannot be used in standard hub-based turbines. The rotor hub is comprised of two radially flexible C-shaped hubs, which have sufficient compliance to follow radial displacement of the heavily loaded composite rim. The feasibility of the proposed inside-out ceramic turbine is demonstrated by addressing the four key challenges of the architecture using proof-of-concept prototypes, namely: (1) rotor dynamics of the flexible hub; (2) thermal viability of the composite rim (3) local tensile stress in the blades, and (4) thermal shock in the ceramic blades in transient mode. Experimental validation with an alumina blade confirms that this architecture supports the use of low tensile strength, brittle ceramic blades.