GATE 2020 CE (CE2) – Question 34
Boundary-layer velocity is $u/U_\infty=\sin[\pi y/(2\delta)]$, with $U_\infty=0.3$ m/s and δ = 1.0 m. Find wall velocity gradient $\partial u/\partial y$ at y = 0 (s⁻¹), to two decimals.
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Correct answer: .45 to .49
Explanation
Differentiation gives $du/dy=U_\infty\pi\cos[\pi y/(2\delta)]/(2\delta)$. At the wall this is $0.3\pi/2=0.471239$ s⁻¹. Rounded, **0.47 s⁻¹**.