scholarly journals Flame Describing Functions of a Confined Premixed Swirled Combustor With Upstream and Downstream Forcing

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
R. Gaudron ◽  
M. Gatti ◽  
C. Mirat ◽  
T. Schuller
Keyword(s):  
Combustion Chamber ◽  
Reference Signal ◽  
Describing Function ◽  
Microphone Signal ◽  
Describing Functions ◽  
Acoustic Dissipation ◽  
Phase Lags ◽  
Specific Impedance ◽  
The Mean ◽  
Flame Describing Function

The frequency response of a confined premixed swirled flame is explored experimentally through the use of describing functions that depend on both the forcing frequency and the forcing level. In these experiments, the flame is forced by a loudspeaker connected to the bottom of the burner in the fresh gas region or by a set of loudspeakers connected to the combustion chamber exhaust tube in the burnt gas region. The experimental setup is equipped with a hot-wire (HW) probe and a microphone, both of which located in front of each other below the swirler. The forcing level is varied between |v′0|/v¯0=0.10 and 0.72 RMS, where v¯0 and v′0 are, respectively, the mean and the fluctuating velocity at the HW probe. An additional microphone is placed on a water-cooled waveguide connected to the combustion chamber backplate. A photomultiplier equipped with an OH* filter is used to measure the heat release rate fluctuations. The describing functions between the photomultiplier signal and the different pressure and velocity reference signals are then analyzed in the case of upstream and downstream forcing. The describing function measured for a given reference signal is shown to vary depending on the type of forcing. The impedance of the injector at the HW location is also determined for both upstream and downstream forcing. For all describing functions investigated, it is found that their phase lags do not depend on the forcing level, whereas their gains strongly depend on |v′0|/v¯0 for certain frequency ranges. It is furthermore shown that the flame describing function (FDF) measured with respect to the HW signal can be retrieved from the specific impedance at the HW location and the describing function determined with respect to the signal of the microphone located in front of the HW. This relationship is not valid when the signal from the microphone located at the combustion chamber backplate is considered. It is then shown that a one-dimensional (1D) acoustic model allows to reproduce the describing function computed with respect to the microphone signal inside the injector from the microphone signal located at the combustion chamber backplate in the case of downstream forcing. This relation does not hold for upstream forcing because of the acoustic dissipation across the swirler which is much larger compared to downstream forcing for a given forcing level set at the HW location. This study sheds light on the differences between upstream and downstream acoustic forcing when measuring describing functions. It is also shown that the upstream and downstream forcing techniques are equivalent only if the reference signal used to determine the FDF is the acoustic velocity in the fresh gases just before the flame.

scholarly journals Flame Describing Functions of a Confined Premixed Swirled Combustor With Upstream and Downstream Forcing

2018 ◽  
Author(s):  
R. Gaudron ◽  
M. Gatti ◽  
C. Mirat ◽  
T. Schuller
Keyword(s):  
Combustion Chamber ◽  
Reference Signal ◽  
Hot Wire ◽  
Describing Function ◽  
Microphone Signal ◽  
Describing Functions ◽  
Wire Probe ◽  
Acoustic Dissipation ◽  
Phase Lags ◽  
Flame Describing Function

The frequency response of a confined premixed swirled flame is explored experimentally through the use of describing functions that depend on both the forcing frequency and forcing level. In these experiments, the flame is forced by a loudspeaker connected to the bottom of the burner in the fresh gas region or by a set of loudspeakers connected to the combustion chamber exhaust tube in the burnt gas region. The experimental setup is equipped with a hot-wire probe and a microphone, both of which located in front of each other below the swirler. The forcing level is varied between |v′0|/v̄0 = 0.10 and 0.72 RMS where v̄0 and v′0 are respectively the mean and fluctuating velocity at the hot-wire probe. An additional microphone is placed on a water-cooled waveguide connected to the combustion chamber backplate. A photomultiplier equipped with an OH* filter is used to measure the heat release rate fluctuations. The describing functions between the photomultiplier signal and the different pressure and velocity reference signals are then analyzed in the case of upstream and downstream forcing. The describing function measured for a given reference signal is shown to vary depending on the type of forcing. The impedance of the injector at the hot-wire location is also measured using the hot-wire and microphone signals for both upstream and downstream forcing. For all describing functions investigated, it is found that their phase lags do not depend on the forcing level whereas their gains strongly depend on |v′0|/v̄0 for certain frequency ranges. It is furthermore shown that the Flame Describing Function measured with respect to the hot-wire signal can be retrieved from the specific impedance at the hot-wire location and the describing function determined with respect to the signal of the microphone located in front of the hot-wire. This relationship is not valid when the signal from the microphone located at the combustion chamber backplate is considered. It is then shown that a ID acoustic model allows to reproduce the describing function computed with respect to the microphone signal inside the injector from the microphone signal located at the combustion chamber backplate in the case of downstream forcing. This relation does not hold for upstream forcing because of the acoustic dissipation across the swirler which is much larger compared to downstream forcing for a given forcing level set at the hot-wire location. This study sheds light on the differences between upstream and downstream acoustic forcing when measuring describing functions. It is also shown that the upstream and downstream forcing techniques are equivalent only if the reference signal used to determine the flame describing function is the acoustic velocity in the fresh gases just before the flame.

