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Development of Finite Volume Method for Coupled Radiative, Convective, and Conductive Heat Transfer in Participating Media

Abrar, Bagher | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 49996 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Darbandi, Masoud
  7. Abstract:
  8. Numerical simulations of participating media need careful solution of the radiation transfer equation (RTE) along the fluid flow governing equations. Evidently, the accuracy of achieved solutions highly depends on the accuracy of radiation transfer calculations. Despite numerous efforts performed in the previous researches, the RTE calculation still faces with several challenges from both accuracy and computational cost perspectives. The main objective of this research is to present new contributions in overcoming such challenges. So, a finite-volume (FV) solver is suitably developed to solve the RTE numerically. This extended solver is then coupled with an existing FV flow solver. The combination is called the FV-RTE solver. This solver is used to present the contribution of this work in three separate parts.As the first contribution, we use the FV-RTE solver and solve the combined natural convection-radiation problem in high-thermobouyant participating flow fields. One important aspect in treating high thermobuoyant flow fields is to impose the compressibility effects accurately in predictions. Literature shows that most of previous researches have used incompressible algorithms to solve the combined natural convection-radiation problem. These algorithms mostly used the Boussinesq assumption, which would not result in solutions with sufficient accuracies in domains with high temperature gradients. In this work, we develop a hybrid incompressible-compressible method to solve the combined natural convection-radiation heat transfer in a participating media without addressing the Boussinesq approximation. Our results show that there are significant differences between the compressible and incompressible results there. We show that the compressibility effects become more dominant in combined natural convection-radiation problems than the pure natural convection problem.As the second contribution, the FV-RTE solver is further developed to calculate the non-gray radiation transfer in combustion domains containing H2O and CO2 as the participating gases. Similar to many past research works, this work also uses the spectral-line weighted-sum-of-gray-gases (SLW) model for the RTE calculations. The SLW model is considered as a modern global model, which can be used in predicting the thermal radiation heat transfer within the combustion fields. The past SLW model users have mostly employed the classical reference approach to calculate the local values of gray gases’ absorption coefficient. However, the accuracy of SLW model incorporated with the classical reference approach, say the classical SLW method, is reduced in serious non-isothermal combustion domains. To improve the accuracy, the current work couples the classical SLW model with an improved reference approach. We call it the improved SLW method. It is shown that the current modified reference approach can enable more accurate calculation of the total emissivity using the classical SLW model. This would be particularly helpful for more accurate calculation of radiation transfer in highly non-isothermal combustion fields. As the third contribution, we focus on the SLW model from the computational cost aspects. As known, the computational cost of SLW is high in treating very large scale problems. The computational efforts of SLW model mainly return to the number of RTEs, which is equal to the number of SLW’s gray gases. Evidently, it is not reasonable to improve the computational efficiency of SLW model via decreasing the number of gray gases. We suitably extend an optimized SLW model, which retains the efficiency of original SLW model despite reducing the number of taken gray gases. The current study shows that the optimized SLW model would result in accurate radiative heat transfer calculations even considering 3 gray gases. This is where the classical SLW model needs 10 gray gases to reach the same accuracy. Indeed, the optimized SLW model can reduce the computational cost more than 50% comparing with the classical method. Finally, this research work focuses on the numerical simulation of several applied combustion problems. The results indicate that the current optimized SLW model can be used as an appropriate model to increase the accuracy and reduce the cost of radiation transfer calculations in numerical simulation of combustion domains
  9. Keywords:
  10. Radiation ; Finite Volume Method ; Combustion ; Numerical Simulation ; Radiative Heat Transfer

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