Over the past decade, stricter noise standards for civil aircraft operations and the need for greater stealth in a military environment have lead to a sustained interest in rotorcraft noise prediction. Although great progress has been made, development of the acoustic codes capable of predicting rotorcraft maneuver noise is lacking. The purpose of this paper is to demonstrate the potential impact maneuvering flight may have on rotor noise generation through initial noise predictions with a new rotor noise prediction code PSU-WOPWOP. This code is a necessary first step toward analyzing and understanding the additional noise generated during maneuvers - especially transient maneuvers. In this paper the predicted acoustic directivity for a helicopter in a transient descent condition is presented and compared to that of a steady three-degree descent path. Both main and tail rotor noise are predicted. The CAMRAD-2 comprehensive analysis code is used to approximate the time-dependent rotor blade loading and flight dynamics. In these initial predictions, a representative (but simplified) maneuver tends to significantly increase the noise intensity and change the directivity. These changes impact both low and mid frequencies - as much as the contribution of the tail rotor. An approximate quasisteady noise prediction is used to demonstrate that the increased noise in the transient maneuver in is not accounted for by the change in rotor thrust alone.
All Science Journal Classification (ASJC) codes
- General Materials Science
- Aerospace Engineering
- Mechanics of Materials
- Mechanical Engineering