Inst. Strömungsmechanik und Technische Akustik (ISTA)

124 Items

Recent Submissions
The dynamics of volcanic jets

Cigala, V. ; Kueppers, U. ; Peña Fernández, J. J. ; Taddeucci, J. ; Sesterhenn, J. ; Dingwell, D. B. (2017-07-24)

Pyroclast ejection during explosive volcanic eruptions occurs under highly dynamic conditions involving great variations in flux, particle sizes, and velocities. This variability must be a direct consequence of complex interactions between physical and chemical parameters inside the volcanic plumbing system. The boundary conditions of such phenomena cannot be fully characterized via field obser...

Contact electrification in aerosolized monodispersed silica microspheres quantified using laser based velocimetry

Alois, Stefano ; Iversen, Jens Jacob ; Merrison, Jonathan ; Sesterhenn, Jörn (2017-04)

The contact electrification of aerosolized micro particles has been studied using a novel technique involving laser velocimetry. This has allowed the simultaneous determination of size and electrical charge of individual silica microspheres (in the range 1 – 8 µm). Interestingly the particles interacting with the injector tube have been seen to become electrified with a relatively narrow range ...

Investigation of the Global Mode in Swirling Combustor Flows: Experimental Observations and Local and Global Stability Analysis

Terhaar, Steffen ; Paredes, P. ; Oberleithner, Kilian ; Theofilis, V. ; Paschereit, Christian Oliver (2015)

Self-excited helical flow oscillations are frequently observed in gas turbine combustors. In the present work a new approach is presented tackling this phenomenon with stability concepts. Three reacting swirling flows are investigated. All of them undergo vortex breakdown, but only two of them show self-excited global flow oscillations at well-defined frequencies. The oscillations feature a pre...

Stability Analysis of Time-averaged Jet Flows: Fundamentals and Application

Oberleithner, Kilian ; Paschereit, Christian Oliver ; Soria, Julio (2015)

We report on experimental and theoretical investigations of shear flow instabilities in jet flows. Linear stability analysis is applied to the time-averaged flow taken from experiments, contrasting the ‘classic’ stability approach that is based on a stationary base flow. To some extend, mean flow stability eigenmodes may deal as a model for instability waves at their nonlinearly saturated state...

The compressible starting jet

Peña Fernández, Juan José (2018)

Jets are involved in numerous industrial applications and in nature: fuel injection, jet engines, volcanic jets, air-bag devices, but also water jet cutters, jet packs (rocket belts), jet injectors for vaccination, astrophysical jets, etc. Continuous jets have been already studied in the incompressible and compressible case for almost a century, focused mainly on the characterization of the flu...

Simulation und Analyse einer Verdichterkaskade mit aktiver Strömungsbeeinflussung

Gmelin, Christoph (2018)

Axiale Verdichter erreichen heutzutage sehr hohe Gesamtdruckverhältnisse, wozu eine hohe Anzahl von Verdichterstufen notwendig ist. Bei Flugtriebwerken stellt das Einsparen ganzer Stufen eine Möglichkeit dar, gleichzeitig das Gewicht und den Bauraum zu reduzieren. Für stationäre Gasturbinen wird der Teillastbetrieb mit steigendem Anteil an regenerativen Energien immer bedeutsamer. Beide Forderu...

Rotierende Instabilität in Axialverdichtern

Pardowitz, Benjamin (2018)

Die vorliegende Arbeit befasst sich mit der Identifikation und experimentellen Analyse von einem physikalischen Effekt der in Verbindung mit instationären Vorgängen in Turbomaschinen und vorwiegend an Axialverdichtern auftritt. Dieser Effekt wird als Rotierende Instabilität (RI) bezeichnet und im Rahmen dieser Arbeit sowohl an einer einzelnen Statorbeschaufelung, als auch an einer axialen Rotor...

Kreiselpumpe mit horizontalem Leistungsverlauf über dem Volumenstrom

Beck, Marcus Klaus (2018-03)

In der Doktorarbeit wurde der neuartige Ansatz verfolgt, eine Kreiselpumpe kleiner Baugröße mit einer Hydraulik zu entwickeln, welche bei Veränderung des Volumenstromes die Leistungsaufnahme der Pumpe konstant hält, so dass sich ein horizontaler Verlauf der elektrischen Leistungskennlinie über den gesamten Volumenstrombereich ergibt. Eine flache Leistungskurve ist für kleine Maschinen interessa...

Development of an aircraft noise emission model accounting for flight parameters

Zellmann, Christoph (2018)

Existing aircraft noise models are only partly suited for the assessment and optimization of noise abatement flight procedures. Either the models are too simplified, or are based on semi-empirical models which require ambitious flight parameters, or are not publicly available. In this thesis, an aircraft noise emission model for turbofan-powered aircraft was developed with the capability to tak...

Reduction in the run-up distance for the deflagration-to-detonation transition and applications to pulse detonation combustion

Gray, Joshua Allen Terry (2018)

Pressure-gain combustion has been a topic of research interest for severald ecades. Due to the potential of pressure-gain thermodynamic cycles of increasing gas turbine effciency by more than 10%, they offer a strategy to combat the growing problem of continually scarcer resources by simultaneous enforcement of ever stricter emissions controls. Furthermore, when hydrogen is used as a fuel, emis...

