Experimental Fluid Mechanics
Slice along the X-Y plane. (1) FE; (2) holders; (3) sealed chamber; (4) flexure; (5) floating frame; (6) pitch moment force transducer; (7) pivot point; (8) WSS transducers; (→) displacement vectors.
Top view without the FE. (9) Outlet to the blower; (10) static pressure taps; (11) acquisition module (drawings are not to scale).
Although widely used, indirect methods for estimating the wall shear stress (WSS) cannot reliably characterize rough wall boundary-layer flows due to the difficulty in accurately estimating the zero-plane displacement, especially if applied to non-equilibrium flows.
We developed a floating element (FE) which is capable of measuring the wall shear stress (WSS) along with the pitching moment, Mz, as a mean to survey the zero-plane displacement (d) using equation (1).
Novel approach for quantifying the zero-plane displacement of rough-wall boundary-layers
The measured skin friction coefficient over the smooth wall, Cf, agrees with hot-wire anemometry to within 2%, when very few studies achieved accuracies higher than 5-7%.