Measurements in the Near-Wall Region of a Relaxing Three-Dimensional Low Speed Turbulent Air Boundary Layer.

摘要

An experimental investigation was conducted at selected locations of the near-wall region of a three-dimensional turbulent air boundary layer relaxing in a nominally zero external pressure gradient behind a transverse hump (in the form of a 30 degree swept, 5-foot chord wing-type model) faired into the side wall of a low speed wind tunnel. Wall shear stresses measured with a flush-mounted hot-film gage and a sublayer fence were in very good agreement with experimental data obtained with two Preston probes. With the upstream unit Reynolds number held constant at 325000/ft approximately one-fourth of the boundary layer thickness adjacent to the wall was surveyed with a single rotated hot-wire probe mounted on a specially designed minimum interference traverse mechanism. The boundary layer (approximately 3.5 in. thick near the first survey station where the length Reynolds number was 5500000) had a maximum crossflow velocity ratio of 0.145 and a maximum crossflow angle of 21.875 degrees close to the wall. The hot-wire data indicated, in agreement with the findings elsewhere, that the apparent dimensionless velocity profiles in the viscous sublayer region are universal and that the wall influence is negligible beyond y(+) =5. The existence of wall similarity in the relaxing flow field was confirmed in the form of a log law based on the resultant mean velocity and resultant friction velocity (obtained from measured skin friction).