The GATE Grind

GATE 2026 AE – Question 42

Propulsion · Turbomachinery: Axial compressors, work and compression, degree of reaction, multi-staging · 2 marks · Multiple choice

The figure below shows a compressor stage with station numbers 1, 2, and 3 as indicated. If $p_{0i}$, $T_{0i}$, and $C_i$ refer to the average values of total pressure, total temperature, and absolute flow speed, respectively, at the $i$th station, select the CORRECT option considering losses.

A compressor stage in the meridional plane: station 1 before the rotor R, station 2 between the rotor and the stator S, and station 3 after the stator.
  1. $p_{01} < p_{02},\ p_{02} > p_{03};\ T_{01} < T_{02},\ T_{02} \approx T_{03};\ C_1 < C_2,\ C_2 > C_3$
  2. $p_{01} < p_{02},\ p_{02} = p_{03};\ T_{01} < T_{02},\ T_{02} \approx T_{03};\ C_1 < C_2,\ C_2 = C_3$
  3. $p_{01} < p_{02},\ p_{02} > p_{03};\ T_{01} < T_{02},\ T_{02} < T_{03};\ C_1 > C_2,\ C_2 > C_3$
  4. $p_{01} < p_{02},\ p_{02} < p_{03};\ T_{01} < T_{02},\ T_{02} < T_{03};\ C_1 = C_2 = C_3$

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Correct answer: (A) $p_{01} < p_{02},\ p_{02} > p_{03};\ T_{01} < T_{02},\ T_{02} \approx T_{03};\ C_1 < C_2,\ C_2 > C_3$

Explanation

The rotor does work, so the total pressure and total temperature rise ($p_{01} < p_{02}$, $T_{01} < T_{02}$) and the absolute velocity increases ($C_1 < C_2$). The stator does no work, so the total temperature stays about the same ($T_{02} \approx T_{03}$). With losses its total pressure falls ($p_{02} > p_{03}$), and the stator diffuses the flow ($C_2 > C_3$).