A key limitation of Reynolds-Average Navier-Stokes (RANS) simulation of mixing and reaction in turbulent flows is the lack of resolution of small-scale structure and associated unsteadiness. Various subgrid models formulated in state space have been developed to complement the RANS solution in this regard. We here introduce a physical-space formulation that captures unsteady advective and diffusive processes at all scales of the turbulent flow. The approach is a 3D construction based on the Linear Eddy Model (LEM), involving three orthogonally intersecting arrays of 1D LEM domains, and coupled so as to capture the 3D character of fluid trajectories. To illustrate the model performance of the 3D LEM-based formulation, here termed LEM3D, multi-stream mixing in a turbulent round jet is simulated using measured mean-flow properties as input. Comparison to scalar crosscorrelation coefficients and other measured properties of this mixing configuration indicate that the LEM3D approach, in conjunction with flow properties that are provided by steady-state models, is a useful representation of complex turbulent mixing processes that would otherwise be difficult to capture within a steady-state CFD framework.
This paper provides detailed comparisons of chemical reaction mechanisms of H 2 applicable at high preheat temperatures and pressures relevant to gas turbine and particularly Alstom's reheat gas turbine conditions. It is shown that the available reaction mechanisms exhibit large differences in several important elementary reaction coefficients. The reaction mechanisms are assessed by comparing ignition delay and laminar flame speed results obtained from CHEMKIN with available data, however, the amount of data at these conditions is scarce and a recommended candidate among the mechanisms can presently not be selected. Generally, the results with the GRI-Mech and Leeds mechanisms deviate from the Davis, Li,Ó Conaire, Konnov and San Diego mechanisms, but there are also significant deviations between the latter five mechanisms that altogether are better adapted to hydrogen. The differences in ignition delay times between the dedicated hydrogen mechanisms (Ó Conaire, Li and Konnov) range from approximately a maximum factor of 2 for the H 2 -air cases, to more than a factor 5 for the H 2 /O 2 /AR cases. The application of the computed ignition delay time to reheat burner development is briefly discussed.
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