GATE AE Compressible Flows: Previous Year Questions

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

All GATE AE papers

GATE AE 2026, Question 21 (1 mark, MCQ)

Aerodynamics - Compressible Flows

In the figure shown below, the flow at the nozzle exit is ________.

GATE AE 2026 question 21

  1. overexpanded
  2. underexpanded
  3. ideally expanded
  4. subsonic

Official answer: A

GATE AE 2026, Question 29 (1 mark, MSQ)

Aerodynamics - Compressible Flows

Which of the following statements is/are TRUE regarding critical and drag divergence Mach numbers of a wing?

  1. Critical Mach number is the minimum freestream Mach number for which sonic condition is attained somewhere over the wing
  2. Drag divergence Mach number is always higher than the critical Mach number
  3. Drag divergence Mach number is the local Mach number over the wing at which the drag increases drastically
  4. Critical Mach number is independent of the angle of attack

Official answer: A, B

GATE AE 2026, Question 30 (1 mark, MSQ)

Aerodynamics - Compressible Flows

A flow is steady, inviscid and one-dimensional, with no shaft work or body forces. Which of the following is/are possible under the given conditions?

  1. Oblique shocks
  2. Sound propagation
  3. Rayleigh flow
  4. Fanno flow

Official answer: B, C

GATE AE 2026, Question 64 (2 marks, NAT)

Aerodynamics - Compressible Flows

Consider a centered Prandtl-Meyer expansion fan at a $\theta = 4^\circ$ corner in a Mach 1.78 air flow, as shown in the figure below. The angle $\psi$ (see figure) made by the ending wave of the fan with respect to the incoming stream is ________ degrees (rounded off to 1 decimal place). An excerpt from the table of Prandtl-Meyer function for air is provided below. $$\begin{array}{|c|c||c|c||c|c|}\hline M & \nu\,[\deg] & M & \nu\,[\deg] & M & \nu\,[\deg] \\ \hline 1.72 & 18.40 & 1.82 & 21.30 & 1.92 & 24.15 \\ 1.74 & 18.98 & 1.84 & 21.88 & 1.94 & 24.71 \\ 1.76 & 19.56 & 1.86 & 22.45 & 1.96 & 25.27 \\ 1.78 & 20.15 & 1.88 & 23.02 & 1.98 & 25.83 \\ 1.80 & 20.73 & 1.90 & 23.59 & 2.00 & 26.38 \\ \hline\end{array}$$

GATE AE 2026 question 64

Official answer: 27.2 to 27.6

GATE AE 2026, Question 65 (2 marks, NAT)

Aerodynamics - Compressible Flows

A Mach 1.5 air flow enters a round duct of length 20 cm and diameter 3 cm. If the flow exits with Mach number 1.1, the average Fanning friction factor $f$ of the duct is ________ $\times 10^{-3}$ (rounded off to 1 decimal place). An excerpt from the Fanno flow table for air is given below. $$\begin{array}{|c|c|c|c|c|c|c|}\hline M & 1.1 & 1.2 & 1.3 & 1.4 & 1.5 & 1.6 \\ \hline \dfrac{4fL^*}{D}\times 10^4 & 99.35 & 336.4 & 648.3 & 997.4 & 1361 & 1724 \\ \hline\end{array}$$

Official answer: 4.5 to 5.0

GATE AE 2025, Question 46 (2 marks, NAT)

Aerodynamics - Compressible Flows

An aircraft is flying at an altitude of 4500 m above sea level, where the ambient pressure, temperature and density are 57 kPa, 259 K and 0.777 kg/m$^3$, respectively. The speed of the aircraft ($V$) is 230 m/s. Gas constant R = 287 J/kg/K, and specific heat ratio $\gamma = 1.4$. If the stagnation pressure is $p_o$, and static pressure is $p$, the value of $\left[\dfrac{p_o - p}{\frac{1}{2}\rho V^2}\right]$ is ________ (rounded off to two decimal places).

Official answer: 1.08 to 1.14

GATE AE 2025, Question 49 (2 marks, NAT)

Aerodynamics - Compressible Flows

A supersonic stream of an ideal gas at Mach number $M_1 = 5$ is turned by a ramp, as shown in the figure. The ramp angle is $20^\circ$. The pressure ratio is $\dfrac{p_2}{p_1} = 7.125$ and the specific heat ratio is $\gamma = 1.4$. The pressure coefficient on the ramp surface is ________ (rounded off to two decimal places).

