Experimentally Determining the Acoustic Damping Rates of a Combustor With a Swirl Stabilized Lean Premixed Flame

2015 ◽  
Author(s):  
Nicolai V. Stadlmair ◽  
Michael Wagner ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Probability Distributions ◽  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Stability Margin ◽  
Open Loop ◽  
Decay Rates ◽  
Acoustic Energy ◽  
Test Rig ◽  
Acoustic Damping ◽  
Lean Premixed

In this study, we employ a method based on Bayesian statistics to determine the rate of acoustic decay from dynamic pressure measurements inside a combustor. It is common, that lean premixed flames tend to drive thermoacoustic instabilities at specific eigenfrequencies. Hence, the dissipation of acoustic energy inside the combustor, its absorption at the boundaries and its transfer over the in- and outlets must always exceed the acoustic excitation from the flame to avoid pulsations. Quantitative measures for the level of stability are of high technical relevance. In that context the occurring eigenfrequencies and their damping rates are important indicators for the stability margin of gas turbine combustors. A modular swirl burner is investigated in an atmospheric single burner test rig under lean premixed conditions. For the experimental determination of the damping rates, a siren is used to externally excite resonant frequencies of the combustion system. After interrupting the forcing abruptly, time series of the decaying signals are recorded by dynamic pressure sensors inside the combustion chamber. For the analysis of this data, an algorithm based on a Bayesian network approach, which uses a Gibbs Sampler is employed. Probability distributions of frequencies and decay rates are obtained with the Markov-Chain Monte-Carlo (MCMC) method. For the investigated configuration, the influence of the acoustic boundary conditions and the preheat temperature on eigenmodes and damping rates is evaluated. Finally, the results are compared to a network model of the test rig. With that approach, the Open-Loop Gain (OLG) is evaluated for the frequency range of interest. Eigenfrequencies as well as their corresponding damping rates are obtained from Nyquist analysis.

scholarly journals Swirler geometry effects (dh/do ratio) on synthetic gas flames. Part 2: dynamic flame behaviour at external y altered acoustic conditions

Energetika ◽  
2021 ◽  
Vol 67 (1) ◽  
Author(s):  
Harun Yilmaz ◽  
Omer Cam ◽  
Ilker Yilmaz
Keyword(s):  
Boundary Conditions ◽  
Pressure Sensors ◽  
Acoustic Energy ◽  
Acoustic Boundary Conditions ◽  
Acoustic Damping ◽  
Pressure Profiles ◽  
Flame Response ◽  
Scale Variable ◽  
A Minor ◽  
Flame Behaviour

In a combustion device, unsteady heat release causes acoustic energy to increase when acoustic damping (energy loss) is not that effective, and, as a result, thermo-acoustic flame instabilities occur. In this study, effects of the swirler dh/do ratio (at different swirl numbers) on dynamic flame behaviour of the premixed 20%CNG/30%H2/30%CO/20%CO2 mixture under externally altered acoustic boundary conditions and stability limits (flashback and blowout equivalence ratios) of such mixture were investigated in a laboratory-scale variable geometric swirl number combustor. Therefore, swirl generators with different dh/do ratios (0.3 and 0.5) and geometric swirl numbers (0.4, 0.6, 0.8, 1.0 1.2 and 1.4) were designed and manufactured. Acoustic boundary conditions in the combustion chamber were altered using loudspeakers, and flame response to these conditions was perceived using photodiodes and pressure sensors. Dynamic flame behaviour of respective mixture was evaluated using luminous intensity and pressure profiles. Results showed that the dh/do ratio has a minor impact on dynamic flame behaviour.

