| Autor(en) | Bernicke, Paul | Akkermans, Rinie | Bharadwaj Ananthan, Varun | Ewert, Roland | Rossian, Lennart | Dierke, Jürgen |
|---|---|
| Titel | Overset LES of a Solid and Porous NACA0012 Trailing Edge |
| Herausgeber | 24rd AIAA/CEAS Aeroacoustics Conference, AIAA 2018–3454, pp. 1-11, Atlanta, 2018 |
| Erscheinungsjahr | 2018 |
| Abstract | In this contribution, a hybrid zonal simulation tool with stochastic volume forcing for inflow turbulence generation is applied to trailing-edge noise computations of a NACA0012 airfoil. The governing equations constitute the non-linear perturbation Equations with viscous terms, i.e., the full Navier-Stokes equations which allows a perturbation analysis. Together with a suitable forcing of inflow turbulence, a hybrid RANS/LES method is established which leads to a significant reduction of the computational domain size to the region containing the sound sources itself. In case of trailing-edge noise this encloses the trailing-edge region. The seeding of inflow turbulence takes place where the upstream domain intersects with the airfoils boundary layer. Here, turbulence is generated with the aid of the Fast Random Particle-Mesh method and subsequently injected in the Overset-LES domain with the eddy-relaxation source term. Once the sound sources are captured, i.e., here in the form of the perturbed Lamb vector, it can be propagated into the far-field with a subsequent CAA-computation. In the present proceeding, simulations of a solid and porous NACA0012 trailing edge are presented. The numerical treatment of porous media by a volume-averaging approach is concisely described. A possible sound reduction by the application of porous materials compared to the solid NACA0012 is described by means of a single vortex convecting over the trailing edge. |
| Autor(en) | Delfs, Jan | Bertsch, Lothar | Zellman, Christoph | Rossian, Lennart | Far, Ehsan Kian | Ring, Tobias | Langer, Sabine C. | Rossian, Lennart | Rossian, Lennart |
|---|---|
| Titel | Aircraft Noise Assessment - From Single Components to Large Scenarios |
| Herausgeber | Energies 2018, 11(2), 429, doi:10.3390/en11020429 |
| Erscheinungsjahr | 2018 |
| Abstract | The strategic European paper “Flightpath 2050” claims dramatic reductions of noise for aviation transport scenarios in 2050: “. . . The perceived noise emission of flying aircraft is reduced by 65%. These are relative to the capabilities of typical new aircraft in 2000. . . ”. There is a consensus among experts that these far reaching objectives cannot be accomplished by application of noise reduction technologies at the level of aircraft components only. Comparably drastic claims simultaneously expressed in Flightpath 2050 for carbon dioxide and NOX reduction underline the need for step changes in aircraft technologies and aircraft configurations. New aircraft concepts with entirely different propulsion concepts will emerge, including unconventional power supplies from renewable energy sources, ranging from electric over hybrid to synthetic fuels. Given this foreseen revolution in aircraft technology the question arises, how the noise impact of these new aircraft may be assessed. Within the present contribution, a multi-level, multi-fidelity approach is proposed which enables aircraft noise assessment. It is composed by coupling noise prediction methods at three different levels of detail. On the first level, high fidelity methods for predicting the aeroacoustic behavior of aircraft components (and installations) are required since in the early stages of the development of innovative noise reduction technology test data is not available. The results are transferred to the second level, where radiation patterns of entire conventional and future aircraft concepts are assembled and noise emissions for single aircraft are computed. In the third level, large scale scenarios with many aircraft are considered to accurately predict the noise exposure for receivers on the ground. It is shown that reasonable predictions of the ground noise exposure level may be obtained. Furthermore, even though simplifications and omissions are introduced, it is shown that the method is capable of transferring all relevant physical aspects through the levels. |
| Autor(en) | Ewert, Roland | Ewert, Roland |
|---|---|
| Titel | Linear and Non-Linear Perturbation Equations with Relaxation Source Terms for Forced Eddy Simulation of Aeroacoustic Sound Generation |
| Herausgeber | 20th AIAA/CEAS Aeroacoustics Conference, Atlanta, USA, AIAA Paper 2016-3053 |
| Erscheinungsjahr | 2018 |
