Structure of Velocity Space-Time Correlations in a Boundary Layer

Abstract

Space‐time correlations of longitudinal velocity fluctuations have been measured in a turbulent boundary layer, with and without frequency filtering. Celerities, relative to various fluctuations scales, are defined as partial derivatives of the isocorrelation curves with respect to both space separation and time delay. An example of the introduction of these celerities into the equations of motion is given for a simple case. The variation of these celerities with respect to fluid velocity is examined as a function of fluctuation scales and of distance to the wall. As a complement to the study of the effect of longitudinal space separation, the effect of space separation orthogonal to the wall resulting in a time delay corresponding to the maximum value of the correlation coefficient has been determined for various filtering frequencies.