Swirl Distribution Effects on the Thermal Characteristics of Premixed Flames

2001 ◽  
Author(s):  
Sean Archer ◽  
Ashwani K. Gupta
Keyword(s):  
Time Scales ◽  
Premixed Flames ◽  
Power Spectra ◽  
Thermal Characteristics ◽  
Recirculation Region ◽  
Emission Characteristics ◽  
Operational Conditions ◽  
Mean Temperature ◽  
Integral Time ◽  
Outer Annulus

Abstract An experimental investigation has been carried out on four premixed flames using a double concentric swirl burner. The influence of radial distribution of swirl on the global flame behavior, thermal and emission characteristics have been determined. Temperature data was compensated with time constant data to generate mean and fluctuating temperature maps, probability density distributions of temperature, power spectra and thermal integral- and micro-time scales in the flames. Direct flame photographs were taken to archive flame shape and light intensity. These data provided valuable information for practical combustors on better swirl configurations. These configurations will depend heavily on the designed power settings. Contributed results directly from this investigation are for a lean premixed flame to achieve low emission and higher efficiency. The results reveal that in a counter-swirl configuration, the swirl strength in inner annulus should be greater than the outer annulus. However, for the co-swirl configuration it is more beneficial to have smaller swirl strength in the inner annulus than the outer annulus. It is found that premixed flames can possess significant circumferential non-uniformities at all flow and operational conditions. Detailed data shows that the flame thermal field and temperature distribution is strongly related to its emissions. High NOx emission is found in flames where the integral time scales and the mean temperature are high in the presumed lower recirculation region. High CO formation is found in flames that have high integral time scales in the lower recirculation region but have a low mean temperature in this same region. Thermal time scales provide important information on the thermal and emission characteristics of premixed flames.

scholarly journals Modelling of a Bluff-Body Stabilised Premixed Flames Close to Blow-Off

Computation ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 43
Author(s):  
Shokri Amzin ◽  
Mohd Fairus Mohd Yasin
Keyword(s):  
Bluff Body ◽  
Fluid Dynamic ◽  
Premixed Flames ◽  
Pollutant Emissions ◽  
Moment Closure ◽  
Recirculation Region ◽  
Scalar Dissipation ◽  
Average Error ◽  
Conditional Moment ◽  
Lean Premixed

As emission legislation becomes more stringent, the modelling of turbulent lean premixed combustion is becoming an essential tool for designing efficient and environmentally friendly combustion systems. However, to predict emissions, reliable predictive models are required. Among the promising methods capable of predicting pollutant emissions with a long chemical time scale, such as nitrogen oxides (NOx), is conditional moment closure (CMC). However, the practical application of this method to turbulent premixed flames depends on the precision of the conditional scalar dissipation rate,. In this study, an alternative closure for this term is implemented in the RANS-CMC method. The method is validated against the velocity, temperature, and gas composition measurements of lean premixed flames close to blow-off, within the limit of computational fluid dynamic (CFD) capability. Acceptable agreement is achieved between the predicted and measured values near the burner, with an average error of 15%. The model reproduces the flame characteristics; some discrepancies are found within the recirculation region due to significant turbulence intensity.

scholarly journals Assessment of dispersion parameterizations through wind data measured by three sonic anemometers in a urban canopy

2009 ◽  
Vol 3 (1) ◽  
pp. 91-98 ◽  
Author(s):  
L. Mortarini ◽  
E. Ferrero ◽  
R. Richiardone ◽  
S. Falabino ◽  
D. Anfossi ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Time Scales ◽  
Vertical Component ◽  
Urban Canopy ◽  
Obukhov Length ◽  
Low Wind Speed ◽  
Integral Time ◽  
Sonic Anemometers ◽  
One Year ◽  
The City

Abstract. One year of continuous wind and turbulence measurements at three levels (5, 9 and 25 m) on a mast located in the suburb of the city of Turin were collected. Those recorded during April 2007 are analyzed and their main characteristics are presented and discussed. The analysis includes, at each level, mean, standard deviation, Skewness, Kurtosis for the 3-D wind components and sonic temperature. The integral time scales for the 3-D wind components are also computed and friction velocity and Monin-Obukhov length are determined as well. In particular, the wind standard deviation profiles as a function of stability are compared to the literature predictions for flat undisturbed terrain. It is found that, while the vertical component agrees reasonably well, the horizontal components deviate from the prescribed values, as expected considering the buildings and other obstacles effects and the high percentage of low-wind conditions. Also the integral time scales, estimated by the autocorrelation functions, are compared to the literature predictions, finding significant differences, again attributed to the low-wind speed occurrences.

