Direct method was applied with an automatically optimization tool

in which the geometrical code and the blade to blade flow solver were integrated into genetic algorithm for searching of the optimal airfoil based on a conventional controlled diffusion airfoil(CDA). The design object was considered as a compromise of losses and operating range. It showed that the attainable incidence of optimized airfoil increased from 11° to 17.5° and the negative incidence range increased 4.5°

with similar design point loss as reference CDA airfoil. Additionally

the loss curve of optimized airfoil was flatter

showing it can remain stable performance in a wider working range. It indicated that the upstream propagation of suction peak shifted from 40% chord to 20% chord

extended the diffusion area and reduced the deceleration gradient

contributing to the increase of stall margin. The increase of negative incidence range can be ascribed to two reasons: first

the optimized airfoil has larger throat area and the throat location is apart from suction peak

thus gaining larger choking range. Secondly

the pressure surface velocity distribution is flatter

even with slight acceleration until 30% chord

as a result

the early separation of boundary layer caused by the leading edge spike and the following continual diffusion can be avoided.