Thermoacoustics of Can-Annular Combustors

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
G. Ghirardo ◽  
C. Di Giovine ◽  
J. P. Moeck ◽  
M. R. Bothien
Keyword(s):  
Experimental Work ◽  
Rotational Symmetry ◽  
Acoustic Response ◽  
Open Area ◽  
Mode Localization ◽  
Downstream Side ◽  
Upstream Side ◽  
Turbine Inlet ◽  
Adjacent Transition ◽  
Thermoacoustic Oscillations

Can-annular combustors consist of a set of independent cans, connected on the upstream side to the combustor plenum and on the downstream side to the turbine inlet, where a transition duct links the round geometry of each can with the annular segment of the turbine inlet. Each transition duct is open on the sides toward the adjacent transition ducts, so that neighboring cans are acoustically connected through a so-called cross-talk open area. This theoretical, numerical, and experimental work discusses the effect that this communication has on the thermoacoustic frequencies of the combustor. We show how this communication gives rise to axial and azimuthal modes, and that these correspond to particularly synchronized states of axial thermoacoustic oscillations in each individual can. We show that these combustors typically show clusters of thermoacoustic modes with very close frequencies and that a slight loss of rotational symmetry, e.g., a different acoustic response of certain cans, can lead to mode localization. We corroborate the predictions of azimuthal modes, clusters of eigenmodes, and mode localization with experimental evidence.

Thermoacoustics of Can-Annular Combustors

2018 ◽  
Author(s):  
G. Ghirardo ◽  
C. Di Giovine ◽  
J. P. Moeck ◽  
M. R. Bothien
Keyword(s):  
Experimental Work ◽  
Rotational Symmetry ◽  
Acoustic Response ◽  
Open Area ◽  
Mode Localization ◽  
Downstream Side ◽  
Upstream Side ◽  
Turbine Inlet ◽  
Adjacent Transition ◽  
Thermoacoustic Oscillations

Can-annular combustors consist of a set of independent cans, connected on the upstream side to the combustor plenum, and on the downstream side to the turbine inlet, where a transition duct links the round geometry of each can with the annular segment of the turbine inlet. Each transition duct is open on the sides towards the adjacent transition ducts, so that neighbouring cans are acoustically connected through a so called cross-talk open area. This theoretical, numerical and experimental work discusses the effect that this communication has on the thermoacoustic frequencies of the combustor. We show how this communication gives rise to axial and azimuthal modes, and that these correspond to particularly synchronised states of axial thermoacoustic oscillations in each individual can. We show that these combustors typically show clusters of thermoacoustic modes with very close frequencies and that a slight loss of rotational symmetry, e.g. a different acoustic response of certain cans, can lead to mode localization. We corroborate the predictions of azimuthal modes, clusters of eigenmodes and mode localization with experimental evidence.

Effect of Noise and Nonlinearities on Thermoacoustics of Can-Annular Combustors

2019 ◽  
Author(s):  
G. Ghirardo ◽  
J. P. Moeck ◽  
M. R. Bothien
Keyword(s):  
Rotational Symmetry ◽  
Turbine Rotor ◽  
Stochastic Simulations ◽  
Linear Solution ◽  
Mode Localization ◽  
Turbine Inlet ◽  
Flame Response ◽  
Linearized System ◽  
Set Up ◽  
The Individual

Abstract Can-annular combustors consist of N distinct cans set up symmetrically around the axis of the gas turbine rotor. Each can is connected to the turbine inlet by means of a transition duct. At the turbine inlet a small gap between the neighbouring transition ducts allows acoustic communication between the individual cans. Thermoacoustic pulsations in the cans are driven by the respective flames, but also the communication between neighbouring cans through the gap plays a significant role. In this study we focus in particular on the effect of the background noise intensity and of the nonlinear flame saturation. We predict how usually clusters of thermoacoustic modes are unstable in the linear regime and compete with each other in the nonlinear regime, with each cluster consisting of axial, azimuthal and push-pull modes. Since linear theory cannot predict the nonlinear solution, stochastic simulations are run to study the non-linear solution in a probabilistic sense. One outcome of these simulations are the various pulsation patterns, which are in principle different from one can to the next. This is done for several configurations, with a focus on the effect of a loss of rotational symmetry of the system. We recover how a stronger flame response in one can give rise to the phenomenon of mode localization, but also how the nonlinearity of the flame saturation and the competition between modes have an effect on the nonlinear average mode shape. We finally predict the coherence and phase pattern between cans on the linearized system subject to stochastic noise, and compare the predictions with direct engine measurements, both in terms of spectra of pulsation amplitude in each can and coherence and phase between different cans, observing a good match.

