Effects of Mean Flow, Entropy Waves, and Boundary Conditions on Longitudinal Combustion Instability

“…The most comprehensive works about low-order modelling of combustion instability (Keller 1995;Dowling & Stow 2003;You et al 2005) rely on the resolution of a wave equation governing the oscillatory field in the chamber. Complemented by experiments (Hield et al 2009;Yu et al 2010;Sisco et al 2011) these low order models show that a new family of instability modes that depends on the mean flow velocity may exist. However, as pointed out by Eckstein et al (2006), one important issue is that the influence of indirect combustion noise is not systematic and a low-frequency instability may appear even without the presence of a nozzle, and vice-versa.…”

Section: Introductionmentioning

confidence: 99%

Mixed acoustic–entropy combustion instabilities in gas turbines

2014

View full text Add to dashboard Cite

A combustion instability in a combustor terminated by a nozzle is analysed and modelled based on a low order Helmholtz solver. A Large Eddy Simulation (LES) of the corresponding turbulent, compressible and reacting flow is first performed and analysed based on Dynamic Mode Decomposition (DMD). The mode with the highest amplitude shares the same frequency of oscillation as the experiment (approx. 320 Hz) and shows the presence of large entropy spots generated within the combustion chamber and convected down to the exit nozzle. The lowest purely acoustic mode being in the range 700 − 750 Hz, it is postulated that the instability observed around 320 Hz stems from a mixed entropy/acoustic mode where the acoustic generation associated with entropy spots being convected throughout the choked nozzle plays a key role. The DMD analysis allows to extract from the LES results a low-order model that confirms that the mechanism of the low-frequency combustion instability indeed involves both acoustic and convected entropy waves. The Delayed Entropy Coupled Boundary Condition (Motheau et al. 2014) is implemented into a numerical Helmholtz solver where the baseline flow is assumed at rest. When fed with appropriate transfer functions to model the entropy generation and convection from the flame to the exit, the Helmholtz/DECBC solver predicts the presence of an unstable mode around 320 Hz, in agreement with both LES and experiments.

show abstract

“…Computational investigations of the experiment indicate the modulation of the CRZ or the VBB occurs at a frequency that corresponds to the 4L acoustic mode. 27,28 This coupling between hydrodynamics and acoustics can also lead to high amplitude fluctuations at this frequency compared to 1L-3L modes. The signals at other locations in the combustion chamber are in phase at the 4 L mode.…”

Section: Effect Of Geometry On Combustion Dynamicsmentioning

confidence: 99%

“…The major dimensions of the combustor, specifically the lengths of the air plenum and combustion chamber, are determined at operating conditions tabulated in Table 1 based on a 1-D linearized Euler equation (LEE) solver. 27 LEE was used to parametrically vary these dimensions to calculate natural acoustic frequencies of the combustor volume at design operating conditions. Choked inlet at the entrance to the air plenum and a short nozzle approximation at the exit nozzle of the combustion chamber were assumed as acoustic boundary conditions to determined natural acoustic modes of the combustor.…”

Section: Experimental Arrangementmentioning

confidence: 99%

Parametric investigation of combustion instabilities in a single-element lean direct injection combustor

Gejji

Huang

Fugger

et al. 2018

International Journal of Spray and Combustion Dynamics

View full text Add to dashboard Cite

Self-excited combustion dynamics in a liquid-fueled lean direct injection combustor at high pressure (1 MPa) are described. Studied variables include combustor and air plenum length, inlet air temperature, equivalence ratio, fuel nozzle location, and fuel composition. Measured pressure oscillations were dependent on combustor geometry and ranged from about 1% of mean chamber pressure at low equivalence ratio, up to 20% at high equivalence ratio. In the most unstable cases, strong pressure modes were measured throughout the frequency spectrum including a band around 1.2-1.5 kHz representing the 4th longitudinal mode, and another band around 7 kHz. The oscillation amplitudes have a non-monotonic dependency on air temperature, and are affected by the placement of the fuel nozzle relative to the throat of the subsonic swirling air flow. The parametric survey provides a rich dataset suitable for validating high-fidelity simulations and their subsequent use in analyzing and interpreting the complex combustion dynamics.

show abstract

Effects of Mean Flow, Entropy Waves, and Boundary Conditions on Longitudinal Combustion Instability

Cited by 43 publications

References 7 publications

An Analytical Investigation Characterizing the Application of Single Frequency Acoustic Modulation for High Frequency Combustion Instability Suppression

An Analytical Investigation Characterizing the Application of Single Frequency Acoustic Modulation for High Frequency Combustion Instability Suppression

Mixed acoustic–entropy combustion instabilities in gas turbines

Parametric investigation of combustion instabilities in a single-element lean direct injection combustor

Contact Info

Product

Resources

About