GATE AE 2025 question 49

Official answer: 0.31 to 0.37

GATE AE 2025, Question 50 (2 marks, NAT)

Aerodynamics - Compressible Flows

A perfect gas flows through a frictionless constant-area duct with heat addition. The inlet conditions are as follows: pressure 100 kPa, density 1 kg/m$^3$, and velocity 100 m/s. At a particular downstream location, the gas velocity is 200 m/s. The static pressure at the downstream location is ______ kPa (answer in integer).

Official answer: 90

GATE AE 2025, Question 51 (2 marks, NAT)

Aerodynamics - Compressible Flows

The mass flow rate in a supersonic wind tunnel is 2 kg/s when the stagnation pressure and stagnation temperature are 1 MPa and 800 K, respectively. If the stagnation pressure and stagnation temperature are changed to 3 MPa and 200 K, the mass flow rate in the tunnel changes to _______ kg/s (answer in integer).

Official answer: 12

GATE AE 2024, Question 22 (1 mark, MCQ)

Aerodynamics - Compressible Flows

On Day 1, an aircraft flies with a speed of $V_1$ m/s at an altitude where the temperature is $T_1$ K. On Day 2, the same aircraft flies with a speed of $\sqrt{1.2}\,V_1$ m/s at an altitude where the temperature is $1.2\,T_1$ K. How does the Mach number $M_2$ on Day 2 compare with the Mach number $M_1$ on Day 1? Assume ideal gas behavior for air. Also assume the ratio of specific heats and molecular weight of air to be the same on both the days.

  1. $M_2 = 0.6\,M_1$
  2. $M_2 = M_1$
  3. $M_2 = \dfrac{1}{\sqrt{1.2}}M_1$
  4. $M_2 = \sqrt{1.2}\,M_1$

Official answer: B

GATE AE 2024, Question 23 (1 mark, MCQ)

Aerodynamics - Compressible Flows

Consider a steady, isentropic, supersonic flow (Mach number $M > 1$) entering a Convergent-Divergent (CD) duct as shown in the figure. Which one of the options correctly describes the flow at the throat?

GATE AE 2024 question 23

  1. Can only be supersonic
  2. Can only be sonic
  3. Can either be sonic or supersonic
  4. Can only be subsonic

Official answer: C

GATE AE 2024, Question 43 (2 marks, MCQ)

Aerodynamics - Compressible Flows

Shock structures for flow at three different Mach numbers over a given wedge are shown in the figure. Assuming that only the weak shock solutions are possible for the attached oblique shocks, which one of the following options is TRUE?

GATE AE 2024 question 43

  1. $M_1 < M_2 < M_3$
  2. $M_1 > M_2 > M_3$
  3. $M_1 < M_3 < M_2$
  4. $M_3 < M_1 < M_2$

Official answer: D

GATE AE 2024, Question 44 (2 marks, MCQ)

Aerodynamics - Compressible Flows

Air flowing at Mach number $M = 2$ from left to right accelerates to $M = 3$ across an expansion corner as shown in the figure. What is the value of $\delta$ (the angle between the Forward and Rearward Mach lines) in degrees? The values of the Prandtl-Meyer functions are $\nu(3) = 49.76^\circ$ and $\nu(2) = 26.38^\circ$.

GATE AE 2024 question 44

  1. 23.38
  2. 19.47
  3. 53.38
  4. 33.91

Official answer: D

GATE AE 2024, Question 59 (2 marks, NAT)

Aerodynamics - Compressible Flows

Consider the following Fanno flow problem: Flow enters a constant area duct at a temperature of 273 K and a Mach number 0.2 and eventually reaches sonic condition (Mach number $= 1$) due to friction. Assume $\gamma = 1.4$. The static temperature at the location where sonic condition is reached is _____________ K (rounded off to 2 decimal places).

