FG Experimentelle Strömungsmechanik

12 Items

Recent Submissions
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...

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...

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...

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, Christian 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....

Development of a swirl-stabilized H2/O2 combustion system under humidified conditions

Tanneberger, Tom ; Schimek, Sebastian ; Kossatz, Max ; Paschereit, Christian Oliver ; Stathopoulos, Panagiotis (2017-04-19)

The use of renewable energy sources raises the demand of fast and flexible storage techniques as well as fast power availability. A promising storage approach is the production of hydrogen and oxygen by electrolysis, which could be burned under humidified, stoichiometric conditions in a steam cycle. In this way the gases are re-electrified to provide balancing of renewable energy production or ...