| Abstract | Turbulence related sound is generated by the dynamics of fluctuating vorticity. For example, trailing edge noise is caused by vorticity traveling past the trailing edge. To excite fluctuating vorticity by forcing the linearized Euler equations (LEE) with right-hand side source terms, one peculiar problem is observable: while the rise of vorticity levels by external sources poses no problem, to properly lower them, the right-hand side terms must act as a sink, being exactly in anti-phase to the vorticity levels as present in the LEE solution. However, the accurate prediction of vorticity in terms of phase cannot be guaranteed, especially for approximately modeled sources e.g. using stochastic methods. Thus in general there will be a mismatch between actual induced and intended levels of vorticity. In this paper a new class of relaxation source terms is introduced that enables the proper excitation of vorticity levels in linear and non-linear perturbation equations and as such enables an accurate control over the vorticity magnitudes. The source can be formulated to act selectively in wave-number space, i.e. without directly affecting the dynamics of resolved low wave-number vorticity components whereas the resolved high wave-number part is piloted by the fluctuating vorticity imposed as a reference solution. The reformulation of the Navier-Stokes equations in primitive variables and non-linear perturbation form is presented. Direct noise computation of sound radiated from a vortex shedding cylinder in laminar cross flow verify their implementation. The relaxation source term without forcing is applied to the unstable jet problem of the 4th CAA Workshop on Benchmark Problems. The forcing of frozen and decaying stochastic turbulence in conjunction with the relaxation source term is studied. First results for high-lift noise prediction with forced eddy simulation are presented. |
| Autor(en) | Faßmann, Benjamin | Rautmann, Christof | Ewert, Roland | Delfs, Jan |
|---|---|
| Titel | Efficient prediction of broadband trailing edge noise and application to porous edge treatment |
| Herausgeber | http://arxiv.org/abs/1810.02642 |
| Erscheinungsjahr | 2018 |
| Abstract | Trailing edge noise generated by turbulent flow traveling past an edge of an airfoil (TBL-TEN) represents one of the most essential paradigms of aeroacoustic sound generation at solid surfaces. It is of great interest for noise problems in various areas of technical application. First principle based Computational Aeroacoustics (CAA) methods with short response time are needed in the industrial design process for reliable prediction of spectral differences in TBL-TEN due to design modifications. In this work an aeroacoustic method is studied that rests on a hybrid two-step CFD/CAA procedure. In a first step Reynolds Averaged Navier-Stokes simulation provides the time-averaged solution to the turbulent flow, including the mean-flow and turbulence statistics such as length- and time-scales and turbulence kinetic energy. Fluctuating sound sources are stochastically generated from RANS statistics with the Fast Random Particle-Mesh Method (FRPM) 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 bandwidth of frequencies reaching 6 to 8dB reduction. Furthermore, sound reduction depends on the porous material parameters, e.g. geometry, porosity, permeability and pore size. This paper presents first results for the extended hybrid CFD/CAA method to include the effect on noise of porous materials with specifically prescribed parameters. To incorporate the effect of porosity, an extended formulation of the Acoustic Perturbation Equations (APE) 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. The reference solid airfoil configurations are compared with published experimental data. Convincing agreement in the prediction of one-third-octave band spectra is found. Simulation with porous edge treatment reveals a broadband noise reduction capability of approximately 6dB with similar trends as seen in experiment. |
| Autor(en) | Han, Zhong-hua | Mohammad, Abu-Zurayk | Stefan, Görtz | Caslav, Ilic |
|---|---|
| Titel | Surrogate-Based Aerodynamic Shape Optimization of a Wing-Body Transport Aircraft Configuration |
| Herausgeber | Notes on Numerical Fluid Mechanics and Multidisciplinary Design, Springer International Publishing, ISBN 978-3-319-72020-3, DOI: 10.1007/978-3-319-72020-3_16 |
| Erscheinungsjahr | 2018 |
