Abstract

The boundary layer ingestion concept has the potential to improve propulsion efficiency that will lead to better fuel economy of commercial aircraft. This design concept has been explored by NASA as the Single-aisle Turboelectric Aircraft with Aft Boundary-Layer propulsor “STARC-ABL.” This paper discusses the 1D-3D aerodynamic design and optimization process as well as the structural analysis of the rotor of a propulsor with incoming distortion. The propulsor is at the tail of the fuselage, and consists of an Inlet Guide Vane (IGV), Rotor, and Outlet Guide Vane (OGV). The design process presented accounts for only the large radial distortion and not the circumferential distortion. The paper also describes a pragmatic way of choosing orthogonal design parameters to proceed with the optimization process using a genetic algorithm. The final optimized design is highly dependent on the objective function to be optimized. A Modified Adiabatic Efficiency (MAE) has been defined to account for the loss of kinetic energy downstream of the propulsor CFD exit plane. This lost kinetic energy is essentially an approximation of the mixing loss of the tangential, axial and radial components of velocity at the OGV exit. The three blade-row adiabatic efficiency and MAE for an intermediate design case was 88.91% and 86.10% respectively. Upon further optimization and a different incoming distortion, using MAE as the objective function improved the MAE by 2.14% and adiabatic efficiency by 0.25% for the final design case presented in this paper. The rotor-only adiabatic efficiency for this case is 94.49%, the IGV-Rotor two blade-row efficiency is 92.71% and the Rotor-OGV two blade-row efficiency is 90.94%. The IGV is necessary to support the nacelle in this configuration. It also allows for the rotor work distribution to be optimized. The resulting rotor blade satisfies the static structural limit of a 1.1 safety factor for titanium at 110% speed. It also includes the pressure loads from the design point. The process uses an open source parametric blade generator whose source and input files for this geometry are on GitHub.

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