scholarly journals Imperfect symmetry of real annular combustors: beating thermoacoustic modes and heteroclinic orbits

2021 ◽  
Vol 925 ◽  
Author(s):  
Abel Faure-Beaulieu ◽  
Thomas Indlekofer ◽  
James R. Dawson ◽  
Nicolas Noiray
Keyword(s):  
Gas Turbines ◽  
Swirling Flow ◽  
Nodal Line ◽  
Heteroclinic Orbits ◽  
Jet Engines ◽  
New Type ◽  
The Mean ◽  
Underlying Mechanisms ◽  
Modal Dynamics ◽  
Periodic Switching

In jet engines and gas turbines, the annular shape of the combustion chamber allows the appearance of self-oscillating azimuthal thermoacoustic modes. We report experimental evidence of a new type of modal dynamics characterised by periodic switching of the spinning direction and develop a theoretical model that fully reproduces this phenomenon and explains the underlying mechanisms. It is shown that tiny asymmetries of the geometry, the mean temperature field, the thermoacoustic response of the flames or the acoustic impedance of the walls, present in any real systems, can induce these heteroclinic orbits. The model also explains experimental observations showing a statistically dominant spinning direction despite the absence of swirling flow, or pairs of preferred nodal line directions.

scholarly journals Demyelination and remyelination detected in an alternative cuprizone mouse model of multiple sclerosis with 7.0 T multiparameter magnetic resonance imaging

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Shuang Ding ◽  
Yu Guo ◽  
Xiaoya Chen ◽  
Silin Du ◽  
Yongliang Han ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Multiple Sclerosis ◽  
Magnetic Resonance ◽  
Mouse Model ◽  
Diffusion Tensor ◽  
Mean Diffusivity ◽  
Blue Staining ◽  
Resonance Imaging ◽  
The Mean ◽  
Underlying Mechanisms

AbstractThe aim of this study was to investigate the mechanisms underlying demyelination and remyelination with 7.0 T multiparameter magnetic resonance imaging (MRI) in an alternative cuprizone (CPZ) mouse model of multiple sclerosis (MS). Sixty mice were divided into six groups (n = 10, each), and these groups were imaged with 7.0 T multiparameter MRI and treated with an alternative CPZ administration schedule. T2-weighted imaging (T2WI), susceptibility-weighted imaging (SWI), and diffusion tensor imaging (DTI) were used to compare the splenium of the corpus callosum (sCC) among the groups. Prussian blue and Luxol fast blue staining were performed to assess pathology. The correlations of the mean grayscale value (mGSV) of the pathology results and the MRI metrics were analyzed to evaluate the multiparameter MRI results. One-way ANOVA and post hoc comparison showed that the normalized T2WI (T2-nor), fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) values were significantly different among the six groups, while the mean phase (Φ) value of SWI was not significantly different among the groups. Correlation analysis showed that the correlation between the T2-nor and mGSV was higher than that among the other values. The correlations among the FA, RD, MD, and mGSV remained instructive. In conclusion, ultrahigh-field multiparameter MRI can reflect the pathological changes associated with and the underlying mechanisms of demyelination and remyelination in MS after the successful establishment of an acute CPZ-induced model.

Stability and Stabilization for Discrete System With Probabilistic Nonlinearities

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Xia Zhao ◽  
Engang Tian
Keyword(s):  
Sufficient Conditions ◽  
Discrete Systems ◽  
System Model ◽  
Linear Matrix ◽  
Time Varying Delay ◽  
Mean Square Stability ◽  
New Type ◽  
Stability And Stabilization ◽  
The Mean ◽  
Varying Delay

This paper investigates stability and stabilization of discrete systems with probabilistic nonlinearities and time-varying delay. New characters of the nonlinearities, the probability of the nonlinearities happening between different bounds, are used to build new type of system model, which can help us make a full use of the inner variation information of the nonlinearities. With the help of the new characters, new system model is proposed. Then, sufficient conditions for the mean square stability of the system can be obtained by using the Lyapunov functional approach and linear matrix inequalities technique. An example is proposed to illustrate the efficiency of the proposed method.