| Abstract | Aerodynamic shape optimization driven by high-fidelity computational fluid dynamics (CFD) simulations is still challenging, especially for complex aircraft configurations. The main difficulty is not only associated with the extremely large computational cost, but also related to the complicated design space with many local optima and a large number of design variables. Therefore, development of efficient global optimization algorithms is still of great interest. This study focuses on demonstrating surrogate-based optimization (SBO) for a wing-body configuration representative of a modern civil transport aircraft parameterized with as many as 80 design variables, while most previous SBO studies were limited to rather simple configurations with fewer parameters. The freeform deformation (FFD) method is used to control the shape of the wing. A Reynolds-averaged Navier-Stokes (RANS) flow solver is used to compute the aerodynamic coefficients at a set of initial sample points. Kriging is used to build a surrogate model for the drag coefficient, which is to be minimized, based on the initial samples. The surrogate model is iteratively refined based on different sample infill strategies. For 80 design variables, the SBO-type optimizer is shown to converge to an optimal shape with lower drag based on about 300 samples. Several studies are conducted on the influence of the resolution of the computational grid, the number and randomness of the initial samples, and the number of design variables on the final result. |
| Autor(en) | Herr, Michaela | Ewert, Roland | Faßmann, Benjamin | Rautmann, Christof | Martens, Sabine | Rohardt, Claas-Hinrich | Suryadi, Alexandre |
|---|---|
| Titel | Noise Reduction Technologies for Wind Turbines |
| Herausgeber | Springer-series "Notes on Numerical Fluid Mechanics and Multidisciplinary Design", |
| Erscheinungsjahr | 2018 |
| Abstract | Results from a numerical and experimental aeroacoustic assessment of 2D wind turbine blade sections are presented. CFD/CAA-based predictions using a synthetic turbulence method were conducted at a NACA 64-618 profile as well as at a new low-noise airfoil design RoH-W-18%c37. Validation experiments were performed in DLR’s Acoustic Wind-Tunnel Braunschweig (AWB) for varying transition locations. A trailing-edge noise reduction benefit of 2–4 dB in overall sound pressure level was predicted for the new airfoil under design conditions. A large laminar extent of the boundary layer significantly reduces the noise emission (by up to 8 dB) compared to equivalent cases with forced transition at the leading edge. An additional noise reduction (with realistic reductions of the peak levels by 4–6 dB) was accomplished by flow-permeable trailing-edge extensions which were successfully transferred to the two profiles from forerunner aerospace-related studies. |
| Autor(en) | Rossian, Lennart | Suryadi, Alexandre | Rossignol, Karl-Stephane | Ewert, Roland | Herr, Michaela | Delfs, Jan | Kumar, Pradeep |
|---|---|
| Titel | Numerical and Experimental Insights into the Noise Generation of a Circulation Control Airfoil |
| Herausgeber | AIAA AVIATION Conference 2018, Atlanta, USA, Paper AIAA-2019-3139 |
| Erscheinungsjahr | 2018 |
| Abstract | With the advances in reduction of propulsion related noise from aircraft, airframe noise gets more and more into focus. During approach and landing, the high-lift system of the wings becomes one major acoustic source region contributing to the overall emitted noise. One promising approach to reduce this airframe noise is to change the complete high-lift system from a classic three element slat-wing-ap configuration to a slit-less system with active blowing and droop nose. Preceding experimental investigations have shown, that such a configuration may provide a noise reduction above 2 kHz on the model scale. In the present abstract both numerical and experimental investigations concerning the acoustics of a high-lift wing with droop nose and active blowing are presented. Thereby, an insight into the acoustic source mechanisms is provided that will serve as a basis for the design of a low-noise high-lift configuration in the future. |
| Autor(en) | Uphoff, Sonja | Krafczyk, Manfred | Kutscher, Konstantin | Rurkowska, Katherina | Langer, Sabine | Lippitz, Nicolas | Faßmann, Benjamin |
|---|---|
| Titel | A HIERARCHICAL APPROACH TO DETERMINING ACOUSTIC ABSORPTION PROPERTIES OF POROUS MEDIA COMBINING PORE-RESOLVED AND MACROSCOPIC MODELS |
| Herausgeber | Journal of Porous Media, Volume 21, Begell House, 83-100, 2018 |
| Erscheinungsjahr | 2018 |
