Exoskeletal 2-Spool Turbofan Engine

This is a new iteration of the exoskeletal design, this time incorporating a twin-spool design. This allows the fan to run more efficiently. However, this comes with the complication of trying to fit overlapping spools in the already extremely limited space available. So far there has been little progress but I've produced the main general cross-section design which manages to tightly fit the two spools. The engine consists of a LP spool with a fan with a two stage LP turbine, a HP spool that has a 9 stage compressor and a 2 stage HP turbine. In the design, the rotors make use of foil bearings instead of regular rolling bearings. Previous designs simply used rolling bearings without active lubrication which realistically would not result well. But due to the lack of space, it would be extremely difficult if not impossible to fit in the required seals and oil system for lubricating the bearing sufficiently. Hence, in this design, I have opted for foil bearings due to their more compact size, no need for an oil system, how it effectively sucks in air for successful operation as well as excellent load capacity. There isn't much information on how to design with foil bearings but it appears that the main issue with them is the startup where the bearings aren't able to form a sufficient load-bearing air layer to support the rotor and thus leading to wear. Nevertheless, foil bearing would be an ideal fit for this concept design. It uses 4 foil bearings for supporting each end of each spool as well as a thrust foil bearing on each spool to take care of axial loads. 

For start up, the idea is to use an integrated pinion underneath the stator behind the front fan, connected to the compressor (HP spool) with the pinion shaft running through a stator. This could be powered by a motor. Additionally, there is intention to attempt to apply variable stators for the fan stator and hopefully also the compressor stators if possible. A method to divert some of the compressor flow for cooling the turbine blades would ideally need to be devised. 

So far, despite the size envelope roughly being 300mm x 600mm, the small size has meant that it's been very difficult to find ways to add systems and to even to just find ways to assemble components (e.g. how are the compressor rotor stages attached together). Nevertheless, it's a fun and complicated project  that challenges me and hopefully there is merit in this concept. The intention it to keep creating concepts and slowly maintain iterating it, adding more and better systems for more viable operation.