Influence of Fuel-Air Mixing on Flame Dynamics of Premixed Swirl Burners

2014 ◽  
Author(s):  
Stefanie Bade ◽  
Michael Wagner ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer ◽  
Bruno Schuermans
Keyword(s):  
Transfer Function ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Detailed Comparison ◽  
Acoustic Oscillation ◽  
Modular System ◽  
Time Behavior ◽  
Flame Dynamics ◽  
Air Mixing ◽  
The Difference

The influence of fuel-air mixing on the flame dynamics of premixed swirl flames is investigated comparing flame transfer functions determined for perfectly premixed (PP) and technically premixed (TP) operation. In PP operation fuel and air are mixed far upstream of the burner so no equivalence ratio fluctuations appear during thermo-acoustic oscillation. In TP operation the fuel is injected in the swirler slots so equivalence ratio fluctuations occur. The employed swirl burner is a modular system that consists of a swirler and a mixing tube with three different lengths. It was investigated in an atmospheric single burner test rig equipped for flame transfer matrix measurements. Flame transfer function data are presented for both the PP and the TP operation for a variation of power at fixed equivalence ratio and a variation of equivalence ratio for constant power. The unforced flame shapes corresponding to these operation points were acquired and analyzed for scaling parameters of the flame response. It was found that a basic frequency scaling can be achieved for both operation modes using the nominal burner velocity and the flame stand-off distance. A detailed comparison of the PP and TP flame transfer functions is performed for the three different mixing tubes at one operation point. Finally the difference between the PP and the TP flame transfer function is presented and discussed. It is shown that the influence of equivalence ratio fluctuations exhibits a generalized delay time behavior.

Optical Measurement of Local and Global Transfer Functions for Equivalence Ratio Fluctuations in a Turbulent Swirl Flame

2013 ◽  
Author(s):  
Bernhard C. Bobusch ◽  
Bernhard Ćosić ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Optical Measurement ◽  
Low Frequencies ◽  
Fuel Flow ◽  
Calibration Measurement

Equivalence ratio fluctuations are known to be one of the key factors controlling thermoacoustic stability in lean premixed gas turbine combustors. The mixing and thus the spatio-temporal evolution of these perturbations in the combustor flow is, however, difficult to account for in present low-order modeling approaches. To investigate this mechanism, experiments in an atmospheric combustion test rig are conducted. To assess the importance of equivalence ratio fluctuations in the present case, flame transfer functions for different injection positions are measured. By adding known perturbations in the fuel flow using a solenoid valve, the influence of equivalence ratio oscillations on the heat release rate is investigated. The spatially and temporally resolved equivalence ratio fluctuations in the reaction zone are measured using two optical chemiluminescence signals, captured with an intensified camera. A steady calibration measurement allows for the quantitative assessment of the equivalence ratio fluctuations in the flame. This information is used to obtain a mixing transfer function, which relates fluctuations in the fuel flow to corresponding fluctuations in the equivalence ratio of the flame. The current study focuses on the measurement of the global, spatially integrated, transfer function for equivalence ratio fluctuations and the corresponding modeling. In addition, the spatially resolved mixing transfer function is shown and discussed. The global mixing transfer function reveals that despite the good spatial mixing quality of the investigated generic burner, the ability to damp temporal fluctuations at low frequencies is rather poor. It is shown that the equivalence ratio fluctuations are the governing heat release rate oscillation response mechanism for this burner in the low-frequency regime. The global transfer function for equivalence ratio fluctuations derived from the measurements is characterized by a pronounced low-pass characteristic, which is in good agreement with the presented convection–diffusion mixing model.

scholarly journals Cross-site investigation on head-related and headphone transfer functions: variabilities in relation to loudness balancing

Acta Acustica ◽  
2021 ◽  
Vol 5 ◽  
pp. 58
Author(s):  
Michael Kohnen ◽  
Florian Denk ◽  
Josep Llorca-Bofi ◽  
Birger Kollmeier ◽  
Michael Vorländer
Keyword(s):  
Transfer Function ◽  
Transfer Functions ◽  
Site Investigation ◽  
Limited Range ◽  
The Difference ◽  
Lower Variability ◽  
Set Up ◽  
Insert Earphones ◽  
High Repeatability ◽  
Cross Site