Deposition of Highly Transparent and Conductive Films on Tilted Substrates by Atmospheric Pressure Plasma Jet

2019 ◽  
Author(s):  
Yu-Chen Chen ◽  
Wen-Kai Chen ◽  
Jing-Chi Huang ◽  
Jia-Yang Juang
Keyword(s):  
Atmospheric Pressure Plasma ◽  
Plasma Jet ◽  
Grazing Incidence ◽  
Oblique Angle Deposition ◽  
Oblique Angle ◽  
Downstream Side ◽  
Upstream Side ◽  
Pressure Plasma ◽  
Flat Substrate ◽  
Angle Deposition

Abstract We study the influence of the substrate tilt angle on the microstructure and optoelectronic properties of gallium-doped zinc oxide (GZO) thin films deposited by the atmosphere pressure plasma jet (APPJ) method. The nozzle trajectories play a key role in oblique angle deposition. In the process of oblique angle deposition, if the nozzle scanned from the upstream side to the downstream side, the electrical properties such as resistivity, carrier concentration and mobility deteriorate considerably. The optical properties also worsen — specular transmittance goes down and diffuse transmittance increase to a significant amount. This degradation can be attributed to the “pre-deposition” of the GZO adsorbed particles (ad-particles) on the downstream side of the raw glass where the nozzle has not scanned. These GZO ad-particles serve as nuclei on which the incoming vapor particles deposit preferentially. Scanning electron microscopy (SEM), and grazing incidence X-ray diffraction (GIXRD confirmed that the film near the downstream is thicker, less smooth, and porous than that near the upstream. The undesirable situation can be mitigated or even completely removed via proper nozzle scanning trajectories — reversing the scanning trajectory of the nozzle. If the nozzle scans from the downstream side to the upstream side, no pre-deposition of the GZO ad-particles to deteriorate the film properties and therefore the obliquely deposited films perform as well as the films deposited without tilt, i.e. flat substrate. This work presents a solution to the challenge of depositing TCO on tilted and curved surfaces.

scholarly journals Mechanism of Tsunami-Induced Erosion of Bridge-Abutment Backfill and Its Countermeasures

Water ◽  
2021 ◽  
Vol 13 (24) ◽  
pp. 3529
Author(s):  
Tomoaki Nakamura ◽  
Chisato Sugiyama ◽  
Yong-Hwan Cho ◽  
Norimi Mizutani
Keyword(s):  
Numerical Analysis ◽  
Sediment Transport ◽  
Numerical Experiments ◽  
Sediment Suspension ◽  
Downstream Side ◽  
Upstream Side ◽  
Bridge Abutment ◽  
Sediment Transportation ◽  
Bedload Sediment ◽  
The Stability

Tsunamis can destroy bridges in coastal areas. Studies have attempted to unravel the mechanism of tsunami-induced damage and develop effective countermeasures against future tsunamis. However, the mechanisms of tsunami-induced erosion of bridge-abutment backfill and its countermeasures have not been studied adequately. This study investigates this topic using numerical analysis. The results show that the tsunami flowing down along the downstream wing of the abutment induces bedload sediment transport on the ogive section of the backfill on the downstream side of the abutment, resulting in the onset of backfill erosion. Sediment suspension and bedload sediment transportation occur when the backfill inside the abutment starts to flow out from below the downstream wing. This leads to subsidence of the backfill at the upstream side of the downstream wing. The subsequent backfill erosion is mainly caused by bedload sediment transport. Numerical experiments on countermeasures show that extending the wings downward can prevent the acceleration of backfill erosion in the presence of the abutment. A combination of multiple countermeasures, including extended wings, would be more effective in maintaining the stability of the abutment after a tsunami. This suggests the application of such countermeasures to actual bridges as an effective countermeasure against backfill erosion.