scholarly journals G-equation modelling of thermoacoustic oscillations of partially premixed flames

2017 ◽  
Vol 9 (4) ◽  
pp. 260-276 ◽  
Author(s):  
Bernhard Semlitsch ◽  
Alessandro Orchini ◽  
Ann P Dowling ◽  
Matthew P Juniper
Keyword(s):  
Heat Release ◽  
Limit Cycle ◽  
Heat Release Rate ◽  
Release Rate ◽  
Large Scale ◽  
Describing Function ◽  
Describing Functions ◽  
Wide Range ◽  
Flame Describing Function ◽  
Thermoacoustic Oscillations

Numerical simulations aid combustor design to avoid and reduce thermoacoustic oscillations. Non-linear heat release rate estimation and its modelling are essential for the prediction of saturation amplitudes of limit cycles. The heat release dynamics of flames can be approximated by a flame describing function. To calculate a flame describing function, a wide range of forcing amplitudes and frequencies needs to be considered. For this reason, we present a computationally inexpensive level-set approach, which accounts for equivalence ratio perturbations on flames with arbitrarily complex shapes. The influence of flame parameters and modelling approaches on flame describing functions and time delay coefficient distributions are discussed in detail. The numerically obtained flame describing functions are compared with experimental data and used in an acoustic network model for limit cycle prediction. A reasonable agreement of the heat release gain and limit cycle frequency is achieved even with a simplistic, analytical velocity fluctuation model. However, the phase decay is over-predicted. For sophisticated flame shapes, only the realistic modelling of large-scale flow structures allows the correct phase decay predictions of the heat release rate response.

Identification of the Flame Describing Function of a Premixed Swirl Flame from LES

2012 ◽  
Vol 184 (7-8) ◽  
pp. 888-900 ◽  
Author(s):  
H. J. Krediet ◽  
C. H. Beck ◽  
W. Krebs ◽  
S. Schimek ◽  
C. O. Paschereit ◽  
...  
Keyword(s):  
Describing Function ◽  
Flame Describing Function ◽  
Swirl Flame

scholarly journals Flame Dynamics Intermittency in the Bi-Stable Region Near a Subcritical Hopf Bifurcation

2017 ◽  
Author(s):  
D. Ebi ◽  
A. Denisov ◽  
G. Bonciolini ◽  
E. Boujo ◽  
N. Noiray
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Acoustic Pressure ◽  
Oscillation Amplitude ◽  
Stable Region ◽  
Describing Function ◽  
Acoustic Damping ◽  
Intermittent Behavior ◽  
Flame Describing Function

We report experimental evidence of thermoacoustic bi-stability in a lab-scale turbulent combustor over a well-defined range of fuel-air equivalence ratios. Pressure oscillations are characterized by an intermittent behavior with “bursts”, i.e. sudden jumps between low and high amplitudes occurring at random time instants. The corresponding probability density functions of the acoustic pressure signal show clearly separated maxima when the burner is operated in the bi-stable region. A flame describing function, which links acoustic pressure to heat release rate fluctuations, is estimated at the modal frequency from simultaneously recorded flame chemiluminescence and acoustic pressure. The representation of its statistics is new and particularly informative. It shows that this describing function is characterized, in average, by a nearly constant gain and by a significant drift of the phase as function of the oscillation amplitude. This finding suggests that the bi-stability does not result from an amplitude-dependent balance between flame gain and acoustic damping, but rather from the non-constant phase difference between the acoustic pressure and the coherent fluctuations of heat release rate.

Optimum Damping in a Randomly Excited Non-Linear Suspension

1969 ◽  
Vol 184 (1) ◽  
pp. 169-184 ◽  
Author(s):  
A. G. Thompson
Keyword(s):  
Function Method ◽  
Analogue Computer ◽  
Describing Function ◽  
Road Roughness ◽  
Automobile Suspension ◽  
Linear Damping ◽  
The Mean ◽  
Spectrum Characteristics ◽  
Describing Function Method ◽  
Computer Studies

Analogue computer studies of an automobile suspension on a simulated random road show that optimum ride and road holding can be achieved with linear damping for all magnitudes of road roughness. Unsymmetrical damping, however, provides better isolation from large bumps and obstacles at the expense of only very moderate increases in the mean-squared values for random inputs. Optimum values for the ratio of bump to rebound damping rates are obtained by use of an integral-square criterion. For a linear system the effects of the seat dynamics and road power spectrum characteristics are illustrated using the results of a digital computer program. The influence of the non-linearities on mean-square values is analysed theoretically and the statistical describing function method applied.

