On The Predictability Of Turbulent Mixing With Implicit Large Eddy Simulation PDF Download

Implicit Large Eddy Simulation (ILES) with high-resolution and high-order computationalmodelling has been applied to flows with turbulent mixing and combustion. Due to the turbulent nature, mixing of fuel and air and the subsequent combustionstill remain challenging for computational fluid dynamics. However, recently ILES, anadvanced numerical approach in Large Eddy Simulation methods, has shown encouragingresults in prediction of turbulent flows. In this thesis the governing equationsfor single phase compressible flow were solved with an ILES approach using a finitevolume Godunov-type method without explicit modelling of the subgrid scales. Up toninth-order limiters were used to achieve high order spatial accuracy. When simulating non chemical reactive flows, the mean flow of a fuel burner was comparedwith the experimental results and showed good agreement in regions of strongturbulence and recirculation. The one dimensional kinetic energy spectrum was alsoexamined and an ideal k?5/3decay of energy could be seen in a certain range, whichincreased with grid resolution and order of the limiter. The cut-off wavenumbers arelarger than the estimated maximum wavenumbers on the grid, therefore, the numericaldissipation sufficiently accounted for the energy transportation between large andsmall eddies. The effect of density differences between fuel and air was investigatedfor a wide range of Atwood number. The mean flow showed that when fuel momentumfluxes are identical the flow structure and the velocity fields were unchanged byAtwood number except for near fuel jet regions. The results also show that the effectsof Atwood number on the flow structure can be described with a mixing parameter. In combustion flows simulation, a non filtered Arrhenius model was applied for thechemical source term, which corresponds to the case of the large chemical time scalecompared to the turbulent time scale. A methane and air shear flow simulation wasperformed and the methane reaction rate showed non zero values against all temperatureranges. Small reaction rates were observed in the low temperature range due tothe lack of subgrid scale modelling of the chemical source term. Simulation was alsoperformed with fast chemistry approach representing the case of the large turbulenttime scale compared to the chemical time scale. The mean flow of burner flames werecompared with experimental data and a fair agreement was observed.