A Strategy to Tune Acoustic Terminations of Single-Can Test-Rigs to Mimic Thermoacoustic Behavior of a Full Engine

2020 ◽  
Author(s):  
Matthias Haeringer ◽  
Guillaume J. J. Fournier ◽  
Max Meindl ◽  
Wolfgang Polifke
Keyword(s):  
Wave Theory ◽  
Bloch Wave ◽  
Reflection Coefficients ◽  
Test Rig ◽  
Helmholtz Resonators ◽  
Flame Dynamics ◽  
Annular Combustor ◽  
Passive Acoustic ◽  
Thermoacoustic Properties ◽  
Dominant Frequencies

Abstract Thermoacoustic properties of can-annular combustors are commonly investigated by means of single-can test-rigs. To obtain representative results, it is crucial to mimic can-can coupling present in the full engine. However, current approaches either lack a solid theoretical foundation or are not practicable for high-pressure rigs. In the present study we employ Bloch-wave theory to derive reflection coefficients that correctly represent can-can coupling. We propose a strategy to impose such reflection coefficients at the acoustic terminations of a single-can test-rig by installing passive acoustic elements, namely straight ducts or Helmholtz resonators. In an iterative process, these elements are adapted to match the reflection coefficients for the dominant frequencies of the full engine. The strategy is demonstrated with a network model of a generic can-annular combustor and a 3D model of a realistic can-annular combustor configuration. For the latter we show that can-can coupling via the compressor exit plenum is negligible for frequencies sufficiently far away from plenum eigenfrequencies. Without utilizing previous knowledge of relevant frequencies or flame dynamics, the test-rig models are adapted within a few iterations and match the full engine with good accuracy. Using Helmholtz resonators for test-rig adaption turns out to be more viable than using straight ducts.

A Strategy to Tune Acoustic Terminations of Single-Can Test-Rigs to Mimic Thermoacoustic Behavior of a Full Engine

2020 ◽  
Author(s):  
Matthias Haeringer ◽  
Guillaume Jean Jacques Fournier ◽  
Maximilian Meindl ◽  
Wolfgang Polifke
Keyword(s):  
Wave Theory ◽  
Bloch Wave ◽  
Reflection Coefficients ◽  
Test Rig ◽  
Helmholtz Resonators ◽  
Flame Dynamics ◽  
Annular Combustor ◽  
Passive Acoustic ◽  
Thermoacoustic Properties ◽  
Dominant Frequencies

Abstract Thermoacoustic properties of can-annular combustors are commonly investigated by means of single-can test-rigs. To obtain representative results, it is crucial to mimic can-can coupling present in the full engine. However, current approaches either lack a solid theoretical foundation or are not practicable for high-pressure rigs. In the present study we employ Bloch-wave theory to derive reflection coefficients that correctly represent can-can coupling. We propose a strategy to impose such reflection coefficients at the acoustic terminations of a single-can test-rig by installing passive acoustic elements, namely straight ducts or Helmholtz resonators. In an iterative process, these elements are adapted to match the reflection coefficients for the dominant frequencies of the full engine. The strategy is demonstrated with a network model of a generic can-annular combustor and a 3D model of a realistic can-annular combustor configuration. For the latter we show that can-can coupling via the compressor exit plenum is negligible for frequencies sufficiently far away from plenum eigenfrequencies. Without utilizing previous knowledge of relevant frequencies or flame dynamics, the test-rig models are adapted within a few iterations and match the full engine with good accuracy. Using Helmholtz resonators for test-rig adaption turns out to be more viable than using straight ducts.

Investigation of Thermoacoustic Stability Limits of an Annular Gas Turbine Combustor Test-Rig With and Without Helmholtz-Resonators

2005 ◽  
Author(s):  
Joachim Lepers ◽  
Werner Krebs ◽  
Bernd Prade ◽  
Patrick Flohr ◽  
Giacomo Pollarolo ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Thermal Power ◽  
Power Input ◽  
Test Rig ◽  
Combustion Chambers ◽  
Thermoacoustic Instabilities ◽  
Helmholtz Resonators ◽  
Annular Combustor ◽  
Computational Analyses

Providing gas turbine combustion chambers with Helmholtz-resonators is a promising approach for extending the operating range of gas turbines towards higher thermal power input whilst minimizing the risk of thermoacoustic instabilities. The work currently being reported gives an overview of experimental and computational analyses carried out for a full annular combustor test-rig located at Gioia del Colle in Italy. The thermoacoustic stability characteristics of this test-rig were thoroughly analyzed both for a base configuration without Helmholtz-resonators and for an extended configuration with 14 Helmholtz-resonators. An increase of power input to the combustor by 8.5–20% can be realized when the test-rig is equipped with resonators. The experimental analyses are reproduced by a computational model.

