Inst. Strömungsmechanik und Technische Akustik (ISTA)

152 Items

Recent Submissions
Microphone Array Benchmark b11: Rotating Point Sources

Herold, Gert (2017-07-28)

This benchmark case is part of a collection of synthetic and experimental array data sets compiled by the microphone array community for testing and comparing different microphone array methods. It consists of two simulated data sets featuring rotating point sources in a resting medium. Sound pressure time data are generated at 64 microphones, which are arranged evenly on a circle. The data are...

Simulation and modeling of a Helmholtz resonator under grazing turbulent flow

Stein, Lewin (2019)

When gas flows along a surface containing a cavity or gap, this fluid-dynamical process is likely linked with acoustical effects. Primarily, in the transport and energy sector, the phenomenon occurs frequently: gas flows around land and air vehicles or streams inside duct systems and engines. A key challenge for these examples is either to prevent cavity noise before it arises or to reduce exis...

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...

Compressible starting jet: pinch-off and vortex ring–trailing jet interaction

Peña Fernández, Juan José ; Sesterhenn, Jörn (2017)

The dominant feature of the compressible starting jet is the interaction between the emerging vortex ring and the trailing jet. There are two types of interaction: the shock–shear layer–vortex interaction and the shear layer–vortex interaction. The former is clearly not present in the incompressible case, since there are no shocks. The shear layer–vortex interaction has been reported in the lit...

Statistics of fully turbulent impinging jets

Wilke, Robert ; Sesterhenn, Jörn (2017)

Direct numerical simulations (DNS) of subsonic and supersonic impinging jets with Reynolds numbers of 3300 and 8000 are carried out to analyse their statistical properties with respect to heat transfer. The Reynolds number range is at low or moderate values in terms of practical applications, but very high regarding the technical possibilities of DNS. A Reynolds number of 8000 is technically re...

Die akustischen Randbedingungen perforierter Wandauskleidungen in Strömungskanälen

Schulz, Anita (2019)

Perforierte, schallabsorbierende Wandauskleidungen werden vielfach in Strömungskanälen, z. B. Flugzeugtriebwerken, zur passiven Lärmminderung eingesetzt. Die komplizierte Wechselwirkung zwischen Schall und Strömung an der strukturierten schalldurchlässigen Wand findet in einer relativ dünnen Grenzschicht statt, so dass der Einfluss auf die Schallausbreitung in guter Näherung durch akustische Ra...

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...

Contact electrification in aerosolized micron-sized solid particles: dependence upon size, chemical composition and gas properties

Alois, Stefano (2018)

Contact electrification is ubiquitously present in our everyday life and acquires significant importance for micron scale particles, where it may be of considerable use in order to prevent/promote charging in a variety of practical applications. Despite being widely studied, a complete understanding of the charge transfer mechanisms is still lacking. In this work, contact electrification of ae...

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 ...

Experimental and numerical results of active flow control on a highly loaded stator cascade

Hecklau, Martin ; Gmelin, C. ; Nitsche, W. ; Thiele, F. ; Huppertz, A. ; Swoboda, M. (2011)

This article presents experimental and numerical results for a compressor cascade with active flow control. Steady and pulsed blowing has been used to control the secondary flow and separation characteristics of a highly loaded controlled diffusion airfoil. Investigations were performed at the design incidence for blowing ratios from approximately 0.7 to 3.0 (jet-to-inlet velocity) and a Reynol...

Time domain modelling and stability analysis of complex thermoacoustic systems

Bothien, Mirko R. ; Moeck, Jonas P. ; Lacarelle, Arnaud ; Paschereit, Christian Oliver (2007)

A methodology allowing for a modular setup of complex acoustic systems is developed. The transfer behaviour of the individual subsystems is formulated in time domain. Subsystem descriptions can be obtained by analytical considerations, numerical methods, or experimental data. Once the complex subsystems have been characterized experimentally, changes in system geometry can be implemented easily...

Kennliniencharakteristik von Diagonalventilatoren mit modifizierter Meridiankontur

Treder, Anne (2018)

Die Durchströmungsrichtung im Laufrad klassifiziert Ventilatoren in die axiale, diagonale und radiale Bauform. Axial- und Radialventilatoren sind in einer Vielzahl unterschiedlicher Formen auf dem Markt vertreten. Für große Volumenströme sind Axialventilatoren bevorzugt einzusetzen, Radialventilatoren sind hingegen für große erforderliche Druckerhöhungen geeignet. Wenn die Anforderungen an den ...

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...

Untersuchung einer neuen Herzklappe für Herzunterstützungssysteme

Lambertz, M. ; Affeld, K. ; Ziemann, A. (1998)

Ein bewährtes Verfahren zur Behandlung erkrankter natürlicher Heizklappen ist die Implantation von Heizklappenprothesen. Neben diesem Einsatz entwickelt sich zur Zeit ein weiteres Anwendungsgebiet; der Einsatz von Herzklappenprothesen in Herzunterstützungssystemen. Eine häufig dabei auftretende Komplikation stellt die Thrombenbildung dar. Diese tritt insbesondere im Bereich der verwendeten Herz...

On the Potential of Power Generation from Thermoelectric Generators in Gas Turbine Combustors

Stathopoulos, Panagiotis ; Fernàndez-Villa, Javier (2018-10-16)

Thermoelectric generators (TEGs) offer an attractive power generation option. They have no moving parts, are robust and emit no pollutants. The current work explores the integration of high temperature TEGs in gas turbine combustors. The latter have a thermal shield at their inner surface to protect them against high temperatures. This is supplemented by convective and film cooling. This work s...

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...