scholarly journals Flame Transfer Functions and Dynamics of a Closely Confined Premixed Body Stabilised Flame with Swirl

2021 ◽  
Author(s):  
Håkon Tormodsen Nygård ◽  
Nicholas Worth
Keyword(s):  
Transfer Functions ◽  
Time Lag ◽  
Operating Conditions ◽  
Flame Height ◽  
Time Lags ◽  
Simple Method ◽  
Temporal Shift ◽  
High Frequencies ◽  
Flame Dynamics ◽  
Wide Range

Abstract The Flame Transfer Function (FTF) and flame dynamics of a highly swirled, closely confined, premixed flame is studied over a wide range of equivalence ratios and bulk velocities at a fixed perturbation level at the dump plane. The operating conditions are varied to examine the ratio of flame height to velocity in scaling the FTF. The enclosure geometry is kept constant, resulting in strong flame-wall interactions for some operating conditions due to varying flame height. The resulting effect on the FTF due to changes in the "effective flame confinement" can therefore be studied. For sufficiently high equivalence ratio, and the resulting sufficiently small effective confinement, modulations of the FTF are observed due to interference of the perturbations created at the swirler and at the dump plane. The small length scales and high velocities results in modulations centered at high frequencies and spanning a wide range of frequencies compared to previous studies of similar phenomena. A critical point was reached for increasing effective confinement, where the modulations are suppressed. This is linked to a temporal shift in the heat release rate where the flame impinges on the combustion chamber walls. The shift reduced the expected level of interference, demonstrating effective confinement is important for the FTF response. Additionally, a Distributed Time Lag (DTL) model with two time lags is successfully applied to the FTFs, providing a simple method to capture the two dominant time scales in the problem, recreate the FTF and examine the effect of effective confinement.

scholarly journals Flame Transfer Functions and Dynamics of a Closely Confined Premixed Bluff Body Stabilised Flame With Swirl

2020 ◽  
Author(s):  
Håkon T. Nygård ◽  
Nicholas A. Worth
Keyword(s):  
Time Scales ◽  
Equivalence Ratio ◽  
Bluff Body ◽  
Transfer Functions ◽  
Time Lag ◽  
Operating Conditions ◽  
Flame Height ◽  
Time Lags ◽  
Temporal Shift ◽  
Wide Range

Abstract The Flame Transfer Function (FTF) and flame dynamics of a single, highly swirled, closely confined, premixed flame is studied over a wide range of operating conditions at a fixed perturbation level at the dump plane. The equivalence ratio and bulk velocity are varied in order to examine the important ratio of flame height to velocity in scaling the flame response function. The enclosure geometry is kept constant, and therefore due to the close confinement and varying flame height, strong flame-wall interactions are present for some operating conditions. The effect of these interactions on the FTF due to changes in the “relative” or “effective confinement” of the flame can therefore be studied. When the equivalence ratio is sufficiently high, and therefore the effective confinement sufficiently small, modulations, or dips, in the gain and phase of the FTF are observed, due to interference of the perturbations created at the swirler and at the dump plane. Due to the small length scales and relatively high velocities in the current configuration, the dip is at a high frequency and spans a wide range of frequencies compared to similar studies which have previously identified similar phenomena. It is also observed that when the equivalence ratio was decreased, increasing the effective confinement, a critical point is reached where the modulations are suppressed. This is linked to a temporal shift in the heat release rate at the downstream location where the flame impinges on the combustion chamber walls during the oscillation cycle. The shift causes a decrease in the expected level of interference, demonstrating that the effective confinement is an important parameter to consider for the nature of the FTF response. Additionally, a Distributed Time Lag (DTL) model with two distinct time lags, capturing the swirler perturbations and the perturbations at the inlet, is successfully applied to the FTFs. The model provides a simple way to accurately capture the two dominant time scales in the problem without the need of prior knowledge of the cause of the perturbations, and a simple expression to recreate the complex valued FTF. In addition the model also provides insight into the time scales of the problem, demonstrating in the current work that time scales recovered from the DTL analysis are offset from simple Strouhal number scaling, due to the effects of increasing effective confinement.

scholarly journals Automatic and Online Detection of Rotor Fault State

2018 ◽  
Vol 7 (1) ◽  
pp. 43 ◽  
Author(s):  
Ali Ouanas ◽  
Ammar Medoued ◽  
Salim Haddad ◽  
Mourad Mordjaoui ◽  
D. Sayad
Keyword(s):  
Induction Motor ◽  
Dimensional Space ◽  
Operating Conditions ◽  
Online Detection ◽  
K Nearest Neighbor ◽  
Simple Method ◽  
Important Place ◽  
Motor Test ◽  
Wide Range ◽  
Fault State

