Penn State

This work focused on the unique aspects of the development of new noise prediction code called PSU-WOPWOP to solve the aeroacoustic problem of maneuvering rotorcrafts. Noise prediction results for different rotorcraft configurations and maneuvers were presented: as a general rule, maneuver tends to increase the intensity of noise an significantly affects its directivity.

Recently, noise certification requirements for new helicopters have elevated the importance of noise to nearly the same level as performance, safety, reliability and manufacturing. A great deal of progress has been made over the past 50 years in fundamental theoretical understanding and computational accuracy of the different noise sources. Current rotor noise prediction technology is well advanced but limited to steady rectilinear flight and periodic conditions. Even the simplest maneuver cannot be fully model, hence the need for a noise prediction code for rotors in both steady and transient maneuvering flight.

The theoretical basis of noise generated by rotating blades was introduced by Ffowcs Williams - Hawkings in 1969 (FW-H equation). For the implementation of PSU-WOPWOP, an integral representation of the solution of the FW-H equation for permeable surface, known as Formulation 1A of Farassat, was used, as well as a source-time-dominant algorithm (see papers for details) . The full rotor-blade motion (rotation, flapping, lead-lag, pitch, etc.) and the complete aircraft motion (non-periodic, time-dependent aircraft translation, pitch, roll, yaw, etc.) are taken into account.

Numerous flight conditions and rotorcraft configurations have been considered. The comparison between the acoustic pressure time history for a steady descent and a transient arrested descent are shown here (single observer located 100 ft below and in front of the helicopter). The noise at this observer position is significantly increased (as much as 5 times greater amplitude) during this rather aggressive maneuver. Overall sound pressure level (OASPL) contours are presented for the same maneuver to demonstrate the impact of maneuvering on the amplitude and directivity of the noise signal (Horizontal measurement plane 30.5m (100 ft) below helicopter at t = 0).

In conclusion, PSU-WOPWOP showed great potential to become a standard rotorcraft noise prediction code, and is still being developed at Penn State under the supervision of Prof. Brentner.

CONFERENCES & PUBLICATIONS:

Maneuvering Rotorcraft Noise Prediction: a new code for a new problem

K.S. Brentner, G. A. Brès, G. Perez and H. E. Jones

AHS Aerodynamics, Acoustic and Test Evaluation meeting, San Francisco, CA (January 2002)

Toward a better understanding of Maneuvering Rotorcraft Noise

G. Perez, K.S. Brentner, G. A. Brès and H. E. Jones

Proceeding Vol. 2, pp. 1552-1562, AHS 58th meeting, Montréal, Canada (June 2002)

Modeling the noise of arbitrary maneuvering rotorcraft: Analysis and implementation of the PSU-WOPWOP noise prediction code

G. A. Brès

M.S. Thesis, Pennsylvania State University, 2002

Maneuvering Rotorcraft Noise Prediction

G. A. Brès, K.S. Brentner, G. Perez and H. E. Jones

Journal of Sound and Vibration 275 (3-5): 719-738, August 2004

A First Step Toward the Prediction of Rotorcraft Maneuver Noise

G. Perez, K.S. Brentner, G. A. Brès and H. E. Jones

Journal of the American Helicopter Society 50 (3): 230-237, July 2005

Work supported by NASA Langley

Last update: January 2006