Trailing-Edge Blowing for Reduction of Turbomachinery Fan Noise

Abstract

A new technique for reducing rotor wake-stator interaction noise was investigated. The approach involves injecting air from near the trailing edge of the rotating fan blades to fill in the mass/momentum deficit of the rotor wakes. Results are presented from experiments on a l/6th-scale high-bypass ratio fan stage with blades incorporating internal passages for trailing edge blowing. Two different spanwise blowing distributions are discussed; for each, the mass flow injected from the trailing edge was less than 2% of the fan throughflow. Time-mean and turbulent profiles of the rotor-relative Mach number are presented, along with stator unsteady loading measurements. Significant filling of the time-mean wake profile was achieved with reductions in the first three BPF harmonic amplitudes of up to 85% at 1.5 chords downstream of the rotor. In addition, stator measurements showed reductions in the stator unsteady loading of up to 10 dB. The results demonstrate that trailing edge blowing is effective for reducing the rotor wakes and their mean harmonic amplitudes. Therefore, with appropriate blade design, significant noise reductions are possible while maintaining rotor-stator spacing; alternately, the rotor-stator spacing may be significantly reduced while maintaining similar radiated noise levels.