| Abstract | Acoustic properties of porous media are very important for numerous industrial applications, the typical goal being to maximize broadband absorption to decrease the sound pressure level of the engineering system under consideration. Up to now acoustic absorption for porous media with complex inner geometry is determined experimentally, as acoustic simulations on the pore scale are computationally challenging due to the tedious geometric reconstruction of computer tomography (CT) data and the corresponding mesh generation as well as substantial computational requirements for the corresponding transient 3D solvers. The lattice Boltzmann method (LBM), which is an established computational approach to simulate pore-resolved porous media transport problems, has been used successfully for aeroacoustic setups and is utilized in this work to fill this gap. This paper presents a comparison of different experimental and numerical approaches to determine the acoustic absorption of different porous media. Experimental work with an impedance tube was carried out for comparison and CT scans were conducted to supply the detailed numerical simulation with geometry data of the porous samples. Results of LB simulations for the acoustic impedance of a microperforated plate and a felt are shown. Finally we demonstrate how microscopic parameters determined by a pore scale approach can be used to feed homogenized models to bridge the gap towards simulations of components where acoustic absorbers are applied to, e.g., wing flaps of airplanes. |
| Autor(en) | Delfs, Jan W. | Appel, Christina | Bernicke, Paul | Blech, Christopher | Blinstrub, Jason | Heykena, Constance | Kumar, Pradeep | Kutscher, Konstantin | Lippitz, Nicolas | Lummer, Markus | Rossian, Lennart | Savoni, Luciana | Delfs, Jan |
|---|---|
| Titel | Aircraft and technology for low noise short take-off and landing |
| Herausgeber | 35th AIAA Applied Aerodynamics Conference |
| Erscheinungsjahr | 2017 |
| Abstract | This paper discusses characteristic multi-disciplinary issues related to quiet short take-off and landing for civil transport aircraft with a typical short to medium range mission. The work reported here is focussing on the noise aspects and is embedded in the collaborative research centre CRC880 in Braunschweig, Germany. This long term aircraft research initiative focusses on a new transport aircraft segment for operation on airports with shorter runway length in commercial air transport. This calls for a community-friendly aircraft designed for operations much closer to the home of its passengers than today. This scenario sets challenging, seemingly contradictory aircraft technology requirements, namely those for extreme lift augmentation at low noise. The Research Centre CRC880 has therefore devised a range of technology projects that aim at significant noise reductions and at the generation of efficient and flexible high lift. The research also addresses flight dynamics of aircraft at takeoff and landing. Two companion papers, reporting about the research in the field of ”Efficient high lift” 1 and ”Flight dynamics” 2 complete the presentation of the CRC880. It is envisaged that in general significant noise reduction -compared to a reference turbofan driven aircraft of year 2000 technology- necessarily requires component noise reduction in combination with a low noise a/c concept. Results are presented from all the acoustics related projects of CRC880 which cover the aeroacoustic simulation of the source noise reduction by flow permeable materials, the characterization, development, manufacturing and operation of (porous) materials especially tailored to aeroacoustics, new UHBR turbofan arrangements for minimum exterior noise due to acoustic shielding as well as the prediction of jet noise vibration excitation of cabin noise by UHBR engines compared to conventional turbofans at cruise. |
| Autor(en) | Görtz, Stefan | Illic, Caslav | Jepsen, Jonas | Leitner, Martin | Schulze, Matthias | Schuster, Andreas | Scherer, Julian | Becker, Richard-Gregor | Zur, Sascha | Petsch, Michael |
|---|---|
| Titel | Multi-Level MDO of a Long-Range Transport Aircraft Using a Distributed Analysis Framework |
| Herausgeber | AIAA Paper 2017-4326, American Institute of Aeronautics and Astronautics, 18th AIAA/ISSMO Multidisciplinary Analysis and Optimization Conference |
| Erscheinungsjahr | 2017 |
| Abstract | DLR's work on developing a distributed collaborative MDO environment is presented. A multi-level Approach combining high-fidelity MDA for aerodynamics and structures with conceptual aircraft design methods is employed. Configuration-specific sizing loads are evaluated and used for sizing the structure. A gradient-free optimization algorithm is used to optimize the fuel burn of a generic long-range wide-body transport aircraft configuration with 9 shape parameters. The results show a truly multidisciplinary improvement of the modified design. The result of a gradient-free high-fidelity MDO with preselected load cases and five shape parameters is also presented, comparing a full mission analysis with results for the Breguet range equation. |
| Autor(en) | Rossian, Lennart | Ewert, Roland | Delfs, Jan |
|---|---|
| Titel | Prediction of Porous Trailing Edge Noise Rediction by Application of COmplex Porous Material |