Specific impedance of rabbit's cortical tissue

1963 ◽  
Vol 205 (1) ◽  
pp. 203-207 ◽  
Author(s):  
A. Van Harreveld ◽  
T. Murphy ◽  
K. W. Nobel
Keyword(s):  
White Matter ◽  
Lateral Ventricle ◽  
Mean Value ◽  
Surface Electrode ◽  
Cortical Tissue ◽  
Specific Impedance ◽  
The Mean

The impedance of a tissue slab consisting of both cortical gray and underlying white matter was measured at 1,000 cycles/sec between a surface electrode and a deep electrode placed in the lateral ventricle or in the underlying tissue. By calibrating the electrode assembly with a KCl solution of known conductivity the mean specific impedance of the slab could be computed. Through a hole in the center of the surface electrode a probe was lowered stepwise, and the potential between its tip and the deep electrode was determined after each change in position. In a graph of the potential plotted against the position of the tip, the ratios of the specific impedances of the various layers of tissues in the slab and the thicknesses of these layers could be determined. From these data and the mean specific impedance of the tissue slab the specific impedance of the cortex was computed. The mean value determined in 14 experiments was 208 ± 6 ohms cm. The specific impedance of the white matter was materially greater. Taking into consideration the conductivity of the blood in the vessels the specific impedance of the cortical tissue proper was estimated as 220 ohms cm.

Heat Transfer in Compression-Ignition Engines: First Paper: Heat Transfer in a Quiescent Chamber Diesel Engine

1970 ◽  
Vol 185 (1) ◽  
pp. 963-975 ◽  
Author(s):  
N. D. Whitehouse
Keyword(s):  
Heat Transfer ◽  
Combustion Chamber ◽  
Realistic Model ◽  
Compression Ignition ◽  
Usual Model ◽  
Mean Values ◽  
Transfer Rates ◽  
Compression Ignition Engines ◽  
Instantaneous Values ◽  
The Mean

Instantaneous and mean values of heat transfer at various positions in the combustion chamber were obtained, by means of surface thermocouples, for different loads and speeds and compared with those obtained theoretically from synthesized cycle calculations. The results show that the usual model of homogeneity in the cylinder is inadequate for heat transfer calculations. Peak rates of heat transfer when in the vicinity of a fuel spray were comparatively little dependent upon load or speed. At the periphery of the combustion chamber the mean heat transfer rates were appreciably lower than to the cylinder head and piston and the rapid rise in instantaneous values occurred appreciably later. The results all suggest the need for a more realistic model based upon the geometry and penetration of the fuel sprays.

Describing Function Analysis of Limit Cycles in a Multiple Flame Combustor

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Frédéric Boudy ◽  
Daniel Durox ◽  
Thierry Schuller ◽  
Grunde Jomaas ◽  
Sébastien Candel
Keyword(s):  
Transfer Function ◽  
Limit Cycle ◽  
Limit Cycles ◽  
Function Analysis ◽  
Combustion Instabilities ◽  
Describing Function ◽  
Variable Size ◽  
Theoretical Predictions ◽  
Flame Describing Function ◽  
Oscillation Frequencies

A recently developed nonlinear flame describing function (FDF) is used to analyze combustion instabilities in a system where the feeding manifold has a variable size and where the flame is confined by quartz tubes of variable length. Self-sustained combustion oscillations are observed when the geometry is changed. The regimes of oscillation are characterized at the limit cycle and also during the onset of oscillations. The theoretical predictions of the oscillation frequencies and levels are obtained using the FDF. This generalizes the concept of flame transfer function by including dependence on the frequency and level of oscillation. Predictions are compared with experimental results for two different lengths of the confinement tube. These results are, in turn, used to predict most of the experimentally observed phenomena and in particular, the correct oscillation levels and frequencies at limit cycles.

scholarly journals Analisa Kinerja Pada Perencanaan TD-LTE ADVANCED Studi Kasus Kota Bandung

AVITEC ◽  
2020 ◽  
Vol 2 (2) ◽  
Author(s):  
Purusadi Hastruman ◽  
Arfianto Fahmi ◽  
Uke Kurniawan Usman
Keyword(s):  
Reference Signal ◽  
Signal Strength ◽  
Advanced Technology ◽  
Frequency Division ◽  
Bit Rate ◽  
Received Power ◽  
Lte Advanced ◽  
Advanced Planning ◽  
The Mean ◽  
Time Division

In LTE Advanced technology there are two methods used in the duplexing process, there are frequency division duplex (FDD) wherein this duplexing concept communication is divided based on the frequency and the other is time division duplex (TDD) where communication is divided based on the time. Duplexing using the TDD method has advantages of handling data-based services that the majority have Non-Guarantee Bit Rate (N-GBR) characteristics because most of these services do not require a minimum bit rate to be able to work and this is an advantages because nowadays people like to use data-based services. So in this LTE Advanced network planning using the TDD method,  frequency 2300 MHz for TD-LTE advanced, and parameters that to be the main focus are throughputs, reference signal received power (RSRP), reference signal strength indicator (RSSI), carrier to interference noise ratio (CINR), and block error rate (BLER). And the result of the simulations from TD-LTE Advanced planning are the mean of throughput value is 3,5 Mbps, mean of RSRP value is -110,8 dBm, mean of RSSI value is -72,36 dBm, mean of CINR value is 4,81 dB, and mean of BLER value is 0,07%.

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