Experimental investigations of mixing characteristics in model rotating detonation engine geometries

Blümner, Richard ; Bohon, Myles D. ; Gutmark, Ephraim J. ; Paschereit, Christian Oliver (2017)

This work examines the mechanisms of reactant mixing in a model Rotating Detonation Engine (RDE) geometry. RDEs are emerging as one of the highest potential applications for achieving Pressure Gain Combustion (PGC). Reactant mixing has been identified as a crucial component of efficient RDE operation. Therefore, a scaled model of a typical RDE engine geometry was examined in a water tunnel usin...

Modern methods for investigating the stability of a pitching floating platform wind turbine

Lennie, Matthew ; Marten, David ; Pechlivanoglou, George ; Nayeri, Christian Navid ; Paschereit, Christian Oliver (2017)

The QBlade implementation of the lifting-line free vortex wake (LLFVW) method was tested in conditions analogous to floating platform motion. Comparisons against two independent test cases using a variety of simulation methods show good agreement in thrust forces, rotor power, blade forces and rotor plane induction. Along with the many verifications already undertaken in the literature, it seem...

Design parameters of vortex pumps

Gerlach, Angela ; Thamsen, Paul Uwe ; Wulff, Sebastian ; Brix Jacobsen, Christian (2017)

Vortex pumps can impel solid-containing fluids and are therefore widely applied, from wastewater transport to the food industry. Despite constant efforts to improve vortex pumps, however, they have remained relatively inefficient compared to conventional centrifugal pumps. To find an optimized design of vortex pumps, this paper provides a systematic analysis on experimental studies that investi...

Stochastisches Verfahren zur Simulation von Breitbandschall in Triebwerkfans

Wohlbrandt, Attila (2017)

Die vorliegende Arbeit beschäftigt sich mit der Anwendung des Random-Particle-Mesh-Verfahrens (RPM) zur Simulation von Fanbreitbandschall. Aus zeitgemittelten, turbulenten Größen erzeugt das Verfahren zeitabhängige Fluktuationen, die zur Vorhersage der Schallentstehung hinreichend sind. Es wird isotrope, freie Turbulenz in Form von divergenzfreien Geschwindigkeitsfluktuationen synthetisiert. D...

Flashback prevention in lean-premixed hydrogen combustion

Reichel, Thoralf G. (2017)

The focus of this study is the combustion of hydrogen in air as it relates to typical gas turbine engines. Hydrogen–air combustion occurs in the absence of any carbon-based emissions and the only combustion products are water vapor and oxides of nitrogen (NOx). However, due to the very low flammability limit of hydrogen, it can be burned at much lower equivalence ratios than typical hydrocarbon...

Recursive dynamic mode decomposition of transient and post-transient wake flows

Noack, Bernd R. ; Stankiewicz, Witold ; Morzyński, Marek ; Schmid, Peter J. (2016)

A novel data-driven modal decomposition of fluid flow is proposed, comprising key features of proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD). The first mode is the normalized real or imaginary part of the DMD mode that minimizes the time-averaged residual. The Nth mode is defined recursively in an analogous manner based on the residual of an expansion using the first...

Weakly nonlinear analysis of thermoacoustic instabilities in annular combustors

Ghirardo, G. ; Juniper, M. P. ; Moeck, Jonas P. (2016)

Rotationally symmetric annular combustors are of practical importance because they generically resemble combustion chambers in gas turbines, in which thermoacoustically driven oscillations are a major concern. We focus on azimuthal thermoacoustic oscillations and model the fluctuating heat release rate as being dependent only on the local pressure in the combustion chamber. We study the dynamic...

Airfoil in a high amplitude oscillating stream

Strangfeld, Christoph ; Müller-Vahl, Hanns ; Nayeri, Christian N. ; Paschereit, Christian Oliver ; Greenblatt, D. (2016)

A combined theoretical and experimental investigation was carried out with the objective of evaluating theoretical predictions relating to a two-dimensional airfoil subjected to high amplitude harmonic oscillation of the free stream at constant angle of attack. Current theoretical approaches were reviewed and extended for the purposes of quantifying the bound, unsteady vortex sheet strength alo...

Spectral proper orthogonal decomposition

Sieber, Moritz ; Paschereit, Christian Oliver ; Oberleithner, Kilian (2016)

The identification of coherent structures from experimental or numerical data is an essential task when conducting research in fluid dynamics. This typically involves the construction of an empirical mode base that appropriately captures the dominant flow structures. The most prominent candidates are the energy-ranked proper orthogonal decomposition (POD) and the frequency-ranked Fourier decomp...

On long-term boundedness of Galerkin models

Schlegel, Michael ; Noack, Bernd R. (2015)

We investigate linear–quadratic dynamical systems with energy-preserving quadratic terms. These systems arise for instance as Galerkin systems of incompressible flows. A criterion is presented to ensure long-term boundedness of the system dynamics. If the criterion is violated, a globally stable attractor cannot exist for an effective nonlinearity. Thus, the criterion can be considered a minimu...