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The uses and abuses of the acoustic analogy in helicopter rotor noise prediction
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Farassat, F. Brentner, Kenneth S. |
| Copyright Year | 1987 |
| Description | This paper is theoretical in nature and addresses applications of the acoustic analogy in helicopter rotor noise prediction. It is argued that in many instances the acoustic analogy has not been used with care in rotor noise studies. By this it is meant that approximate or inappropriate formulations have been used. By considering various mechanisms of noise generation, such abuses are identified and the remedy is suggested. The mechanisms discussed are thickness, loading, quadrupole, and blade-vortex interaction noise. The quadrupole term of the Ffowcs Williams-Hawkings equation is written in a new form which separates the contributions of regions of high gradients such as shock surfaces. It is shown by order of magnitude studies that such regions are capable of producing noise with the same directivity as the thickness noise. The inclusion of this part of quadrupole sources in current acoustic codes is quite practical. Some of the difficulties with the use of loading noise formulations of the first author in predictions of blade-vortex interaction noise are discussed. It appears that there is a need for development of new theoretical results based on the acoustic analogy in this area. Because of the impulsive character of the blade surface pressure, a time scale of integration different from that used in loading and thickness computations must he used in a computer code for prediction of blade-vortex interaction noise. |
| File Size | 783516 |
| Page Count | 8 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_20040161126 |
| Archival Resource Key | ark:/13960/t1jh8fk26 |
| Language | English |
| Publisher Date | 1987-01-01 |
| Access Restriction | Open |
| Subject Keyword | Acoustics Blade-vortex Interaction Rotor Aerodynamics Aerodynamic Noise Noise Generators Aeroacoustics Noise Prediction Computer Programs Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Article |