Heat Transfer and Fluid Flow Characteristics of a Turbulent Dual Jet Impinging on a Wavy Surface

2020 ◽  
Vol 12 (4) ◽  
Author(s):  
Tej Pratap Singh ◽  
Amitesh Kumar ◽  
Ashok Kumar Satapathy
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Flow Characteristics ◽  
Thermal Characteristics ◽  
Wavy Surface ◽  
Bottom Wall ◽  
Recirculation Region ◽  
Flow Strength

Abstract A simple and effective technique is proposed to enhance the heat transfer rate significantly. The current study deals with the analysis of a fluid flow and thermal characteristics of a turbulent dual jet impinging on a wavy surface. The surface area of the wall has been varied by considering different wavy profiles. The amplitude of the wavy surface is varied between 0.1 and 0.7 with an interval of 0.1. The number of cycles and the offset ratio (OR) are fixed to 10 and 7, respectively, thus, providing a complete parametric analysis of flow characteristics and thermal characteristics of the turbulent dual jet. The decay of maximum streamwise velocity, the variation of bottom wall pressure, and the variation of local heat flux and local Nusselt number have been computed. The variation of the bottom wall temperature for adiabatic wavy wall boundary condition for various amplitudes are also presented in this paper. It is found that the pressure decreases in the recirculation region when the amplitude increases. There is a sudden drop in pressure in the recirculation region when the wavy surface is present as compared with the dual jet with a plane wall surface and this drop goes on increasing as the amplitude increases. The wavy surface provides a favorable condition for the flow which results in the increased flow strength. The increase in the flow strength ultimately enhances the heat transfer rate. But, the increase in heat transfer is not monotonous. The heat transfer rate increases till the amplitude 0.5 thereafter it decreases. A maximum increase of 12% in the heat transfer rate is observed at A = 0.5. It is hoped that the present study opens a new line for the industries which deal with the cooling phenomenon.

Atomic Emission Characteristics of Laser-Induced Plasmas in an Argon Atmosphere at Reduced Pressure

1989 ◽  
Vol 43 (2) ◽  
pp. 229-234 ◽  
Author(s):  
Yasuo Iida
Keyword(s):  
Thermal Characteristics ◽  
Sample Surface ◽  
Atomic Emission ◽  
Argon Atmosphere ◽  
Emission Characteristics ◽  
Reduced Pressure ◽  
Spatially Resolved ◽  
Emissive Region ◽  
Resultant Increase ◽  
Atomic Lines

The emission characteristics of laser-induced plasma, with the use of a Q-switched ruby laser of 1.5 J, were studied in argon atmosphere at reduced pressure. The time- and spatially resolved emission profiles were measured. In argon atmosphere at reduced pressure, the emission period of plasma is elongated to over a hundred microseconds, and the emissive region expands to more than a few tens of millimeters above the sample surface. The emission intensities of atomic lines increase severalfold in an argon atmosphere, in comparison with those obtained in air at the same pressure. Moderate confinement of plasmas and a resultant increase of emission intensities are achieved at 50 Torr. These results are explained by the chemical inertness and the thermal characteristics of the argon atmosphere and the decrease in absorption of the laser pulse by the plasma plume. The re-excitation of emissive species by collisions with metastable argon atoms seems to be less important.

