GATE AE Turbomachinery: Previous Year Questions

GATE AE (Aerospace Engineering) Turbomachinery previous year questions from the Propulsion section, with figures and the official answer key where available.

All GATE AE papers

GATE AE 2026, Question 27 (1 mark, MSQ)

Propulsion - Turbomachinery

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?

GATE AE 2026 question 27

  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

Official answer: A, D

GATE AE 2026, Question 28 (1 mark, MSQ)

Propulsion - Turbomachinery

A multi-stage axial compressor can be operated at two points, A and B, both of which lie on the same speed line, as shown in the figure below. If $\eta$ is the isentropic efficiency of the compressor, select the statements that is/are TRUE.

GATE AE 2026 question 28

  1. $\eta_A > \eta_B$
  2. $\eta_B > \eta_A$
  3. In comparison to point B, point A is closer to the surge point
  4. In comparison to point A, point B is closer to the choke point

Official answer: A, C, D

GATE AE 2026, Question 42 (2 marks, MCQ)

Propulsion - Turbomachinery

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 $i^{\text{th}}$ station, select the CORRECT option considering losses.

GATE AE 2026 question 42

  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. $p_{01} < p_{02},\ p_{02} < p_{03};\ T_{01} < T_{02},\ T_{02} < T_{03};\ C_1 = C_2 = C_3$

Official answer: A

GATE AE 2026, Question 46 (2 marks, MSQ)

Propulsion - Turbomachinery

The figure below shows the velocity triangles at the inlet and outlet of the rotor of a low hub-to-tip ratio axial compressor at the mid-span of the blade. The absolute and relative velocities of the flow are denoted by $\mathbf{C}$ and $\mathbf{W}$, respectively. The subscripts 1 and 2 refer to the locations before and after the rotor, respectively. The blade velocity is denoted by $\mathbf{U}$. Select the CORRECT statement(s) for this device.

GATE AE 2026 question 46

  1. The axial velocity is constant across the rotor
  2. The flow coefficient is 0.6
  3. The blade loading coefficient is 0.6
  4. If the acoustic velocity at the rotor inlet is 350 m/s, then the inlet relative Mach number is 0.333

GATE AE 2026, Question 61 (2 marks, NAT)

Propulsion - Turbomachinery

A centrifugal compressor has a constant-width radial diffuser. The diameters at the diffuser inlet and outlet are 0.2 m and 0.3 m, respectively. The flow at the diffuser inlet and outlet is assumed to be steady and uniform. The average velocity at the diffuser inlet and outlet are $(60\,\hat{\mathbf{e}}_r + 75\,\hat{\mathbf{e}}_\theta)$ m/s and $(u\,\hat{\mathbf{e}}_r + 50\,\hat{\mathbf{e}}_\theta)$ m/s, respectively. If the flow through the diffuser is treated as steady and incompressible, the value of $u$ is ________ (rounded off to the nearest integer).

Official answer: 39 to 41

GATE AE 2026, Question 62 (2 marks, NAT)

Propulsion - Turbomachinery

A gas mixture at a pressure of 800 kPa and a density of 5 kg/m$^3$ enters a turbine stage. The temperature of the gas at the nozzle exit and the stage exit are 790 K and 750 K, respectively. Assume the specific heats are constant for the gas mixture in the range of temperatures considered. The specific heat at constant pressure is 0.72 kJ/kg-K and the ratio of specific heats is 1.33. The value of the degree of reaction of the turbine stage is ________ (rounded off to 2 decimal places).

Official answer: 0.26 to 0.29

GATE AE 2025, Question 35 (1 mark, NAT)

Propulsion - Turbomachinery

In a centrifugal compressor, the eye tip diameter is 10 cm. For a shaft rotational speed of 490 rotations per second, the tangential speed at the inducer tip is ___ m/s (rounded off to one decimal place).

Official answer: 151.0 to 154.0

GATE AE 2025, Question 65 (2 marks, NAT)

Propulsion - Turbomachinery

A single-stage axial compressor, with a 50 % degree of reaction, runs at a mean blade speed of 250 m/s. The overall pressure ratio developed is 1.3. Inlet pressure and temperature are 1 bar and 300 K, respectively. Axial velocity is 200 m/s. Specific heat at constant pressure, $C_p = 1005$ J/kg/K and specific heat ratio, $\gamma = 1.4$. The rotor blade angle at the outlet is ___ degrees (rounded off to two decimal places).

Official answer: 21.00 to 22.00

GATE AE 2024, Question 40 (2 marks, MCQ)

Propulsion - Turbomachinery

A multistage axial compressor, with overall isentropic efficiency of 0.83, is used to compress air at a stagnation temperature of 300 K through a pressure ratio of 10:1. Each stage of the compressor is similar, and the stagnation temperature rise across each compressor stage is 20 K. Assume $C_p = 1005$ J/kg K and $\gamma = 1.4$ for air. How many stages are there in the compressor?