Effect of Noise and Nonlinearities on Thermoacoustics of Can-Annular Combustors

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
G. Ghirardo ◽  
J. P. Moeck ◽  
M. R. Bothien
Keyword(s):  
Background Noise ◽  
Noise Intensity ◽  
Stochastic Simulations ◽  
Linear Regime ◽  
Good Match ◽  
Mode Localization ◽  
Nonlinear Solution ◽  
Turbine Inlet ◽  
Flame Response ◽  
Linearized System

Abstract Can-annular combustors consist of N distinct cans setup symmetrically around the axis of the gas turbine. Each can is connected to the turbine inlet by means of a transition duct. At the turbine inlet, a small gap between the neighboring transition ducts allows acoustic communication between the cans. Thermoacoustic pulsations in the cans are driven by the respective flames, but also the communication between neighboring cans through the gap plays a significant role. In this study, we focus on the effect of the background noise intensity and of the nonlinear flame saturation. We predict how usually clusters of thermoacoustic modes are unstable in the linear regime and compete with each other in the nonlinear regime, each cluster consisting of axial, azimuthal and push-pull modes. Since linear theory cannot predict the nonlinear solution, stochastic simulations are run to study the nonlinear solution in a probabilistic sense. One outcome of these simulations is the various pulsation patterns, which are in principle different from one can to the next. We recover how not only a stronger flame response in one can gives rise to the phenomenon of mode localization, but also how the nonlinearity of the flame saturation and the competition between modes have an effect on the nonlinear mode shape. We finally predict the coherence and phase between cans on the linearized system subject to noise, and compare the predictions with engine measurements, in terms of spectra of amplitude in each can and coherence and phase, observing a good match.

Temperature Measurement and Data Analysis of the Roller Compected Concrete Dam

2012 ◽  
Vol 212-213 ◽  
pp. 942-946
Author(s):  
Zhen Xian Xing ◽  
Lei Ni ◽  
Rong Jia Ma
Keyword(s):  
Temperature Field ◽  
High Temperature ◽  
Concrete Dam ◽  
Effective Measure ◽  
Downstream Side ◽  
Upstream Side ◽  
Rcc Dam ◽  
Concrete Temperature ◽  
Dam Operation ◽  
Dam Concrete

Prototype observation of the concrete dam is an important and effective measure to master the operating condition of dams. Analysis of changes of concrete temperature for dams is the basis of studying the safety of dam operation. By analyzing the raw monitoring data of temperature of a RCC dam, this paper researches the changing process of concrete temperature and internal concrete partitions temperature variation of dams. It also draws the temperature field of the dam concrete. The results show that the isothermals of downstream side parallel with the surface of the downstream dam, and the isothermals of upstream side intersect with the dam. Isothermals which are near to the dam’s surface are close. This suggests that temperature gradient there is large. There is a high temperature nucleus and two low temperature nucleuses in the temperature field of the dam in summer, while in winter there is only one high temperature nucleus. So it suggests that the temperature field in summer is more complex.

Characterization of Flat Sheet Pd/Ag Membrane Using Pure Hydrogen

2016 ◽  
Vol 819 ◽  
pp. 449-453
Author(s):  
Hasan Mohd Faizal ◽  
Yuki Kawasaki ◽  
Takeshi Yokomori ◽  
Toshihisa Ueda
Keyword(s):  
Hydrogen Permeation ◽  
Pure Hydrogen ◽  
Permeation Flux ◽  
Square Root ◽  
Feed Flow Rate ◽  
Temperature Level ◽  
Downstream Side ◽  
Upstream Side ◽  
Flat Sheet

