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Large Eddy Simulation Turbulenter Str Mungen

Author: Jochen Fröhlich
Publisher: Springer-Verlag
ISBN: 9783835101043
Size: 39.52 MB
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Die Large Eddy Simulation (LES) ist eine Methode zur Modellierung und Berechnung turbulenter Strömungen. Insbesondere für den praxisrelevanten Fall hoher Reynoldszahlen besitzt sie Vorteile gegenüber anderen Verfahren und findet in den letzten Jahren sehr schnell Verbreitung. Das Buch motiviert den Ansatz auf der Basis physikalischer Grundlagen. Alle Modelltypen, die in derartigen Simulationen auftreten, werden detailiert erläutert und vergleichend diskutiert. Anhand verschiedener Anwendungsbeispiele werden typische Resultate diskutiert und unterschiedliche Techniken zur Auswertung der gewonnenen Daten vorgestellt.

Numerische Simulation Des Ger Usches Massiv Abgel Ster Str Mung Bei Gro Er Reynoldszahl Und Kleiner Machzahl

Author: Knacke, Thilo
Publisher: Universitätsverlag der TU Berlin
ISBN: 3798327351
Size: 43.30 MB
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Strömungsinduzierte Geräusche stellen heute ein zunehmendes Problem dar, besonders in der Umgebung von Flughäfen. Eine flächendeckende Lärmminderung ließe sich hier in erster Linie durch konstruktive Maßnahmen zur Abschwächung der wesentlichen Schallentstehungsmechanismen am Flugzeug erzielen. Dies setzt jedoch voraus, dass verlässliche aeroakustische Vorhersagen getroffen werden können, wozu nicht nur präzise Berechnungsverfahren für die Schallausbreitung, sondern auch für das mittlere Strömungsfeld und für die aerodynamischen Geräuschquellen erforderlich sind. In der vorliegenden Arbeit wird ein im Bereich subsonischer Strömungssimulationen etabliertes, druckbasiertes 3D-Finite-Volumen-Verfahren für den Einsatz in aeroakustischen Grobstruktursimulationen weiterentwickelt. Der hier vordergründig betrachtete Strömungszustand und Kennzahlbereich ist typisch für das Entstehen von „airframe noise“, aerodynamischem Lärm, welcher primär durch die turbulente Umströmung von Fahrwerk und Hochauftriebshilfen startender oder landender Flugzeuge verursacht wird. Die Kopplung von kompressiblen Grobstruktursimulationen im Quellgebiet mit nachgeschalteten akustischen Extrapolationen ermöglicht eine Berechnung dieser Umströmungsgeräusche bis ins Fernfeld. Nach kurzer Darstellung der physikalischen Grundlagen und verschiedener Möglichkeiten zur numerischen Simulation wird das ausgewählte Verfahren im Detail analysiert und eine Schwachstelle in der zur Berechnung der Massenflüsse eingesetzten Interpolation nach Rhie & Chow identifiziert. Der Schwerpunkt der Weiterentwicklung liegt anschließend auf der sorgfältigen Herleitung einer Familie konsistenter Approximationen zur Bestimmung von Massenflüssen über Kontrollvolumengrenzflächen auf nichtversetzten Gittern. Zwei neue Varianten der Massenflussberechnung werden in das bestehende Druckkorrekturverfahren integriert. Deren Verhalten wird im Vergleich zur ursprünglichen Implementierung an einem akademischen Testfall bewertet. Es folgt eine Abstimmung von Numerik und Feinstrukturmodell am Zerfall isotroper Turbulenz und nach der Qualifizierung des verbesserten Verfahrens schließlich dessen Anwendung zur Berechnung von Strömungsgeräuschen an einer generischen Fahrwerksverstrebung und an einer 3-Komponenten-Hochauftriebskonfiguration. Die Ergebnisse dieser Simulationen weisen überwiegend eine sehr gute Übereinstimmung mit experimentell ermittelten Daten auf. Auf Basis einer aeroakustischen Analyse der hochaufgelösten Simulationsergebnisse am Vorflügel gelingt letztlich ein statistischer Nachweis für den dort dominierenden Schallentstehungsmechanismus. Flow-induced noise represents an increasing problem today, particularly in the vicinity of airports. Comprehensive aircraft noise reduction could primarily be achieved through design changes which mitigate the major noise generation mechanisms. However, such changes require reliable aeroacoustic predictions, which is only possible if appropriate numerical tools are available. These must allow the precise calculation of the sound and mean flow fields as well as the most relevant aerodynamic noise sources. In this work a pressure-based 3D finite volume method, which is already well-established in the area of subsonic flow computation, is further developed in order to enable its application for aeroacoustic large-eddy simulations. The flow state and the range of similarity parameters considered here are chosen to be representative of typical airframe noise. This is mainly caused by separated flow around deployed landing gear and high-lift devices during aircraft takeoff and landing. The coupling of compressible large-eddy simulations in the main sound source regions with subsequent acoustic extrapolations provides access to the prediction of such aerodynamic noise up to the farfield. The selected method is analysed in detail following a brief overview of the physical background and state-of-the-art numerical simulation techniques. A weak point is identified in the Rhie & Chow interpolation which is employed for the calculation of mass fluxes. Particular emphasis is then placed on the careful derivation of a family of consistent approximations for the determination of mass flux over control volume faces on co-located grids. Two new flux formulations are integrated into the existing pressure correction method. Their behaviour is validated and compared to that of the original implementation on an academic test case. Following a thorough reassessment of the balance between numerical and modelled dissipation on the decay of isotropic turbulence, the improved method is finally applied to compute the flow-induced noise around a generic two-struts configuration and around a three-component high-lift configuration. The simulation results predominantly exhibit very good agreement with experimental data. Based on highly-resolved flow field data acquired from the simulation of the high-lift system, a concise aeroacoustic analysis is offered. Statistical evidence of the dominant noise generation mechanism near a leading edge slat is provided.

