In order to improve predictions of flow behavior in numerous applications there is a great need to understand the physics of three-dimensional turbulent boundary layers, dominated by near-wall behavior. To that end, an experiment was performed to measure near-wall velocity and Reynolds stress profiles in a pressure-driven three-dimensional turbulent boundary layer. The flow was achieved by placing a 30 deg wedge in a straight duct in a wind tunnel, with-additional pressure gradient control above the test surface. An initially two-dimensional boundary layer (Re approx. equal 4000) was exposed to a strong spanwise pressure gradient. At the furthest downstream measurement locations there was also a fairly strong favorable 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 nearly spherical measuring volume approximately 35 microns in diameter. Good agreement with previous two-dimensional boundary layer data was achieved. The three-dimensional turbulent boundary layer data presented include mean velocity measurements and Reynolds stresses, all extending well below y(+) = 10, at several profile locations. Terms of the Reynolds stress transport equations are calculated at two profile locations. The mean flow is nearly collateral 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.

Turbulence measurements with a Laser Doppler Velocimeter (LDV) using the dual scatter or differential Doppler mode have been made in a subsonic, fully developed channel flow. The measurements were made using only those light scattering particles occurring naturally in air. Results include mean velocity profiles, turbulence intensities, Reynolds stress distributions and a skewness measurement of the velocity distribution function across the channel. Statistical techniques were used to obtain the various turbulence parameters. Guidelines have been established for the amount of data needed to obtain results with a specified accuracy and confidence level. Measurements have also been made to determine the particle-size distribution. An aerodynamic means was used to determine the size distribution, in contrast to the usual optical procedures. (Modified author abstract).