Observations on large scale motions in highly disturbed boundary layers

Large scale motions in a turbulent boundary layer which is disturbed by a screen element are studied by comparing how the longitudinal and transverse integral length scales behave downstream of the element. Noticeable differences in their relaxation to undisturbed values have been observed which suggest changes in the non-isotropic character of large scale motions during relaxation. Scaling laws for the zero-pressure-gradient undisturbed boundary layer also indicate that the non-isotropy of large scale motions undergoes small, but detectable, changes with Reynolds number.