Nonlinear Unsteady Motions and NOx Production in Gas Turbine Combustors

Chiefly for improved efficiency, the trend to increasing use of gas turbine engines in stationary powerplants has been firmly established. The requirement for minimum NOx production has motivated operation as close as practically possible near the lean flammability limit, to reduce flame temperatures and consequently reduce formation of nitrogen oxides via the Zeldovich thermal mechanism. However, experience has shown that under these conditions, stability of the chamber is compromised, often leading to the presence of sustained oscillations in the combustor. That possibility raises the problem of the influence of oscillatory motions on the production of nitrogen oxides. Numerically calculating these influences for a complex geometry gas turbine combustor is too computationally expensive at this ?me. Nonlinear analytical methods making use of these influences are a promising direction for simplei ways to design and develop operational gas turbine combustors. However, this analysis needs results on which to base unsteady models of the interaction between nonlinear oscillations and species production within a gas turbine combustor. In this paper, two methods are explored briefly as an initial step. The first is based on a configuration of perfectly stirred and plug flow reactors to approximate the flow in a combustion chamber. A complete representation of the chemical processes is accommodated, but the geometry is simplified. The second is a full numerical simulation for a realistic geometry, but at this stage the chemistry is simplified

Phase resolved PLIF and chemiluminescence for measuring combustion dynamics

Transient behavior of combustion systems has long been a subject of both fundamental and practical concerns. Extreme cases of very rapid changes include the ignition of reacting mixtures and detonation. At the other extreme is a wide range of quasi-steady changes of behavior, for example adjustments of the operating point of a combustion chamber. Between the limiting cases of 'infinitely fast' and 'infinitesimally slow' lie important fundamental problems of time-dependent behavior and a wide array of practical applications. Among the latter are combustion instabilities and their active control, a primary motivation for the work reported in this paper. Owing to the complicated chemistry, chemical kinetics and flow dynamics of actual combustion systems, numerical simulations of their behavior remains in a relatively primitive state. Even as that situation continually improves, it is an essential part of the field that methods of measuring true dynamical behavior be developed to provide results having both fine spatial resolution and accuracy in time. This paper is a progress report of recent research carried out in the Jet Propulsion Center of the California Institute of Technology

Possible TeV Source Candidates In The Unidentified EGRET Sources

We study the $\gamma$-ray emission from the pulsar magnetosphere based on outer gap models, and the TeV radiation from pulsar wind nebulae (PWNe) through inverse Compton scattering using a one-zone model. We showed previously that GeV radiation from the magnetosphere of mature pulsars with ages of $\sim 10^5-10^6$ years old can contribute to the high latitude unidentified EGRET sources. We carry out Monte Carlo simulations of $\gamma$-ray pulsars in the Galaxy and the Gould Belt, assuming the pulsar birth rate, initial position, proper motion velocity, period, and magnetic field distribution and evolution based on observational statistics. We select from the simulation a sample of mature pulsars in the Galactic plane ($|b|\leq 5^\circ$) and in the high latitude ($|b|> 5^\circ$) which could be detected by EGRET. The TeV flux from the pulsar wind nebulae of our simulated sample through the inverse Compton scattering by relativistic electrons on the microwave cosmic background and synchrotron seed photons are calculated. The predicted fluxes are consistent with the present observational constraints. We suggest that strong EGRET sources can be potential TeV source candidates for present and future ground-based TeV telescopes.Comment: Minor changes, MNRAS in pres

Unsteady flow around a Rectangular Cylinder

This paper describes an investigation into the unsteady flow behaviour around a rectangular cylinder using particle image velocimetry (PIV). Instantaneous and average velocity fields were obtained from PIV images. Analysis of the structures observed in the instantaneous velocity fields reveals the presence of small scale (Kelvin-Helmholtz) vortex structures in the shear layer that separates at the leading edge of the rectangular cylinder, and evidence of von Karman vortex shedding was observed in the wake region

Eder, Tower of

Permeability is a key parameter for the evaluation of subsurface formations in groundwater and hydrocarbon exploration. We utilize broadband full-waveform sonic data to exploit Pride's relationship between P-wave velocity dispersion and permeability for porous, fluid-filled media. Frequency dependent P-wave velocities are extracted from multi-channel sonic data during a two-step process: computation of semblance-based velocity spectra at two or more center frequencies followed by a 2D cross-correlation of the velocity spectra. A comparison with MRI-derived permeability logs confirm that P-wave velocity dispersion logs can be used to map permeability variations

Extracting frequency dependent velocities from full waveform sonic data

In porous, fluid-filled rock formations, compressional seismic wave velocities show a strong dependence on frequency. The potential linkage between P-wave velocity dispersion and permeability would make the use of broadband sonic waveform data suitable for determining reservoir parameters. Automatic velocity analysis of multi-channel sonic data can be tailored to detect and measure frequency dependent velocities.This seismic data processing strategy enables the creation of velocity dispersion logs for fluid-filled porous media