Large Eddy Simulation has been applied to a piloted methane/air diffusion flamethe Sandia D flame-for which detailed experimental data are available. To evaluate the reacting density, temperature and species mass fractions a conserved scalar laminar flamelet formulation is employed, utilising a single virtually unstrained flamelet. The results of two simulations are discussed, comparing the use of the standard Smagorinsky model and a dynamic variant for closure of the unknown sub-grid stress. The chosen sub-grid scale model is shown to be extremely influential on the final solution. Whilst the use of the standard model results in a relatively poor simulation the dynamic closure offers an excellent velocity field prediction throughout the flame. Although the flame does show some strain rate influence on burning, particularly close to the inlet nozzle, the relatively simple 'unstrained' flamelet model applied is shown to provide an accurate representation of temperature and major species distribution.
Large eddy simulation (LES) has been applied to a representative primary combustion zone in an isothermal constant density simulation. The primary combustion zone of a gas turbine combustor is known to be one of the most challenging combustor regions to study numerically. The main flow features are typically governed by the impingement characteristic of the multiple air admission jets that stem from the coupled feed annulus, resulting in high levels of turbulence, recirculation and unsteady/periodic flow conditions. The chosen cylindrical geometry consists of an annular passage that feeds a row of six port-holes. The resulting radial jets impinge strongly within a confined core cross-flow. Both uncoupled (core only) and coupled (core and annulus) simulations are considered. In the uncoupled simulation detailed experimental data is used to provide port boundary conditions, whilst the coupled simulation models the flow within the annulus and port openings. The findings conclude that the coupled LES can adequately reproduce the port characteristics resulting in a good description of the core combustor flow field, potentially superior to that given by the uncoupled case and far superior to that given by RANS.
With renewed interest in disposal of heat-generating waste in bedded or domal salt formations, scoping analyses were conducted to estimate rates of waste package vertical movement. Vertical movement is found to result from thermal expansion, from upward creep or heave of the near-field salt, and from downward buoyant forces on the waste package. A two-pronged analysis approach was used, with thermal-mechanical creep modeling, and coupled thermal-viscous flow modeling. The thermal-mechanical approach used well-studied salt constitutive models, while the thermal-viscous approach represented the salt as a highly viscous fluid. The Sierra suite of coupled simulation codes was used for both approaches. The waste package in all simulations was a right-circular cylinder with the density of steel, in horizontal orientation. A time-decaying heat generation function was used to represent commercial spent fuel with typical burnup and 50-year age.Results from the thermal-mechanical base case showed approximately 27 cm initial uplift of the package, followed by gradual relaxation closely following the calculated temperature history. A similar displacement history was obtained with the package density set equal to that of salt. The slight difference in these runs is attributable to buoyant displacement (sinking) and is on the order of 1 mm in 2,000 years. Without heat generation the displacement stabilizes at a fraction of millimeter after a few hundred years. Results from thermal-viscous model were similar, except that the rate of sinking was constant after cooldown, at approximately 0.15 mm per 1,000 yr. In summary, all calculations showed vertical movement on the order of 1 mm or less in 2,000 yr, including calculations using well-established constitutive models for temperature-dependent salt deformation. Based on this finding, displacement of waste packages in a salt repository is not a significant repository performance issue.
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