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28

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## Publications

Publications (28)

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...

Final journal version here:
https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/amplitude-statistics-prediction-in-thermoacoustics/B11F37A2D6A3D3921A23EA234DEE999A
We discuss the statistics of acoustic pressure of thermoacoustic oscillations, either axial or azimuthal in nature. We derive a model where the describing functio...

Rotationally symmetric systems can exhibit acoustic fluctuations in the azimuthal direction. In experimental works the nature (standing/spinning) of these fluctuations is often described by a set of indicators. These indicators either depend on the chosen frame of reference or are not state space variables for the acoustic field. Conversely, in the...

Can-annular combustors consist of N distinct cans set up symmetrically around the axis of the gas turbine rotor. Each can is connected to the turbine inlet by means of a transition duct. At the turbine inlet a small gap between the neighbouring transition ducts allows acoustic communication between the individual cans. Thermoacoustic pulsations in...

We consider the acoustic flow field of rotationally symmetric systems, like an annular combustor and the flow in a round duct, in absence of a mean azimuthal flow field. We focus on azimuthal instabilities, which manifest as either spinning (rotating) waves or standing waves, or a linear combination of the two. These instabilities are often excited...

Existing experimental results show that swirling flames in annular combustors respond with a different gain to acoustic azimuthal modes rotating in either the clockwise or anti-clockwise direction. The ratio $R$ of these two gains is introduced, with $R=1$ being the conventional case of flames responding the same to the two forcing directions. To a...

The stability of thermoacoustic systems is often regulated by the time delay between acoustic perturbations and corresponding heat release fluctuations. An accurate estimate of this value is of great importance in applications since even small modifications can introduce significant changes in the system behavior. Different studies show that the no...

In the current study azimuthal forcing of an annular combustor with swirling flames has been performed to present for the first time the Heat Release Rate (HRR) response to all possible pressure fields of the first azimuthal mode up to a finite amplitude limit. The response is first quantified through the conventional Flame Describing Function (FDF...

This paper presents a RANS turbulent combustion model for CH4/H2/air mixtures which includes the effect of heat losses and flame stretch. This approach extends a previous model concept designed for methane/air mixtures and improves the prediction of flame stabilization when hydrogen is added to the fuel. Heat loss and stretch effects are modelled b...

Heavy-duty land-based gas turbines are often designed with can-annular combustors, which consist of a set of identical cans, acoustically connected on the upstream side via the compressor plenum, and, downstream, with a small annular gap located at the transition with the first turbine stage. The modeling of this cross-talk area is crucial to predi...

The stability of thermoacoustic systems is often regulated by the time delay between acoustic perturbations and corresponding heat release fluctuations. An accurate estimate of this value is of great importance in applications, since even small modifications can introduce significant changes in the system behavior Different studies show that the no...

This paper presents a RANS turbulent combustion model for CH4/H2/air mixtures which includes the effect of heat losses and flame stretch. This approach extends a previous model concept designed for methane/air mixtures and improves the prediction of flame stabilization when hydrogen is added to the fuel. Heat loss and stretch effects are modelled b...

Heavy-duty land-based gas turbines are often designed with can-annular combustors, which consist of a set of identical cans, acoustically connected on the upstream side via the compressor plenum, and, downstream, with a small annular gap located at the transition with the first turbine stage. The modeling of this cross-talk area is crucial to predi...

Identification of thermoacoustic systems usually requires low-order modeling, often obtained by means of a Galerkin projection onto a single acoustic mode. The resulting dissipative self-excited oscillator equation describes the dynamic balance between acoustic energy sources (i.e. the flame) and sinks. Previous works studied the case of a nonlinea...

This paper first characterizes the acoustic field of two annular combustors by means of data from acoustic pressure sensors. In particular the amplitude, orientation, and nature of the acoustic field of azimuthal order n is characterized. The dependence of the pulsation amplitude on the azimuthal location in the chamber is discussed, and a protecti...

We consider the acoustic flow field of rotationally symmetric systems, like an annular combustor and the flow in a round duct, in absence of a mean azimuthal flow field. We focus on azimuthal instabilities, which manifest as either spinning (rotating) waves or standing waves, or a linear combination of the two. These instabilities are often excited...

Annular combustors can exhibit azimuthal thermoacoustic instabilities, which can rotate as a spinning wave at the speed of sound in the azimuthal direction, oscillate as a standing wave with pressure nodes fixed in space, or be a linear combination of these. These oscillations happen if a positive feedback loop between acoustics and the response of...

This paper first characterizes the acoustic field of two annular combustors by means of data from acoustic pressure sensors. In particular the amplitude, orientation, and nature of the acoustic field of azimuthal order n is characterized. The dependence of the pulsation amplitude on the azimuthal location in the chamber is discussed, and a protecti...

Can-annular combustors consist of $N$ distinct cans set up symmetrically around the axis of the gas turbine. Each can is connected to the turbine inlet by means of a transition duct. At the turbine inlet a small gap between the neighbouring transition ducts allows acoustic communication between the cans. Thermoacoustic pulsations in the cans are dr...

Azimuthal instabilities occur in rotationally symmetric systems, either as spinning (rotating) waves or standing waves. We make use of a novel ansatz to derive a differential equation characterizing the state of these instabilities in terms of their amplitude, orientation, nature (standing/spinning) and temporal phase. For the first time we show ho...

Can-annular combustors consist of a set of independent cans, connected on the upstream side to the combustor plenum and on the downstream side to the turbine inlet, where a transition duct links the round geometry of each can with the annular segment of the turbine inlet. Each transition duct is open on the sides toward the adjacent transition duct...

Can-annular combustors consist of a set of independent cans, connected on the upstream side to the combustor plenum, and on the downstream side to the turbine inlet, where a transition duct links the round geometry of each can with the annular segment of the turbine inlet. Each transition duct is open on the sides towards the adjacent transition du...

This paper concerns the influence of the phase of the heat release response on thermoacoustic systems. We focus on one pair of degenerate azimuthal acoustic modes, with frequency ω0. The same results apply for an axial acoustic mode. We show how the value φ0 and the slope −τ of the flame phase at the frequency ω0 affects the boundary of stability,...

A successful low-order model introduced by Schuermans et al. [19], Noiray et al. [13] studies thermoacoustic instabilities assuming the fluctuating heat release rate q to be in phase with the acoustic pressure p, by neglecting the component of q out of phase with p. In this investigation we remove this hypothesis and consider a model in which, if p...

Rotationally symmetric annular combustors are of practical importance because they generically resemble combustion chambers in gas turbines and aeroengines, in which thermoacoustically driven oscillations are a major concern. We focus on thermoacoustic oscillations of azimuthal type, neglect the effect of the transverse acoustic velocity in the azi...

The describing function is a powerful tool for characterizing nonlinear dynamical systems in the frequency domain. In some cases, it is the only available description of a nonlinear operator characterizing a certain subcomponent of the system. This paper presents a methodology to provide a state-space realization of one given describing function, i...

We presented on this poster some on-going work on mapping nonlinear operators from frequency to time domain. This lead to the article "2015 - Giulio Ghirardo , Bernhard Ćosić, Matthew P. Juniper, Jonas P. Moeck - State-space realization of a describing function - Nonlinear Dynamics, doi:10.1007/s11071-015-2134-x"

This theoretical study investigates spinning and standing modes in azimuthally symmetric annular combustion chambers. Bot modes are observed in experiments and simulations, and an existing model predicts that spinning modes are the only stabl state of the system. We extend this model to take into account the effect that the acoustic azimuthal veloc...