For steady laminar incompressible boundary layer flow over a flat plate (Blasius solution), which of the following statements are TRUE?

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

(B) The local skin friction coefficient scales as $C_{f,x} \propto \frac{1}{\sqrt{Re_x}}$.

(C) The displacement thickness is $\delta^* \approx 1.72 \frac{x}{\sqrt{Re_x}}$.

(D) Wall shear stress $\tau_w$ increases as $x$ increases downstream.

Answer Key:

A,B,C

### Solution: In Blasius flow, $\delta = 5.0 x / \sqrt{Re_x} \propto x^{0.5}$ (A is true). $C_{f,x} = 0.664 / \sqrt{Re_x}$ (B is true). $\delta^* = 1.72 x / \sqrt{Re_x}$ (C is true). Wall shear stress $\tau_w \propto x^{-0.5}$ decreases downstream, so D is false. Correct: A, B, C.

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