In high-pressure gas turbine stages, film cooling protects rotor blade exterior surfaces from turbine entry temperatures exceeding the blade alloy melting point by:

(A) Discharging relatively cool compressor bleed air through inclined holes in the airfoil skin to form an insulating thermal protective layer

(B) Circulating liquid sodium through closed-loop rotor blade conduits

(C) Applying a reflective metallic mirror coating to reflect gas radiation

(D) Throttling combustor fuel flow to maintain gas temperatures strictly below 800 K

Answer Key:

A

### 5-Stage Derivation & Analytical Solution: 1. **Stage 1: Thermal Challenge:** Turbine entry temperature (TET) exceeds 1700 K, well above the melting point of nickel superalloys (~1550 K). 2. **Stage 2: Film Cooling Mechanism:** Compressor bleed air (~900 K) is bled through tiny shaped holes to create a protective boundary layer film. 3. **Stage 3: Selection:** Option A accurately describes film cooling.

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