scholarly journals Experimental Investigation of Injection-Coupled High-Frequency Combustion Instabilities

2020 ◽  
pp. 249-262
Author(s):  
Wolfgang Armbruster ◽  
Justin S. Hardi ◽  
Michael Oschwald
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Acoustic Resonance ◽  
Dynamic Mode Decomposition ◽  
Coupling Mechanism ◽  
Rocket Engines ◽  
Combustion Instabilities ◽  
High Speed Imaging ◽  
Flame Dynamics ◽  
Flame Response

Abstract Self-excited high-frequency combustion instabilities were investigated in a 42-injector cryogenic rocket combustor under representative conditions. In previous research it was found that the instabilities are connected to acoustic resonance of the shear-coaxial injectors. In order to gain a better understanding of the flame dynamics during instabilities, an optical access window was realised in the research combustor. This allowed 2D visualisation of supercritical flame response to acoustics under conditions similar to those found in European launcher engines. Through the window, high-speed imaging of the flame was conducted. Dynamic Mode Decomposition was applied to analyse the flame dynamics at specific frequencies, and was able to isolate the flame response to injector or combustion chamber acoustic modes. The flame response at the eigenfrequencies of the oxygen injectors showed symmetric and longitudinal wave-like structures on the dense oxygen core. With the gained understanding of the BKD coupling mechanism it was possible to derive LOX injector geometry changes in order to reduce the risks of injection-coupled instabilities for future cryogenic rocket engines.

scholarly journals Flame response to high-frequency oscillations in a cryogenic oxygen/hydrogen rocket combustor

2019 ◽  
Author(s):  
N. Fdida ◽  
J. Hardi ◽  
H. Kawashima ◽  
B. Knapp ◽  
M. Oschwald ◽  
...  
Keyword(s):  
High Frequency ◽  
Acoustic Resonance ◽  
High Amplitude ◽  
Operating Conditions ◽  
Test Facility ◽  
Response Analysis ◽  
Rocket Engines ◽  
Acoustic Oscillations ◽  
Spatially Resolved ◽  
Flame Response

Experiments presented in this paper were conducted with the BKH rocket combustor at the European Research and Technology Test Facility P8, located at DLR Lampoldshausen. This combustor is dedicated to study the effects of high magnitude instabilities on oxygen/hydrogen flames, created by forcing high-frequency (HF) acoustic resonance of the combustion chamber. This work addresses the need for highly temporally and spatially resolved visualization data, in operating conditions representative of real rocket engines, to better understand the flame response to high amplitude acoustic oscillations. By combining ONERA and DLR materials and techniques, the optical setup of this experiment has been improved to enhance the existing database with more highly resolved OH* imaging to allow detailed response analysis of the flame. OH* imaging is complemented with simultaneous visible imaging and compared to each other here for their ability to capture flame dynamics.

Experimental Measurement of In-Plane Rolling Nonpneumatic Tire Vibrations Using High-Speed Imaging

2019 ◽  
Vol 47 (3) ◽  
pp. 196-210
Author(s):  
Meghashyam Panyam ◽  
Beshah Ayalew ◽  
Timothy Rhyne ◽  
Steve Cron ◽  
John Adcox
Keyword(s):  
High Speed ◽  
Image Correlation ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
High Speed Imaging ◽  
Correlation Algorithm ◽  
Mode Decomposition ◽  
Series Of Experiments ◽  
Plane Deformations ◽  
Dominant Frequencies

ABSTRACT This article presents a novel experimental technique for measuring in-plane deformations and vibration modes of a rotating nonpneumatic tire subjected to obstacle impacts. The tire was mounted on a modified quarter-car test rig, which was built around one of the drums of a 500-horse power chassis dynamometer at Clemson University's International Center for Automotive Research. A series of experiments were conducted using a high-speed camera to capture the event of the rotating tire coming into contact with a cleat attached to the surface of the drum. The resulting video was processed using a two-dimensional digital image correlation algorithm to obtain in-plane radial and tangential deformation fields of the tire. The dynamic mode decomposition algorithm was implemented on the deformation fields to extract the dominant frequencies that were excited in the tire upon contact with the cleat. It was observed that the deformations and the modal frequencies estimated using this method were within a reasonable range of expected values. In general, the results indicate that the method used in this study can be a useful tool in measuring in-plane deformations of rolling tires without the need for additional sensors and wiring.

