A preliminary method to estimate impacts of inlet flow distortion on boundary layer ingesting propulsion system design point performance

Abstract

Boundary layer ingestion by fans in propulsion system improves the propulsive efficiency. However, inlet flow distortion will dramatically eliminate these benefits. This paper puts forward a method to deal with inlet flow distortions and examines their impacts on turbofan performance at engine design point. The method models both radial and circumferential distortion and their impacts separately. Firstly, a distorted fan map is calculated by parallel compressor method. Then, the new map is utilised to find the fan exit flow conditions by parallel stream method. Finally, we assume that all the flows mixed well before entering the nozzle without any pressure losses. At all examined fan pressure ratios, boundary layer ingesting improved fuel consumption. However, the benefits reduced by the new method are lower than previous predictions without considering intake distortion. If the fan pressure loss and efficiency drop due to inlet distortion are too high, boundary layer ingestion should not be used with a traditional fan design. Large boundary layer ingestion for future propulsion system should consider new fan blade design.