The dissipation rate of a scalar variance is related to the mean heat release rate in turbulent combustion. Mixture fraction is the scalar of interest for non-premixed combustion, and a reaction progress variable is relevant for premixed combustion. A great deal of work is conducted in past studies to understand the spectra of passive scalar transport in turbulent flows. A very brief summary of these studies to bring out the salient characteristics of the passive scalar spectrum is given first. Then, the classical analysis of the reactive scalar spectrum is revisited in the lights of recent understanding gained through analyzing the scalar spectrum deduced from direct numerical simulation data of both non-premixed and premixed combustion. The analysis shows that the reactive scalar spectral density in premixed combustion has a dependence on Karlovitz and Damköhler numbers, which comes through the mean scalar dissipation rate appearing in the spectral expression. In premixed combustion, the relevant scale for the scalar dissipation rate is shown to be of the order of the chemical length scale, and the dissipation rate is not influenced by the scales in the inertial-convective range unlike for the passive scalar dissipation rate. The scalar fluctuations produced near the chemical scales cascade exponentially to larger scales. These observations imply that the passive scalar models cannot be extended to premixed combustion.
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January 2021
Research Article|
January 25 2021
Scalar fluctuation and its dissipation in turbulent reacting flows
Special Collection:
In Memory of Edward E. (Ted) O’Brien
N. Swaminathan
;
N. Swaminathan
a)
1
Hopkinson Lab, Department of Engineering, Cambridge University
, Cambridge, United Kingdom
a)Author to whom correspondence should be addressed: [email protected]
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N. Chakraborty
N. Chakraborty
b)
2
School of Engineering, Newcastle University
, Newcastle-Upon-Tyne, United Kingdom
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a)Author to whom correspondence should be addressed: [email protected]
b)
Electronic mail: [email protected]
Note: This paper is part of the Special Topic, In Memory of Edward E. (Ted) O’Brien.
Physics of Fluids 33, 015121 (2021)
Article history
Received:
December 02 2020
Accepted:
December 28 2020
Citation
N. Swaminathan, N. Chakraborty; Scalar fluctuation and its dissipation in turbulent reacting flows. Physics of Fluids 1 January 2021; 33 (1): 015121. https://doi.org/10.1063/5.0039222
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