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Article information
Simulations of turbulent flow in a plane asymmetric diffuser
| Authors: |
Herbst, A. H.,
Schlatter, P.,
Henningson, D.S.H.,
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| Type: |
Article |
| Pubstate: |
Published |
| Journal: |
Flow, Turbulence and Combustion |
| Volume: |
79
275-306 |
| Year: |
2007 |
Abstract
Large-eddy simulations (LES) of a planar, asymmetric diffuser flow have
been performed. The diverging angle of the inclined wall of the diffuser is chosen as
8.5 degrees, a case for which recent experimental data are available. Reasonable agreement
between the LES and the experiments is obtained. The numerical method is further
validated for diffuser flow with the diffuser wall inclined at a diverging angle of 10 degrees,
which has served as a test case for a number of experimental as well as numerical
studies in the literature (LES, RANS). For the present results, the subgrid-scale
stresses have been closed using the dynamic Smagorinsky model. A resolution study
has been performed, highlighting the disparity of the relevant temporal and spatial
scales and thus the sensitivity of the simulation results to the specific numerical
grids used. The effect of different Reynolds numbers of the inflowing, fully turbulent
channel flow has been studied, in particular, Reb = 4,500, Reb = 9,000 and
Reb = 20,000 with Reb being the Reynolds number based on the bulk velocity and
channel half width. The results consistently show that by increasing the Reynolds
number a clear trend towards a larger separated region is evident; at least for the
studied, comparably low Reynolds-number regime. It is further shown that the small
separated region occurring at the diffuser throat shows the opposite behaviour as the
main separation region, i.e. the flow is separating less with higher Reb .Moreover, the
influence of the Reynolds number on the internal layer occurring at the non-inclined
wall described in a recent study has also been assessed. It can be concluded that this
region close to the upper, straight wall, is more distinct for larger Reb . Additionally the influence of temporal correlations arising from the commonly used periodic
turbulent channel flow as inflow condition (similar to a precursor simulation) for
the diffuser is assessed.
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