Effect of Geometric Variation of Root Fillet on the Flow Characteristic of a Transonic Compressor Rotor

The effects of root fillet on the flow behavior of high loading compressor rotor tends to be much more crucial in practice, and it's necessary to explore the internal relations between the geometric effects of root fillet and the flow behaviors of rotor blade. Therefore, eight types of root fillet with different radius were designed and installed around the blade root of NASA Rotor67. With the aids of fillet, the corner separation near suction side of blade root has been suppressed significantly in that the root fillet reconstructs the circumferential bending distributon of the suction-side curve from leading edge to trailing edge, and reduces the genmetric turning angle in the latter part of root section near trailing edge. However, apart from the improvement of corner flow characteristic caused by root fillet, both the tip flow deterioration and the decrease of stall margin occur in the new rotors, which indicates an indirect correlation between tip flow characteristic and root fillet exists indeed in the three-dimensional flowfields of transonic rotor. Actually, by means of the new radial pressure equilibrium affected by root fillet, a larger radius of root fillet contributes to much larger blade loading and stronger leakage flow in tip region of compressor rotor. As a result, a monotonic decrease of stall margin was present in the transonic rotor with increase of the root fillet radius. Subsequently, the positive bending of blade tip was introduced to deal with the negative effect caused by the root fillet indirectly. Combined with the effects of root fillet and positive tip-bending on the radial pressure equilibrium existing in channels, both the radial and streamwise loading distributions tend to be much more reasonable in new rotors, and the static pressure difference in former 1/3 chord of blade tip has decreased clearly which benefits to reduce the strength of leakage flow in tip region. Therefore, the flow deterioration in tip region of transonic rotor induced by root fillet has been well suppressed, with an obvious improvement of overall performance occurring in new rotors.