In this work, we propose a new and simple method to insure an online and automatic detection of faults that affect induction motor rotors. Induction motors now occupy an important place in the industrial environment and cover an extremely wide range of applications. They require a system installation that monitors the motor state to suit the operating conditions for a given application. The proposed method is based on the consideration of the spectrum of the single-phase stator current envelope as input of the detection algorithm. The characteristics related to the broken bar fault in the frequency domain extracted from the Hilbert Transform is used to estimate the fault severity for different load levels through classification tools. The frequency analysis of the envelope gives the frequency component and the associated amplitude which define the existence of the fault. The clustering of the indicator is chosen in a two-dimensional space by the fuzzy c mean clustering to find the center of each class. The distance criterion, the K-Nearest Neighbor (KNN) algorithm and the neural networks are used to determine the fault type. This method is validated on a 5.5-kW induction motor test bench.Article History: Received July 16th 2017; Received: October 5th 2017; Accepted: Januari 6th 2018; Available onlineHow to Cite This Article: Ouanas, A., Medoued, A., Haddad, S., Mordjaoui, M., and Sayad, D. (2017) Automatic and online Detection of Rotor Fault State. International Journal of Renewable Energy Development, 7(1), 43-52.http://dx.doi.org/10.14710/ijred.7.1.43-52

An Investigation of the Sources of Blowby in Single-Cylinder Supercharged Diesel Engines

1978 ◽  
Vol 192 (1) ◽  
pp. 39-48 ◽  
Author(s):  
B. Bull ◽  
M. A. Voisey
Keyword(s):  
Carbon Dioxide ◽  
Diesel Engines ◽  
Piston Ring ◽  
Carbon Dioxide Concentration ◽  
Operating Conditions ◽  
Exhaust Valve ◽  
Simple Method ◽  
Single Cylinder ◽  
Carbon Dioxide Concentrations ◽  
Wide Range

Measurements of carbon dioxide concentrations in the exhaust and in the crankcase of two different types of single-cylinder, supercharged diesel engines have been used to determine the amount of exhaust gas reaching the crankcase as piston ring blowby and as leakage through the exhaust valve stem-to-guide clearance. Over a wide range of operating conditions in both engines the carbon dioxide concentration was found to be more dependent on engine fuelling rate per hour than on fuel input per stroke. It was established that blowby through the exhaust valve guide was a major contributor to crankcase contamination. A simple method has been devised, requiring only minor modifications to the engine, that permits the blowby through the piston ring pack and the exhaust valve guides to be determined separately in turbocharged production engines.

Forced Aeration Composting

1983 ◽  
Vol 15 (1) ◽  
pp. 169-180 ◽  
Author(s):  
George B Willson
Keyword(s):  
Agricultural Research ◽  
Land Application ◽  
Operating Conditions ◽  
Moisture Removal ◽  
Simple Method ◽  
Wide Range ◽  
Design Requirements ◽  
Forced Aeration ◽  
Density Population ◽  
Pilot Tests

Composting enhances the acceptability of sewage sludge for land application especially in high density population areas. A relatively simple method of forced-aeration pile composting was developed at the Beltsville Agricultural Research Center. Pilot tests of full scale composting were conducted to determine process control and facility design requirements. The amount of bulking materials needed to condition the sludge for composting is related to the percentage of sludge solids. Aeration is discussed as it relates to oxygen consumption, temperature control and moisture removal. The process is readily adaptable to many operating conditions, to a variety of materials, and to a wide range of levels of compost production.

Pressure Influence on the Flame Transfer Function of a Premixed Swirling Flame

2006 ◽  
Author(s):  
E. Freitag ◽  
H. Konle ◽  
M. Lauer ◽  
C. Hirsch ◽  
T. Sattelmayer
Keyword(s):  
High Pressure ◽  
Transfer Function ◽  
High Speed ◽  
Transfer Functions ◽  
Ambient Pressure ◽  
Operating Conditions ◽  
Phase Lag ◽  
Operating Pressure ◽  
Common Procedure ◽  
Wide Range

