Aircraft noise

About: Aircraft noise is a research topic. Over the lifetime, 3051 publications have been published within this topic receiving 32039 citations.

The Prediction of STOVL Noise- Current Semi-Empirical Methods and Comparisons with Jet Noise Data

Abstract: The prediction of conventional or STOVL turbojet propulsion system-using aircraft noise is presently undertaken by means of a method incorporating empirical models for jet-mixing noise, engine core noise, and broadband shock noise. The free-jet noise is coupled with a novel empirical equation for ground-interaction noise generated by a vertically impinging jet, and supplemented with the out-of-ground-effect free-jet acoustic directivity pattern of a Harrier-type vectoring nozzle installation. This acoustic-prediction method yielded reasonable agreement with measured far-field Harrier noise during hover in and out of ground effect. Unlike small-scale studies of jet impingement on a hard surface, no tones were found in the present Harrier nozzle spectra.

On the Use of Acoustic Wind Tunnel Data for the Simulation of sUAS Flyover Noise

Abstract: Acoustic measurements of a small, unmanned aerial system were recently acquired during a ground test campaign. The purposes of the ground test, conducted in the NASA Langley Low Speed Aeroacoustic Wind Tunnel, were to characterize the source noise in terms of its tonal and broadband content, and to identify conditions under which multirotor and rotor-airframe interactions are present. The focus of this work is to assess the effectiveness of using those data for the simulation of flyover noise at a ground observer. The assessment is made at two levels of fidelity using different sets of tools. In the first, 1/3 octave band spectra at a ground receiver will be simulated in a frequency domain approach using the NASA Aircraft NOise Prediction Program. In the second, the pressure time history at a ground receiver is simulated in a time domain approach using the NASA Auralization Framework. Various objective measures are used to verify the simulation process. Acoustic wind tunnel and flight test data are used to gain insight into perceptually important effects.

Measurement and Characterization of Helicopter Noise in Steady-State and Maneuvering Flight

Abstract: A special acoustic flight test program was performed on the Bell 206B helicopter outfitted with an in-flight microphone boom/array attached to the helicopter while simultaneous acoustic measurements were made using a linear ground array of microphones arranged to be perpendicular to the flight path. Air and ground noise measurements were made in steady-state longitudinal and steady turning flight, and during selected dynamic maneuvers. Special instrumentation, including direct measurement of the helicopter s longitudinal tip-path-plane (TPP) angle, Differential Global Positioning System (DGPS) and Inertial Navigation Unit (INU) measurements, and a pursuit guidance display were used to measure important noise controlling parameters and to make the task of flying precise operating conditions and flight track easier for the pilot. Special care was also made to test only in very low winds. The resulting acoustic data is of relatively high quality and shows the value of carefully monitoring and controlling the helicopter s performance state. This paper has shown experimentally, that microphones close to the helicopter can be used to estimate the specific noise sources that radiate to the far field, if the microphones are positioned correctly relative to the noise source. Directivity patterns for steady, turning flight were also developed, for the first time, and connected to the turning performance of the helicopter. Some of the acoustic benefits of combining normally separated flight segments (i.e. an accelerated segment and a descending segment) were also demonstrated.

Towards Prediction of Dual-Stream Jet Noise: Database Generation

Abstract: The accurate prediction of jet noise from dual-stream nozzle exhaust geometries typical of high bypass ratio turbofan engines has practical relevance for aircraft design studies and in aircraft noise certification. Existing empirical methods do not provide good predictions against measured data; in addition, they are restricted to lower area ratio (secondary to primary) nozzle geometries and lower bypass ratios (BPR). The area ratio and BPR of newer engines have increased substantially, well beyond the range of validity of existing prediction methods. Therefore, there is a dire need to develop an accurate empirical prediction method that is valid over a wider range of jet operating conditions and nozzle geometries that are representative of current engines. A wind tunnel test has been completed and a comprehensive database from realistic geometries and operating conditions has been generated. The data have been analyzed and investigated with an eye towards modeling that would lead to an empirical prediction method. The area ratio and BPR cover wide ranges that encompass all current engines and potential ultra-high BPR engines of the future. The spectral characteristics have been examined and the effects of the following parametric variations are reported in this paper: (1) impact of area ratio with fixed, but over a range of, power settings; (2) at a given As/Ap, fixed primary jet and systematically varying secondary conditions; (3) at a given As/Ap, fixed secondary jet and systematically varying primary conditions; and (4) the effects of forward flight for the above situations. It is established that the characteristics of dual-stream jets with velocity ratio less than 0.5 are similar to those for a single jet, with the velocity ratio being the main controlling parameter and the area ratio playing a lesser role. At higher velocity ratios, contributions from the secondary shear layer is dominant at higher frequencies and the contributions from the mixed jet component controls the peak spectral levels in the peak radiation sector at large aft angles. At low inlet angles, the spectral shape remains invariant for all jet and geometric conditions.