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.

Wind energy has been a research focus of the last few decades, promoting the topic to a much more matured level. However, the body of literature is built around a limited number of turbine types and it is still beneficial to increase turbine diversity for the opportunity to select optimal turbine for a given purpose. The radial (inflow) turbines known in gas and hydro turbine industries for pressurized pipe flows are undiscovered turbines for free-stream wind harvesting both in air and underwater. In such case, the wind tangentially interacts with each blade by an external casing; therefore, all blade angular positions may, at least in theory, contribute equally to power production. Enclosed compact architecture with low rotational speeds and narrow intake ports may possess advantages in enabling the use of much weaker but more recyclable and long-lasting blades and in applications such as integrated wind harvesting for blunt bodies like buildings, vessels and devices or for any application where an open rotor is not feasible. Using experimentally validated Reynolds-averaged Navier–Stokes simulations, mass swallowing capacities and corresponding efficiencies of such turbines are parametrically investigated at low Reynolds numbers, Re chord=11 × 103, and finally enhancement is shown in 88 × 103. Findings provide first insights into such turbines. Considering the investigated very low Reynolds numbers and three-dimensional effects, comparable performance with other small turbines are observed. Moreover, undiscovered potential for performance optimization persists.