Inst. Strömungsmechanik und Technische Akustik (ISTA)

115 Items

Recent Submissions
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, C. 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, C. 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...

Mean flow stability analysis of oscillating jet experiments

Oberleithner, Kilian ; Rukes, Lothar ; Soria, Julio (2014)

Linear stability analysis (LSA) is applied to the mean flow of an oscillating round jet with the aim of investigating the robustness and accuracy of mean flow stability wave models. The jet’s axisymmetric mode is excited at the nozzle lip through a sinusoidal modulation of the flow rate at amplitudes ranging from 0.1 % to 100 %. The instantaneous flow field is measured via particle image veloci...

On the impact of swirl on the growth of coherent structures

Oberleithner, Kilian ; Paschereit, C. Oliver ; Wygnanski, I. (2014)

Spatial linear stability analysis is applied to the mean flow of a turbulent swirling jet at swirl intensities below the onset of vortex breakdown. The aim of this work is to predict the dominant coherent flow structure, their driving instabilities and how they are affected by swirl. At the nozzle exit, the swirling jet promotes shear instabilities and, less unstable, centrifugal instabilities....

Simulations of turbulent channels with prescribed velocity profiles

Tuerke, Florian ; Jiménez, Javier (2013)

Direct numerical simulations of turbulent channels with artificially prescribed velocity profiles are discussed, using both natural and purposely incorrect profiles. It is found that turbulence develops correctly when natural profiles are prescribed, but that even slightly incorrect ones modify the Reynolds stresses substantially. That is used to study the dynamics of the energy-containing velo...

On least-order flow representations for aerodynamics and aeroacoustics

Schlegel, Michael ; Noack, Bernd R. ; Jordan, Peter ; Dillmann, Andreas ; Gröschel, Elmar ; Schröder, Wolfgang ; Wei, Mingjun ; Freund, Jonathan B. ; Lehmann, Oliver ; Tadmor, Gilead (2012)

We propose a generalization of proper orthogonal decomposition (POD) for optimal flow resolution of linearly related observables. This Galerkin expansion, termed ‘observable inferred decomposition’ (OID), addresses a need in aerodynamic and aeroacoustic applications by identifying the modes contributing most to these observables. Thus, OID constitutes a building block for physical understanding...

Numerical simulation of a regional train in cross-wind

Eichinger, Sándor ; Sima, Mikael ; Thiele, Frank (2015)

In this work numerical investigations of regional trains were carried out studying the prediction accuracy of the aerodynamic load in cross-wind assessment of rail vehicles. The main focus is on 30° yaw angle. Two domain setups, one representing the wind tunnel setup and another more generic one, were investigated and validated against available measurements comparing load coefficients. Importa...

The impinging jet

Wilke, Robert (2017)

The internal cooling of turbine blades and vertical take off and landing aircraft engines are just two of many examples where impinging jets are used. In order to save global resources, an increase of cooling efficiency is wanted. Therefore, enormous research activities have been and are presently being carried out with respect to impinging jets. Despite substantial advances within the last dec...

Ein Mikrofonarray-Verfahren zur Untersuchung der Schallabstrahlung von Turbofantriebwerken

Funke, Stefan (2017)

Diese Arbeit zeigt die Entwicklung und die Validierung eines Mikrofonarray-Verfahrens, mit dem erstmals die Untersuchung der gerichteten Schallabstrahlung von Turbofantriebwerken und die Trennung der Schallfeldanteile des Einlaufs, der Düse(n) und des Strahls möglich ist. Das inverse Verfahren mit dem Namen SODIX (source directivity modeling in the cross-spectral matrix) reproduziert die Kreuzs...

On the response of a generic swirl flame to transverse planar acoustics

Saurabh, Aditya (2017)

Heat release rate fluctuations are invariably generated at flames under the influence of acoustic and/or hydrodynamics fluctuations. At the same time, heat release rate fluctuations support acoustic fluctuations, such that, when flames are placed in a confined environment (as is usually the case in practical applications driven by combustion), a feedback loop may establish between heat release ...

Aufbau und Validierung eines laseroptischen Normal-Durchfluss-Messgeräts für die metrologische Rückführung einer Hochtemperatur-Prüfanlage

Steinbock, Jonas Johannes (2017)

Die klassischen gravimetrischen oder volumetrischen Methoden zur Kalibrierung von Durchflussmessgeräten sind aufgrund ihrer drucklosen Ausführung in ihrer Anwendung für das Medium Wasser auf Temperaturen unter 100 °C beschränkt. Eine Kalibrierung unter Prozessbedingungen ist daher zum Beispiel für Anwendungen in der Kraftwerkstechnik nicht möglich. Zur Ausweitung des metrologisch abgesicherten ...