Validation of the Source Localization Method SODIX for Coherent Sound Sources

A new validation of the source localization method SODIX for coherent sound sources is presented. The DLR fan noise prediction tool PropNoise is used to model the tonal noise of a low-speed fan stage that is generated by the interaction of the rotor wakes with the stator vanes. The simulated data is used to evaluate the capabilities of the source localization method SODIX to determine the coherent sound radiation from the intake and the nozzle exit. The analysis technique includes a parameterization of the source directivities using cubic B-splines. A parametric study on the number of base elements is carried out for the simulated tones with different radiation patterns. The results show that SODIX is able to accurately reproduce the coherent sound radiation of the simulated tones from the intake and the nozzle exit. The results also indicate that a number of base elements from 20 to 100 is a reasonable choice for a large frequency range

Correlation analysis between the jet exhaust velocity field and microphone-array acoustic measurements for a turbo-fan engine

Simultaneous flow and acoustic measurements have been acquired for an aircraft, during ground operation. Measurements of velocity field data with stereoscopic particle image velocimetry (SPIV) on the engine-exhaust jet are correlated with the acoustic-pressure signals of a 120 microphone linear array. The turbulent velocity and the applied-stress components of the Lighthill- and Lilley-analogy source terms in the SPIV region are correlated with the microphone array. Convection effects on the propagating sound waves are neglected in the present study. The self-noise term in the Lighthill quadrupole, shows a hot spot for the correlation in the by-pass to ambient shear layer. This high correlation region is clearly visible in one of the analysed test points only, while in general a poor statistical convergence seems to affect the test-source correlation

Detektion von tonalen Geräuschen von Flugzeugen im Landeanflug

Analyse von tonalen Geräuschen, die bei einigen Typen von modernen Verkehrsflugzeugen im Landeanflug auftreten. Die Daten stammen von den Lärmüberwachungsstationen der Flughhäfen und liegen im MP3 Format vor. Die Analyse der akustischen Daten zusammen mit FLugschreiberdaten legt nahe, dass ein Zusammenhang zwischen kurzfristigen Erhöhungen des Schubs und dem Auftreten von kurzzeitigen tonalen Geräuschen besteht, aber eine genaue Ursache konnte noch nicht identifiziert werden

Low Noise ATRA - Phased Array Measurements of Jet Noise in Flight

DLR performed flight tests with retro-fit modifications for noise reduction on its Airbus A320 research aircraft ATRA. Phased array measurements were performed in 2016 with the baseline aircraft and in 2019 with the noise modified aircraft. The array data were processed with acoustic source localisation methods based on the deconvoluton of beamforming maps for moving sources. The resulting sound source maps show the distribution of the sound sources on the aircraft for three emission angles, in the forward arc, overhead, and in the rear arc. Frequency spectra for individual source regions like the engine inlet, the nozzle, and the jet are averaged over all fly-overs in the same configuration for the baseline and the modified aircraft. The comparison of the baseline with the modified aircraft data for the engine nozzle and jet regions confirms that the modified nozzle reduces jet noise

Evaluation of Microphone Array Methods for Aircraft Flyover Measurements: Quantification of Performance through Virtual Test Environments

Microphone arrays have become a vital tool for the analysis of complex acoustic sources. Many well documented evaluation methods are available for stationary source regions such as wind tunnels and stationary engine tests. This makes it possible to choose from a variety of algorithms, like DAMAS, CLEAN and SODIX. Methods for moving sources however are fewer and less researched. While some of the above-mentioned methods where successfully adapted to moving sources, compromises were made in terms quality or calculation times. . The project LION aims at improving the state of knowledge about the available and new methods by introducing a virtual test environment which includes simulations with varying degrees of complexity and realism, focusing on flyover measurements. The performance of microphone array techniques is assessed by applying them to a set of simulations representing different fly-over scenarios and a comparison of the results. The Virtual Test Cases are used to quantify the quality of the different algorithmic approaches in the context of flyovers. The goal of the presentation is to establish a method assessing new approaches and provide information about application areas, similar to what is available in the stationary case

