The S2 inverse problem is very important in a design process. With the use of a reasonable and verified loss model, an evaluation method is developed for the civil high bypass ratio fan, and the effect of key geometric parameters on the efficiency of the turbofan is investigated. It is shown that, when the radius of the inlet casing is increased to a certain extent, the further increase of the radius does not obviously improve the turbofan efficiency. When the hub ratio is greater than 0.295, the fan efficiency will fall sharply. The constant case diameter design is effective in the improvement of the turbofan efficiency. In the determination of the outlet size, not only the requirement of the flow coefficient, but also the matching with the downstream part have to be taken into account to improve the efficiency of the whole compression system.

civil high bypass ratio turbofan  /  S2 inverse problem  /  key geometric parameter