An Experimental Study of Chemically Reacting Turbulent Free Shear Layers

An Experimental Study of Chemically Reacting Turbulent Free Shear Layers
Author: Robert K. Gould
Publisher:
Total Pages: 0
Release: 1978
Genre: Chemiluminescence
ISBN:

The objective of this program is to measure species concentrations and their statistical properties at points in well-characterized chemically reacting turbulent flows. Such measurements are required for (i) testing theories of reacting turbulent systems and (ii) as input to models which predict the behavior of practical combustors. The model chemical reaction being used to study turbulent mixing/reacting flows is the NO/O3 reaction. A photolysis/chemiluminescence technique is used to measure reactant concentrations, (NO) and (O3), and a product concentration, (NO2), simultaneously at points in the flow field. From such measurements, the required statistical quantities, i.e., probability density functions (pdf) and correlations of reactants and product concentrations, are being developed. These data are supplemented by measurements of the turbulence power spectra and intensity at the same points. During this quarter an examination of the signal collection optics has led to readjustments with reduced errors.

Turbulent Mixing in Nonreactive and Reactive Flows

Turbulent Mixing in Nonreactive and Reactive Flows
Author: S. Murthy
Publisher: Springer Science & Business Media
Total Pages: 469
Release: 2013-11-11
Genre: Science
ISBN: 1461587387

Turbulence, mixing and the mutual interaction of turbulence and chemistry continue to remain perplexing and impregnable in the fron tiers of fluid mechanics. The past ten years have brought enormous advances in computers and computational techniques on the one hand and in measurements and data processing on the other. The impact of such capabilities has led to a revolution both in the understanding of the structure of turbulence as well as in the predictive methods for application in technology. The early ideas on turbulence being an array of complicated phenomena and having some form of reasonably strong coherent struc ture have become well substantiated in recent experimental work. We are still at the very beginning of understanding all of the aspects of such coherence and of the possibilities of incorporating such structure into the analytical models for even those cases where the thin shear layer approximation may be valid. Nevertheless a distinguished body of "eddy chasers" has come into existence. The structure of mixing layers which has been studied for some years in terms of correlations and spectral analysis is also getting better understood. Both probability concepts such as intermittency and conditional sampling as well as the concept of large scale structure and the associated strain seem to indicate possibilities of distinguishing and synthesizing 'engulfment' and molecular mixing.

Direct Simulations of Chemically Reacting Turbulent Mixing Layers

Direct Simulations of Chemically Reacting Turbulent Mixing Layers
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
Total Pages: 64
Release: 2018-07-06
Genre:
ISBN: 9781722357658

The results of direct numerical simulations of chemically reacting turbulent mixing layers are presented. This is an extension of earlier work to a more detailed study of previous three dimensional simulations of cold reacting flows plus the development, validation, and use of codes to simulate chemically reacting shear layers with heat release. Additional analysis of earlier simulations showed good agreement with self similarity theory and laboratory data. Simulations with a two dimensional code including the effects of heat release showed that the rate of chemical product formation, the thickness of the mixing layer, and the amount of mass entrained into the layer all decrease with increasing rates of heat release. Subsequent three dimensional simulations showed similar behavior, in agreement with laboratory observations. Baroclinic torques and thermal expansion in the mixing layer were found to produce changes in the flame vortex structure that act to diffuse the pairing vortices, resulting in a net reduction in vorticity. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers were shown to result from vorticity generation by baroclinic torques. Metcalfe, Ralph W. and Mcmurtry, Patrick A. and Jou, Wen-Huei and Riley, James J. and Givi, Peyman Unspecified Center...

Direct Simulations of Chemically Reacting Turbulent Mixing Layers

Direct Simulations of Chemically Reacting Turbulent Mixing Layers
Author: National Aeronautics and Space Adm Nasa
Publisher: Independently Published
Total Pages: 64
Release: 2018-11-03
Genre: Science
ISBN: 9781730760235

The results of direct numerical simulations of chemically reacting turbulent mixing layers are presented. This is an extension of earlier work to a more detailed study of previous three dimensional simulations of cold reacting flows plus the development, validation, and use of codes to simulate chemically reacting shear layers with heat release. Additional analysis of earlier simulations showed good agreement with self similarity theory and laboratory data. Simulations with a two dimensional code including the effects of heat release showed that the rate of chemical product formation, the thickness of the mixing layer, and the amount of mass entrained into the layer all decrease with increasing rates of heat release. Subsequent three dimensional simulations showed similar behavior, in agreement with laboratory observations. Baroclinic torques and thermal expansion in the mixing layer were found to produce changes in the flame vortex structure that act to diffuse the pairing vortices, resulting in a net reduction in vorticity. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers were shown to result from vorticity generation by baroclinic torques. Metcalfe, Ralph W. and Mcmurtry, Patrick A. and Jou, Wen-Huei and Riley, James J. and Givi, Peyman Unspecified Center...

