For steady, laminar, incompressible flow over a flat plate of length $L$ with zero pressure gradient (Blasius boundary layer), which of the following statements is/are TRUE?

(A) The boundary layer thickness $\delta(x)$ grows proportionally to $\sqrt{x}$.

(B) The local skin friction coefficient $C_{f,x}$ is inversely proportional to $\sqrt{Re_x}$.

(C) The velocity profile in similarity coordinates is independent of the Reynolds number.

(D) The wall shear stress increases monotonically from leading edge to trailing edge.

Answer Key:

A,B,C

### Solution: In Blasius flow, $\delta = 5.0 \frac{x}{\sqrt{Re_x}} \propto \sqrt{x}$ (A is true). Local skin friction $C_{f,x} = \frac{0.664}{\sqrt{Re_x}}$ (B is true). The normalized velocity $u/U_\infty = f'(\eta)$ is self-similar (C is true). Wall shear stress $\tau_w \propto 1/\sqrt{x}$ decreases downstream (D is false). Correct: A, B, C.

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