Inst. Strömungsmechanik und Technische Akustik (ISTA)

165 Items

Recent Submissions
Operating mode dynamics in rotating detonation combustors

Blümner, Richard (2020)

Druckerhöhende Verbrennung (engl. Pressure Gain Combustion, PGC) gilt als Schlüsseltechnologie zur Erschließung einer signifikanten Effizienzsteigerung in technischen Verbrennungssystemen. Auf dem derzeitigen Entwicklungsstand stellen Brenner mit kontinuierlich umlaufender Detonationswelle (engl. Rotating Detonation Combustors, RDCs) eines der vielversprechendsten Konzepte für die Realisierung ...

Untersuchung der Wirksamkeit der Schülerlabore an der Technischen Universität Berlin

Derda, Mareen (2020)

Die vorliegende publikationsbasierte Dissertation beinhaltet vier Aufsätze, die entweder bereits angenommen und im Druck sind oder derzeit in Peer-Review-Verfahren begutachtet werden. Diese vier Manuskripte, die teils ähnliche teils thematisch verwandte Forschungsfragen behandeln, werden von einer Einführung in das Thema der Arbeit und einer Gesamtdiskussion gerahmt. Das Dissertationsprojekt u...

Wake Structures and Surface Patterns of the DrivAer Notchback Car Model under Side Wind Conditions

Wieser, Dirk ; Nayeri, Christian Navid ; Paschereit, Christian Oliver (2020-01-09)

The flow field topology of passenger cars considerably changes under side wind conditions. This changes the surface pressure, aerodynamic force, and drag and performance of a vehicle. In this study, the flow field of a generic passenger vehicle is investigated based on three different side wind angles. The study aimed to identify vortical structures causing changes in the rear pressure distribu...

Akustischer Kohärenzverlust in offenen Windkanälen aufgrund der turbulenten Scherschicht

Ernst, Daniel (2020)

Die vorliegende Arbeit beschäftigt sich mit dem Kohärenzverlust von akustischen Wellen durch eine turbulente Scherschicht. Dieser Kohärenzverlust führt in aeroakustischen Windkanälen dazu, dass die Kohärenzen von Mikrofonpaaren außerhalb der Strömung mit steigendem Abstand, steigender Frequenz und steigender Strömungsgeschwindigkeit absinken. Bei Mikrofonarraymessungen, die mithilfe von Beamfor...

Heat metering with glycol-water-mixtures

Baack, Sebastian (2020)

Due to its physical properties, glycol-water-mixtures cause typical heat meters to measure with increased deviations. Both the volume flow measurement and the fluid’s heat coefficient are affected. For the determination of the exchanged energy, for example in cooling or solar thermal installations, heat meters which are suitable for commonly used glycol-based heat conveying media are necessary....

Data Mining to Uncover Heterogeneous Water Use Behaviors From Smart Meter Data

Cominola, Andrea ; Nguyen, K. ; Giuliani, Matteo ; Stewart, Rodney A. ; Maier, Holger R. ; Castelletti, Andrea (2019-11-19)

Knowledge on the determinants and patterns of water demand for different consumers supports the design of customized demand management strategies. Smart meters coupled with big data analytics tools create a unique opportunity to support such strategies. Yet, at present, the information content of smart meter data is not fully mined and usually needs to be complemented with water fixture invento...

Causes, effects and solutions of operational problems in wastewater systems due to nonwoven wet wipes

Mitchell, Raja-Louisa (2019)

Operational problems due to sewer system incompatible nonwoven wipes in wastewater systems affect nearly all wastewater system operators in regions where nonwoven wipes are used as convenience products. They disrupt the operation of the critical infrastructure, cause equipment failures, and large additional expenditures. To date, however, there is no agreement as to which nonwoven wet wipes are...

Maximum Entropy Analysis of Flow Networks: Theoretical Foundation and Applications

Niven, Robert K. ; Abel, Markus ; Schlegel, Michael ; Waldrip, Steven H. (2019-08-08)

The concept of a “flow network”—a set of nodes and links which carries one or more flows—unites many different disciplines, including pipe flow, fluid flow, electrical, chemical reaction, ecological, epidemiological, neurological, communications, transportation, financial, economic and human social networks. This Feature Paper presents a generalized maximum entropy framework to infer the state ...

Aeroacoustic transfer of leading edge serrations from single aerofoils to low-pressure fan applications

Biedermann, Till (2019)

Leading edge serrations are well-known for their aeroacoustic potential in reducing aerofoil-turbulence interaction noise and are also associated with certain aerodynamic advantages. To prepare leading edge serrations for industrial application, two obstacles remain to be addressed. First is a combined analysis of the aeroacoustic and the aerodynamic performance of leading edge serrations to de...

Efficient computation of thermoacoustic modes

Mensah, Georg Atta (2019)

Modern gas turbines are a key technology for reliable and sustainable power generation. In order to meet strict emission regularizations they utilize lean premixed combustion. This renders the engines susceptible to self-excited pressure oscillations known as thermoacoustic instabilities. These oscillations arise from an interaction of the unsteady heat release of the flame and the acoustic res...

Excitation of the precessing vortex core by active flow control to suppress thermoacoustic instabilities in swirl flames

Lückoff, Finn ; Oberleithner, Kilian (2019-07-04)

In this study, we apply periodic flow excitation of the precessing vortex core at the centerbody of a swirl-stabilized combustor to investigate the impact of the precessing vortex core on flame shape, flame dynamics, and especially thermoacoustic instabilities. The current control scheme is based on results from linear stability theory that determine the precessing vortex core as a global hydro...

Comprehensive Thermodynamic Analysis of the Humphrey Cycle for Gas Turbines with Pressure Gain Combustion

Stathopoulos, Panagiotis (2018-12-18)

Conventional gas turbines are approaching their efficiency limits and performance gains are becoming increasingly difficult to achieve. Pressure Gain Combustion (PGC) has emerged as a very promising technology in this respect, due to the higher thermal efficiency of the respective ideal gas turbine thermodynamic cycles. Up to date, only very simplified models of open cycle gas turbines with pre...

Experimental Study of Advanced Helmholtz Resonator Liners with Increased Acoustic Performance by Utilising Material Damping Effects

Dannemann, Martin ; Kucher, Michael ; Kunze, Eckart ; Modler, Niels ; Knobloch, Karsten ; Enghardt, Lars ; Sarradj, Ennes ; Höschler, Klaus (2018-10-15)

In aero engines, noise absorption is realised by acoustic liners, e.g., Helmholtz resonator (HR) liners, which often absorb sound only in a narrow frequency range. Due to developments of new engine generations, an improvement of overall acoustic damping performance and in particular more broadband noise absorption is required. In this paper, a new approach to increase the bandwidth of noise abs...

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 ...