Question

If \( k \) is the average height of irregularities and \( \delta \) is the thickness of the laminar sublayer, then the boundary is known to be hydrodynamically rough when:

• A. \(\frac{k}{\delta}>:6\)
• B. \(2.5<:\frac{k}{\delta}<:6\)
• C. \( \frac{k}{\delta} = 0\)
• D. \( \frac{k}{R}<:0\)

Hint:

For smooth flows, the ratio \( \frac{k}{\delta} \) is small, while for rough flows, this ratio is larger, contributing to increased turbulence.

Answer 1

The Correct Option is A

The boundary is considered hydrodynamically rough when the ratio of the average height of surface irregularities to the thickness of the laminar sublayer is greater than 6. This condition results in turbulence near the surface.