Practical Bypass Mixing Systems for Fan Jet Aero Engines

1966 ◽  
Vol 17 (2) ◽  
pp. 141-160 ◽  
Author(s):  
T. H. Frost
Keyword(s):  
Gas Turbines ◽  
Minimum Weight ◽  
Jet Engines ◽  
Metal Interface ◽  
Combustion Chambers ◽  
Propulsion Systems ◽  
Jet Engine ◽  
Aero Engines ◽  
Corrugated Metal ◽  
Constant Static Pressure

SummaryMixing systems have many applications in gas turbines and aircraft jet propulsion, e.g. mixing zones in combustion chambers, ejectors for jet lift thrust augmentors and supersonic propulsion systems. A further application similar to that of combustion chamber mixing is that of mixing the cold and hot exhausts of a bypass jet engine. These are both characterised by mixing at constant static pressure and approximately constant total pressure as opposed to the more general case of unequal pressures in ejector systems (Fig. 1).The exhaust mixing process as used in Rolls-Royce bypass jet engines, e.g. Spey and Conway, enables the potential of the bypass principle, in terms of minimum weight and fuel consumption, to be exploited by a simple practical device.This is achieved by mixing the two streams in a common duct of fairly short dimensions with a corrugated metal interface on the inlet side. The consideration of these practical systems forms the main topic of this paper.

Experimental Investigation of the Acoustic Reflection Coefficient of a Modeled Gas Turbine Impingement Cooling Section

2012 ◽  
Author(s):  
Christoph Jörg ◽  
Michael Wagner ◽  
Thomas Sattelmayer
Keyword(s):  
Reflection Coefficient ◽  
Flow Velocity ◽  
Gas Turbines ◽  
Acoustic Energy ◽  
Quality Data ◽  
Mean Flow ◽  
Impingement Cooling ◽  
Acoustic Reflection ◽  
The Mean ◽  
Mean Flow Velocity

The thermoacoustic stability of gas turbines depends on a balance of acoustic energy inside the engine. While the flames produce acoustic energy, other areas like the impingement cooling system contribute to damping. In this paper, we investigate the damping potential of an annular impingement sleeve geometry embedded into a realistic environment. A cold flow test rig was designed to represent real engine conditions in terms of geometry, and flow situation. High quality data was delivered by six piezoelectric dynamic pressure sensors. Experiments were carried out for different mean flow velocities through the cooling holes. The acoustic reflection coefficient of the impingement sleeve was evaluated at a downstream reference location. Further parameters investigated were the number of cooling holes, and the geometry of the chamber surrounding the impingement sleeve. Experimental results show that the determining parameter for the reflection coefficient is the mean flow velocity through the impingement holes. An increase of the mean flow velocity leads to significantly increased damping, and to low values of the reflection coefficient.

The Use of Electrostatic Charge Measurements as an Early Warning of Distress in Heavy-Duty Gas Turbines

2001 ◽  
Author(s):  
G. L. Lapini ◽  
M. Zippo ◽  
G. Tirone
Keyword(s):  
Monitoring System ◽  
Early Warning ◽  
Gas Turbines ◽  
Electrostatic Charge ◽  
Electric Utility ◽  
Operating Conditions ◽  
System Response ◽  
Jet Engines ◽  
Heavy Duty ◽  
Demonstration Program

