Measurements in the Near-Wall Region of a Relaxing Three-Dimensional Low Speed Turbulent Air Boundary Layer.
MARYLAND UNIV COLLEGE PARK DEPT OF AEROSPACE ENGINEERING
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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 325000ft 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.
- Fluid Mechanics