Time scales in turbulent channel flow

Scaling laws for turbulent channel flow were studied, with emphasis on the near-wall region. The scaling behavior of power spectra and autocorrelations, as well as frequency of occurrence and duration of events detected with the variable-interval time-averaging (VITA) technique was investigated for Reynolds numbers ranging from 13 800 to 123 000 (based on centerline velocity and channel height). The governing time scale for the near wall region (of channel flow) was found to be a mixture (the geometric mean) of inner and outer time scales. This time scale collapsed data for different Reynolds numbers on, e.g., frequency of occurrence (cf. ‘‘bursting frequency’’) of VITA-events detected in the near-wall region. It is tentatively proposed that this behavior is due to interaction between the outer flow and the flow in the near-wall region.