A Model for the Thermo-Acoustic Feedback of Transverse Acoustic Modes and Periodic Oscillations in Flame Position in Cylindrical Flame Tubes

2012 ◽  
Author(s):  
Joachim Schwing ◽  
Felix Grimm ◽  
Thomas Sattelmayer
Keyword(s):  
Heat Release ◽  
High Frequency ◽  
Circular Cross Section ◽  
Experimental Investigations ◽  
Constant Density ◽  
Rayleigh Criterion ◽  
Velocity Fluctuations ◽  
Acoustic Modes ◽  
High Frequency Oscillations ◽  
Transverse Acoustic

In the past decades, several feedback mechanisms for longitudinal acoustic modes in gas turbine combustors have been investigated. These mechanisms are successfully used in predictive tools like acoustic network models to analyze low-frequency instabilities in combustion systems. In contrast, little is known about high-frequency oscillations — fluctuations at several kHz. Most theories are derived from experimental investigations of afterburners in the 1950s and 1960s, indicating an interaction of vortex shedding, fluctuating vorticity and heat release. In this work a different feedback mechanism for high-frequency oscillations in cylindrical flame tubes related to transverse acoustic modes is suggested and analysed: Transverse acoustic pressure fluctuations are linked to an oscillating velocity field. A time-dependent but periodic displacement field can be derived from these velocity fluctuations. The model assumes that the zone of heat release is displaced by the velocity fluctuations. Pressure oscillations and periodically deflected heat release lead to a contribution to the Rayleigh criterion without fluctuations in the global heat release. This effect is studied in a circular cross section presuming a circular zone of heat release. Expressions for the displacement of the flame front are derived from the analytical solution of the wave equation in cylindrical geometries assuming a quiescent medium, constant density and speed of sound. The Rayleigh criterion is integrated and growth rates are evaluated whereas damping effects are neglected as they are not subject to this study. Characteristics of the model are assessed and compared to experimental observations to check the validity and the applicability of the theory.

Identification of High-Frequency Transverse Acoustic Modes in Multi-Nozzle Can Combustors

2021 ◽  
Author(s):  
Jeong-Won Kim ◽  
Wesley Gillman ◽  
David Wu ◽  
Benjamin Emerson ◽  
Vishal Acharya ◽  
...  
Keyword(s):  
High Frequency ◽  
Acoustic Modes ◽  
Transverse Acoustic

A Driving Mechanism for High Frequency Combustion Instability in Liquid Fuel Rocket Engines

1964 ◽  
Vol 68 (645) ◽  
pp. 633-637 ◽  
Author(s):  
P. D. McCormack
Keyword(s):  
High Frequency ◽  
Liquid Fuel ◽  
Low Frequency ◽  
Pressure Oscillation ◽  
Experimental Investigations ◽  
Driving Mechanism ◽  
Rocket Engines ◽  
High Frequency Oscillations ◽  
The Subject ◽  
Motor Operation

The problem of combustion pressure oscillation in liquid-fuel rocket motor operation has long been the subject of theoretical and experimental investigations.The low frequency (less than 200 cps) type of oscillation, known as “chugging”, has been thoroughly analysed and the problem solved (see Crocco, 5th Combustion Symposium, p. 164).This Note is concerned with the more complex (and more destructive) high frequency oscillations, covering a range from about 1000 to 6000 cps. Such oscillations can resonate with the acoustical modes of the combustion chamber. Longitudinal, tangential and radial oscillating modes have been observed.

Swirl Flame Response to Simultaneous Axial and Transverse Velocity Fluctuations

2016 ◽  
Author(s):  
Aditya Saurabh ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit
Keyword(s):  
Relative Phase ◽  
Transverse Velocity ◽  
Experimental Investigations ◽  
Velocity Fluctuations ◽  
Transverse Acoustic ◽  
Flame Response ◽  
Acoustic Velocities ◽  
Acoustic Forcing ◽  
Swirl Flame ◽  
The Impact

In this experimental study we investigate the impact of transverse acoustic velocity fluctuations on the flame transfer function in response to axial velocity fluctuations. A generic swirl flame is exposed to transverse acoustic velocities of varying amplitude and relative phase simultaneously with axial acoustic forcing. Results obtained indicate that transverse velocity affects flame response, and both the magnitude of transverse velocity and its phase with respect to axial forcing are important factors. In addition to this key results, considerations for experimental investigations dealing with transverse acoustic forcing have been discussed.

Forced Flame Response of a Lean Premixed Multi-Nozzle Can Combustor

2011 ◽  
Author(s):  
Michael T. Szedlmayer ◽  
Bryan D. Quay ◽  
Janith Samarasinghe ◽  
Alex De Rosa ◽  
Jong Guen Lee ◽  
...  
Keyword(s):  
Heat Release ◽  
High Frequency ◽  
Transfer Functions ◽  
Low Frequency ◽  
Forced Response ◽  
Operating Conditions ◽  
Velocity Fluctuations ◽  
Lean Premixed ◽  
Flame Response ◽  
Rate Of Heat Release

An experimental investigation was conducted to determine the air-forced flame response of a five-nozzle, 250 kW, lean premixed gas turbine can combustor. Operating conditions were varied over a range of inlet temperatures, inlet velocities, and equivalence ratios, while the forcing frequency was varied from 100 to 450 Hz with constant normalized velocity fluctuations of approximately 5%. The response of the flame’s rate of heat release to inlet velocity fluctuations is expressed in terms of the phase and gain of a flame transfer function. In addition, chemiluminescence imaging is used to characterize the time-averaged and phase-averaged spatial distribution of the flame’s heat release. The resulting flame transfer functions and chemiluminescence flame images are compared to each other to determine the effects of varying the operating conditions. In addition, they are compared to data obtained from a single-nozzle combustor with the same injector. The forced response of the multi-nozzle flame demonstrates a similar pattern to those obtained in a single-nozzle combustor with the same injector. An exception occurs at high frequency where the multi-nozzle flame responds to a greater degree than the single-nozzle flame. At low frequency the multi-nozzle flame dampens the perturbations while the single-nozzle flame amplifies them. A number of minima and maxima occur at certain frequencies which correspond to the interference of two mechanisms. The frequency of these minima is nearly the same for the single- and multi-nozzle cases. When plotted with respect to Strouhal number instead of frequency there is a degree of collapse that occurs around the first observed minima.

scholarly journals Can we use intraoperative high‐frequency oscillations to guide tumor‐related epilepsy surgery?

Epilepsia ◽  
2021 ◽  
Author(s):  
Nicole E. C. Klink ◽  
Willemiek J. E. M. Zweiphenning ◽  
Cyrille H. Ferrier ◽  
Peter H. Gosselaar ◽  
Kai J. Miller ◽  
...  
Keyword(s):  
Epilepsy Surgery ◽  
High Frequency ◽  
High Frequency Oscillations

scholarly journals High-frequency oscillations recorded with surface EEG in neonates with seizures

2021 ◽  
Author(s):  
Lotte Noorlag ◽  
Maryse A. van 't Klooster ◽  
Alexander C. van Huffelen ◽  
Nicole E.C. van Klink ◽  
Manon J.N.L. Benders ◽  
...  
Keyword(s):  
High Frequency ◽  
High Frequency Oscillations ◽  
Surface Eeg
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