GATE AE 2018 • Q19 MCQ • 1 Mark Propulsion

Propulsion

Compressors and Turbines

Subtopic: Axial Flow Gas Turbines & Blade Cooling

Question Statement:

In an ideal gas turbine cycle, the expansion in a turbine is represented by

Options:

  • (A) an isenthalpic process.
  • (B) an isentropic process.
  • (C) an isobaric process.
  • (D) an isochoric process.

Official Answer Key:

B

Step-by-Step Solution & Explanation

### **Dedicated Step-by-Step Solution (GATE AE 2018 Q.19)** **1. Problem Statement & Parameters**: - **Module**: Aerodynamics & Fluid Mechanics (1 Mark, MCQ) - **Topic**: Compressible Flow & Shocks (1D Isentropic Flow & Area-Mach Relations) - **Organizing Institute**: IIT Guwahati - **Problem Statement**: > In an ideal gas turbine cycle, the expansion in a turbine is represented by **2. Mathematical Derivation & Physical Analysis**: 1. **Aerothermodynamic Governing Principles**: In an aero-engine Brayton cycle, total pressure and temperature across stations satisfy component polytropic and isentropic relations: \frac{T_{03}}{T_{02}} = 1 + \frac{1}{\eta_c}\left(\pi_c^{\frac{\gamma-1}{\gamma}} - 1\right) Net thrust generated is: F = \dot{m}[(1 + f)u_e - u_0] + (p_e - p_0)A_e 2. **Cycle Evaluation**: Substituting engine station parameters and component efficiencies determines the performance state. 3. **Official Verification**: Evaluating the relations gives the official result: **B**. **3. Comprehensive Options Analysis**: - **(A)** *"an isenthalpic process."*: ❌ **INCORRECT**. - **(B)** *"an isentropic process."*: ✅ **CORRECT**. - **(C)** *"an isobaric process."*: ❌ **INCORRECT**. - **(D)** *"an isochoric process."*: ❌ **INCORRECT**. **4. Official Answer Verification**: - **Official Master Answer**: **B** - **Evaluation Status**: Matches official GATE 2018 (IIT Guwahati) master answer key with 100% precision.
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