Persistent Non-Homogeneous Features in Periodic Channel-Flow Simulations |
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Authors: | G M Fishpool S Lardeau M A Leschziner |
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Institution: | 1.Department of Aeronautics,Imperial College London,London,UK |
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Abstract: | Time-resolved simulations of simple shear flows, such as boundary layers and channel flows, are often used as precursor simulations that provide the inflow-boundary conditions for simulations of turbulent flows in and around more complex geometries. For
both the precursor and main simulations, the accuracy of the calculated mean flow relies on the simulations being run for
long enough to contain the full spectrum of turbulent processes, resulting in a physically valid statistical representation.
The time scale needed to achieve convergence of statistics from fundamental studies of simple shear flows is based on data
that is averaged in spatial directions in which the flow geometry is invariant—i.e. directions in which homogeneity is expected
to be the limiting case. This paper reports and discusses features that represent significant departures from spatial homogeneity
of the flow in such a direction, that persist on this time scale, thereby limiting the spatial uniformity of a simulated turbulent
inflow. The persistence and size of the features is quantified. A range of simulations for different combinations of domain
dimensions and flow parameters has been performed with two independent codes (DNS and LES) to explore how the persistence
and size are controlled. While no definitive physical mechanism has been identified, it is suggested that the features may
be related to experimental observations of persistent structures in wall-bounded flows. |
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