Experimental Study of Damper Position on Instabilities in an Annular Combustor

2018 ◽  
Author(s):  
Marek Mazur ◽  
Håkon T. Nygård ◽  
James Dawson ◽  
Nicholas Worth
Keyword(s):  
Bluff Body ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Mode Switching ◽  
Periodic Mode ◽  
Pressure Oscillations ◽  
Helmholtz Resonators ◽  
Flame Dynamics ◽  
Annular Combustor

The present study experimentally investigates the effects of different circumferential damper configurations on the instabilities in an annular combustor. The combustor consists of multiple bluff body swirl stabilized flames. It is operated with an ethylene-air premixture at a power of 66 kW. Combinations of Helmholtz resonators are used as dampers circumferentially arranged around the combustion chamber. The tests are performed at operating conditions where the combustor is self-excited and characterized by a strong standing mode and periodic mode switching. For each test, the dynamic pressure is measured at different locations and overhead imaging of OH* of the entire combustor is conducted simultaneously at a high sampling frequency. The measurements are then used to compare the pressure fluctuations of the different cases in order to find the best positioning of the dampers. The azimuthal modes in the chamber are determined and the phase shift between OH* and pressure is analysed. Based on the Rayleigh criterion, these investigations allow us to find out if the dampers only remove energy from the pressure oscillations, or if they also influence the instability margins of the combustor and the flame dynamics. Finally, the results are compared with the theoretical findings in literature and observed discrepancies are discussed.

Time-Domain Bloch Boundary Conditions for Efficient Simulation of Thermoacoustic Limit Cycles in (Can-)Annular Combustors

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Matthias Haeringer ◽  
Wolfgang Polifke
Keyword(s):  
Boundary Conditions ◽  
State Space ◽  
Time Domain ◽  
Cfd Simulation ◽  
Rotational Symmetry ◽  
Wave Theory ◽  
Bloch Wave ◽  
Cfd Simulations ◽  
Suggested Approach ◽  
Combustion Dynamics

Abstract Thermo-acoustic eigenmodes of annular or can-annular combustion chambers, which typically feature a discrete rotational symmetry, may be computed in an efficient manner by utilizing the Bloch-wave theory. Unfortunately, the application of the Bloch-wave theory to combustion dynamics has hitherto been limited to the frequency domain. In this study, we present a time-domain formulation of Bloch boundary conditions (BBC), which allows to employ them in time domain simulations, e.g., computational fluid dynamics (CFD) simulations. The BBCs are expressed as acoustic scattering matrices and translated to complex-valued state-space systems. In a hybrid approach an unsteady, compressible CFD simulation of the burner-flame zone is coupled via characteristic-based state-space boundary conditions to a reduced order model of the combustor acoustics that includes BBCs. The acoustic model with BBC accounts for cross-can acoustic coupling and the discrete rotational symmetry of the configuration, while the CFD simulation accounts for the nonlinear flow–flame acoustic interactions. This approach makes it possible to model limit cycle oscillations of (can-)annular combustors at drastically reduced computational cost compared to CFD simulations of the full configuration and without the limitations of weakly nonlinear approaches that utilize a flame describing function. In this study, the suggested approach is applied to a generic multican combustor. Results agree well with a fully compressible CFD simulation of the complete configuration.

Air Splits Research of Multi-Sector Combustor With Flow Network Approach and Experiments

2019 ◽  
Author(s):  
Shanping Shen ◽  
Guoqian Song
Keyword(s):  
Pressure Drop ◽  
Pressure Loss ◽  
Effective Area ◽  
Network Approach ◽  
Test Rig ◽  
Flow Network ◽  
Wide Range ◽  
Aero Engine ◽  
Annular Combustor ◽  
Good Agreement

