The effects of ambient conditions on helicopter rotor source noise modeling

Eric Greenwood, Fredric H. Schmitz

Research output: Chapter in Book/Report/Conference proceedingConference contribution

3 Scopus citations

Abstract

A new physics-based method called "Fundamental Rotorcraft Acoustic Modeling from Experiments" (FRAME) is used to demonstrate the change in rotor harmonic noise of a helicopter operating at different ambient conditions. FRAME is based upon a non-dimensional representation of the governing acoustic and performance equations of a single rotor helicopter. Measured external noise is used together with parameter identification techniques to develop a model of helicopter external noise that is a hybrid between theory and experiment. The FRAME method is used to evaluate the main rotor harmonic noise of a Bell 206B3 helicopter operating at different altitudes. The variation with altitude of Blade-Vortex Interaction (BVI) noise, known to be a strong function of the helicopter's advance ratio, is dependent upon which definition of airspeed is flown by the pilot. If normal flight procedures are followed and indicated airspeed (IAS) is held constant, the true airspeed (TAS) of the helicopter increases with altitude. This causes an increase in advance ratio and a decrease in the speed of sound which results in large changes to BVI noise levels. Results also show that thickness noise on this helicopter becomes more intense at high altitudes where advancing tip Mach number increases because the speed of sound is decreasing and advance ratio increasing for the same indicated airspeed. These results suggest that existing measurement-based empirically derived helicopter rotor noise source models may give incorrect noise estimates when they are used at conditions where data were not measured and may need to be corrected for mission land-use planning purposes.

Original languageEnglish (US)
Title of host publication67th American Helicopter Society International Annual Forum 2011
Pages47-65
Number of pages19
Publication statusPublished - Jul 28 2011
Event67th American Helicopter Society International Annual Forum 2011 - Virginia Beach, VA, United States
Duration: May 3 2011May 5 2011

Publication series

NameAnnual Forum Proceedings - AHS International
Volume1
ISSN (Print)1552-2938

Other

Other67th American Helicopter Society International Annual Forum 2011
CountryUnited States
CityVirginia Beach, VA
Period5/3/115/5/11

    Fingerprint

All Science Journal Classification (ASJC) codes

  • Engineering(all)

Cite this

Greenwood, E., & Schmitz, F. H. (2011). The effects of ambient conditions on helicopter rotor source noise modeling. In 67th American Helicopter Society International Annual Forum 2011 (pp. 47-65). (Annual Forum Proceedings - AHS International; Vol. 1).