Rotorcraft noise prediction system validation and analysis for generating noise abatement procedures
Open Access
- Author:
- Botre, Mrunali
- Graduate Program:
- Aerospace Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 18, 2020
- Committee Members:
- Kenneth Steven Brentner, Dissertation Advisor/Co-Advisor
Kenneth Steven Brentner, Committee Chair/Co-Chair
Philip John Morris, Committee Member
Joseph Francis Horn, Committee Member
Victor Ward Sparrow, Outside Member
Amy Ruth Pritchett, Program Head/Chair - Keywords:
- Rotorcraft
Acoustics
PSU-WOPWOP
Validation - Abstract:
- The main contribution from the current work is the enhancement of a comprehensive noise prediction system for rotorcraft and a methodology to analyze flight test procedures in the interest of understanding the noise source generation mechanisms and aid development of noise abatement procedures. This dissertation describes a rotorcraft noise prediction system and its development to incorporate time-dependent information–including trajectory, attitude, blade loads and rotor thrust–for predicting noise generated during a complex maneuver. The validation process is carried out by comparing the predicted noise levels (SELdBA, OASPL and A–weighted SPL) and processed flight test data. The examples considered are: level flight; descent flight; level turns; level, decelerating turns; and descending turns. This range of operations is considered to analyze the prediction system and understand its capabilities and deficiencies for future work. Overall the predicted noise levels were able to match the trends and levels within a 2–4 dB of that measured during the flight test. The time histories are studied in detail to understand the influence of events (such as steady flight conditions, with constant speed, roll angle or descent rate, and transient flight conditions, including roll-in and roll-out of turn, start and end of deceleration or acceleration) occurring during the flight procedure on noise levels and directivity. The key takeaways are that the noise prediction system was able to capture the noise levels but missed blade-vortex-interaction (BVI) noise directivity during some complex maneuvers. Transient maneuvers generate higher-harmonic loading and BVI noise and the intensity depends on the rate of change of flight conditions. The tail rotor not only contributes the thickness noise below the flight path but has significant contribution at sideline observer locations during a maneuver. The radiation distance and directivity have shown a stronger effect on noise levels than the harmonic noise sources. Lastly, the broadband noise dominates the A–weighted SPL for the steady maneuvers (except descent) and its importance is less during the transient flight segments. A final thing to note is that the noise generated during a 6° steady descent (the standard descent angle for approach) was much higher than any other complex procedures studied in the current work.