Fig. 3.

(A) Superimposed contour lines for the normalized mean streamwise velocity $⟨U⟩/U_{\mathrm{\infty }}$. Solid lines, smooth; dashed lines, coated. The smooth case shows an ∼60% larger area with negative flow (black level). (B and C) Velocity profiles for $⟨U⟩/U_{\mathrm{\infty }}$ and $⟨V⟩/U_{\mathrm{\infty }}$, respectively. Smooth, $\mathrm{\square }$; coated, •. B, Inset shows the region near the wall for $⟨U⟩/U_{\mathrm{\infty }}$, where a larger negative portion in the smooth case can be observed. Error bars represent SE (=$u_{rms}/\sqrt{N}$, where $N$ is the number of samples); for $U$ the error bars (not shown) are smaller than the symbol size.