Official answer: 227.0 to 231.0

GATE AE 2023, Question 33 (1 mark, NAT)

Aerodynamics - Compressible Flows

The ratio of the speed of sound in H$_2$ (molecular weight 2 kg/kmol) to that in N$_2$ (molecular weight 28 kg/kmol) at temperature 300 K and pressure 2 bar is ____. (round off to two decimal places)

Official answer: 3.5 to 4.0

GATE AE 2023, Question 37 (2 marks, MCQ)

Aerodynamics - Compressible Flows

A supersonic aircraft has an air intake ramp that can be rotated about the leading edge $\mathbf{O}$ such that the shock from the leading edge meets the cowl lip as shown in the figure. Select all the correct statement(s) as per oblique shock theory when the flight Mach number $M$ is increased.

GATE AE 2023 question 37

  1. It is always possible to find a ramp setting $\theta_{RAMP}$ such that the shock still meets the cowl lip ($\beta_{SHOCK}$ remains the same).
  2. If $\theta_{RAMP}$ is held fixed, the shock angle $\beta_{SHOCK}$ will increase.
  3. If $M$ exceeds a critical value, it would NOT be possible to find a ramp setting $\theta_{RAMP}$ such that the shock still meets the cowl lip ($\beta_{SHOCK}$ remains the same).
  4. Shock angle $\beta_{SHOCK} < \sin^{-1}\left(\dfrac{1}{M}\right)$

Official answer: A

GATE AE 2023, Question 39 (2 marks, MCQ)

Aerodynamics - Compressible Flows

A perfect gas stored in a large reservoir exhausts into the atmosphere through a convergent duct. The reservoir pressure is $P_0$ and temperature is $T_0$. The jet emerges from the nozzle with average velocity $u$, Mach number $M$, pressure $p$, temperature $T$, and density $\rho$. If the reservoir pressure is increased, then

  1. $u$, $M$, $p$, $T$, and $\rho$ increase
  2. $u$, $p$, $T$, and $\rho$ increase, but $M$ remains the same
  3. $u$, $M$, and $T$ remain the same, but $p$ and $\rho$ increase
  4. $u$, $M$, $T$ and $\rho$ remain the same, but $p$ increases

Official answer: C

GATE AE 2023, Question 44 (2 marks, MSQ)

Aerodynamics - Compressible Flows

Consider a one-dimensional inviscid supersonic flow in a diverging duct with heat addition ($Q_{in}$) as shown. Which of the following statement(s) is/are always TRUE?

GATE AE 2023 question 44

  1. Mach number, $M_2 > M_1$
  2. Stagnation pressure, $P_1^o > P_2^o$
  3. Static pressure, $P_2 > P_1$
  4. Stagnation temperature, $T_1^o < T_2^o$

Official answer: B, D

GATE AE 2022, Question 14 (1 mark, MCQ)

Aerodynamics - Compressible Flows

The point of maximum entropy on a Fanno-curve in a Temperature-Entropy (T-s) diagram represents the

  1. maximum flow Mach number
  2. minimum flow Mach number
  3. sonic Mach number
  4. normal shock in the flow

Official answer: C

GATE AE 2022, Question 25 (1 mark, MSQ)

Aerodynamics - Compressible Flows

Across an oblique shock wave in a calorifically perfect gas,

  1. the stagnation enthalpy changes
  2. the stagnation entropy changes
  3. the stagnation temperature changes
  4. the speed of sound changes

Official answer: B, D

GATE AE 2022, Question 44 (2 marks, MSQ)

Aerodynamics - Compressible Flows

A convergent nozzle fed from a constant pressure, constant temperature reservoir, is discharging air to atmosphere at 1 bar (absolute) with choked flow at the exit (marked as $Q$). Flow through the nozzle can be assumed to be isentropic. If the exit area of the nozzle is increased while all the reservoir parameters and ambient conditions remain the same, then at steady state

GATE AE 2022 question 44

  1. the nozzle will remain choked
  2. the nozzle will be un-choked
  3. the Mach number at section P will increase
  4. the Mach number at section P will decrease

Official answer: A, C

GATE AE 2022, Question 53 (2 marks, NAT)

Aerodynamics - Compressible Flows

In a converging duct, area and velocity at section P are 1 m$^2$ and 15 m/s, respectively. The temperature of the fluid is 300 K. Air flow through the nozzle can be assumed to be inviscid and isothermal. Characteristic gas constant is 287 J/(kg-K) and ratio of specific heats is 1.4 for air. To ensure that the air flow remains incompressible (Mach number, $M \le 0.3$) in the duct, the minimum area required at section Q is _____ m$^2$ (rounded off to two decimal places).

