Efficient prediction of broadband trailing edge noise and application to porous edge treatment

Trailing edge noise generated by turbulent flow traveling past an edge of an airfoil is one of the most essential aeroacoustic sound generation mechanisms. It is of great interest for noise problems in various areas of industrial application. First principle based CAA with short response time are needed in the industrial design process for reliable prediction of spectral differences in turbulent-boundary-layer trailing-edge noise due to design modifications. In this paper, an aeroacoustic method is studied, resting on a hybrid CFD/CAA procedure. In a first step RANS simulation provides a time-averaged solution, including the mean-flow and turbulence statistics such as length-scale, time-scale and turbulence kinetic energy. Based on these, fluctuating sound sources are then stochastically generated by the Fast Random Particle-Mesh Method to simulate in a second CAA step broadband aeroacoustic sound. From experimental findings it is well known that porous trailing edges significantly lower trailing edge noise level over a large range of frequencies reaching up to 8dB reduction. Furthermore, sound reduction depends on the porous material parameters, e.g. geometry, porosity, permeability and pore size. The paper presents first results for an extended hybrid CFD/CAA method including porous materials with prescribed parameters. To incorporate the effect of porosity, an extended formulation of the Acoustic Perturbation Equations with source terms is derived based on a reformulation of the volume averaged Navier-Stokes equations into perturbation form. Proper implementation of the Darcy and Forchheimer terms is verified for sound propagation in homogeneous and anisotropic porous medium. Sound generation is studied for a generic symmetric NACA0012 airfoil without lift to separate secondary effects of lift and camber on sound from those of the basic edge noise treatments.Comment: 37 page

Latest research on the reduction of aircraft noise at the source

Der Vortrag gibt einen Überblick zum Stand der Quelllärmforschung und der Minderungs von Schallquellen bei Verkehrsflugzeugen. Es werden zunächst die Hauptschallquellen an modernen Verkehrsflugzeugen Triebwerk, Flugwerk und Installationschallquellen diskutiert. Im zweiten Schritte werden entwickelte Lärmminderungstechnologien besprochen und schließlich ein kurzer Ausblick auf hochinnovative Lärmminderungsansätze in Richtung neuer lärmarmer Flugzeugkonfigurationen gegebe

Installation Effects of a Propeller Mounted on a High-Lift Wing with a Coanda Flap. Part I: Aeroacoustic Experiments

In this contribution, we present aeroacoustic experiments concerning installation effects of propellers. Such installation effects are important as they can significantly alter the sound radiation as compared to an isolated propeller. For this purpose, detailed experiments have been conducted in the NWB aeroacoustic wind tunnel in Braunschweig, Germany. The considered geometry is a nine-bladed propeller installed in front of a high-lift wing (employing a Coanda flap). The results illustrate the influence of propeller rotational speed, blade pitch angle, wind tunnel velocity, and angle of attack variations on the sound radiation. Furthermore, with a source localisation technique insight is gained in the dominant sound sources, and reveals the importance of periodic as well as broadband noise for the considered geometry

Entwicklung, Umsetzung und Flugerprobung von Minderungstechnologien bei Schallquellen am Flugversuchsträger ATRA des DLR

Der Vortrag gibt einen Überblick über Minderungstechnologien für Außengeräuschquellen an einem aktuellen Mittelstreckenverkehrsflugzeug, die ihm Rahmen des Projekts ''Low Noise ATR'' am Deutschen Zentrum für Luft- und Raumfahrt e.V. (DLR) in Braunschweig entwickelt, umgesetzt und flugerprobt wurden. Ziel dieses Forschungsprojekts war es, die mit heute aus vorangegangenen Forschungsprojekten bekannten Technologien erreichbare Minderung des Überfluggeräuschs zu quantifizieren. Nach einer Vorauswahl solcher nachrüstbaren Technologien waren diese auf die einschränkenden Randbedingungen eines realen Flugzeugs prototypisch umzusetzen und zu implementieren. Wenngleich auch eine Maßnahme zur Minderung von Strahlgeräusch implementiert wurde, lag das Hauptaugenmerk auf der Reduzierung des Umströmungsgeräuschs, das beim Landeanflug von größter Bedeutung ist und sowohl Fahrwerk wie Klappensysteme betrifft. Hintergrund dieser Schwerpunktsetzung war der Umstand, dass Aktualisierungen von Verkehrsflugzeugen i.d.R. über neue Triebwerksgenerationen erfolgen, womit typischerweise Pegel des Triebwerksgeräuschs reduziert werden, während das Umströmungsgeräusch an der Flugzeugzelle unverändert bleibt. Hiermit wächst dessen Anteil und damit Bedeutung am Gesamtgeräusch. Anwendung fanden speziell konfigurierte aerodynamische Verkleidungen wie poröse Materialien, die an den bekannten Hauptschallquellen appliziert wurden. Als Ergebnis der Überflugmessungen konnten signifikante Absenkungen des Überflugschalldruckpegels nachgewiesen werden

