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An Experimental Study of Flamelet Surfaces in Turbulent Combustion

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The major objective of the research reported was to study the properties of constant scalar property surfaces in turbulent reacting flows. Two dimensional image measurements were made in premixed turbulent flames and in jets and jet flames. Point-in-space, time-series measurements were also made, and the data used to study the properties of surface crossing statistics in jets and premixed flames. In addition, the hypothesis that, for the purpose of estimating the mean surface area per unit volume, surfaces in turbulent flow can be represented by fractal surfaces was used to develop models for the mean chemical reaction rate in premixed flames and for the source term in the equation for intermittency in free jets. Also a new method for making conditional velocity measurements in premixed flames was developed and applied to obtain unique data for velocity in these flames and to study jumps, across flamelets, of certain velocity statistics. Major findings for the flows and conditions studied include 1 for the premixed case flamelet surfaces are fractal as are constant mixture fraction surfaces in jets and constant temperature surfaces in jet flames 2 in jets the surface fractal dimension is between 2.3 to 2.4 3 level crossing sets from time-series data are not simple fractal sets 4 the idea of fractal bursts is introduced to help interpret the crossing sets and 5 unique fully-conditional velocity data give a measure of velocity jumps across flamelets in premixed combustion.

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  • Combustion and Ignition

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