Modal Decomposition Analysis of Combustion Instability Due to External Perturbation in a Mesoscale Burner Array

2022 ◽  
Author(s):  
Jeongan Choi ◽  
Rajavasanth Rajasegar ◽  
Qili Liu ◽  
Tonghun Lee ◽  
Jihyung Yoo
Keyword(s):  
Growth Rates ◽  
High Speed ◽  
Combustion Instability ◽  
Decomposition Analysis ◽  
External Perturbation ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Combustion Instabilities ◽  
Thermoacoustic Instability ◽  
Growth Regime

Abstract In this work, the growth regime of combustion instability was studied by analyzing 10 kHz OH planar laser induced fluorescence (PLIF) images through a combination of dynamic mode decomposition (DMD) and spectral proper orthogonal decomposition (SPOD) methods. Combustion instabilities were induced in a mesoscale burner array through an external speaker at an imposed perturbation frequency of 210 Hz. During the transient onset of combustion instabilities, 10 kHz OH PLIF imaging was employed to capture spatially and temporally resolved flame images. Increased acoustic perturbations prevented flame reignition in the central recirculation zone and eventually led to the flame being extinguished inwards from the outer burner array elements. Coherent modes and their growth rates were obtained from DMD spectral analyses of high-speed OH PLIF images. Positive growth rates were observed at the forcing frequency during the growth regime. Coherent structures, closely associated with thermoacoustic instability, were extracted using an appropriate SPOD filter operation to identify mode structures that correlate to physical phenomena such as shear layer instability and flame response to longitudinal acoustic forcing. Overall, a combination of DMD and SPOD was shown to be effective at analyzing the onset and propagation of combustion instabilities, particularly under transient burner operations.

scholarly journals Flame Edge Dynamics and Interaction in a Multi-Nozzle Can Combustor With Fuel Staging

2019 ◽  
Author(s):  
Daniel Doleiden ◽  
Wyatt Culler ◽  
Ankit Tyagi ◽  
Stephen Peluso ◽  
Jacqueline O’Connor
Keyword(s):  
Vortex Shedding ◽  
High Speed ◽  
Pollutant Emissions ◽  
Destructive Interference ◽  
Combustion Instabilities ◽  
Acoustic Oscillations ◽  
Oscillation Phase ◽  
Phase Cancellation ◽  
Flame Dynamics ◽  
Fuel Staging

Abstract The characterization and mitigation of thermoacoustic combustion instabilities in gas turbine engines is necessary to reduce pollutant emissions, premature wear, and component failure associated with unstable flames. Fuel staging, a technique in which the fuel flow to a multi-nozzle combustor is unevenly distributed between the nozzles, has been shown to mitigate the intensity of self-excited combustion instabilities in multiple nozzle combustors. In our previous work, we hypothesized that staging suppresses instability through a phase-cancellation effect in which the heat release rate from the staged nozzle oscillates out of phase with that of the other nozzles, leading to destructive interference that suppresses the instability. This previous theory, however, was based on chemiluminescence imaging, which is a line-of-sight integrated technique. In this work, we use high-speed laser-induced fluorescence to further investigate instability suppression in two staging configurations: center-nozzle and outer-nozzle staging. An edge-tracking algorithm is used to compute local flame edge displacement as a function of time, allowing instability-driven edge oscillation phase coherence and other instantaneous flame dynamics to be spectrally and spatially resolved. Analysis of flame edge oscillations shows the presence of convecting coherent fluctuations of the flame edge caused by periodic vortex shedding. When the system is unstable, these two flame edges oscillate together as a result of high-intensity longitudinal-mode acoustic oscillations in the combustor that drive periodic vortex shedding at each of the nozzle exits. In the stable cases, however, the phase between the oscillations of the center and outer flame edges is greater than 90 degrees (∼114 degrees), suggesting that the phase-cancellation hypothesis may be valid. This analysis allows a better understanding of the instantaneous flame dynamics behind flame edge oscillation phase offset and fuel staging-based instability suppression.

