Fan design and operation for ultra low noise

In this thesis, a new approach to the selection of key fan design parameters is presented and a methodology to optimise engine operation for minimum take-off noise is developed. These techniques are applied to the detailed design of a fan system for the Cambridge-MIT Silent Aircraft Initiative engine to which ultra low noise is the principle design objective. Reduction of jet mixing noise is identified as being crucial to the design process leading to jet area at take-off having to be increased significantly compared to current trends. Whilst increasing the number of engines from two to three and optimisation of the departure profile reduced this area increase, the introduction of variable cycle technology is required in order to deliver low cruise fuel burn. A variable area nozzle, identified as the most promising technology, is linked to operation of the fan through a simple model. This is used to show that it is possible to enable large increases in exit nozzle area at take-off without compromising fan performance at cruise. For the fan design, stage loading is shown to be a critical parameter as it impacts competing requirements. Increasing loading increases efficiency and part speed capacity but makes designing fixed outlet guide vanes harder. The method to optimise the departure profile was combined with the completed fan design and extended to include fan and airframe noise sources. The results of this show that by modifying the nozzle area at all times during take-off to maximise mass flow rate, the final podded SAI design is estimated to have a noise footprint of approximately 65.5 dBA outside the baseline airport at take-off. This leads to an ICAO take-off certification noise level of approximately 73 EPNdB at both flyover and sideline, 23 dB below existing requirements at each measuring location.EThOS - Electronic Theses Online ServiceGBUnited Kingdo