GATE AE 2022 question 53

Official answer: 0.14 to 0.15

GATE AE 2022, Question 55 (2 marks, NAT)

Aerodynamics - Compressible Flows

A convergent-divergent nozzle with adiabatic walls is designed for an exit Mach number of 2.3. It is discharging air to atmosphere under the conditions indicated in the figure. Flow through the nozzle is inviscid, the characteristic gas constant for air is 287 J/(kg-K), and $\gamma = 1.4$. When the reservoir pressure is 25 bar (absolute), and temperature is 300 K, Prandtl-Meyer expansion waves appear at the nozzle exit as shown. The minimum percentage change in the reservoir pressure required to eliminate the wave system at the nozzle exit under steady state is _______%.

GATE AE 2022 question 55

GATE AE 2018, Question 24 (1 mark, MCQ)

Aerodynamics - Compressible Flows

A thermocouple, mounted flush in an insulated flat surface in a supersonic laminar flow of air measures the

  1. static temperature.
  2. temperature greater than static but less than total temperature.
  3. total temperature.
  4. temperature greater than total temperature.

Official answer: B

GATE AE 2018, Question 25 (1 mark, MCQ)

Aerodynamics - Compressible Flows

A shock wave is moving into still air in a shock tube. Which one of the following happens to the air?

  1. static temperature increases, total temperature remains constant.
  2. static temperature increases, total temperature increases.
  3. static temperature increases, total temperature decreases.
  4. static pressure increases, total temperature remains constant.

Official answer: B

GATE AE 2018, Question 37 (2 marks, MCQ)

Aerodynamics - Compressible Flows

The relation between pressure ($p$) and velocity ($V$) for a steady, isentropic flow at two points along a streamline is, ($c$ is a constant)

  1. $c\left(p_2^{\gamma} - p_1^{\gamma}\right) = \dfrac{V_1^2}{2} - \dfrac{V_2^2}{2}$
  2. $c\left(p_2^{\frac{\gamma}{\gamma-1}} - p_1^{\frac{\gamma}{\gamma-1}}\right) = \dfrac{V_1^2}{2} - \dfrac{V_2^2}{2}$
  3. $c\left(p_2^{\frac{\gamma-1}{\gamma}} - p_1^{\frac{\gamma-1}{\gamma}}\right) = \dfrac{V_1^2}{2} - \dfrac{V_2^2}{2}$
  4. $c\left(p_2^{\gamma-1} - p_1^{\gamma-1}\right) = \dfrac{V_1^2}{2} - \dfrac{V_2^2}{2}$

Official answer: C

GATE AE 2018, Question 38 (2 marks, MCQ)

Aerodynamics - Compressible Flows

A thin airfoil is mounted in a low-speed, subsonic wind tunnel, in which the Mach number is 0.1. At a point on the airfoil, the pressure coefficient is measured to be $-1.2$. If the flow velocity is increased such that the free-stream Mach number is 0.6, the pressure coefficient at the same point on the airfoil will approximately be:

  1. -3.5
  2. -2.9
  3. -1.5
  4. -0.75

Official answer: C

GATE AE 2018, Question 55 (2 marks, NAT)

Aerodynamics - Compressible Flows

Air at 50 kPa pressure and 400 K temperature flows in a duct at Mach 3.0. A part of the flow leaks through an opening on the duct wall into the ambient, where the pressure is 30 kPa. The maximum Mach number achieved in the discharge is _______ (accurate to two decimal places). (Ratio of specific heats of air is $\gamma = 1.4$).

Official answer: 3.30 to 3.40

GATE AE 2018, Question 56 (2 marks, NAT)

Aerodynamics - Compressible Flows

Consider a $20^\circ$ half-angle wedge in a supersonic flow at Mach 3.0 at standard sea-level conditions. If the shock-wave angle on the wedge is $36^\circ$, the Mach number of the tangential component of the flow post-shock is _______ (accurate to two decimal places).

Official answer: 1.90 to 2.20

GATE AE 2016, Question 15 (1 mark, MCQ)

Aerodynamics - Compressible Flows

Which of the following statement is NOT TRUE across an oblique shock wave?