Headphone transfer function (HpTF) and head-related transfer function (HRTF) measurements are crucial in acoustic science and in binaural virtual acoustic applications. Yet, their measurement set-up, procedure or post-processing is different for nearly every lab, especially for the HRTF measurements. To compare findings between different labs, these measurement deviations have to be quantified alongside with their influence on perceptual aspects. In the scope of a cross-site investigation on loudness balancing between headphone and loudspeaker listening, a set of HpTFs with three different headphones (open, closed, insert earphones) and HRTF close to the eardrum were measured in 14 participants travelling to two different measurement sites at Aachen and Oldenburg. Though set-ups for measuring the HRTF are very different between sites, the gathered HRTFs are quite consistent across them. For the measured HpTFs, across sites the open headphones consistently yield a slightly lower variability in the range from 70 to 5000 Hz than the closed one while the insert earphones exhibit much higher variabilities and a limited range of reproducible results. The difference in loudness balancing across labs could well be predicted by site-specific systematic differences in HpTFs with the exception of 1 kHz narrowband stimulus. This clearly indicates the limits in comparability of HpTFs and loudness balancing across labs and the importance of using headphones with high repeatability like the open ones used in this investigation.

Thermoacoustic Modeling of a Gas Turbine Using Transfer Functions Measured Under Full Engine Pressure

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Bruno Schuermans ◽  
Felix Guethe ◽  
Douglas Pennell ◽  
Daniel Guyot ◽  
Christian Oliver Paschereit
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Gas Turbine ◽  
Mass Flow ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Test Facility ◽  
Optical Technique ◽  
Optical Techniques ◽  
Acoustic Technique

Thermoacoustic transfer functions of a full-scale gas turbine burner operating under full engine pressure have been measured. The excitation of the high-pressure test facility was done using a siren that modulated a part of the combustion airflow. Pulsation probes have been used to record the acoustic response of the system to this excitation. In addition, the flame’s luminescence response was measured by multiple photomultiplier probes and a light spectrometer. Three techniques to obtain the thermoacoustic transfer function are proposed and employed: two acoustic-optical techniques and a purely acoustic technique. The first acoustical-optical technique uses one single optical signal capturing the chemiluminescence intensity of the flame as a measure for the heat release in the flame. This technique only works if heat release fluctuations in the flame have only one generic source, e.g., equivalence ratio or mass flow fluctuations. The second acoustic-optical technique makes use of the different response of the flame’s luminescence at different optical wavelengths bands to acoustic excitation. It also works, if the heat release fluctuations have two contributions, e.g., equivalence ratio and mass flow fluctuation. For the purely acoustic technique, a new method was developed in order to obtain the flame transfer function, burner transfer function, and flame source term from only three pressure transducer signals. The purely acoustic method could be validated by the results obtained from the acoustic-optical techniques. The acoustic and acoustic-optical methods have been compared and a discussion on the benefits and limitations of each is given. The measured transfer functions have been implemented into a nonlinear, three-dimensional, time domain network model of a gas turbine with an annular combustion chamber. The predicted pulsation behavior shows a good agreement with pulsation measurements on a field gas turbine.

scholarly journals A difference in a transfer function of two horizontal components between the ground level and the borehole at KiK-net Mashiki Station Anisotropy of shear wave propagation in Kyushu area based on seismic interferometry

2020 ◽  
Author(s):  
Kentaro Motoki ◽  
Kenichi Kato
Keyword(s):  
Transfer Function ◽  
Travel Time ◽  
Transfer Functions ◽  
Source Region ◽  
Seismic Interferometry ◽  
Polarization Direction ◽  
S Wave ◽  
Before And After ◽  
The Difference ◽  
Kyushu District