In order to assess the stability of gas turbine combustors measured flame transfer functions are frequently used in thermoacoustic network models. Although many combustion systems operate at high pressure, the measurement of flame transfer functions was essentially limited to atmospheric conditions in the past. With the test rig employed in the study presented in the paper transfer function measurements were made for a wide range of combustor pressures. The results show similarities of the amplitude response in the entire pressure range investigated. However, the increase of the pressure leads to a considerable amplitude gain at higher frequencies. In the low frequency regime the phase is also independent of pressure, whereas above this region the pressure increase results in a considerably smaller phase lag. These observations are particularly important when evaluating Rayleigh’s criterion: Interestingly, the choice of the operating pressure can render a system stable or unstable, so that the common procedure of applying flame transfer functions measured at ambient pressure for the high pressure engine case may not always be appropriate. The detailed analysis of high speed camera images, which were recorded to get locally resolved information on the flame response reveal different regions of activity within the flame that change in strength, size and location with changing operating conditions. The observed transfer function phase behavior is explained by the interaction of those regions and it is shown that the region of highest dynamic activity dominates the phase.

The impulse breakdown voltage and time-lag characteristics of long gaps in air II. The negative discharge

1964 ◽  
Vol 256 (1069) ◽  
pp. 213-234 ◽  
Keyword(s):  
Wave Front ◽  
Breakdown Voltage ◽  
Breakdown Strength ◽  
Time Lag ◽  
Time Lags ◽  
Impulse Wave ◽  
Time Resolved ◽  
Wide Range ◽  
Negative Impulse ◽  
Long Time

Oscillographic measurement and time-resolved photographic recording have been used to examine the breakdown of rod/rod, rod/sphere and rod/plane gaps with long-duration negative impulse potentials of up to 1 MV crest. As in the positive discharge, the breakdown process is found often to cease for considerable periods on the impulse wave tail. Breakdown then occurs after a long time lag for gaps composed of rod cathodes and rod or small sphere anodes. Where the anode is large, no long time lags are observed. Measurement of the variation of breakdown strength with time during the impulse duration has been made by the superimposition of a second impulse upon the first, following a controllable delay. The results show a minimum probability of breakdown initiation after 15 μs of the applied impulse, and a subsequent slow recovery. It is suggested that this confirms the effect of the initial corona phase in causing space charge fouling of the gap. The breakdown voltage of rod/rod gaps is shown to decrease by up to 30 % when the impulse wave front is reduced from 0.50 to 0.06 μs. The breakdown strength with negative impulses is thus less than with positive impulses for wave fronts faster than 0.20 μs. For the wave form 0.50/2000 μs, the breakdown voltage is found to depend more critically upon the dimensions of the earthed electrode than is the case with positive impulses. The breakdown voltage for a rod/25 cm sphere gap is 73 % greater than for a rod/rod gap, yet also 15 % greater than for a rod/plane gap. For gap lengths between 25 and 65 cm, the breakdown voltage of the rod/plane gap is found to increase with decreasing wave front duration. The variation of the negative impulse corona with rate of potential rise and with crest voltage is examined photographically. Many of the observed variations of breakdown voltage and time-lag characteristics can be accounted for in terms of the impulse corona phase. The time-resolved photography of the negative discharge over a wide range of conditions suggests that in the range of gap lengths investigated the formation of the positive leader rather than the negative leader is the necessary forerunner of sparkover.

Simplified Simulation Block Diagram of Twin-Shaft Gas Turbines

2003 ◽  
Author(s):  
Luca Bozzi ◽  
Giampaolo Crosa ◽  
Angela Trucco
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
High Speed ◽  
Transfer Functions ◽  
Block Diagram ◽  
Operating Conditions ◽  
Computational Time ◽  
Plant Design ◽  
Algebraic Equations ◽  
Wide Range

This paper provides a simplified mathematical model of twin shaft gas turbine suitable for use in dynamic studies of both electric power generation plants and variable speed mechanical drive applications. The main purpose was to define a simulation block diagram, constituted by algebraic equations and simplified transfer functions, which can be easily derived from the gas plant design data utilising the suitable equations and nomographs presented in the paper. The 3 to 30 MW power range of twin shaft gas turbines is covered. The set-up parameters and details applicable to the model are listed, in the paper, for the various machine sizes and model series. The dynamic model has been developed by simplifying a more detailed one, also here presented, with relatively little loss in dynamic accuracy but considerable advantages in terms of computational time. In the proposed test case, the results of both models have been compared simulating the transient response of a twin shaft gas turbine powering a water-jet propulsor for high-speed ships. The accurate performance prediction capability of both models is verified, for a wide range of operating conditions, by comparison with test results from actual field installations.