  1. Static temperature increases, total temperature remains constant.
  2. Static pressure increases, static temperature increases.
  3. Static temperature increases, total pressure decreases.
  4. Static pressure increases, total temperature decreases.

Official answer: D

GATE AE 2016, Question 16 (1 mark, MCQ)

Aerodynamics - Compressible Flows

For a completely subsonic isentropic flow through a convergent nozzle, which of the following statement is TRUE?

  1. Pressure at the nozzle exit > back pressure.
  2. Pressure at the nozzle exit < back pressure.
  3. Pressure at the nozzle exit = back pressure.
  4. Pressure at the nozzle exit = total pressure.

Official answer: C

GATE AE 2016, Question 44 (2 marks, MCQ)

Aerodynamics - Compressible Flows

Consider 1-D, steady, inviscid, compressible flow through a convergent nozzle. The total temperature and total pressure are $T_o$, $P_o$ respectively. The flow through the nozzle is choked with a mass flow rate of $\dot{m}_o$. If the total temperature is increased to $4T_o$, with total pressure remaining unchanged, then the mass flow rate through the nozzle

  1. remains unchanged.
  2. becomes half of $\dot{m}_o$.
  3. becomes twice of $\dot{m}_o$.
  4. becomes four times of $\dot{m}_o$.

Official answer: B

GATE AE 2014, Question 17 (1 mark, MCQ)

Aerodynamics - Compressible Flows

For inviscid, supersonic flow over a diamond shaped airfoil, shown in the figure, which statement is correct among the following?

GATE AE 2014 question 17

  1. The airfoil will experience zero lift and positive drag force
  2. The airfoil will experience positive lift and zero drag force
  3. The airfoil will experience negative lift and zero drag force
  4. The airfoil will experience positive lift and positive drag force

Official answer: D

GATE AE 2014, Question 18 (1 mark, MCQ)

Aerodynamics - Compressible Flows

Consider supersonic flow near a corner (at an angle $\theta$ from the horizontal) with an attached oblique shock (at an angle $\beta$ with horizontal) as shown in figure. If Mach number $M$ decreases gradually from a high supersonic value, which of the following statements is correct?

GATE AE 2014 question 18

  1. $\beta$ will decrease if the shock is a weak shock
  2. $\beta$ will decrease if the shock is a strong shock
  3. $\beta$ will increase for both weak and strong shocks
  4. $\beta$ remains unchanged for both weak and strong shocks

Official answer: B

GATE AE 2014, Question 43 (2 marks, NAT)

Aerodynamics - Compressible Flows

A student needs to find velocity across a stationary normal shock. He measures density and pressure across the shock as shown in the figure below. 1 bar = $10^5$ Pa. (No shock table is needed for the calculations). The value of $u_1$ in m/s is ____. ($p_1 = 1$ bar, $\rho_1 = 1.2$ kg/m$^3$; $p_2 = 29$ bar, $\rho_2 = 6$ kg/m$^3$)

GATE AE 2014 question 43

Official answer: 1705 to 1720

GATE AE 2014, Question 44 (2 marks, MCQ)

Aerodynamics - Compressible Flows

For inviscid, compressible flow past a thin airfoil, shown in the figure, free-stream Mach number and pressure are denoted by $M_\infty$ and $p_\infty$ respectively. Ratio of pressure at point A and $p_\infty$ is 0.8 and specific heat ratio is 1.4. If the Mach number at point A is 1.0 and rest of the flow field is subsonic, the value of $M_\infty$ is

GATE AE 2014 question 44

  1. 2.95
  2. 0.79
  3. 1.18
  4. 0.64

Official answer: B

GATE AE 2014, Question 59 (2 marks, MCQ)

Aerodynamics - Compressible Flows

An aircraft is flying at Mach 3.0 at an altitude where the ambient pressure and temperature are 50 kPa and 200 K respectively. If the converging-diverging diffuser of the engine (considered isentropic with ratio of specific heats, $\gamma = 1.4$ and specific gas constant $R = 287$ J/kgK) has a throat area of 0.05 m$^2$, the mass flow rate through the engine in kg/s is

  1. 197
  2. 232
  3. 790
  4. 157

Official answer: D