Conceptual Design of a Counter- Rotating Fan System for Distributed Boundary Layer Ingesting Propulsion

The present paper details the design of counter rotating fans for a Turboelectric Distributed Propulsion (TeDP) system. Sixteen propulsors installed are embedded on an aerodynamically optimized hybrid wing-body configuration in mail-slot-shape nacelles. The hybrid wing-body configuration which was previously designed to satisfy the conditions of trim, longitudinally static stability and specific cargo space is employed as the influencing body configuration in pursuing an optimal distributed propulsion system. A counter-rotating fan system for the distributed propulsors is conceptually designed and the performance is evaluated against the target thrust mandated by the mission requirements. The concept of the distributed propulsion allows the fan pressure ratio to be around 1.30 to achieve the target thrust. In addition, further splitting of the fan pressure ratio by using the counter-rotating fans for each slot realizes the target pressure ratio with low tip speed. Aerodynamic shape optimizations of the fan blades are performed in a sequential multi-objective optimization process for various design objectives, such as mass flow rate condition, fan pressure ratio, efficiency and the exit flow angle of the fan stage by using a genetic algorithm, NSGA-II. The radial chord distribution, and meanline distribution of the rotors are designed on the circumferentially averaged axisymmetric inlet profiles and tested on the profiles from six divided sectors to reckon the flow distortion. The performances of the counter rotating fans are, thus, evaluated and compared with a conventional high-speed fan accordingly to find distortion tolerant characteristics of the present concept.