Desider A European Effort On Hybrid Rans Les Modelling

Author: Werner Haase
Publisher: Springer Science & Business Media
ISBN: 3540927735
Size: 46.73 MB
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Preface “In aircraft design, efficiency is determined by the ability to accurately and rel- bly predict the occurrence of, and to model the development of, turbulent flows. Hence, the main objective in industrial computational fluid dynamics (CFD) is to increase the capabilities for an improved predictive accuracy for both complex flows and complex geometries”. This text part taken from Haase et al (2006), - scribing the results of the DESider predecessor project “FLOMANIA” is still - and will be in future valid. With an ever-increasing demand for faster, more reliable and cleaner aircraft, flight envelopes are necessarily shifted into areas of the flow regimes exhibiting highly unsteady and, for military aircraft, unstable flow behaviour. This undou- edly poses major new challenges in CFD; generally stated as an increased pred- tive accuracy whist retaining “affordable” computation times. Together with highly resolved meshes employing millions of nodes, numerical methods must have the inherent capability to predict unsteady flows. Although at present, (U)RANS methods are likely to remain as the workhorses in industry, the DESider project focussed on the development and combination of these approaches with LES methods in order to “bridge” the gap between the much more expensive (due to high Reynolds numbers in flight), but more accurate (full) LES.

Progress In Hybrid Rans Les Modelling

Author: Shia-Hui Peng
Publisher: Springer Science & Business Media
ISBN: 9783642141683
Size: 58.31 MB
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Hybrid modelling of turbulent flows, combining RANS and LES techniques, has received increasing attention over the past decade to fill the gap between (U)RANS and LES computations in aerodynamic applications at industrially relevant Reynolds numbers. With the advantage of hybrid RANS-LES modelling approaches, being considerably more computationally efficient than full LES and more accurate than (U)RANS, particularly for unsteady aerodynamic flows, has motivated numerous research and development activities. These activities have been increasingly stimulated by the provision of modern computing facilities. The present book contains the contributions presented at the Third Symposium on Hybrid RANS-LES Methods, held in Gdansk, Poland, 10-12 June 2009. To a certain extent, this conference was a continuation of the first symposium taking place in Stockholm (Sweden, 2005) and the second in Corfu (Greece, 2007). Motivated by the extensive interest in the research community, the papers presented at the Corfu symposium were published by Springer in the book entitled “Advances in Hybrid RANS-LES Modelling” (in Notes on Numerical Fluid Mechanics and Multidisciplinary Design, Vol. 97). At the Gdansk symposium, along with four invited keynotes, given respectively by S. Fu, U. Michel, M. Sillen and P. Spalart, another 28 papers were presented on the following topics: Unsteady RANS, LES, Improved DES Methods, Hybrid RANS-LES Methods, DES versus URANS and other Hybrid Methods, Modelli- related Numerical Issues and Industrial Applications. After the symposium all full papers have been further reviewed and revised for publication in the present book.

Advances In Les Of Complex Flows

Author: Rainer Friedrich
Publisher: Springer Science & Business Media
ISBN: 0306483831
Size: 63.61 MB
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The articles focus on new developments in the field of large-eddy simulation of complex flows and are related to the topics: modelling and analysis of subgrid scales, numerical issues in LES cartesian grids for complex geometries, curvilinear and non-structured grids for complex geometries. DES and RANS-LES coupling, aircraft wake vortices, combustion and magnetohydrodynamics. Progress has been made not only in understanding and modelling the dynamics of unresolved scales, but also in designing means that prevent the contamination of LES predictions by discretization errors. Progress is reported as well on the use of cartesian and curvilinear coordinates to compute flow in and around complex geometries and in the field of LES with unstructured grids. A chapter is dedicated to the detached-eddy simulation technique and its recent achievements and to the promising technique of coupling RANS and LES solutions in order to push the resolution-based Reynolds number limit of wall-resolving LES to higher values. Complexity due to physical mechanisms links the last two chapters. It is shown that LES constitutes the tool to analyse the physics of aircraft wake vortices during landing and takeoff. Its thorough understanding is a prerequisite for reliable predictions of the distance between consecutive landing airplanes. Subgrid combustion modelling for LES of single and two-phase reacting flows is demonstrated to have the potential to deal with finite-rate kinetics in high Reynolds number flows of full-scale gas turbine engines. Fluctuating magnetic fields are more reliably predicted by LES when tensor-diffusivity rather than gradient-diffusion models are used. An encouraging result in the context of turbulence control by magnetic fields.

Aiaa Journal

Author: American Institute of Aeronautics and Astronautics
Publisher:
ISBN:
Size: 33.93 MB
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