An experiment was performed to measure near-wall velocity and Reynolds stress profiles in
a pressure-driven three-dimensional turbulent boundary layer. An initially two-dimensional
boundary layer (Reθ≈4000) was exposed to a strong spanwise
pressure gradient. At the furthest downstream measurement locations there was also a fairly
strong favourable streamwise pressure gradient.
Measurements were made using a specially designed near-wall laser-Doppler anemometer
(LDA), in addition to conventional methods. The LDA used short focal length optics, a mirror
probe suspended in the flow, and side-scatter collection to achieve a measuring volume 35 μm
in diameter and approximately 65 μm long.
The data presented include mean velocity measurements and Reynolds stresses, all extending
well below y+=10, at several profile locations. Terms of the
turbulent kinetic energy transport equation are presented at two profile locations. The mean
flow is nearly collateral (i.e. W is proportional to U) at
the wall. Turbulent kinetic energy is mildly suppressed in the near-wall region and the
shear stress components are strongly affected by three-dimensionality. As a result, the
ratio of shear stress to turbulent kinetic energy is suppressed throughout most of the
boundary layer. The angles of stress and strain are misaligned, except very near the wall
(around y+=10) where the angles nearly coincide with the mean
flow angle. Three-dimensionality appears to mildly reduce the production of turbulent
kinetic energy.