On Environmental Vibration Power Spectra and Accelerated Testing for Medical Devices

1999 ◽  
Author(s):  
Jingshu Wu ◽  
Ruichong Zhang ◽  
Karl K. Stevens
Keyword(s):  
Medical Devices ◽  
Random Vibration ◽  
Power Spectra ◽  
Field Testing ◽  
Accelerated Testing ◽  
Quality Analysis ◽  
Ground Vehicles ◽  
Operational Conditions ◽  
Analysis And Design ◽  
Environmental Vibration

Abstract This paper proposes field-testing-based power spectra of vibration in such environments as helicopters and ground vehicles. The spectra could then be used as important input data to guide accelerated testing, quality analysis and design for medical devices (or products) used in the aforementioned transportation means. Specifically, a broad spectrum of environmental vibration is first measured in a series of field vibration tests at various locations inside the transportation means and at different operational conditions (e.g., take-off, cruise, and landing conditions if medical devices are used in helicopters). Consequently, comprehensive field-testing-based power spectra are constructed, in an attempt to catch the inherent nature of random vibration environment in each and every type of the transportation means, which is not adequately specified in standard codes. As one of the applications of the proposed spectra, accelerated random vibration testing for medical devices used in either helicopters or ground vehicles is proposed, which could be used not only for product field life prediction but also for its consequent reliability analysis and design.

Cointegration and the Empirical Mode Decomposition for the Analysis of Diagnostic Data

2013 ◽  
Vol 569-570 ◽  
pp. 884-891 ◽  
Author(s):  
Ifigeneia Antoniadou ◽  
Elizabeth J. Cross ◽  
Keith Worden
Keyword(s):  
Empirical Mode Decomposition ◽  
Time Scales ◽  
Energy Operator ◽  
Frequency Separation ◽  
Operational Conditions ◽  
Multi Scale ◽  
Mode Decomposition ◽  
Detection Approach ◽  
Empirical Mode Decomposition Method ◽  
The Hilbert Transform

The use of cointegration has been proposed recently as a potentially powerful means of removing confounding influences from structural health monitoring (SHM) data. On the other hand the Empirical Mode Decomposition method is a recent multi-scale decomposition technique with the ability to decompose a signal into meaningful signal components. In this paper the EMD method will be used to highlight the dominant time-scales that have been affected by varying environmental and operational conditions and the time-scales that are related to damage. Then cointegration will be used to remove the nonstationary effects not associated with damage at the time-scales of interest in the data. The final step of the damage detection approach proposed, will be the use of two different amplitude-frequency separation methods, the Hilbert Transform and the more recent Teager Kaiser energy operator approach in order to compare the merits of both, concerning the estimation of the instantaneous characteristics of the signals.

How Important Is Air–Sea Coupling in ENSO and MJO Evolution?

2009 ◽  
Vol 22 (11) ◽  
pp. 2958-2977 ◽  
Author(s):  
Matthew Newman ◽  
Prashant D. Sardeshmukh ◽  
Cécile Penland
Keyword(s):  
Time Scales ◽  
Evolution Operator ◽  
Power Spectra ◽  
Dynamical Evolution ◽  
Atmospheric Variability ◽  
Basic Premise ◽  
Strongly Coupled ◽  
Dominant Period ◽  
Linear Inverse Model ◽  
Daily Time

Abstract The effect of air–sea coupling on tropical climate variability is investigated in a coupled linear inverse model (LIM) derived from the simultaneous and 6-day lag covariances of observed 7-day running mean departures from the annual cycle. The model predicts the covariances at all other lags. The predicted and observed lag covariances, as well as the associated power spectra, are generally found to agree within sampling uncertainty. This validates the LIM’s basic premise that beyond daily time scales, the evolution of tropical atmospheric and oceanic anomalies is effectively linear and stochastically driven. It also justifies a linear diagnosis of air–sea coupling in the system. The results show that air–sea coupling has a very small effect on subseasonal atmospheric variability. It has much larger effects on longer-term variability, in both the atmosphere and the ocean, including greatly increasing the amplitude of ENSO and lengthening its dominant period from 2 to 4 years. Consistent with these results, the eigenvectors of the system’s dynamical evolution operator also separate into two distinct, but nonorthogonal, subspaces: one governing the nearly uncoupled subseasonal dynamics and the other governing the strongly coupled longer-term dynamics. These subspaces arise naturally from the LIM analysis; no bandpass frequency filtering need be applied. One implication of this remarkably clean separation of the uncoupled and coupled dynamics is that GCM errors in anomalous tropical air–sea coupling may cause substantial errors on interannual and longer time scales but probably not on the subseasonal scales associated with the MJO.

Sign in / Sign up

Export Citation Format

Share Document