Abstract In this study, we evaluated the travel time of S-wave between the vertical array stations based on seismic interferometry, focusing on the difference in transfer function due to two horizontal components at the KiK-net Mashiki station (KMMH16). At that time, we surveyed the differences by back azimuth (BAZ) and the polarization direction of seismic waves. Furthermore, we expanded the survey to all KiK-net stations in the Kyushu district, to confirm whether the phenomena seen at KMMH16 is specific to this location. The result shows that the difference by the polarization direction in the travel time was larger than the difference by the BAZ. This result suggests that the difference in transfer function at KMMH16 were affected by the anisotropy of the S-wave velocity. We evaluated the leading S-wave polarization directions (LSPDs) and the strength of anisotropy (ΔV) for all KiK-net stations in the Kyushu district. The LSPDs roughly correspond to the results of previous studies. The LSPDs in the forearc area are nearly perpendicular to the crustal deformation whereas those in the back-arc area are nearly parallel to it. This characteristic is similar to one found by Nakajima and Hasegawa (2008) in the Tohoku district. We examined the change in anisotropy before and after the Kumamoto earthquake at two stations, KMMH16 and KMMH14 that are located near the source region. The changes in the LSPD and the ΔV before and after the earthquake were not notable. At stations that observed weak anisotropy, transfer functions of two horizontal components show similar shape. At stations that observed strong anisotropy, however, the shape of the transfer function differs greatly, depending on the horizontal direction. This suggests that an evaluation of site amplification using a single velocity model may reduce the reproducibility of ground motions.

scholarly journals A difference in a transfer function of two horizontal components between the ground level and the borehole at KiK-net Mashiki Station Anisotropy of shear wave propagation in Kyushu area based on seismic interferometry

2020 ◽  
Author(s):  
Kentaro Motoki ◽  
Kenichi Kato
Keyword(s):  
Transfer Function ◽  
Travel Time ◽  
Transfer Functions ◽  
Source Region ◽  
Seismic Interferometry ◽  
Polarization Direction ◽  
S Wave ◽  
Before And After ◽  
The Difference ◽  
Kyushu District

Abstract In this study, we evaluated the travel time of S-wave between the vertical array stations based on seismic interferometry, focusing on the difference in transfer function due to two horizontal components at the KiK-net Mashiki station (KMMH16). At that time, we surveyed the differences by back azimuth (BAZ) and the polarization direction of seismic waves. Furthermore, we expanded the survey to all KiK-net stations in the Kyushu district, to confirm whether the phenomena seen at KMMH16 is specific to this location. The result shows that the difference by the polarization direction in the travel time was larger than the difference by the BAZ. This result suggests that the difference in transfer function at KMMH16 were affected by the anisotropy of the S-wave velocity. We evaluated the leading S-wave polarization directions (LSPDs) and the strength of anisotropy (ΔV) for all KiK-net stations in the Kyushu district. The LSPDs roughly correspond to the results of previous studies. The LSPDs in the forearc area are nearly perpendicular to the crustal deformation whereas those in the back-arc area are nearly parallel to it. This characteristic is similar to one found by the previous research in the Tohoku district. We examined the change in anisotropy before and after the Kumamoto earthquake at two stations, KMMH16 and KMMH14 that are located near the source region. The changes in the LSPD and the ΔV before and after the earthquake were not notable. At stations that observed weak anisotropy, transfer functions of two horizontal components show similar shape. At stations that observed strong anisotropy, however, the shape of the transfer function differs greatly, depending on the horizontal direction. This suggests that an evaluation of site amplification using a single velocity model may reduce the reproducibility of ground motions.

Thermoacoustic Modeling of a Gas Turbine Using Transfer Functions Measured at Full Engine Pressure

2009 ◽  
Author(s):  
Bruno Schuermans ◽  
Felix Guethe ◽  
Douglas Pennel ◽  
Daniel Guyot ◽  
Christian Oliver Paschereit
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Gas Turbine ◽  
Mass Flow ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Optical Methods ◽  
Test Facility ◽  
Optical Technique ◽  
Acoustic Technique

