Research On Aerodynamic Design Of Core Driven Fan Stage

As a key part of the variable cycle engine, core driven fan stage (CDFS) must work steadily attwo different operation modes: single bypass mode and double bypass mode. This is different fromthe conventional compressor. In order to accomplish the CDFS aerodynamic design, this paper firstdesigned the compressor to meet the design goal of single bypass mode using the conventionalcompressor design methods, then tested the double bypass mode and investigated on the methods ofmode conversion. The main contents and conclusions in this paper are as follows:(1) One dimension and two dimension designs have been completed using the traditionalcompressor design methods; CFD is used to test the design results. It is found that hub-cornerseparation exists in the stator passage. Bowed stator is applied to decrease the strength of thehub-corner separation. Efficiency has been improved so that this design case can meet the CDFSsingle bypass mode design target.(2) Based on the single bypass design case, the methods of mode conversion have beeninvestigated in detail. The results show that conventional inlet guide vane is not suitable in CDFS.CDFS should use the variable inlet guide vane. Different locations of vane rotational center andclosing angles are simulated. Increasing the closing angle or decreasing the distance of the location ofvane rotational center to the leading edge can regulate the flow mass more effectively. The profile ofthe vane rotational center can affect the performance of variable inlet guide vane significantly.(3) The aerodynamic parameters of CDFS at different operation mode have been analyzed. Atsingle bypass mode, the outlet flow angle of variable inlet guide vane at blade tip is bigger than theangle at blade root. But at double bypass mode, the situation is reverse. These are beneficial to theCDFS performance. The rotor of CDFS takes advantage of shock wave to increase pressure at singlebypass mode, so the rotor is preferable to adopt positive prewhirl design. At double bypass mode, therotor uses the curved passage with increasing area to increase pressure. Because of rotor passageshock and flow separation resulting from shock wave-boundary layer interaction at single bypassmode, the adiabatic efficiency at single bypass mode is lower than double bypass mode. The stator ispreferable to adopt negative incidence because the incidence and load increase largely when CDFSchanges from single bypass mode to double bypass mode.