Transient Pressure Pulsations of a Model Pump-Turbine During Power Failure

2017 ◽  
Author(s):  
Jinhong Hu ◽  
Wei Zeng ◽  
Jiandong Yang ◽  
Renbo Tang
Keyword(s):  
Rotational Speed ◽  
Guide Vane ◽  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Open Loop ◽  
Operating Conditions ◽  
Pressure Pulsations ◽  
Transient Pressure ◽  
Pump Turbine ◽  
Power Failure

Pump-turbine can operate in either pump mode or turbine mode. The quick response to load changes as well as the ability to store energy makes it essential to the stability of power grid. When a pump-turbine works in different condition, flow-induced instabilities occur, including Rotor Stator Interaction (RSI) between the runner and vanes, vortex formations and back flow regions. To understand these complicated flow dynamics, experimental and numerical investigations have been conducted by many researchers. Among these researches, many experiments on model test rigs are mainly focused on steady state, and knowledge for instabilities during transients is still lacking. In this paper, power failure experiments with constant guide van opening are conducted on an open-loop test rig. During the process, the operating point of the pump-turbine in the 4 quadrant characteristics moves from pump region through the brake region, turbine region to turbine brake region. Finally the pump-turbine settled down at runaway rotational speed. In our experiments, flow rate, rotational speed, torque, pressure in the spiral casing and the draft tube inlet are measured. Especially, dynamic pressure sensors mounted in the guide vane channels are used to measure transient pressure pulsations. Measured data are analyzed in both time domain and frequency domain. Results indicate that during power failure pressure pulsations in the vane channels vary significantly with the operating conditions. In the pump region, pressure pulsations are mainly composed of RSI. In the brake region, intensive stochastic noises occur, and the amplitude of RSI rises. In the turbine region, the magnitude of pressure pulsations drops sharply as the noise intensity goes down. In the turbine brake region, significant noises appear, and the amplitude of RSI increases dramatically.

Online Combustor Stability Margin Assessment Using Dynamic Pressure Data

2004 ◽  
Author(s):  
Tim Lieuwen
Keyword(s):  
Dynamic Stability ◽  
Environmental Changes ◽  
Dynamic Pressure ◽  
Stability Boundary ◽  
Stability Margin ◽  
Operating Conditions ◽  
Margin Assessment ◽  
Pressure Oscillations ◽  
Acoustic Damping ◽  
The Stability

This paper describes a strategy for determining a combustor’s dynamic stability margin. Currently, when turbines are being commissioned or simply going through day to day operation, the operator has no idea how the dynamic stability of the system is affected by changes to fuel splits/operating conditions unless, of course, pressure oscillations are actually present. We have developed a methodology for ascertaining stability margin from passive monitoring of the acoustic pressure. This method consists of signal processing and analysis that determines a real-time measure of combustor damping. When the calculated damping is positive, the combustor is stable. When the damping goes to zero, the combustor approaches its stability boundary. Changes in the stability margin of each of the combustor’s stable modes due to tuning, aging or environmental changes can then be monitored through online analysis of the pressure signal. This paper outlines the basic approach used to quantify acoustic damping and demonstrates the technique on combustor test data.

Visualisation of Diffuser Instabilities in a Wet Gas Compressor

2015 ◽  
Author(s):  
Veronica Ferrara ◽  
Lars E. Bakken
Keyword(s):  
Oil And Gas ◽  
New Technologies ◽  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Petroleum Industry ◽  
Research Programme ◽  
Open Loop ◽  
Ongoing Research ◽  
Wet Gas ◽  
Response Dynamic

The continuous demand for oil and gas pushes the petroleum industry to develop new technologies in order to increase production and exploit existing fields. The wet gas process, based on direct compression of unprocessed well stream subsea is a powerful means to expand the extraction of crude oil and gas and reach remote regions. Consequently centrifugal compressors are key elements that need to be developed in this area. Since no commercial subsea compressors are available and the liquid phase inside the standard process has to be avoided, it is essential to fully understand the machine behaviour, particularly investigate the presence of a gas-liquid mixture. Because of liquid impact, the performance of compressors and consequently the margin of stability may have to be modified. Here, delayed instability inception should be identified. An ongoing research programme is conducted at the Norwegian University of Science and Technology (NTNU) concerning the influence of wet gas on performance and aerodynamic stability. An open loop wet gas test rig is designed and employed in an experimental campaign. The main goal of this study is the visualisation of flow in a vaneless diffuser by means of special windows in Plexiglas, in correspondence with the diffuser and volute. Most attention is focused on the behaviour that leads to unstable phenomena, like stall and surge, in order to expose wet effects. Interactions between the diffuser and volute will also be taken into account. Simultaneously, the analysis will be supported by measurements from high-response dynamic pressure sensors. A fast Fourier transform (FFT) examination will be realised, in order to identify characteristic frequencies of unsteady events.

