Use of direct numerical simulation (DNS) data to investigate spatial resolution issues in measurements of wall-bounded turbulence

The effect of limited spatial resolution for hot-wire anemometry (HWA) is investigated by analysing the two-dimensional energy spectra from direct numerical simulation (DNS) of turbulent channel flow at Re-tau approximate to 950. Various spanwise filter lengths are applied to the streamwise velocity components in order to mimic the limited spatial resolution of a single-normal hot-wire experiment. Clear attenuation of the small-scale DNS energy is observed as the filter length is increased and good agreement is noted between the missing energy from filtered DNS and that from hot-wire experiments over a range of sensing lengths. The missing energy in the near-wall region is shown to be highly anisotropic in nature, thus bringing into question existing correction schemes that rely on small-scale isotropic flow assumptions. An empirical model of the missing streamwise component energy spectra is formulated, as a function of wire length, and is shown to be useful as a new correction function for the missing energy and streamwise turbulence intensity at the near-wall energetic peak.