Abstract Multi-sector combustor tests are essential to aero-engine annular combustor development. For the test rig design, it is necessary to ensure that the pressure drop and flow split to the various portions of multi-sector combustor are consistent with the combustor component. This paper introduces a new kind of multi-sector combustor rig. The diffuser system of the test rig is different with the combustor component. This test rig is simple in structure and easy to machine. To evaluate the flow split and pressure drop of the test rig, a 1D-flow network approach is applied to multi-sector combustor rig design. The calculated results show good agreement with the experiment data. In order to study whether the test rig can simulate flow split and pressure loss of combustor components, flow split and pressure loss under different design features are analyzed. Result shows that by changing the effective area of inner/outer annular inlet baffle and inner/outer bleed air plate, inner/outer liner pressure drop and the ratio of air flow to W31c can be changed in a wide range. Thus, this kind of multi-sector combustor rig is convenient to change the multi-sector combustor test rig design to meet the requirements of the pressure drop and flow split design of combustor component, even when the rig has been manufactured.

Acoustic Damper Placement and Tuning for Annular Combustors: An Adjoint-Based Optimization Study

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Georg A. Mensah ◽  
Jonas P. Moeck
Keyword(s):  
Helmholtz Equation ◽  
Gas Turbines ◽  
Algebraic Models ◽  
Combustion Chambers ◽  
Thermoacoustic Instabilities ◽  
Helmholtz Resonators ◽  
Major Threat ◽  
Optimization Study ◽  
Annular Combustor ◽  
Parameter Values

Thermoacoustic instabilities pose a major threat to modern gas turbines. The use of acoustic dampers, like Helmholtz resonators, has proven useful for the mitigation of such instabilities. However, assessing the effect of acoustic dampers on thermoacoustic modes in annular combustion chambers remains an intricate task. This results from the implicit nature of the thermoacoustic Helmholtz equation associated with the high number of possible parameter values for the positioning of the dampers and their impedance design. In the present work, the principal challenges of the effective placement and the design of the impedance of acoustic dampers in annular chambers are discussed. This includes the choice of an appropriate objective function for the optimization, the combinatorial challenges when dealing with different possible damper arrangements, and the numerical complexities when using the thermoacoustic Helmholtz equation to approach this issue. As a key aspect, the paper proposes a new adjoint-based approach to tackle these problems. The new algorithm establishes algebraic models that predict the effect of acoustic dampers on the growth rates of the thermoacoustic modes. The theory is exemplified on the basis of a generic annular combustor model with 12 burners.

scholarly journals Multiphase Flow Large-Eddy Simulation Study of the Fuel Split Effects on Combustion Instabilities in an Ultra-Low-NOx Annular Combustor

2015 ◽  
Vol 138 (6) ◽  
Author(s):  
M. Bauerheim ◽  
T. Jaravel ◽  
L. Esclapez ◽  
E. Riber ◽  
L. Y. M. Gicquel ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Multiphase Flow ◽  
Analytical Model ◽  
Vortex Shedding ◽  
Gaseous Fuel ◽  
Combustion Instabilities ◽  
Eddy Simulation ◽  
Flame Dynamics ◽  
Large Eddy ◽  
Annular Combustor

This paper describes the application of a coupled acoustic model/large-eddy simulation approach to assess the effect of fuel split on combustion instabilities in an industrial ultra-low-NOx annular combustor. Multiphase flow LES and an analytical model (analytical tool to analyze and control azimuthal modes in annular chambers (ATACAMAC)) to predict thermoacoustic modes are combined to reveal and compare two mechanisms leading to thermoacoustic instabilities: (1) a gaseous type in the multipoint zone (MPZ) where acoustics generates vortex shedding, which then wrinkle the flame front, and (2) a multiphase flow type in the pilot zone (PZ) where acoustics can modify the liquid fuel transport and the evaporation process leading to gaseous fuel oscillations. The aim of this paper is to investigate these mechanisms by changing the fuel split (from 5% to 20%, mainly affecting the PZ and mechanism 2) to assess which mechanism controls the flame dynamics. First, the eigenmodes of the annular chamber are investigated using an analytical model validated by 3D Helmholtz simulations. Then, multiphase flow LES are forced at the eigenfrequencies of the chamber for three different fuel split values. Key features of the flow and flame dynamics are investigated. Results show that acoustic forcing generates gaseous fuel oscillations in the PZ, which strongly depend on the fuel split parameter. However, the correlation between acoustics and the global (pilot + multipoint) heat release fluctuations highlights no dependency on the fuel split staging. It suggests that vortex shedding in the MPZ, almost not depending on the fuel split, is the main feature controlling the flame dynamics for this engine.

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