Impact of Damper Placement on the Stability Margin of an Annular Combustor Test Rig

2019 ◽  
Author(s):  
Michael Betz ◽  
Max Zahn ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Dynamic Pressure ◽  
Thermal Power ◽  
Stability Margin ◽  
Linear Increase ◽  
Axial Position ◽  
Pressure Amplitude ◽  
Test Rig ◽  
Worst Case ◽  
Damping Rate ◽  
Annular Combustor

Abstract In the presented study a lab scale lean-premixed annular combustor comprising different axial and azimuthal patterns of dampers as well as several symmetrical and unsymmetrical damper placement patterns is investigated in five steps: In the first step the number of the dampers is increased considering only optimal distributions obtained from literature. As a result a nearly linear increase of damping with the number of dampers is observed. Second, other damper patterns are examined, which perform worse than the ideal distributions. It can be seen that a mode split can lead to differing damping rates of the two decomposed modes. In the worst case one of the modes isn’t damped any stronger than in the baseline measurement without any dampers. A number of selected representative circumferential damper patterns is investigated at two axial locations. It is generally observed that the axial position has an influence on damper performance as the upstream configurations with dampers in the flame region perform better than the downstream configurations. Using an optimum configuration with four dampers equally distributed around the circumference the increase of the window of operation of the annular combustor test rig in terms of equivalence ratio and thermal power is demonstrated. The azimuthal distribution of the dynamic pressure amplitude of the annular combustor test rig is determined and compared with the local damping rate. A correlation can be found which reveals that already very moderate damping rates lead to very low dynamic pressure amplitudes.

Online Combustor Stability Margin Assessment Using Dynamic Pressure Data

2005 ◽  
Vol 127 (3) ◽  
pp. 478-482 ◽  
Author(s):  
Tim Lieuwen
Keyword(s):  
Environmental Changes ◽  
Dynamic Pressure ◽  
Stability Boundary ◽  
Stability Margin ◽  
Operating Conditions ◽  
Pressure Data ◽  
Pressure Oscillations ◽  
Acoustic Damping ◽  
On Line ◽  
The Stability

This paper describes a strategy for determining a combustor’s dynamic stability margin. Currently, when turbines are being commissioned or simply going through day to day operation, the operator does not know how the stability of the system is affected by changes to fuel splits or operating conditions unless, of course, pressure oscillations are actually present. We have developed a methodology for ascertaining the stability margin from dynamic pressure data that does not require external forcing and that works even when pressure oscillations have very low amplitudes. This method consists of signal processing and analysis that determines a real-time measure of combustor damping. When the calculated damping is positive, the combustor is stable. As the damping goes to zero, the combustor approaches its stability boundary. Changes in the stability margin of each of the combustor’s stable modes due to tuning, aging, or environmental changes can then be monitored through an on-line analysis of the pressure signal. This paper outlines the basic approach used to quantify acoustic damping and demonstrates the technique on combustor test data.

scholarly journals Detection of vaneless diffuser rotating stall by means of dynamic pressure sensors and acoustic measurements

2021 ◽  
Vol 312 ◽  
pp. 11007
Author(s):  
Luca Romani ◽  
Lorenzo Bosi ◽  
Alberto Baroni ◽  
Lorenzo Toni ◽  
Davide Biliotti ◽  
...  
Keyword(s):  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Experimental Tests ◽  
Rotating Stall ◽  
Accurate Estimation ◽  
Sufficient Information ◽  
Acoustic Measurements ◽  
Vaneless Diffuser ◽  
Test Rig ◽  
Ensemble Averaging

An accurate estimation of rotating stall is one of the key technologies for high-pressure centrifugal compressors. Several techniques have been proposed to detect the stall onset; inter alia, few dynamic pressure probes have been shown to not only properly detect the phenomenon, but also reconstruct the stall characteristics after an ensemble averaging approach. The massive use of this technique in the field is, however, not a common practice yet. In the present study, the use of dynamic pressure probes has been combined with that of an environmental microphone to evaluate the prospects of this latter for a possible stall onset detection. To this end, experimental tests have been carried out in the experimental test rig of the Department of Industrial Engineering (DIEF) of Università degli Studi di Firenze. Results show that the microphone was able to distinguish the onset of rotating stall accurately and promptly, even though – differently from dynamic pressure sensors - it does not provide sufficient information to determine the characteristics of the stall pattern. On this basis, the use of acoustic measurements could find room for automatic detection of rotating stall onset.

