W. W. Willmarth

Measurements of the structure of the Reynolds stress in a turbulent boundary layer

Additional experimental studies of the structure of Reynolds stress which supplement our previous work (Willmarth & Lu 1971) are reported. The velocity at the edge of the viscous sublayer is again used as a detector signal for bursts and sweeps. The signal uv obtained from an X-wire probe at various locations is conditionally sampled and sorted into four quadrants of the u, v plane. Using this method it is found that, when the velocity u w at the edge of the viscous sublayer becomes low and decreasing, a burst occurs. On the other hand, a sweep occurs when u w becomes large and increasing. The convection speeds of the bursts and the sweeps are found to be equal and are about 0·8 times the local mean velocity and 0·425 times the free-stream velocity at a distance y ≈ 0·15δ* from the wall (δ* is the displacement thickness). Throughout the turbulent boundary layer, the bursts are the largest contributors to

STRUCTURE OF THE REYNOLDS STRESS NEAR THE WALL

\overline{uv}

Reynolds-number effects on the structure of a turbulent channel flow

with the sweeps the second largest. On average, the bursts account for 77% of

Measurements of the fluctuating pressure at the wall beneath a thick turbulent boundary layer

\overline{uv}

Steady and Unsteady Motions and Wakes of Freely Falling Disks

, while the sweeps provide 55%; the excess percentage over 100% is due to the other small negative contributions. Characteristic mean time intervals are obtained for both bursts and sweeps from certain unique features of the measurements of fractional contributions to

Resolution and structure of the wall pressure field beneath a turbulent boundary layer

\overline{uv}

Modifying turbulent structure with drag-reducing polymer additives in turbulent channel flows

from different events. Both mean time intervals are approximately equal and constant for most of the turbulent boundary layer. The scaling of the mean time interval between bursts with outer flow variables is confirmed. It is suggested that many of the features of the fluctuating flow revealed by the measurements may be explained by convection past the measuring station of an evolving deterministic flow pattern such as the hairpin vorticity model of Willmarth & Tu (1967).

Survey and new measurements of turbulent structure near the wall

Experimental studies of the flow field near the wall in a turbulent boundary layer using hot-wire probes are reported. Measurements of the product uv are studied using the technique of conditional sampling with a large digital computer to single out special events (bursting) when large contributions to turbulent energy and Reynolds stress occur. The criterion used to determine when the product uv is sampled is that the streamwise velocity at the edge of the sublayer should have attained a certain value. With this simple criterion we find that 60% of the contribution to

Axially Symmetric Turbulent Boundary Layers on Cylinders: Mean Velocity Profiles and Wall Pressure Fluctuations.

\overline{uv}

Structure of Turbulence in the Boundary Layer near the Wall

is produced when the sublayer velocity is lower than the mean. This result is true at both low, R θ = 4230, and high, R θ = 38 000, Reynolds numbers. With a more strict sampling criterion, that the filtered sublayer velocity at two side-by-side points should be simultaneously low and decreasing, individual contributions to