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Lookup NU author(s): Professor Nilanjan ChakrabortyORCiD
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The effects of Lewis number Le on the reactive scalar gradient alignment with the local strain rate have been studied using Direct Numerical Simulation data of freely propagating statistically planar turbulent premixed flames with Le ranging from 0.34 to 1.2. The alignment characteristics of the reaction progress variable gradient are explained using the statistics of dilatation rate, and flame normal and tangential strain rates. The strength of dilatation rate is shown to increase with decreasing Le and this effect becomes particularly strong for the flames with Le < 1 because of thermo-diffusive instability. The dilatation rate is shown to be responsible for the preferential alignment of the reactive scalar gradient with the most extensive principal strain rate in the reaction zone for flames with Le close to unity, contrary to the alignment of scalar gradient with the most compressive principal strain rate in turbulent passive scalar transport. However, stronger dilatation rate effects in Le ≪ 1 flames (e.g. Le = 0.34) gives rise to the preferential alignment of the reactive scalar gradient with the most extensive principal strain rate for the major portion of the flame-brush. The scalar gradient alignment with local strain rate plays an important role in the transport of scalar dissipation rate and the flame surface density. The observed alignment with the most extensive principal strain rate destroys the scalar gradient and the magnitude of this sink is found to increase with decreasing Lewis number for a given turbulent Reynolds number and Damköhler number.
Author(s): Chakraborty N, Klein M, Swaminathan N
Publication type: Article
Publication status: Published
Journal: Proceedings of the Combustion Institute
ISSN (print): 1540-7489
ISSN (electronic): 1873-2704
Publisher: Elsevier Inc
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