Turbulence measurements in the wake of a thin flat plate.

Abstract

First the two-dimensionality of the flow was checked by measuring mean velocity and turbulence level profiles at different spanwise positions, and the flow was found uniform over 75% of the span (wind-tunnel width) at the trailing edge and over 60% of the span at the last downstream station, x = 240 cm, where wake measurements were taken. No detectable periodic components were found in the wake at any downstream station as evidenced either by wave analyzer or by correlation measurements taken with two probes located symmetrically to the centerline and placed near the location of maximum shear stress in the wake. The characteristics of the turbulent boundary layer at the trailing edge (x = 0) were the following: conventional thickness (U/Um = 0.99) d = 5.50 cm, momentum thickness d = 0.58 cm, and shape parameter H = 5*/6 = 1.44. At the same location, the friction velocity was found to be u*/Um = 0.046. This value was obtained by using Clauser's logarithmic law.5 The wall slope method using hot-wire measurements with correction for proximity of the boundary due to Wills 4 yielded a value of u*/Ua = 0.037. The thickness of the trailing edge expressed nondimensionally was quite small, u*h/v = 3; in other words, much smaller than the viscous sublayer. All data is presented in dimensionless form using 00, the momentum thickness at the trailing edge and the undisturbed flow velocity Um as reference quantities. Symmetry of the wake was found to be excellent and representative