  1. 17
  2. 13
  3. 19
  4. 11

Official answer: A

GATE AE 2024, Question 49 (2 marks, MSQ)

Propulsion - Turbomachinery

Which of the following statements is/are TRUE for an axial turbine?

  1. For a fixed rotational speed, the mass flow rate increases with increase in the flow coefficient
  2. The absolute stagnation enthalpy of the flow decreases across the nozzle row
  3. The relative stagnation enthalpy remains unchanged through the rotor
  4. For a fixed rotational speed, the mass flow rate remains unchanged with a change in the flow coefficient

Official answer: A, C

GATE AE 2024, Question 50 (2 marks, MSQ)

Propulsion - Turbomachinery

Which of the following statements is/are TRUE for a single stage axial compressor?

  1. Starting from design condition and keeping the mass flow rate constant, if the blade RPM is increased, the compressor rotor may experience positive incidence flow separation (actual relative flow angle greater than the design blade angle)
  2. Starting from design condition at the same blade RPM, if the mass flow rate is increased, the compressor rotor may experience positive incidence flow separation (actual relative flow angle greater than the design blade angle)
  3. Keeping the mass flow rate constant, if the blade RPM is increased, the compressor may experience surge
  4. At the same blade RPM, if the mass flow rate is increased, the compressor may experience surge

Official answer: A, C

GATE AE 2024, Question 58 (2 marks, NAT)

Propulsion - Turbomachinery

A centrifugal compressor is designed to operate with air. At the leading edge of the tip of the inducer (eye of the impeller), the blade angle is $45^\circ$, and the relative Mach number is 1.0. The stagnation temperature of the incoming air is 300 K. Consider $\gamma = 1.4$. Neglect pre-whirl and slip. The inducer tip speed is ________ m/s (rounded off to the nearest integer).

Official answer: 230 to 240

GATE AE 2023, Question 20 (1 mark, MCQ)

Propulsion - Turbomachinery

In a single-spool aviation turbojet engine, which of the following is the correct relationship between the total work output $W_T$ of a 2-stage axial turbine and the total work required $W_C$ by a 6-stage axial compressor, neglecting losses?

  1. $W_T = 2W_C$
  2. $W_T = 6W_C$
  3. $W_T = W_C$
  4. $W_T = 3W_C$

Official answer: C

GATE AE 2023, Question 21 (1 mark, MCQ)

Propulsion - Turbomachinery

For a stage of a 50% reaction ideal axial flow compressor (symmetrical blading), select the correct statement from the options given.

  1. The stagnation enthalpy rise across the rotor is 50% of the rise across the stage.
  2. The static enthalpy rise across the rotor is 50% of the rise across the stage.
  3. Axial velocity component of the flow at the rotor exit is 50% of that at the rotor entry.
  4. The static pressure rise across the rotor is 50% of the rise across the stator.

Official answer: B

GATE AE 2023, Question 55 (2 marks, NAT)

Propulsion - Turbomachinery

The operating characteristics of a pump were measured to be $C_P = a\Phi^2$, where power coefficient $C_P = \dfrac{P}{\rho\omega^3D^5}$, $\Phi$ is the flow coefficient, $a$ is a constant, $D$ is a length scale, $\omega$ is the rotation rate, $\rho$ is fluid density, and $P$ is the power required. The flow coefficient is a dimensionless volume flow rate scaled with $\omega$ and $D$. Assuming that the flow rate remains the same, if the rotation rate is increased to $1.25\,\omega$, the power changes to $\alpha P$. The value of $\alpha$ is ________. (round off to two decimal places)

Official answer: 1.24 to 1.26

GATE AE 2023, Question 64 (2 marks, NAT)

Propulsion - Turbomachinery

A centrifugal air compressor has inlet root diameter of 0.25 m and the outlet diameter of the impeller is 0.6 m. The pressure ratio is 5.0. The air at the inlet of the rotor is at 1 atm and 25 °C. The polytropic efficiency is 0.8 and slip factor is 0.92. Use $C_p = 1.004$ kJ/kg-K and $\gamma = 1.4$. The impeller speed in revolutions per minute (RPM) is _________. (round off to the nearest integer)

Official answer: 15948 to 16048

GATE AE 2022, Question 30 (1 mark, MSQ)

Propulsion - Turbomachinery

A high-pressure-ratio multistage axial compressor encounters an extreme loading mismatch during starting. Which of the following technique(s) can be used to alleviate this problem?

  1. Blade cooling
  2. Variable angle stator vanes
  3. Blow-off valves
  4. Multi-spool shaft

Official answer: B, C, D

GATE AE 2022, Question 35 (1 mark, NAT)

Propulsion - Turbomachinery

In a single stage turbine, the hot gases come out of stator/ nozzle at a speed of 500 m/s and at an angle of 70 degrees with the turbine axis as shown. The design speed of the rotor blade is 250 m/s at the mean blade radius. The rotor blade angle, $\beta$, at the leading edge is ________ degrees (round off to one decimal place).