Thermoacoustic transfer functions have been measured of a full-scale gas turbine burner operating at full engine pressure. Excitation of the high-pressure test facility was done using a siren that modulated part of the combustion airflow. Pulsation probes have been used to record the acoustic response of the system to this excitation. In addition, the flame’s luminescence response was measured by multiple photomultiplier tubes and a light spectrometer. Three techniques to obtain the thermoacoustic transfer function are proposed and employed: two combined acoustical-optical technique and a purely acoustic technique. The first acoustical-optical technique uses one single optical signal capturing the chemiluminescence intensity of the flame as a measure for the heat release in the flame. It only works, if heat release fluctuations in the flame have only one contribution, e.g. equivalence ratio or mass flow fluctuations. The second acoustic-optical acoustic-optical technique makes use of the different response of the flame’s luminescence at different optical wavelengths bands to acoustic excitation. It also works, if the heat release fluctuations have two contributions, e.g. equivalence ratio and mass flow fluctuation. For the purely acoustic technique, a new method was developed in order to obtain the flame transfer function, burner transfer function and flame source term from only three pressure transducer signals. The purely acoustic method could be validated by the results obtained from the acoustic-optical techniques. The acoustic and acoustic-optical methods have been compared and a discussion on the benefits and limitations of the methods is given. The measured transfer functions have been implemented into a non-linear, three-dimensional, time domain network model of a gas turbine with an annular combustion chamber. The predicted pulsation behavior shows a good agreement with pulsation measurements on a field gas turbine.

scholarly journals Spatial orientation and distribution of reservoir fractures from scattered seismic energy

Geophysics ◽  
2006 ◽  
Vol 71 (5) ◽  
pp. O43-O51 ◽  
Author(s):  
Mark E. Willis ◽  
Daniel R. Burns ◽  
Rama Rao ◽  
Burke Minsley ◽  
M. Nafi Toksöz ◽  
...  
Keyword(s):  
Transfer Function ◽  
Seismic Waves ◽  
Transfer Functions ◽  
Full Range ◽  
Seismic Energy ◽  
Field Measurements ◽  
Discrete Systems ◽  
Fractured Reservoir ◽  
Fracture Spacing ◽  
The Difference

We present the details of a new method for determining the reflection and scattering characteristics of seismic energy from subsurface fractured formations. The method is based upon observations we have made from 3D finite-difference modeling of the reflected and scattered seismic energy over discrete systems of vertical fractures. Regularly spaced, discrete vertical fracture corridors impart a coda signature, which is a ringing tail of scattered energy, to any seismic waves which are transmitted through or reflected off of them. This signature varies in amplitude and coherence as a function of several parameters including: (1) the difference in angle between the orientation of the fractures and the acquisition direction, (2) the fracture spacing, (3) the wavelength of the illuminating seismic energy, and (4) the compliance, or stiffness, of the fractures. This coda energy is most coherent when the acquisition direction is parallel to the strike ofthe fractures. It has the largest amplitude when the seismic wavelengths are tuned to the fracture spacing, and when the fractures have low stiffness. Our method uses surface seismic reflection traces to derive a transfer function that quantifies the change in an apparent source wavelet before and after propagating through a fractured interval. The transfer function for an interval with no or low amounts of scattering will be more spikelike and temporally compact. The transfer function for an interval with high scattering will ring and be less temporally compact. When a 3D survey is acquired with a full range of azimuths, the variation in the derived transfer functions allows us to identify subsurface areas with high fracturing and to determine the strike of those fractures. We calibrated the method with model data and then applied it to the Emilio field with a fractured reservoir. The method yielded results which agree with known field measurements and previously published fracture orientations derived from PS anisotropy.

Optical Measurement of Local and Global Transfer Functions for Equivalence Ratio Fluctuations in a Turbulent Swirl Flame

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Bernhard C. Bobusch ◽  
Bernhard Ćosić ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Optical Measurement ◽  
Low Frequencies ◽  
Fuel Flow ◽  
Calibration Measurement

