Noise and Wake Structure Measurements in a Subsonic Tip Speed Fan |
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1/3-octave band acoustic aerodynamic air angle approximately band blade passing frequency blade wake broadband noise CALCULATION characteristics Comparison COMPARISON OF MEASUREMENTS constant CONTRIBUTION DEG BLADE ANGLE DIAMETER FAN NOISE difference DIRECTION discussion disturbance earlier effect ENDWALL LOSS FAN PRESSURE RATIO fan tested FIGURE Flow Condition fluctuations FRACTIONAL frequency FT/S ft/sec given harmonic harmonic noise higher INCLUDING increase indicated inlet INVISCID FLOW locations lower m/sec mean measured microphone minimum noise modulation narrow band noise levels obtained occurs operating PERCEIVED NOISE LEVEL percent span Performing periodic plotted PN dB PNdB predicted presented pressure ratio probe procedure recording reference region Report response root rotor rotor coordinate system scaled seen sensor shown shown in figure shows sideline signal similar solidity spectra spectrum stationary stator TEST CONDITION test data thrust tip speed trends values vanes velocity defect velocity profiles wake data WAKE WIDTH