| Herausgeber | New Results in Numerical and Experimental Fluid Mechanics XI, Springer Verlag, 2017, Pages 647-657 |
| Erscheinungsjahr | 2017 |
| Abstract | Reduction of noise generated at geometric edges can be achieved by replacing solid material with porous inlays. The acoustic benefit for airfoil trailing edge noise was experimentally found to yield a reduction in sound pressure level of approximately 6 dB. Numerical methods are of interest to find optimal properties of the porosity. A successful method of modeling porous materials is the volume-averaging approach. Prior simulations have been enhanced by implementing a modified numerical treatment of the interface between the free fluid and the porous parts to model the interaction of the acoustic and flow quantities in these two regimes. Furthermore, numerical simulations have been run to show the influence of an anisotropic, respectively non-uniform porous trailing edge on the emitted sound. |
| Autor(en) | Rossian, Lennart | Ewert, Roland | Delfs, Jan |
|---|---|
| Titel | Evaluation of Acoustic Jump Conditions at Discontinuous Porous Interfaces |
| Herausgeber | AIAA AVIATION 2017, Denver, Paper 2017-3505 |
| Erscheinungsjahr | 2017 |
| Abstract | Over the past years, the reduction of airfoil trailing edge noise has been addressed amongst others by the application of porous, permeable materials directly at the geometric edges, as these present a prominent noise source location. In experimental investigations, the beneficial influence of porous materials was found to be approximately 6 dB with a broadband nature. On the numerical side, with the approach of volume averaging a promising means to model complex porous materials has been found. Therewith, successful simulations have been run, that relate to experimental findings. In the following, an explicit modeling of the discontinuous interface between the porous material and the surrounding free flow by specific interface conditions was formulated. In the present paper an approach to evaluate different formulations of said interface conditions is presented and applied. The results are discussed concerning their physical background. Last, application simulations of a NACA0012 airfoil with solid and porous trailing edge are shown and compared to experimental data. |
| Autor(en) | Rossian, Lennart | Ewert, Roland | Jan, Delfs |
|---|---|
| Titel | Simulation von Hinterkantenlärm an Tragflügelprofilen mit porösen Elementen |
| Herausgeber | Jahrestagung für Akustik DAGA 2017 |
| Erscheinungsjahr | 2017 |
| Abstract | Mit der erfolgreichen Reduktion von Antriebslärm heutiger Verkehrsflugzeugen gewinnt Umströmungslärm eine immer größere Bedeutung. Dieser entsteht unter anderem durch die Interaktion der Wirbelstrukturen der turbulenten Grenzschicht mit der Hinterkante der Tragflügel. Zur Reduzierung dieser Lärmquelle werden verschiedene Ansätze verfolgt, unter anderem gezackte Hinterkanten, so genannte Serrations. Ein weiterer Ansatz besteht im Einsatz von strömungsdurchlässigen, porösen Materialien. Experimentelle Untersuchungen haben bereits gezeigt, dass mit porösen Metallen eine breitbandige Lärmreduktion erreicht werden kann. Bei der numerischen Modellierung solcher Materialien im DLR CAA-Code PIANO wird auf eine volumengemittelte Beschreibung mittels charakteristischer Materialparameter zurückgegriffen. Eine besondere Modellierung wird dabei für die Ränder des porösen Materials benötigt, da hier eine Unstetigkeit beim Übergang zwischen porösem Material und freier Umströmung vorliegt. Dafür wurden akustische Sprungbedingungen formuliert, die eine Umrechnung zwischen den beiden Bereichen ermöglichen. Mit diesen Methoden ist es möglich, den Einfluss von verschiedenen Materialparametern auf den erzeugten Lärm zu untersuchen. Von besonderem Interesse ist hierbei die Betrachtung von anisotropen und gradierten Materialien. |
| Autor(en) | Ewert, Roland |
|---|---|
| Titel | Canonical Stochastic Realization of Turbulent Sound Sources via Forced Linear Advection-Diffusion-Dissipation Equation |
| Herausgeber | 22nd AIAA/CEAS Aeroacoustic Conference, Lyon, 2016, Paper 2016-2965 |
| Erscheinungsjahr | 2016 |
