Time Scales and Correlations in a Turbulent Boundary Layer

Space‐time correlations with large streamwise separation were obtained in a turbulent boundary layer with a zero‐pressure gradient. The auto and cross correlations of the velocities u and υ with streamwise spatial separation distances up to 20 boundary layer thicknesses revealed a difference in their structure and decay rate. Using conditional averaging techniques, the velocity product, uυ, was sampled in both the turbulent and nonturbulent zones. Further conditional sampling led to an average picture of the velocities in the interfacial bulges. Near the wall the space‐time correlation results are consistent with the idea of retarded fluid being ejected outward from the wall region and influencing the intermittent region.