Human respiratory input impedance between 32 and 800 Hz, measured by interrupter technique and forced oscillations

1997 ◽  
Vol 82 (3) ◽  
pp. 1018-1023 ◽  
Author(s):  
Urs Frey ◽  
Bela Suki ◽  
Richard Kraemer ◽  
Andrew C. Jackson
Keyword(s):  
High Frequency ◽  
Input Impedance ◽  
High Speed ◽  
Signal To Noise Ratio ◽  
Acoustic Resonance ◽  
Face Mask ◽  
Forced Oscillations ◽  
Tissue Resistance ◽  
Wide Range ◽  
The Face

Frey, Urs, Bela Suki, Richard Kraemer, and Andrew C. Jackson. Human respiratory input impedance between 32 and 800 Hz, measured by interrupter technique and forced oscillations. J. Appl. Physiol. 82(3): 1018–1023, 1997.—Respiratory input impedance (Zin) over a wide range of frequencies ( f) has been shown to be useful in determining airway resistance (Raw) and tissue resistance in dogs or airway wall properties in human adults. Zin measurements are noninvasive and, therefore, potentially useful in investigation of airway mechanics in infants. However, accurate measurements of Zin at these f values with the use of forced oscillatory techniques (FOT) in infants are difficult because of their relatively high Raw and large compliance of the face mask. If pseudorandom noise pressure oscillations generated by a loudspeaker are applied at the airway opening (FOT), the power of the resulting flow decreases inversely with f because of capacitive shunting into the volume of the gas in the speaker chamber and in the face mask. We studied whether high-frequency respiratory Zin can be measured by using rapid flow interruption [high-speed interrupter technique (HIT)], in which we expect the flow amplitude in the respiratory system to be higher than in the FOT. We compared Zin measured by HIT with Zin measured by FOT in a dried dog lung and in five healthy adult subjects. The impedance was calculated from two pressure signals measured between the mouth and the HIT valve. The impedance could be assessed from 32 to 800 Hz. Its real part at low f as well as the f and amplitude of the first and second acoustic resonance, measured by FOT and by HIT, were not significantly different. The power spectrum of oscillatory flow when the HIT was used showed amplitudes that were at least 100 times greater than those when FOT was used, increasing at f > 400 Hz. In conclusion, the HIT enables the measurement of high-frequency Zin data ranging from 32 to 800 Hz with particularly high flow amplitudes and, therefore, possibly better signal-to-noise ratio. This is particularly important in systems with high Raw, e.g., in infants, when measurements have to be performed through a face mask.

Dynamics of a Transversely Excited Swirling, Lifted Flame: Part I — Experiments and Data Analysis

2013 ◽  
Author(s):  
Michael Malanoski ◽  
Michael Aguilar ◽  
Vishal Acharya ◽  
Tim Lieuwen
Keyword(s):  
High Speed ◽  
Acoustic Excitation ◽  
Response Model ◽  
Combustion Instabilities ◽  
Excitation Field ◽  
Azimuthal Mode ◽  
Flow Response ◽  
Flame Response ◽  
Swirling Flame ◽  
Helical Mode

This paper is the first of two parts, and describes measurements of the response of a transversely forced, single nozzle, swirling flame. This study is motivated by combustion instabilities coupling with azimuthal combustor modes. Two different forcing configurations are applied, where the flame/nozzle are located at a pressure node and anti-node, respectively. High speed velocimetry and chemiluminescence measurements were made of the forced and unforced flow in multiple orthogonal planes, revealing both the axial and azimuthal development of the unsteady flow. Spectra and azimuthal mode decompositions of these data show the dominance of the m = 1 helical mode in the unforced flow. Depending upon the nature of the forcing, the flow response at the forcing frequency can be dominated by the axisymmetric, m = 0 mode, or the m = 1 mode. These results clearly show that the dominant fluid mechanic structures exciting flames during transverse instabilities varies from nozzle to nozzle, depending upon the phase characteristics of the acoustic excitation field. Part II of this paper uses these time averaged and fluctuating measurements as inputs to a flame response model of the unsteady global heat release fluctuations.

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