Unified low-pressure compressor concept for engines of future high-speed micro-unmanned aerial vehicles

Abstract

The vast majority of unmanned aerial vehiches are propeller-driven with low speed. For higher speeds and longer ranges, new cost-effective microjets, which operate efficiently in both “fly-fast” and “loiter” modes are required. As a solution, a novel variable-cycle geared micro-turbofan architecture without the typical components of booster and low-pressure turbine is considered. This study discusses a key element, the low-pressure compression system. Instead of a separate and complicated booster to extract more power from the basic turbine, it is proposed to incorporate its positive functionality in the fan root. By preliminary and detailed fluid models, and structural concerns, systematic comparisons are made on demonstrative and representative cases to explore the feasibility of the proposal. Beyond the required very wide-chord design, the concept yields to a significantly increased pressurization and axial velocity at the fan root and exact opposite at the rest, causing extreme twist. The corresponding transonic stator root greatly increases downstream mixing losses. Moreover, a limitation is found to be the downstream compressor duct due to a notable increase in the diffusion requirements. Findings present that the concept is dramatically different from typical highly-loaded fans and this paper attempts to present new design guidelines.