Comparison of the Accuracy of Time-Domain Measurement Methods for Combustor Damping

2013 ◽  
Author(s):  
Michael Wagner ◽  
Christoph Jörg ◽  
Thomas Sattelmayer
Keyword(s):  
Time Domain ◽  
Gas Turbines ◽  
Dynamic Pressure ◽  
Random Noise ◽  
Decay Rates ◽  
Acoustic Energy ◽  
Performance Accuracy ◽  
Flame Dynamics ◽  
Sinusoidal Shape

Combustors of modern gas turbines for power generation and mechanical drive are predominantly operated in premixed mode, which is sensitive to coupling between flame dynamics and combustor acoustics. In practice, combustor flames tend to drive instabilities at certain eigenfrequencies of the systems, according to the classical Rayleigh criterion. In order to guarantee combustor stability in the entire operation range of the engine it has to be avoided under all circumstances that the flame excites the system beyond its damping potential. One option to accomplish this is to provide sufficient damping capabilities of the combustor system so that the decay of acoustic energy inside the system always exceeds the excitation provided by the flame. Experimental methods for the determination of combustor damping rates therefore may become a valuable tool for combustor design in the future. In the past, methods with different accuracy, complexity and capabilities have been developed to gain experimental access to decay rates of the acoustic energy inside combustor systems. In this study we compare accuracy and capabilities of three different time-domain methods that allow the determination of pressure decay rates from experimental dynamic pressure traces: A simple exponential fit to the measured dynamic pressure, a method based on the decay of acoustic energy and a newly developed statistical method are examined. In the first step, the methods are tested using artificially generated test signals. The simple signals decaying exponentially with the known rate α are of pure sinusoidal shape and have discrete frequencies. As practical dynamic pressure traces are in general corrupted with noise, in the second step of the analysis a certain amount of random noise is added to the test signal. The last step of the analysis involves realistic pressure signals obtained from a simple duct with throughflow. The results obtained from the different methods are compared with each other and differences regarding performance, accuracy, robustness as well as computational costs are presented.

scholarly journals Experimental Study on Dynamic Combustion Characteristics in Swirl-Stabilized Combustors

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1609
Author(s):  
Donghyun Hwang ◽  
Kyubok Ahn
Keyword(s):  
Experimental Study ◽  
Heat Release ◽  
Dynamic Pressure ◽  
Combustion Instability ◽  
Flame Structure ◽  
Pressure Sensors ◽  
Necessary Condition ◽  
Rayleigh Criterion ◽  
Pressure Oscillations ◽  
Geometric Conditions

An experimental study was performed to investigate the combustion instability characteristics of swirl-stabilized combustors. A premixed gas composed of ethylene and air was burned under various flow and geometric conditions. Experiments were conducted by changing the inlet mean velocity, equivalence ratio, swirler vane angle, and combustor length. Two dynamic pressure sensors, a hot-wire anemometer, and a photomultiplier tube were installed to detect the pressure oscillations, velocity perturbations, and heat release fluctuations in the inlet and combustion chambers, respectively. An ICCD camera was used to capture the time-averaged flame structure. The objective was to understand the relationship between combustion instability and the Rayleigh criterion/the flame structure. When combustion instability occurred, the pressure oscillations were in-phase with the heat release oscillations. Even if the Rayleigh criterion between the pressure and heat release oscillations was satisfied, stable combustion with low pressure fluctuations was possible. This was explained by analyzing the dynamic flow and combustion data. The root-mean-square value of the heat release fluctuations was observed to predict the combustion instability region better than that of the inlet velocity fluctuations. The bifurcation of the flame structure was a necessary condition for combustion instability in this combustor. The results shed new insight into combustion instability in swirl-stabilized combustors.

Sign in / Sign up

Export Citation Format

Share Document