Preliminary investigations of jet installation noise influenced by a vortex generating liner at the nozzle inner wall

Preliminary investigations on a novel noise reduction technology, the Vortex Generating Liner (VoGeL), are presented. The VoGeL is a bias-flow acoustic liner for the inner wall of flow ducts. Through the vectorization of the face sheet perforate or through the permeability distribution, the VoGeL generates streamwise vorticity that influences the in-duct boundary layer, or, in the nozzle case, the shear layer of a jet. A single realization of a VoGel Nozzle has been tested in isolated configuration and with a simulated jet-wing interaction at the DLR JExTRA small-scale jet facility, validation of the facility is presented by comparing frequency spectra with similar measurements from other jet rigs in the EU

SODIX for fully and partially coherent sound sources

The source localisation method SODIX is capable of determining the amplitudes and the directivity of sound sources based on measurements with a microphone array. The source model of the method has recently been extended with fully coherent sound sources which improves the application of SODIX to tonal noise. This paper presents a further extension of the SODIX source model with partially coherent sources in order to overcome residual effects that cannot be correctly modelled with a fully coherent source model, e.g. due to propagation effects that decorrelate the sound field radiated by a sound source for different receiver positions. The extension relies on a parameterisation of the source directivities and a compressed-sensing based algorithm in combination with an eigenvalue decomposition of the measured cross-spectral matrix to determine the unknown source directivities. The extended localization method with the partially coherent source model is validated using simulated sound sources that have different source directivities and mutual coherence. The results show that only the new source model with partially coherent sound sources is able to resolve the simulated source directivities accurately, when the sources are partially coherent or both coherent and incoherent sources are present

Source localization and far-field extrapolation for wind tunnel measurements of jet installation noise

Experimental data from the AWB aeroacoustic wind tunnel of DLR in Braunschweig measured with linear microphone arrays is analyzed using the SODIX method. The data from the European project DJINN for isolated and installed jets is processed in order to achieve a far-field projection of the source directivity based on the near field data using the capability of SODIX to reconstruct a set of equivalent sources with directive radiation on the engine axis that matches the data measured in the near field

Effizienzsteigerung im Flugbetrieb unter Berücksichtigung des Umweltschutzes und der Wirtschaftlichkeit

Das direkte Bedürfnis der Flughafen-Anwohner nach Schutz vor Fluglärm wird den wirtschaftlichen Interessen sowie dem allgemeinen Bedürfnis nach Mobilität stets gegenüberstehen. Um eine effizientere Planung des Flugbetriebs unter Berücksichtigung der Lärmimmission zu ermöglichen wurden daher zwei Workflows entwickelt. Die Workflows kombinieren die Daten und Software der beteiligten Projektpartner miteinander, wodurch nicht nur die Leistungsfähigkeit der Einzelkomponenten erhöht, sondern auch das gesamte Anwendbarkeitsspektrum gesteigert wurde. Der Workflow zur Immissionsberechnung baut auf detaillierten Flugbahnberechnungen mit den Hersteller-Tools WinPEP (Airbus) und BCOP (Boeing) auf. Solche Flugbahnen werden im Rahmen des Workflows auf die entsprechende Route unter Berücksichtigung einer lateralen Streuung projiziert. Die anschließende Lärmberechnung erfolgt basierend auf DIN 45689, wobei die Zusatzpegel basierend auf dem druckkorrigierten Schub bestimmt werden. Für die Lärmberechnung eines Verkehrsszenarios werden die berechneten Einzelflug-Immissionsgitter entsprechend der Bewegungszahlen superponiert. Optional können auch bestehende AzB/DIN-Datensätze berücksichtigt werden. Der Workflow zur Schallquellenanalyse ermöglicht eine Detektion von störenden Geräuschen bzw. Tönen aus den komprimierten Audiodaten der Lärmmessstellen der Flughäfen. Diese Detektion ist Grundvoraussetzung, um technische Lösungen zu deren Vermeidung zu entwickeln. Die Anwendbarkeit des Workflows und der darin entwickelten Methoden wurde anhand des Problems von Heultönen an einer Gruppe von modernen Triebwerken demonstriert