Low-Order Modeling of Low-Frequency Combustion Instabilities in AeroEngines

2006 ◽  
Vol 22 (2) ◽  
pp. 425-432 ◽  
Author(s):  
Johannes Eckstein ◽  
Thomas Sattelmayer
Keyword(s):  
Low Frequency ◽  
Combustion Instabilities ◽  
Low Order

scholarly journals Low-Frequency Variability, Coherence Resonance, and Phase Selection in a Low-Order Model of the Wind-Driven Ocean Circulation

2011 ◽  
Vol 41 (9) ◽  
pp. 1585-1604 ◽  
Author(s):  
Stefano Pierini
Keyword(s):  
Ocean Circulation ◽  
Kuroshio Extension ◽  
Global Bifurcation ◽  
Low Frequency ◽  
Galerkin Projection ◽  
Coherence Resonance ◽  
Primitive Equation ◽  
Phase Selection ◽  
Low Frequency Variability ◽  
Low Order

Abstract In this paper, a low-order spectral quasigeostrophic (QG) model of the wind-driven ocean circulation is derived and used to analyze the low-order character of the intrinsic low-frequency variability of the midlatitude double-gyre ocean circulation and of the related coherence resonance and phase selection phenomena. The model includes an exponential in the basis functions that allows for westward intensification, retains only four modes in the Galerkin projection, is defined in a rectangular domain, and is forced by deterministic and stochastic winds, thus extending previous low-order QG ocean models. The solution under steady forcing is first obtained, and the results are also analyzed in terms of dynamical systems theory. A homoclinic bifurcation (with the wind amplitude chosen as the control parameter) leads to intrinsic decadal relaxation oscillations (ROs) similar in several respects to those obtained with primitive equation models. The system is then forced with an additional red noise wind, and, in a parameter range preceding the global bifurcation, a coherence resonance scenario very similar to the one found with a primitive equation model of the Kuroshio Extension is obtained: this suggests that such a phenomenon is of low-order character. To study the RO excitation mechanism, a method denoted as phase selection is proposed. The system is forced with additional fictitious periodic winds that produce an emergence of ROs yielding strong phase dependence with the periodic forcing. The subsequent analysis reveals the character of the wind forcing that is most likely to excite a RO. All the results are discussed within the general framework of climate dynamics.

Estimates of Low-Frequency Sound Speed and Attenuation in a Surface Mud Layer Using Low-Order Modes

2020 ◽  
Vol 45 (1) ◽  
pp. 201-211
Author(s):  
Lin Wan ◽  
Mohsen Badiey ◽  
David P. Knobles ◽  
Preston S. Wilson ◽  
John A. Goff
Keyword(s):  
Sound Speed ◽  
Low Frequency ◽  
Frequency Sound ◽  
Low Order

On the Effect of Pressure Oscillations on Droplet Autoignition

2011 ◽  
Author(s):  
Christian Eigenbrod ◽  
Konstantin Klinkov ◽  
Fernando Filho Fachini
Keyword(s):  
High Frequency ◽  
Gas Turbines ◽  
Low Frequency ◽  
Combustion Instabilities ◽  
Driving Mechanisms ◽  
Temperature Oscillations ◽  
Large N ◽  
Main Driver ◽  
Droplet Sizes ◽  
Induction Times

The paper discusses the possible interaction between combustion instabilities and induction times of droplets (and sprays) to autoignition. It is shown that acoustic pressure/temperature oscillations significantly affect the induction times of n-heptane droplets. This may play an additional role in low frequency dynamics and might be the main driver of high frequency dynamics. Experiments on single droplets in an acoustic field were used to validate numerical simulations on the autoignition of large n-heptane droplets. The simulations were then extended towards technical droplet sizes and a gas turbine typical pressure range of 17 bar. It was found that the acoustic-scale changes of the pressure and temperature result in significant changes of the ignition delay. Applying numerical calculations to micro-sized droplets enabled to study the thermo-acoustic effects under conditions approximating real gas-turbines. The findings reveal the importance of thermo-acoustic effects on ignition processes in the instability-driving mechanisms of combustion and indicate that “acoustics-ignition”-interactions must be taken into account for low-frequency as well as for high-frequency dynamics; this in addition to the flow and mixture perturbations which are well known to drive combustion instabilities in gas-turbines.