The permeation characteristic of a flat sheet Pd/Ag membrane was investigated experimentally by using pure hydrogen. A 77wt.%Pd/23wt.%Ag membrane with 25μm thickness and 0.02m diameter was used. The hydrogen permeation mole flux was investigated under various reference membrane temperatures (423-723K), for upstream pressures of 0.21-0.29MPa, and feed flow rate of 1.39x10-4mol/s. In all cases, the downstream pressure was set at atmospheric. Experimental results demonstrate the linear relationship between the hydrogen permeation flux and difference in square root of hydrogen partial pressure between the upstream side and downstream side, regardless of reference temperatures. This indicates the compatibility of the Pd/Ag membrane used in the present study with Sieverts’ Law. At sufficiently low temperature level, the hydrogen permeation flux is found to be very sensitive with the changes in the temperature.

scholarly journals Generation of solitary waves by transcritical flow over a step

2007 ◽  
Vol 587 ◽  
pp. 235-254 ◽  
Author(s):  
R. H. J. GRIMSHAW ◽  
D.-H. ZHANG ◽  
K. W. CHOW
Keyword(s):  
Analytical Solutions ◽  
Water Waves ◽  
Numerical Solutions ◽  
Vries Equation ◽  
Undular Bore ◽  
Downstream Side ◽  
Upstream Side ◽  
Transcritical Flow ◽  
De Vries ◽  
Positive Step

It is well-known that transcritical flow over a localized obstacle generates upstream and downstream nonlinear wavetrains. The flow has been successfully modelled in the framework of the forced Korteweg–de Vries equation, where numerical and asymptotic analytical solutions have shown that the upstream and downstream nonlinear wavetrains have the structure of unsteady undular bores, connected by a locally steady solution over the obstacle, which is elevated on the upstream side and depressed on the downstream side. Inthispaper we consider the analogous transcritical flow over a step, primarily in the context of water waves. We use numerical and asymptotic analytical solutions of the forced Korteweg–de Vries equation, together with numerical solutions of the full Eulerequations, to demonstrate that a positive step generates only an upstream-propagating undular bore, and a negative step generates only a downstream-propagating undular bore.

Enhancement of reperfusion injury by elevation of microvascular pressures

2002 ◽  
Vol 282 (4) ◽  
pp. H1387-H1394 ◽  
Author(s):  
Shinya Takase ◽  
Laurence Lerond ◽  
John J. Bergan ◽  
Geert W. Schmid-Schönbein
Keyword(s):  
Cell Death ◽  
Tissue Injury ◽  
Leukocyte Adhesion ◽  
Venous Pressure ◽  
Parenchymal Cell ◽  
Venous Occlusion ◽  
Venous Hypertension ◽  
Radical Scavenger ◽  
Downstream Side ◽  
Upstream Side

Elevated venous pressure can be associated with severe tissue injury. Few links, however, between venous hypertension and tissue damage have been established. We examined here the effects of micropressure elevation on the outcome of venular occlusion/reperfusion in the mesenteric microvasculature of male Wistar rats. One hour of venular occlusion (diameter ∼50 μm) by micropipette occlusion followed by reperfusion were carried out with sham surgery without occlusion as control. Leukocyte rolling, adhesion, and migration, oxygen radicals detected by dichlorofluorescein (DCF), and parenchymal cell death detected by propidium iodide (PI) were recorded simultaneously in the same vessel at a location upstream of the occlusion site with elevated micropressure and at a downstream location with low micropressure. The number of rolling, adhering, and migrating leukocytes increased on the upstream side of the occlusion to a higher level than downstream of the occlusion site. During occlusion, DCF intensity on the venular endothelium was greater on the upstream side than in the downstream side, but there were no differences during reperfusion. The number of PI-positive cells adjacent to the venules increased significantly compared with controls, and it remained greater on the upstream higher-pressure side than the downstream side. Leukocyte adhesion and transvascular migration in postcapillary venules as well as parenchymal cell death could be significantly reduced by the hydroxyl radical scavenger dimethylthiourea. Microhemorrhages of blood cells into the mesentery interstitium were observed only on the upstream side of the occlusion. These results indicate that an elevation of the venular blood pressure during occlusion/reperfusion exacerbates the inflammatory cascade and tissue injury. Venous occlusion may constitute an important mechanism for tissue injury.

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