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A Priori Investigation of Laminar Flamelet Decomposition and Conditional Source-term Estimation Methods in Turbulent Premixed Flames

Mahdipour, Amir Hossein | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54000 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Salehi, Mohammad Mahdi
  7. Abstract:
  8. An a priori analysis is performed to assess the performances of Laminar Flamelet Decomposition (LFD) and Conditional Source-term Estimation (CSE) methods in predicting conditional and unconditional filtered production rates and mass fractions for turbulent premixed flames over a wide range of Karlovitz numbers, which is an indicator for the level of turbulence-chemistry interaction in premixed combustion.In LFD, it is assumed that a turbulent flame is composed of strained laminar flamelets. By presuming the functional form of the probability density function (PDF) of the progress variable and inverting the integral equation for the unconditional filtered mass fractions of one of the species, the coefficients of the strained flamelets are obtained. The coefficients are viewed as the probability mass function of the flamelets and then are used to calculate the unconditional filtered mass fractions and the production rates of the species. The results show that LFD has a superior performance compared to the widely used unstrained flamelet method and has the potential to reasonably predict pollutants, such as CO, in turbulent combustion systems. In CSE, by presuming the functional form of the PDF of the progress variable and inverting the equation for the unconditional filtered mass fractions of each species, the conditional mass fractions are obtained. Next, by applying the first order Conditional Moment Closure (CMC) hypothesis, the conditional production rates are calculated. Results show that CSE can predict the species production rates with less limiting assumptions for the turbulent combustion regime. In addition to the regular CSE method, in this work, it is proposed to use Bernstein polynomials as the basis functions for solving the integral equations.Using this functional form, the accuracy of the solution both in solving the integral equation and the locality of the conditional means, which also contributes to accuracy, is increased. Also, the performance of CSE is compared with the performance of the ideal CMC method
  9. Keywords:
  10. Premixed Flame ; Large Eddy Simulation (LES) ; Combustion Modeling ; Turbulent Combustion ; Laminar Flamelet ; Laminar Flamelets Decomposition ; Conditional Moment Closure (CMC) ; Conditional Source-Term Estimation

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