Browsing by Author "Leitch, Thomas A."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Method and apparatus for reducing high-cycle fatigue and suppressing noise in rotating machinery
    (United States Patent and Trademark Office, 2000-02-22)
    A stator apparatus for mounting upstream of an intake to a rotating machine which blows pressurized air, or other media, from discharge orifices at a pressure and velocity to minimize velocity defects or turbulence in the wake of the stator prior to the plane of rotation of a rotating member of the machine. The rotating member then encounters a substantially uniform velocity medium at the plane of incidence, which substantially reduces uneven loading on the rotating member, thereby reducing noise and reducing high-cycle failure of that rotating element. The distribution and size of the orifices is determinable by placing the stator apparatus in a wind tunnel, or on the intake of a apparatus simulating the intake of the rotating machine, measuring the turbulence or velocity defects in the stator wake, and modifying the distribution and size of the orifices until the turbulence is minimized.
  • Thumbnail Image
    Reduction of Unsteady Rotor-Stator Interaction Using Trailing Edge Blowing
    Leitch, Thomas A. (Virginia Tech, 1997-01-16)
    An aeroacoustic investigation was performed to assess the effects of adding mass flow at the trailing edges of four 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. In these experiments a reduced number of stators (four) was used in a 1/14 scale model inlet which was coupled to a 4.1 in (10.4 cm) turbofan engine simulator with 18 rotors and 26 downstream stators. This study is a preliminary step toward a more in depth investigation of using trailing edge blowing to reduce unsteady rotor-stator interaction. 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: 40%, 60%, and 88% of the design speed. The lowest test speed of 40% design speed showed the most dramatic reduction in radiated noise. Noise reductions as large as 8.9 dB in the blade passing tone were recorded at 40% design speed, while a tone reduction of 5.5 dB was recorded at 60% design speed. At 88% design speed a maximum tone reduction of 2.6 dB was recorded. In addition, trailing edge blowing reduced the overall sound pressure level in every case. For both the 40% design speed and the 60% design speed, the fan face distortion was significantly reduced due to the trailing edge blowing. The addition of trailing edge blowing from the four upstream stators did not change the total pressure ratio, and the mass flow added by the blowing was approximately 1%. The results of these experiments clearly demonstrate that blowing from the trailing edges of the stators is effective in reducing unsteady rotor-stator interaction and the subsequent forward radiated noise.