The idea of measuring the electrostatic charge associated with the debris contained in the exhaust gases of a gas turbine (sometimes named EDMS, Engine Debris Monitoring System, or EEMS, Electrostatic Engine Monitoring System) has been demonstrated by several authors as an interesting diagnostic tool for the early warning of possible internal distresses (rubs, coating wear, hot spots in combustors, improper combustion, etc.) especially for jet engines or aeroderivative gas turbines. While potentially applicable to machines of larger size, the possibility of transferring this monitoring technology to heavy-duty gas turbines, which have exhaust ducts much bigger in size and different operating conditions, should be demonstrated. The authors present a synthesis of their experience and of the most significant data collected during a demonstration program performed on behalf of ENEL, the main Italian electric utility. The purpose of this program was to test this concept in real operating conditions on large turbines, and hence to evaluate the influence of the operating conditions on the system response and to assess its sensitivity to possible distresses. A good amount of testing has been performed, during this program, both on a full scale combustion rig, and on two machines rated at about 120 MW, during their normal and purposely perturbed operating conditions in a power plant. The authors, on the basis of the encouraging results obtained to date, comment on the work still required to bring this technology to full maturity.

Design Parameters Prediction of New Type Gas Turbine Based on a Hybrid GRA-SVM Prediction Model

2017 ◽  
Author(s):  
Tingting Wei ◽  
Dengji Zhou ◽  
Jinwei Chen ◽  
Yaoxin Cui ◽  
Huisheng Zhang
Keyword(s):  
Prediction Model ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Technology Development ◽  
Design Parameters ◽  
Support Vector ◽  
Performance Parameters ◽  
New Type ◽  
Equipment Manufacture ◽  
Grey Relational

Since the late 1930s, gas turbine has begun to develop rapidly. To improve the economic and safety of gas turbine, new types were generated frequently by Original Equipment Manufacture (OEM). In this paper, a hybrid GRA-SVM prediction model is established to predict the main design parameters of new type gas turbines, based on the combination of Grey Relational Analysis (GRA) and Support Vector Machine (SVM). The parameters are classified into two types, system performance parameters reflecting market demands and technology development, and component performance parameters reflecting technology development and coupling connections. The regularity based on GRA determines the prediction order, then new type gas turbine parameters can be predicted with known system parameters. The model is verified by the application to SGT600. In this way, the evolution rule can be obtained with the development of gas turbine technology, and the improvement potential of several components can be predicted which will provide supports for overall performance design.

Liquid Sheet Disintegration and Atomization Process on a Simplified Airblast Atomizer

1993 ◽  
Vol 115 (3) ◽  
pp. 461-466 ◽  
Author(s):  
G. Lavergne ◽  
P. Trichet ◽  
P. Hebrard ◽  
Y. Biscos
Keyword(s):  
High Speed ◽  
Swirling Flow ◽  
Video Camera ◽  
Frequency Instability ◽  
Liquid Sheet ◽  
Processing Unit ◽  
Spray Formation ◽  
High Speed Video Camera ◽  
The Mean ◽  
Component Phase

Liquid sheet break-up in coflowing shear flow is the mean by which liquids are atomized in practical injectors for gas turbine combustors. The present study explores experimentally the mechanisms of liquid sheet instabilities and spray formation. Experiments are conducted on four airblast geometries. A high-speed video camera associated with an image processing unit was used to study the liquid sheet instabilities. A microphone and a frequency analyzer were used to track the disintegration frequency. Instability amplitude and disintegration length of the liquid sheet were measured. A two-component Phase Doppler Particle Analyzer was used to characterize the resultant spray. The spatial distribution of the particle size is influenced by the swirling flow field. These experimental results will be used to assess models of fuel sheet instabilities and disintegration.

The United States Navy “Standard Day” for Marine Gas Turbines

2017 ◽  
Author(s):  
John Hartranft ◽  
Bruce Thompson ◽  
Dan Groghan
Keyword(s):  
United States ◽  
Gas Turbine ◽  
United States Navy ◽  
Gas Turbines ◽  
The United States ◽  
Industrial Applications ◽  
Jet Engines ◽  
Jet Engine ◽  
Advantages And Disadvantages ◽  
Power Capability