| Abstract | Stochastic sound sources derived from Reynolds Averaged Navier-Stokes (RANS) solution are recognized in Computational Aeroacoustics as one possible way to effciently predict broadband sound. In this paper a stochastically forced linear advection-diffusion-dissipation equation is introduced. The model provides spectra and anisotropic two-point correlations that otherwise have to be incorporated in datum stochastic methods as additional model assumptions. The output are fluctuating velocity components, from which vortex sound sources derive. The forcing is white (delta-correlated) in time and possess a finite correlation length scale in space. The well-posedness is demonstrated in the paper. A solenoidal forcing term is shown to realize the correlation tensor of homogeneous isotropic turbulence together with a longitudinal turbulence spectrum that exhibits a plateau for lower frequencies followed by a characteristic power law roll-off and final cut-off. Exponent of decay and cut-off are adjustable. The stochastic partial differential equation involves a diffusion parameter, a time-scale, a re-distribution tensor, and a forcing variance. Transport equations for Reynolds stresses and turbulence kinetic energy derive from it that have the canonical form of major RANS transport equations. In particular, all parameters needed can be assigned to corresponding RANS parameters so that an accurate reproduction of RANS one-point statistics becomes feasible. For the generation of two-point statistics the hypothesis from turbulence modeling is adopted that the present model calibrated for homogeneous isotropic turbulence is also applicable for more general flows. |
| Autor(en) | Rossian, Lennart | Faßmann, Benjamin | Ewert, Roland | Delfs, Jan |
|---|---|
| Titel | Prediction of Porous Trailing Edge Noise Reduction Using Acoustic Jump-Conditions at Porous Interfaces |
| Herausgeber | 22nd AIAA/CEAS Aeroacoustic Conference, Lyon, 2016, Paper 2019-2920 |
| Erscheinungsjahr | 2016 |
| Abstract | Reduction of noise generated at geometric edges can be achieved by replacing solid material with porous inlays. The acoustic benefit for airfoil trailing edge noise was ex- perimentally found to yield a reduction in sound pressure level of approximately 6 dB. Numerical methods are of interest to and optimal properties of the porosity. A successful method of modeling porous materials is the Volume-Averaging approach. In prior simulations, the prediction of the sound reduction was comparable to measurements over a limited frequency range. This has been enhanced to obtain simulation results which show a better agreement with the experimental findings. At the interface between the free fluid and the porous parts jump conditions are required to model the interaction of the acoustic and flow quantities in these two regimes when it comes to nonhomogeneous materials. This paper presents the perturbation formulation of a set of jump conditions for Computational Aeroacoustics (CAA), already known from Computational Fluid Dynamics (CFD). For the numerical implementation, a high-order compact boundary scheme is derived. Furthermore, the description of complex anisotropic materials is pursued. In a hybrid two-step CAA/CFD procedure, the turbulence statistics from the corresponding solution of the Volume-Averaged Navier-Stokes-Equations (VANS) is used to trigger vortices generating turbulent-boundary-layer trailing-edge noise (TBL-TEN). |
| Autor(en) | Delfs, Jan | Faßmann, Benjamin | Lippitz, Nicolas | Mößner, Michael | Müller, Lars | Rurkowska, Katherina |
|---|---|
| Titel | SFB 880 – AEROACOUSTIC RESEARCH FOR LOW NOISE TAKE-OFF AND LANDING |
| Herausgeber | CEAS Aeronautical Journal |
| Erscheinungsjahr | 2014 |
| Abstract | This paper gives an overview about prediction capabilities and the development of noise reduction technologies appropriate to reduce high lift noise and propeller noise radiation for future low noise transport aircraft with short take-off and landing capabilities. The work is embedded in the collaborative research centre SFB880 in Braunschweig, Germany. Results are presented from all the acoustics related projects of SFB880 which cover the aeroacoustic simulation of the effect of flow permeable materials, the characterization, development, manufacturing and operation of (porous) materials especially tailored to aeroacoustics, new propeller arrangements for minimum exterior noise due to acoustic shielding as well as the prediction of vibration excitation of aircraft structures, reduced by porous materials. |
| Autor(en) | Ewert, Roland | Dierke, Jürgen | Neifeld, Andrej | Alavi Moghadam, Seyed Mohsen |
|---|---|
| Titel | Linear and Non-Linear Perturbation Equations with Relaxation Source Terms for Forced Eddy Simulation of Aeroacoustic Sound Generation |
| Herausgeber | 20th AIAA/CEAS Aeroacoustics Conference Atlanta, Georgia, 2014 |
| Erscheinungsjahr | 2014 |
