Spatial and temporal filtering of experimental data for a priori studies of subgrid-scale stresses

The viability of utilizing experimental time series for the investigation of SGS physics is investigated by filtering temporal and spatial data from a DNS of fully developed turbulent channel flow. It is found that temporal filtering of single-point data corresponds to filtering in the streamwise direction, if an appropriate convection velocity is introduced. One-dimensional filtering, however, is not effective at separating the large and small scales in the near-wall region due to the strong flow anisotropy. Two-dimensional filtering in planes parallel to the wall is equivalent to three-dimensional filtering above y(+) similar or equal to 10. Away from the wall, for y(+) greater than or similar to 50, where the turbulent eddies tend towards isotropy, streamwise (or temporal) filtering, is adequate. (C) 1996 American Institute of Physics.