DLR's Laser Sound Source, a Status Review

Because of the growing interest in noise abatement through the shielding of aircraft component noise (including engine noise), there has been, in the past few years, an increased necessity for the development of appropriate evaluation methodologies for the shielding properties of new aircraft designs. Progress in this domain is necessary to develop technologies which allow the accurate prediction of the noise reduction potential of an aircraft design. Part of DLR's effort, in this respect, is focused on the development and application of a laser-generated reference sound source. While most applications of this type of sound source deal with very high intensity, non-linear, shock-like phenomena, here the focus is on generating an isentropic sound source as a valuable tool to realize dedicated shielding experiments in a non-intrusive manner. Due to its small size, its non-intrusiveness and its monopole character, the laser source is also very well suited for the assessment of sensors transfer function in a wind tunnel environment. Its application in hybrid anechoic wind tunnels also provides appealing prospects. The laser sound source was shown to display the characteristics of a moving monopole i.e. a sound source convecting with the surrounding medium [1]. Experimental evidences presented revealing that the laser sound source displays, in fact, the characteristics of a moving monopole i.e. a sound source convecting with the surrounding medium are presented. A solution to the convected wave equation for a moving point heat source in a uniform subsonic flow is derived, providing i) means for an appropriate scaling of experimental results and ii) an appropriate closed-form sound source easily reproducible in numerical simulations. In order to establish a sound aeroacoustic shielding database for a firsthand validation of acoustic prediction codes, a set of interrelated aeroacoustic shielding tests were planned and executed [2]. The emphasis was put on an extensive 2D diffraction study of NACA 0012 airfoil. These studies laid the groundwork for which the characterization of acoustic shielding properties of actual aircraft geometries was done. The 2D shielding tests presented herein were conducted in DLR's Acoustic Wind Tunnel Braunschweig (AWB), ONERA's F2 Low-Speed Wind Tunnel and NASA's Quiet Flow Facility (QFF)[3] for nominally the same test conditions in order to learn about the measurement scatter across different facilities. A major objective of this study was to determine how consistent the measured data would be across the three facilities, since each has a different test section configuration. The AWB and QFF have, respectively, a fully open and partially open test section, while the F2 tunnel has a closed hard-wall test-section. The aim of this oral presentation is thus to give an overview of the current development status of the laser sound source methodology developed at DLR. Aspects of numerical and experimental realizations as well as analytical representation will be discussed. The content of this oral contribution was already, in part, presented at the 21st and 24th AIAA/CEAS Aeroacoustics Conferences [1][2] and at the STAB symposium 2018 [4

Fast Non-Empiric Tonal Noise Prediction Model for Installed Propulsors

The increasing demand for cuts in environmental pollution is driving aircraft manufacturers towards sustainable aviation concepts that integrate unconventional propulsion configurations on the airframe. To aid the design process of new aircraft, a reliable prediction of installed rotor noise emissions would be required. Therefore, in this work an advanced rotor noise prediction approach is presented, which was developed to be fast and physical-principles-based, in order to be able to represent current and possibly newly arising noise sources mechanisms in complex configurations. The tool-chain proposed relies on aerodynamic predictions based on Actuator Disc (AD) Reynolds Averaged Navier Stokes (RANS) computations that provide the background flow solution for the Computational Aeroacoustics (CAA) method, which considers Gaussian regularized line-source distributions of strengths defined from either the obtained AD surface loads solution, or tabulated aerodynamic data used in combination with a model based on Blade Element Momentum Theory (BEMT). In this work initial successful results are reported for simplified test cases, outlining future possible applications

Aeroacoustics research in Europe: The CEAS-ASC report on 2020 & 2021 highlights

The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on a European scale and European aeronautics activities internationally. In this context, “aeroacoustics” encompasses all aerospace acoustics and related areas. Each year the committee highlights some of the research and development projects in Europe. Due the effects of the Covid 19 pandemic it was not possible to publish an edition in 2021 and so this paper is a report on highlights of aeroacoustics research in Europe in both 2020 and 2021, compiled from information provided to the ASC of the CEAS. In addition, during 2020 and 2021, a number of research programmes involving aeroacoustics were funded by the European Commission. Some of the highlights from these programmes are also summarized in this article. Enquiries concerning all contributions should be addressed to the authors who are given at the end of each subsection