Turbulent Reactive Flows

Turbulent Reactive Flows
Author: R. Borghi
Publisher: Springer Science & Business Media
Total Pages: 958
Release: 2013-03-08
Genre: Science
ISBN: 146139631X

Turbulent reactive flows are of common occurrance in combustion engineering, chemical reactor technology and various types of engines producing power and thrust utilizing chemical and nuclear fuels. Pollutant formation and dispersion in the atmospheric environment and in rivers, lakes and ocean also involve interactions between turbulence, chemical reactivity and heat and mass transfer processes. Considerable advances have occurred over the past twenty years in the understanding, analysis, measurement, prediction and control of turbulent reactive flows. Two main contributors to such advances are improvements in instrumentation and spectacular growth in computation: hardware, sciences and skills and data processing software, each leading to developments in others. Turbulence presents several features that are situation-specific. Both for that reason and a number of others, it is yet difficult to visualize a so-called solution of the turbulence problem or even a generalized approach to the problem. It appears that recognition of patterns and structures in turbulent flow and their study based on considerations of stability, interactions, chaos and fractal character may be opening up an avenue of research that may be leading to a generalized approach to classification and analysis and, possibly, prediction of specific processes in the flowfield. Predictions for engineering use, on the other hand, can be foreseen for sometime to come to depend upon modeling of selected features of turbulence at various levels of sophistication dictated by perceived need and available capability.

Chemical Reactions in Turbulent Mixing Flows

Chemical Reactions in Turbulent Mixing Flows
Author: Paul E. Dimotakis
Publisher:
Total Pages: 72
Release: 1998
Genre: Gas dynamics
ISBN:

This program focused on fundamental investigations of mixing, chemical-reaction, and combustion processes, in turbulent, subsonic, and supersonic free-shear flows. The program was comprised of an experimental effort; an analytical, modeling, and computational effort; and a diagnostics, instrumentation, and data-acquisition-development effort, with significant progress in each. With regard to gas-phase shear-layer mixing and combustion, effects of inflow/initial conditions, compressibility, and Reynolds number were experimentally investigated and, to a large extent, clarified. New measures to characterize level sets in turbulence were developed and successfully employed to characterize experimental data of liquid-phase turbulent-jet flows as well as three-dimensional direct-numerical-simulation data of Rayleigh-Taylor-instability flows. The computational effort has added to our understanding of the (H2+NO)/F2 chemical system employed in the shear-layer-mixing investigations as well as mixing in high-speed flows, along with further developments in Riemann-Invariant-Manifold gasdynamic simulation techniques and their application to unsteady detonation phenomena. On the diagnostic front, developments in digital imaging and Image Correlation Velocimetry have continued, and been used to investigate turbulent-jet mixing, the unsteady flow over an accelerating airfoil, to mitigate aliasing problems in the computer reconstruction of (2+1)-dimensional isosurface data, and in other applications.

An Experimental Study of Chemically Reacting Turbulent Free Shear Layers

An Experimental Study of Chemically Reacting Turbulent Free Shear Layers
Author: Robert K. Gould
Publisher:
Total Pages: 32
Release: 1978
Genre: Chemiluminescence
ISBN:

The objective of this program is to measure species concentrations and their statistical properties at points in well-characterized chemically reacting turbulent flows. Such measurements are required for (i) testing theories of reacting turbulent systems and (ii) as input to models which predict the behavior of practical combustors. The model chemical reaction being used to study turbulent mixing/reacting flows is the NO/O3 reaction. A photolysis/chemiluminescence technique is used to measure reactant concentrations, (NO) and (O3), and a product concentration, (NO2), simultaneously at points in the flow field. From such measurements, the required statistical quantities, i.e., probability density functions (pdf) and correlations of reactants and product concentrations, are being developed. These data are supplemented by measurements of the turbulence power spectra and intensity at the same points. During this quarter an examination of the signal collection optics has led to readjustments with reduced errors.