GATE AE 2022 question 35

Official answer: 51.5 to 52.6

GATE AE 2022, Question 65 (2 marks, NAT)

Propulsion - Turbomachinery

A multistage axial compressor takes in air at 1 atm, 300 K and compresses it to a minimum of 5 atm. The mean blade speed is 245 m/s and work coefficient, $\dfrac{\Delta C_\theta}{U}$ is 0.55 for each stage. For air, use $C_p = 1005$ J/(kg-K), $R = 287$ J/(kg-K) and $\gamma = 1.4$. If the compression is isentropic, the number of stages required is ____________ (rounded off to the next higher integer).

GATE AE 2018, Question 44 (2 marks, MCQ)

Propulsion - Turbomachinery

An axial compressor that generates a stagnation pressure ratio of 4.0, operates with inlet and exit stagnation temperatures of 300 K and 480 K, respectively. If the ratio of specific heats ($\gamma$) is 1.4, the isentropic efficiency of the compressor is

  1. 0.94
  2. 0.81
  3. 0.72
  4. 0.63

Official answer: B

GATE AE 2018, Question 63 (2 marks, NAT)

Propulsion - Turbomachinery

An axial compressor rotor with 50 % degree of reaction, operates with an axial velocity of 200 m/s. The absolute flow angle at the inlet of the rotor is $22^\circ$ with reference to the axial direction. If the axial velocity is assumed to remain constant through the rotor, the magnitude of the relative velocity (in m/s) at the rotor exit is ___________ (accurate to one decimal place).

Official answer: 215.0 to 216.5

GATE AE 2018, Question 64 (2 marks, NAT)

Propulsion - Turbomachinery

The relative velocity of air leaving a straight radial impeller of a centrifugal compressor is 100 m/s. If the impeller tip speed is 200 m/s, for a slip free operation, the absolute velocity (in m/s) at the impeller exit is _________ (accurate to one decimal place).

Official answer: 222.0 to 225.0

GATE AE 2016, Question 37 (2 marks, MCQ)

Propulsion - Turbomachinery

A single-stage gas turbine operates with an axial absolute flow at the entry and exit from the stage. The absolute flow angle at the nozzle exit is $70^\circ$. The turbine stage generates a specific work of 228 kJ/kg when operating with a mean blade speed of 440 m/s. The absolute velocity at the rotor entry is

  1. 275.7 m/s
  2. 551.5 m/s
  3. 1103.0 m/s
  4. 1654.5 m/s

Official answer: B

GATE AE 2016, Question 38 (2 marks, NAT)

Propulsion - Turbomachinery

An axial compressor operates such that it has an inlet and an exit total temperature of 300 K and 430 K, respectively. The isentropic efficiency of the compressor is 85 %. If the ratio of specific heats is 1.4, then the total pressure ratio across the compressor is ____________.

Official answer: 2.9 to 3.1

GATE AE 2014, Question 28 (1 mark, MCQ)

Propulsion - Turbomachinery

For a fifty percent reaction axial compressor stage, following statements are given: I. Velocity triangles at the entry and exit of the rotor are symmetrical. II. The whirl or swirl component of absolute velocity at the entry of rotor and entry of stator are same. Which of the following options are correct?

  1. Both I and II are correct statements
  2. I is correct but II is incorrect
  3. I is incorrect but II is correct
  4. Both I and II are incorrect

Official answer: B

GATE AE 2014, Question 56 (2 marks, NAT)

Propulsion - Turbomachinery

A gas turbine engine is operating under the following conditions: stagnation temperature at turbine inlet 1350 K; stagnation pressure at turbine inlet 10 bar; static temperature at turbine exit 800 K; velocity at turbine exit 200 m/s; total-to-total efficiency of turbine 0.96; $\gamma$ (ratio of specific heats) 1.33; $C_p$ (specific heat at constant pressure) 1.147 kJ/kgK. The stagnation pressure (in bar) in the nozzle (considering isentropic nozzle) is equal to _______.

Official answer: 1.10 to 1.25

GATE AE 2014, Question 57 (2 marks, NAT)

Propulsion - Turbomachinery

Air at a stagnation temperature of 300 K (ratio of specific heats, $\gamma = 1.4$ and specific gas constant $R = 287$ J/kgK) enters the impeller of a centrifugal compressor in axial direction. The stagnation pressure ratio between the diffuser outlet and impeller inlet is 4.0. The impeller blade radius is 0.3 m and it is rotating at 15000 rev/min. If the slip factor $\sigma_s$ (Ratio of tangential component of air velocity at the blade tip to the blade tip speed) is 0.88, the overall efficiency (total-to-total) of the compressor (in %) is ___________.

Official answer: 74 to 76