Trailing-edge blowing for reduction of turbomachinery fan noise

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 rotor. wakes. Results are presented from experiments on a 1/6th-scale high-bypass-ration 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 blade-passing frequency harmonic amplitudes of up to 85% at 1.5 chord 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 makes 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.