Design-for-Additive-Manufacturing Approach for Support-Free Pre-Assembled Micro Gas Turbines

Abstract This study presents a preliminary design approach for pre-assembled microgas turbine engines for unmanned aerospace propulsion systems, intended for fabrication via direct metal laser sintering, and demonstrates the feasibility of additively manufacturing nested, self-supporting turbomachinery systems from Inconel 718 in their operational configuration. The layout consists of two primary components: a monolithic rotor integrating the compressor and turbine, connected by a shaft that functions as a hybrid journal bearing lubricated by the engine's liquid fuel prior to combustion, and a stationary casing that incorporates turbomachinery stators, a bearing housing, and a porous inert media combustor. Each component is designed to be self-supporting within powder bed fusion constraints and to facilitate the build of connected geometries above it, enabling the entire engine to be formed in a single uninterrupted process. Using a multidisciplinary gradient-based optimization framework, the radial compressor and mixed-flow turbine are parametrically designed to maximize mass flow and aerodynamic efficiency while maintaining structural integrity. The porous inert media combustor comprising isotruss lattices achieves prevaporized lean premixed combustion with minimal pressure drop. A fluidic conical hybrid bearing is considered with effective surface scaling, providing sufficient axial/radial load capacity at reduced power requirements. To ensure printability, precompensation optimization mitigates residual process stress-induced deformations, resulting in a pre-assembled architecture with manufacturing deviations of 70 μm and surface roughness of 3 μm for all critical surfaces. This work demonstrates a scalable, system-level additive manufacturing (AM) approach that eliminates postassembly and significantly simplifies the production of complex turbomachinery, offering a practical pathway toward integrated AM-driven propulsion systems.