Equivalence ratio fluctuations are known to be one of the key factors controlling thermoacoustic stability in lean premixed gas turbine combustors. The mixing and thus the spatiotemporal evolution of these perturbations in the combustor flow is, however, difficult to account for in present low-order modeling approaches. To investigate this mechanism, experiments in an atmospheric combustion test rig are conducted. To assess the importance of equivalence ratio fluctuations in the present case, flame transfer functions for different injection positions are measured. By adding known perturbations in the fuel flow using a solenoid valve, the influence of equivalence ratio oscillations on the heat release rate is investigated. The equivalence ratio fluctuations in the reaction zone are measured spatially and temporally resolved using two optical chemiluminescence signals, captured with an intensified camera. A steady calibration measurement allows for the quantitative assessment of the equivalence ratio fluctuations in the flame. This information is used to obtain a mixing transfer function, which relates fluctuations in the fuel flow to corresponding fluctuations in the equivalence ratio of the flame. The current study focuses on the measurement of the global, spatially integrated, transfer function for equivalence ratio fluctuations and the corresponding modeling. In addition, the spatially resolved mixing transfer function is shown and discussed. The global mixing transfer function reveals that, despite the good spatial mixing quality of the investigated generic burner, the ability to damp temporal fluctuations at low frequencies is rather poor. It is shown that the equivalence ratio fluctuations are the governing heat release rate oscillation response mechanism for this burner in the low-frequency regime. The global transfer function for equivalence ratio fluctuations derived from the measurements is characterized by a pronounced low-pass characteristic, which is in good agreement with the presented convection–diffusion mixing model.

Analytic integration of contrast transfer functions

1988 ◽  
Vol 46 ◽  
pp. 822-823
Author(s):  
Peter Rez
Keyword(s):  
Wave Function ◽  
Transfer Function ◽  
Transfer Functions ◽  
Spherical Aberration ◽  
Continuous Distribution ◽  
Objective Lens ◽  
Direction Parallel ◽  
Scattering Angle ◽  
Analytic Integration ◽  
Image Position

In high resolution microscopy the image amplitude is given by the convolution of the specimen exit surface wave function and the microscope objective lens transfer function. This is usually done by multiplying the wave function and the transfer function in reciprocal space and integrating over the effective aperture. For very thin specimens the scattering can be represented by a weak phase object and the amplitude observed in the image plane is1where fe (Θ) is the electron scattering factor, r is a postition variable, Θ a scattering angle and x(Θ) the lens transfer function. x(Θ) is given by2where Cs is the objective lens spherical aberration coefficient, the wavelength, and f the defocus.We shall consider one dimensional scattering that might arise from a cross sectional specimen containing disordered planes of a heavy element stacked in a regular sequence among planes of lighter elements. In a direction parallel to the disordered planes there will be a continuous distribution of scattering angle.

Trombone Transfer Functions: Comparison Between Frequency-Swept Sine Wave and Human Performer Input

2012 ◽  
Vol 37 (4) ◽  
pp. 447-454
Author(s):  
James W. Beauchamp
Keyword(s):  
Transfer Function ◽  
Transfer Functions ◽  
Cutoff Frequency ◽  
Sine Wave ◽  
Nonlinear Propagation ◽  
Linear Filter ◽  
Wave System ◽  
General Effect ◽  
Filter Characteristic ◽  
High Pass

Abstract Source/filter models have frequently been used to model sound production of the vocal apparatus and musical instruments. Beginning in 1968, in an effort to measure the transfer function (i.e., transmission response or filter characteristic) of a trombone while being played by expert musicians, sound pressure signals from the mouthpiece and the trombone bell output were recorded in an anechoic room and then subjected to harmonic spectrum analysis. Output/input ratios of the signals’ harmonic amplitudes plotted vs. harmonic frequency then became points on the trombone’s transfer function. The first such recordings were made on analog 1/4 inch stereo magnetic tape. In 2000 digital recordings of trombone mouthpiece and anechoic output signals were made that provide a more accurate measurement of the trombone filter characteristic. Results show that the filter is a high-pass type with a cutoff frequency around 1000 Hz. Whereas the characteristic below cutoff is quite stable, above cutoff it is extremely variable, depending on level. In addition, measurements made using a swept-sine-wave system in 1972 verified the high-pass behavior, but they also showed a series of resonances whose minima correspond to the harmonic frequencies which occur under performance conditions. For frequencies below cutoff the two types of measurements corresponded well, but above cutoff there was a considerable difference. The general effect is that output harmonics above cutoff are greater than would be expected from linear filter theory, and this effect becomes stronger as input pressure increases. In the 1990s and early 2000s this nonlinear effect was verified by theory and measurements which showed that nonlinear propagation takes place in the trombone, causing a wave steepening effect at high amplitudes, thus increasing the relative strengths of the upper harmonics.

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