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GATE 2026 AE – Question 27

Propulsion · Turbomachinery: Axial compressors, work and compression, degree of reaction, multi-staging · 1 mark · Multiple select

The figure below shows the blading of the rotors of two different axial turbomachines under their typical operating conditions, labelled as Configuration I and Configuration II. Which of the following statements is/are TRUE?

Flow goes from left to right through two rows of three blades. In Configuration I the blades are thin, lightly curved and rise towards the trailing edge. In Configuration II the blades are thick, with a rounded leading edge and strong curvature, and the trailing edge points downwards. The +$\theta$ direction is up the page.
  1. Configuration I corresponds to the rotor of a compressor and Configuration II corresponds to the rotor of a turbine
  2. Configuration I corresponds to the rotor of a turbine and Configuration II corresponds to the rotor of a compressor
  3. The rotor blades of the turbomachine in Configuration I move along the $+\theta$ direction
  4. The rotor blades of the turbomachine in Configuration II move along the $+\theta$ direction

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Show answer and explanation

Correct answer: (A) Configuration I corresponds to the rotor of a compressor and Configuration II corresponds to the rotor of a turbine; (D) The rotor blades of the turbomachine in Configuration II move along the $+\theta$ direction

Explanation

Compressor blades are thin and lightly cambered to diffuse the flow, while turbine blades are thick with a rounded leading edge and large turning, so I is a compressor and II a turbine (A). In a turbine rotor the relative flow leaves with a velocity component opposite to the blade speed. Here the relative flow leaves Configuration II pointing towards $-\theta$, so the blades move along $+\theta$ (D). In the compressor the relative inflow has a $+\theta$ component, so its blades move along $-\theta$.

Official GATE 2026 answer key: https://gate2026.iitg.ac.in/doc/download/2026/Keys/AE_Keys.pdf