Two-point statistics for turbulent boundary layers and channels at Reynolds numbers up to δ+ ≈ 2000

Two-point statistics are presented for a new direct simulation of the zero-pressure-gradient turbulent boundary layer in the range Reo = 2780-6680, and compared with channels in the same range of Reynolds numbers, 8+ 1000-2000. Threedimensional spatial correlations are investigated in very long domains to educe the average structure of the velocity and pressure fluctuations. The streamwise velocity component is found to be coherent over longer distances in channels than in boundary layers, especially in the direction of the flow. For weakly correlated structures, the maximum streamwise length is O(7(S) for boundary layers and O(18(S) for channels, attained at the logarithmic and outer regions, respectively. The corresponding lengths for the spanwise and wall-normal velocities and for the pressure are shorter, O(8-28). The correlations are shown to be inclined to the wall at angles that depend on the distance from the wall, on the variable being considered, and on the correlation level used to define them. All these features change little between the two types of flows. Most the above features are also approximately independent of the Reynolds number, except for the pressure, and for the streamwise velocity structures in the channel. Further insight into the flow is provided by correlations conditioned on the intensity of the perturbations at the reference point, or on their sign. The statistics of the new simulation are available in our website. (C) 2014 AIP Publishing LLC.