| Abstract | Turbulence related sound is generated by the dynamics of fluctuating vorticity. For example, trailing edge noise is caused by vorticity traveling past the trailing edge. To excite fluctuating vorticity by forcing the linearized Euler equations (LEE) with right-hand side source terms, one peculiar problem is observable: while the rise of vorticity levels by external sources poses no problem, to properly lower them, the right-hand side terms must act as a sink, being exactly in anti-phase to the vorticity levels as present in the LEE solution. However, the accurate prediction of vorticity in terms of phase cannot be guaranteed, especially for approximately modeled sources e.g. using stochastic methods. Thus in general there will be a mismatch between actual induced and intended levels of vorticity. In this paper a new class of relaxation source terms is introduced that enables the proper excitation of vorticity levels in linear and non-linear perturbation equations and as such enables an accurate control over the vorticity magnitudes. The source can be formulated to act selectively in wave-number space, i.e. without directly affecting the dynamics of resolved low wave-number vorticity components whereas the resolved high wave number part is piloted by the uctuating vorticity imposed as a reference solution. The reformulation of the Navier-Stokes equations in primitive variables and non-linear perturbation form is presented. Direct noise computation of sound radiated from a vortex shedding cylinder in laminar cross flow verify their implementation. The relaxation source term without forcing is applied to the unstable jet problem of the 4th CAA Workshop on Benchmark Problems. The forcing of frozen and decaying stochastic turbulence in conjunction with the relaxation source term is studied. First results for high-lift noise prediction with forced eddy simulation are presented. |
| Autor(en) | Herr, Michaela | Rossignol, Karl-Stephane | Delfs, Jan | Lippitz, Nicolas | Mößner, Michael |
|---|---|
| Titel | Specification of Porous Materials for Low-Noise Trailing-Edge Applications |
| Herausgeber | 20th AIAA/CEAS Aeroacoustics Conference Atlanta, Georgia, 2014 |
| Erscheinungsjahr | 2014 |
| Abstract | Systematic testing of the microstructural and aeroacoustic properties of porous metals applicable as low-noise trailing-edge (TE) treatments has been initiated within the Collaborative Research Center SFB 880 Fundamentals of High-Lift for Future Civil Aircraft. Generic TE noise experiments were performed at Re = 800,000 to 1,200,000 in DLR's open-jet AWB facility. Complementary flow measurements in the closed test section MUB wind-tunnel of the TU Braunschweig served to quantify the induced aerodynamic effects. The presented database forms part of an ongoing cumulative effort, combining experimental and numerical methods, to gain a deeper understanding of the prevalent TE noise reduction mechanisms. For the large variety of porous materials tested herein a clear dependence of the achieved broadband noise reduction (reaching 2{6 dB at maximum) on the flow resistivity was identified. Basic design recommendations for material resistivity and pore sizes, the latter to minimize high-frequency self-noise contributions, were deduced for low-noise TE applications. An acoustic nearfield pressure release across the porous region, adversely coupled with a loss in lift performance for porous TE replacements, appears as the major noise-reduction requirement. |
| Autor(en) | Delfs, Jan |
|---|---|
| Titel | Anordnung eines Aerodynamischen Bauteils mit einer geschlitzten Hinter- oder Seitenkante in einer Strömung |
| Herausgeber | Deutsches Patent- und Markenamt 2010, Deutsches Patent DE10 2006 049 616 |
| Erscheinungsjahr | 2010 |
| Abstract | Die Erfindung bezieht sich auf ein aerodynamisches Bauteil mit einer turbulent überströmten Kante, an der zwei Hauptfläche des Bauteils aneinander stoßen und eine Strömung teilen oder zwei getrennte Teilströme zu einer Strömung zusammenführen, wobei das Bauteil im Bereich der Kante mit Schlitzen versehen ist. Bei der turbulent überströmten Kante handelt es sich insbesondere um eine Hinter- oder Abströmkante des aerodynamischen Bauteils, es kann sich aber auch um eine turbulent überströmte Seiten- oder sogar eine turbulent überströmte Vorder- oder Zuströmkante des Bauteils handeln. An der Kante stoßen zwei Hauptflächen des Bauteils aneinander. Bei diesen Hauptflächen handelt es sich in der Regel um eine Überdruckseite und eine Unterdruckseite des Bauteils. Die vorliegende Erfindung ist aber auch dann anwendbar, wenn keine Druckunterschiede vorliegen. Konkret geht es bei der vorliegenden Erfindung um die Minderung der Schallabstrahlung von aerodynamischen Bauteilen, bei denen Kanten turbulent überströmt werden. Unter einer Kante eines aerodynamischen Bauteils wird ein knickartiges Geometrieelement an dem umströmten aerodynamischen Bauteil verstanden, das scharfkantig, stumpf oder abgerundet sein kann und an dem zwei Hauptflächen des Bauteils derart aneinander stoßen, dass eine Strömung geteilt oder zwei getrennte Teilströme zu einer Strömung zusammengeführt werden. |