Hybrid Axial and Cross-Flow Fan Propulsion for Transonic Blended Wing Body Aircraft

Ideally, standard fan/engine designs can directly be embedded within the airframe of a vehicle. Unfortunately, doing so causes both performance penalties and structural challenges due to boundary layer flow ingested into the propulsors. For the present design concept, a dual-propulsion axial fan (AF) and cross-flow fan (CFF) system is investigated. This system provides the excellent efficiency of the axial fan, but with the benefit of the cross-flow fan system providing boundary layer flow mitigation. The purpose of this research was to develop the necessary computational tools to analyze this configuration, and then to show that the combined propulsor solution has performance benefits over the single axial fan system. Using both 2D and 3D CFD simulations, axial fan compression efficiency improvements of up to 2.5% were shown when the CFF propulsor was included. Also, the CFD data showed significant changes in the flow field due to the inclusion (or exclusion) of the distributed propulsors, demonstrating that it is impossible to segregate the airframe force calculations from those for the individual fans, thus necessitating a coupled airframe and propulsion approach to the design of such a vehicle.