Measurements of turbulent velocity fluctuations in a planar Couette cell

The anisotropy of turbulent velocity fluctuations in a planar Couette cell has been investigated by using homodyne photon correlation spectroscopy (HCS). We find that 〈δvq(l)〉, the mean velocity difference between two points separated by a distance l, is consistent with the scaling behavior 〈δvq(l)〉∝l0.55. These measurements were made at a Reynolds number Re much greater than Rec, where the subcritical transition first occurs. The HCS technique was also used to measure Rec itself.