It is well known that fan/compressor blade flutter stability increases with the increase of reduced frequency.Less well-known is that the least stable inter blade phase angle(IBPA)increases with the drop of reduced frequency.However,it is quite striking that little can be found in the open literature about the mechanism to the observations.In this paper,a numerical investigation is carried out to uncover the mechanism of the effect of reduced frequency on flutter stability and the least stable IBPA.The NASA rotor 67 has been used as the test vehicle with its first bending and torsion modes being considered.The time domain harmonic balance method together with the influence coefficient method is used to obtain the worksum-IBPA curves for all cases.It is found that:1)the deterioration of flutter stability with the decrease of reduced frequency is dictated by the dominant decrease of aerodamping due to a blade own vibration;2)the increase of the least stable IBPA with the decrease of reduced frequency arises largely from the increase of the least stable IBPA of the aerodamping from the nearest blade on a blade pressure side.