Effect of Port Gas Injection on the Combustion Instabilities in a Spark-Ignition Lean-Burn Natural Gas Engine

2018 ◽  
Vol 28 (10) ◽  
pp. 1850124
Author(s):  
Li-Yuan Wang ◽  
Li-Ping Yang ◽  
En-Zhe Song ◽  
Chong Yao ◽  
Xiu-Zhen Ma
Keyword(s):  
Natural Gas ◽  
High Frequency ◽  
Gas Injection ◽  
Low Frequency ◽  
Combustion System ◽  
Combustion Instabilities ◽  
Lean Burn ◽  
Engine Load ◽  
Gas Engine ◽  
Natural Gas Engine

The combustion instabilities in a lean-burn natural gas engine have been studied. Using statistical analysis, phase-space reconstruction, and wavelet transforms, the effect of port gas injection on the dynamics of the indicated mean effective pressure (IMEP) fluctuations have been examined at a speed of 800[Formula: see text]rpm and engine load rates of 25% and 50%. The excessive air coefficient is 1.6 for each engine load, and the port gas injection timing (PGIT) ranges from 1 to 120 degrees of crankshaft angle ([Formula: see text]CA) after top dead center (ATDC) of the intake process. The results show that the PGIT has a significant effect on cyclic combustion fluctuations and the dynamics of the combustion system for all studied engine loads. An unreasonable PGIT leads to increased combustion fluctuations, and loosened and bifurcated structures of combustion system attractors. Furthermore, for both low and medium engine loads, the IMEP time series at earlier gas injections ([Formula: see text]CA and [Formula: see text]CA ATDC) undergoes low-frequency fluctuation together with high-frequency fluctuations in an intermittent fashion. For other PGITs, high-frequency intermittent fluctuations become persistent combined with weak low-frequency oscillations. Our results can be used to understand the oscillation characteristics and the complex dynamics of combustion system in a lean-burn natural gas engine. In addition, they may also be beneficial to the development of more sophisticated engine control strategies.

H 2-Optimal Low Order Transmission Line Models

2019 ◽  
Author(s):  
Bernhard Manhartsgruber
Keyword(s):  
Power Systems ◽  
Transmission Line ◽  
Code Generation ◽  
Transfer Functions ◽  
Linear Time ◽  
State Space Model ◽  
Low Frequency ◽  
Transmission Line Model ◽  
Line Model ◽  
Low Order

Abstract Transmission line modeling has played a crucial role in understanding the dynamics of fluid power systems. A vast body of literature exists from simple lumped parameter approaches to fully coupled three-dimensional fluid structure interaction models. When it comes to computationally efficient, yet physically sound low order models needed for fast computations iteratively called by optimization codes or for the purpose of model based control design, there is still room for improvement. Modal approximations of the input-output behaviour of liquid transmission lines have been around for decades. The basic idea of tuning the parameters of a canonical linear time invariant state space model to fit the transfer functions of a transmission line model in the H2-optimal sense under passivity constraints has been published by the author of the present paper in the past. However, the method so far was barely usable due to numerical difficulties in the underlying optimization process. A new implementation of the method employing quadruple-precision floating point numbers has recently been found to resolve the convergence problems and is reported in the present paper. The new version of the method is based on analytic computation of the cost and constraint functions as well as their gradients in the computer algebra package Maple and automatic code generation for compilation in FORTRAN. Results are very promising because both the entire low frequency behaviour and the first three eigenmodes of a transmission line model can be accurately covered by a model of order eight only.

Low-frequency combustion instabilities of an airblast swirl injector in a liquid-fuel combustor

2018 ◽  
Vol 196 ◽  
pp. 424-438 ◽  
Author(s):  
Byeonguk Ahn ◽  
Jeongjae Lee ◽  
Seungchai Jung ◽  
Kyu Tae Kim
Keyword(s):  
Liquid Fuel ◽  
Low Frequency ◽  
Combustion Instabilities ◽  
Swirl Injector

Vortex-driven acoustically coupled combustion instabilities

1987 ◽  
Vol 177 ◽  
pp. 265-292 ◽  
Author(s):  
Thierry J. Poinsot ◽  
Arnaud C. Trouve ◽  
Denis P. Veynante ◽  
Sebastien M. Candel ◽  
Emile J. Esposito
Keyword(s):  
Heat Release ◽  
Vortex Shedding ◽  
Combustion Instability ◽  
Low Frequency ◽  
Combustion Instabilities ◽  
Rayleigh Criterion ◽  
Phase Average ◽  
Steady Heat

Combustion instability is investigated in the case of a multiple inlet combustor with dump. It is shown that low-frequency instabilities are acoustically coupled and occur at the eigenfrequencies of the system. Using spark-schlieren and a special phase-average imaging of the C2-radical emission, the fluid-mechanical processes involved in a vortex-driven mode of instability are investigated. The phase-average images provide maps of the local non-steady heat release. From the data collected on the combustor the processes of vortex shedding, growth, interactions and burning are described. The phases between the pressure, velocity and heat-release fluctuations are determined. The implications of the global Rayleigh criterion are verified and a mechanism for low-frequency vortex-driven instabilities is proposed.

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