Following the successful development of aircraft jet engines during World War II (WWII), the United States Navy began exploring the advantages of gas turbine engines for ship and boat propulsion. Early development soon focused on aircraft derivative (aero derivative) gas turbines for use in the United States Navy (USN) Fleet rather than engines developed specifically for marine and industrial applications due to poor results from a few of the early marine and industrial developments. Some of the new commercial jet engine powered aircraft that had emerged at the time were the Boeing 707 and the Douglas DC-8. It was from these early aircraft engine successes (both commercial and military) that engine cores such as the JT4-FT4 and others became available for USN ship and boat programs. The task of adapting the jet engine to the marine environment turned out to be a substantial task because USN ships were operated in a completely different environment than that of aircraft which caused different forms of turbine corrosion than that seen in aircraft jet engines. Furthermore, shipboard engines were expected to perform tens of thousands of hours before overhaul compared with a few thousand hours mean time between overhaul usually experienced in aircraft applications. To address the concerns of shipboard applications, standards were created for marine gas turbine shipboard qualification and installation. One of those standards was the development of a USN Standard Day for gas turbines. This paper addresses the topic of a Navy Standard Day as it relates to the introduction of marine gas turbines into the United States Navy Fleet and why it differs from other rating approaches. Lastly, this paper will address examples of issues encountered with early requirements and whether current requirements for the Navy Standard Day should be changed. Concerning other rating approaches, the paper will also address the issue of using an International Organization for Standardization, that is, an International Standard Day. It is important to address an ISO STD DAY because many original equipment manufacturers and commercial operators prefer to rate their aero derivative gas turbines based on an ISO STD DAY with no losses. The argument is that the ISO approach fully utilizes the power capability of the engine. This paper will discuss the advantages and disadvantages of the ISO STD DAY approach and how the USN STD DAY approach has benefitted the USN. For the future, with the advance of engine controllers and electronics, utilizing some of the features of an ISO STD DAY approach may be possible while maintaining the advantages of the USN STD DAY.

A New Type of One-Bit Digital Correlator

1980 ◽  
Vol 4 (1) ◽  
pp. 21-23
Author(s):  
T. W. Cole
Keyword(s):  
Ordered Set ◽  
New Type ◽  
The Mean ◽  
Digital Correlator

Given an ordered set of samples {ai} of some function, then the autocorrelation of that function is the mean lagged product of these samples.

scholarly journals Improvements on Learning Kernel Extended Dictionary for Face Recognition

2020 ◽  
Vol 34 (4) ◽  
pp. 387-394
Author(s):  
Soodabeh Amanzadeh ◽  
Yahya Forghani ◽  
Javad Mahdavi Chabok
Keyword(s):  
Sparse Representation ◽  
Face Image ◽  
Collaborative Representation ◽  
Training Images ◽  
Input Face ◽  
Proposed Model ◽  
Eigen Values ◽  
New Type ◽  
The Mean ◽  
Better Than

Kernel extended dictionary learning model (KED) is a new type of Sparse Representation for Classification (SRC), which represents the input face image as a linear combination of dictionary set and extended dictionary set to determine the input face image class label. Extended dictionary is created based on the differences between the occluded images and non-occluded training images. There are four defaults to make about KED: (1) Similar weights are assigned to the principle components of occlusion variations in KED model, while the principle components of the occlusion variations have different weights, which are proportional to the principle components Eigen-values. (2) Reconstruction of an occluded image is not possible by combining only non-occluded images and the principle components (or the directions) of occlusion variations, but it requires the mean of occlusion variations. (3) The importance and capability of main dictionary and extended dictionary in reconstructing the input face image is not the same, necessarily. (4) KED Runtime is high. To address these problems or challenges, a novel mathematical model is proposed in this paper. In the proposed model, different weights are assigned to the principle components of occlusion variations; different weights are assigned to the main dictionary and extended dictionary; an occluded image is reconstructed by non-occluded images and the principle components of occlusion variations, and also the mean of occlusion variations; and collaborative representation is used instead of sparse representation to enhance the runtime. Experimental results on CAS-PEAL subsets showed that the runtime and accuracy of the proposed model is about 1% better than that of KED.

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