Multiprobe techniques were used to study the coherent flow-oriented eddy pattern that exists close to a wall in a turbulent flow. Simultaneous measurements of the spanwise component sz of the fluctuating wall velocity gradient at a number of locations in the spanwise direction were used to detect different aspects of the secondary flows that are superimposed on the mean flow. Conditionally averaged measurements of the streamwise component of the wall velocity gradient and of the streamwise component of the velocity at a number of locations on a line perpendicular to the wall show how the streamwise velocity fluctuations are related to the eddy structure, as detected by the sz(z) variation.
The results are consistent with the suggestion by Sirkar & Hanratty (1970a) that the flow-oriented eddies are approximately homogeneous in the flow direction and, on average, have inflows and outflows of equal magnitude coupled in the spanwise direction; i.e. they may be modelled, on average, by a sinusoidal sz(z) variation with dimensionless wavelength λ+ = 100. The results are also consistent with explanations by Fortuna and Hanratty (see Fortuna 1971; Hanratty, Chorn & Hatziavramidis 1977) and by Hatziavramidis & Hanratty (1979) of how these secondary flows are affecting momentum transport to the wall.