An Experimental and Theoretical Study on Cavitating Cascades and Their Application to Cavitating Propellers

1985 ◽  
Vol 29 (01) ◽  
pp. 23-38
Author(s):  
Okitsugu Furuya ◽  
Shin Maekawa
Keyword(s):  
Experimental Data ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Two Dimensional ◽  
Simple Method ◽  
Cascade Theory ◽  
Wide Range ◽  
Line Theory ◽  
Lifting Line ◽  
Lifting Line Theory

In order to develop an analytical tool for predicting the off-design performance of supercavitating propellers over a wide range of operating conditions, a lifting-line theory was combined with a two-dimensional supercavitating cascade theory. The results of this simple method provided fairly accurate predictions for the performance at fully developed cavitating conditions. It was indicative that the fully developed supercavitating (s/c) propellers had strong cascade effects on their performance, and also that the three-dimensional propeller geometry corrections could properly be made by the lifting-line theory. However, the predicted performance with this propeller theory showed a significant deviation from experimental data in the range of J's larger than Jdesign, where partially cavitating conditions are expected to occur. Effort was then made on improving the prediction capability of the above propeller theory at partially cavitating (p/c) conditions. A new nonlinear partially cavitating cascade theory was then developed to provide a proper 2-D loading basis under such conditions. Two-dimensional cascade experiments were then conducted to prove the accuracy of the p/c and s/c cascade theories. The measured forces and flow observations obtained in these experiments shed a new light on the relationship between the forces and cavitation numbers at small angles of incidence. Corrected lift and drag forces were then used in the propeller program. The calculated results for KT and KQ with the new force data successfully correlated with the experimental data, now covering a large J-range where the partially cavitating conditions exist.

Comparison of Deterministic and Linear Cosine Spatial Filtering of Transmission Electron Micrographs

1972 ◽  
Vol 30 ◽  
pp. 596-597
Author(s):  
David A. Ansley
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Spatial Filter ◽  
Operating Conditions ◽  
Objective Lens ◽  
List Type ◽  
Spatial Filters ◽  
Transmission Electron ◽  
Wide Range

The coherence of the electron flux of a transmission electron microscope (TEM) limits the direct application of deconvolution techniques which have been used successfully on unmanned spacecraft programs. The theory assumes noncoherent illumination. Deconvolution of a TEM micrograph will, therefore, in general produce spurious detail rather than improved resolution.A primary goal of our research is to study the performance of several types of linear spatial filters as a function of specimen contrast, phase, and coherence. We have, therefore, developed a one-dimensional analysis and plotting program to simulate a wide 'range of operating conditions of the TEM, including adjustment of the:(1) Specimen amplitude, phase, and separation(2) Illumination wavelength, half-angle, and tilt(3) Objective lens focal length and aperture width(4) Spherical aberration, defocus, and chromatic aberration focus shift(5) Detector gamma, additive, and multiplicative noise constants(6) Type of spatial filter: linear cosine, linear sine, or deterministic

A simple way for producing holographic filters suitable for image improvement

1978 ◽  
Vol 36 (1) ◽  
pp. 226-227
Author(s):  
K.-H. Herrmann ◽  
E. Reuber ◽  
P. Schiske
Keyword(s):  
Transfer Functions ◽  
Diffraction Order ◽  
Lateral Position ◽  
Simple Method ◽  
Spatial Frequencies ◽  
Resolution Electron ◽  
Wiener Filters ◽  
Image Improvement ◽  
Optical Reconstruction ◽  
Set Up

Aposteriori deblurring of high resolution electron micrographs of weak phase objects can be performed by holographic filters [1,2] which are arranged in the Fourier domain of a light-optical reconstruction set-up. According to the diffraction efficiency and the lateral position of the grating structure, the filters permit adjustment of the amplitudes and phases of the spatial frequencies in the image which is obtained in the first diffraction order.In the case of bright field imaging with axial illumination, the Contrast Transfer Functions (CTF) are oscillating, but real. For different imageforming conditions and several signal-to-noise ratios an extensive set of Wiener-filters should be available. A simple method of producing such filters by only photographic and mechanical means will be described here.A transparent master grating with 6.25 lines/mm and 160 mm diameter was produced by a high precision computer plotter. It is photographed through a rotating mask, plotted by a standard plotter.

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