Distributed Electric Propulsion Configuration Trade Study for the SUSAN Electrofan

Distributed electric propulsion (DEP) is a novel propulsion technology that can reduce aviation energy usage and emissions by enabling ultra-high effective bypass ratios. Further improvements to propulsive efficiency can also be obtained when considering configurations that leverage boundary layer ingestion (BLI). However, the design of DEP systems can prove to be challenging at transonic conditions, especially when considering configurations with high levels of aeropropulsive coupling, such as those including BLI. The aeropropulsive benefits of DEP must also trade favorably against increases in drag that come from including many smaller individual propulsive units. In this paper, a DEP configuration trade study is performed for the hybrid-electric SUSAN Electrofan regional jet aircraft concept based on Reynolds-averaged Navier-Stokes computational design and analysis tools in order to address aeropropulsive design challenges while assessing the potential benefits of various configurations. Results show that configurations with wing-mounted mail-slotted DEP systems require much less thrust at cruise when compared to a non-DEP configuration. However, the DEP configuration developed for BLI was found to require more thrust than the non-BLI configuration due to the thin boundary layers on the wing and the influence of the wing flow field on the inlet flow of the DEP systems. The shaft power required at cruise across all aircraft configurations was also found to be similar when accounting for propulsion-airframe integration effects, although this may be due in a large part to insufficient inlet diffusion. Nonetheless, the DEP configurations were found to experience significantly less thrust-induced drag than the non-DEP configuration, which appears to be one of the main benefits of the technology.