REDUCTION OF UNSTEADY STATOR–ROTOR INTERACTION USING TRAILING EDGE BLOWING

Abstract An aeroacoustic investigation was performed to assess the effects of adding mass flow at the trailing edges of stators upstream of an aircraft engine simulator. By using trailing edge blowing to minimize the shed wakes of the stators, the flow into the rotor was made more uniform, hence reducing the unsteady stator–rotor interaction. In these experiments, a reduced number of stators (four) was used in a 1/14 scale model inlet which was coupled to a 4·1in (10·4 cm) turbofan engine simulator. Steady state measurements of the aerodynamic flow field and acoustic far field were made in order to evaluate the aeroacoustic performance at three simulator speeds: 30k, 50k, and 70kr.p.m. The lowest test speed (30k r.p.m.) showed a noise reduction as large as 8·9dB in the blade passing tone. At 50k and 70kr.p.m., the reduction in blade passing tone was 5·5 and 2·6dB respectively. In addition, trailing edge blowing reduced the overall sound pressure level in every case. Aerodynamic measurements showed that fan face distortion was significantly reduced due to trailing edge blowing. The addition of trailing edge blowing from the four upstream stators did not change the operating point of the fan, and the mass flow added by the blowing was less than 1% of the fan mass flow rate. The results of these experiments clearly demonstrate that blowing from the trailing edges of the stators is effective in reducing unsteady stator–rotor interaction and the subsequent forward radiated noise.