For a supersonic compressible flow passing through a normal shock wave, which of the following statements is/are TRUE?

(A) The downstream flow is always strictly subsonic ($M_2 < 1$)

(B) The static pressure and static temperature both increase across the shock

(C) The total (stagnation) pressure decreases across the shock wave

(D) The total (stagnation) enthalpy decreases across the shock wave

Answer Key:

A,B,C

### 5-Stage Derivation & Analytical Solution: 1. **Stage 1: Governing Concept & Domain Context:** * This question evaluates **Grammar & Vocabulary** under *Verbal Aptitude* in GATE AE. 2. **Stage 2: Mathematical Derivation:** * Energy equation across adiabatic shock: $h_{01} = h_{02} = \text{constant}$, so stagnation enthalpy is invariant (D is false). Second law requires $\Delta s > 0$, leading to stagnation pressure loss $p_{02} < p_{01}$ (C is true). Continuity and momentum dictate $M_2 < 1$ and $p_2 > p_1, T_2 > T_1$ (A and B are true). 3. **Stage 3: Distractor Elimination Forensics:** * The evaluated correct answer is derived using standard physical equations. * Distractor values correspond to typical unit conversion omissions or inverted formulas. 4. **Stage 4: Common Student Trap:** * *Trap:* Believing that total enthalpy decreases across an adiabatic normal shock wave. *Reference: T.H.G. Megson, Aircraft Structures for Engineering Students (Butterworth-Heinemann).*

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