FG Experimentelle Strömungsmechanik

25 Items

Recent Submissions
Sparse reduced-order modelling: sensor-based dynamics to full-state estimation

Loiseau, Jean-Christophe ; Noack, Bernd R. ; Brunton, Steven L. (2018-04-06)

We propose a general dynamic reduced-order modelling framework for typical experimental data: time-resolved sensor data and optional non-time-resolved particle image velocimetry (PIV) snapshots. This framework can be decomposed into four building blocks. First, the sensor signals are lifted to a dynamic feature space without false neighbours. Second, we identify a sparse human-interpretable non...

The interaction between a spatially oscillating jet emitted by a fluidic oscillator and a cross-flow

Ostermann, Florian ; Woszidlo, Rene ; Nayeri, Christian Navid ; Paschereit, Christian Oliver (2019)

This experimental study investigates the fundamental flow field of a spatially oscillating jet emitted by a fluidic oscillator into an attached cross-flow. Dominant flow structures, such as the jet trajectory and dynamics of streamwise vortices, are discussed in detail with the aim of understanding the interaction between the spatially oscillating jet and the cross-flow. The oscillating jet is ...

Properties of a sweeping jet emitted from a fluidic oscillator

Ostermann, Florian ; Woszidlo, Rene ; Nayeri, Christian Navid ; Paschereit, Christian Oliver (2018)

This experimental study investigates the flow field and properties of a sweeping jet emitted from a fluidic oscillator into a quiescent environment. The aspect ratio of the outlet throat is 1. Stereoscopic particle image velocimetry is employed to measure the velocity field plane-by-plane. Simultaneously acquired pressure measurements provide a reference for phase correlating the individual pla...

The time-resolved natural flow field of a fluidic oscillator

Woszidlo, Rene ; Ostermann, Florian ; Nayeri, Christian Navid ; Paschereit, Christian Oliver (2015)

The internal and external flow field of a fluidic oscillator with two feedback channels are examined experimentally within the incompressible flow regime. A scaled-up device with a square outlet nozzle is supplied with pressurized air and emits a spatially oscillating jet into quiescent environment. Time-resolved information are obtained by phase-averaging pressure and PIV data based on an inte...

Phase-Averaging Methods for the Natural Flowfield of a Fluidic Oscillator

Ostermann, Florian ; Woszidlo, Rene ; Nayeri, Christian Navid ; Paschereit, Christian Oliver (2015)

The presented study examines various methods for phase averaging the naturally oscillating flowfield of a scaled-up fluidic oscillator. No external trigger is employed to control the oscillation of the flow. Mathematical and signal conditioning approaches for phase averaging the data are categorized and described. The results of these methods are evaluated for their accuracy in capturing the na...

Active control of the aerodynamic performance and tonal noise of axial turbomachines

Neuhaus, L. ; Schulz, J. ; Neise, W. ; Möser, M. (2003)

Two projects on axial fans are presented in this paper. The first aims at improving the aerodynamic performance and reducing the tip clearance noise caused by the rotating instability. This is achieved by injecting air into the radial gap between the impeller blade tips and the fan casing. Steady air injection with small mass flows results in remarkable reductions in the noise level along with ...

Measurement and modeling of the generation and the transport of entropy waves in a model gas turbine combustor

Wassmer, Dominik ; Schuermans, Bruno ; Paschereit, Christian Oliver ; Moeck, Jonas P. (2017)

Indirect combustion noise is caused by entropy spots that are accelerated at the first turbine stage. These so-called entropy waves originate from the equivalence ratio fluctuations in the air–fuel mixture upstream of the flame. As entropy waves propagate convectively through the combustion chamber, they are subject to diffusion and dispersion. Because of the inherent difficulty of accurately m...

An acoustic time-of-flight technique for unsteady temperature measurements in combustion chambers

Waßmer, Dominik (2018)

In consideration of the manifold alternative electric energy sources, load flexibility in modern gas turbines is an essential requirement. To this end, the operational range of the engines must be extended. However, this is often impeded by low-frequency combustion instabilities that are associated with acoustics generated within the gas turbine combustor. These high-amplitude pressure oscillat...

Modification of a high pressure test rig for thermoacoustic measurements

Niether, Sebastian (2018)

Current stationary gas turbines for power generation rely on lean premixed combustion, in order to achieve low emissions of detrimental exhaust gases, such as NOx. However, employment of this combustion process can lead to the occurrence of thermoacoustic instabilities. Characterized by strong pressure fluctuations inside the combustion chamber, this phenomenon has negative effects on exhaust g...

Experimental Three-Dimensional Velocity Data of a Sweeping Jet from a Fluidic Oscillator

Ostermann, Florian ; Woszidlo, Rene ; Nayeri, Christian Navid ; Paschereit, Christian Oliver (2018-09-28)

The dataset contains three-dimensional, quasi time-resolved velocity field of a sweeping jet from a fluidic oscillator. The data is acquired experimentally at the Technische Universität Berlin by employing a traversable stereoscopic particle image velocimetry system. The presented data served as the basis for several publications. Detailed information on the scientific background, the associate...

Experimental Three-Dimensional Velocity Data of a Sweeping Jet from a Fluidic Oscillator Interacting with a Crossflow

Ostermann, Florian ; Woszidlo, Rene ; Nayeri, Christian Navid ; Paschreit, Christian Oliver (2018-09-28)

The dataset contains three-dimensional, quasi time-resolved velocity fields of the complex flow field that is caused by a sweeping jet from a fluidic oscillator interacting with an attached turbulent crossflow. The data is acquired experimentally at the Technische Universität Berlin by employing a traversable stereoscopic particle image velocimetry system. The presented data served as the basis...

Drag reduction of a bluff body model in water and air

Schmidt, Hanns-Joachim (2018)

The presented work describes and discusses the results of wind tunnel and towing tank experiments carried out on a rectangular bluff body model equipped with base flaps as passive and fluidic oscillators as active means for drag reduction. The geometry of the model is based on the Generic European Transport System (GETS) which is similar to a 10 % scaled truck trailer combination without any ge...

Fundamental properties of a spatially oscillating jet emitted by a fluidic oscillator

Ostermann, Florian (2018)

A jet is a fundamental flow scenario underlying several technical applications. Recently, spatially oscillating jets emitted by fluidic oscillators are employed to enhance mixing or control separation. Fluidic oscillators are able to emit a jet that spatially oscillates within a plane. Although their efficacy has been proven for many applications, the reasons for their performance remain unknow...

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...