Aerodynamic Optimization Design Of Core Driven Fan Stage On The Balance Of Two Operation Modes’ Performance

Variable cycle engine is an important developing direction of the aero-engine, and the core driven fan stage(CDFS) is one of the key components of double bypass variable cycle engine. The design difficulty of the CDFS lies on the high-performance working in two different operation modes. This paper advanced a new method, using automatic optimization method to balance the performance of the different operation modes, to complete the aerodynamic design of the CDFS.Firstly, the paper combined S2 stream surface through-flow calculation method with automatic optimization method based on genetic algorithm to balance the performance of the different operation modes during the S2 stream surface through-flow calculation. The mass flow and the total pressure ratio in two different modes were been chosen as the constraints, the radial distribution of the rotor total pressure ratio、the IGV outlet flow angle in single bypass mode and the closed angle of IGV in double bypass mode were been chosen as design variables. The purpose of the calculation was to find the minimum differentiation of the rotor inlet/outlet relative flow angle and the rotor outlet absolute flow angle in two different modes to complete the balance of two different modes’ performance.Secondly, completed the original design of the CDFS rotor blade profile based on the result of the S2 stream surface through-flow calculation and found the defects of original blade according to the 3D flow filed calculation. To solve the shortage, optimization design on arbitrary rotating surfaces and 3D blade was processed. And the performance improved in two operation modes after the optimization design. The paper also researched the influence of the IGV closed angle to the performance of double bypass mode, the studies have showed that the 30 degrees IGV closed angle when switching from single bypass mode to double bypass mode was the best angle.Lastly, the paper completed the aerodynamic design of CDFS stator in two different modes’ design indexes. Because of the great differences of the stator inlet flow angle at the tip of the blade in two different modes, the stator designed in one mode’s design index was badly performed in the other mode. So the optimization design method on arbitrary rotating surfaces was proposed to improve the performance of two different operation modes. The CDFS which was designed in the new method highly performed in two different modes, and the isentropic efficiency at working point reached 88.54% in single bypass mode while 88.01% in double bypass mode.