GATE AE concept:axial-compressors PYQs & Answers

Questions 1–10 of 17. Imported answers require independent review unless marked reviewed.

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

is the isentropic efficiency of the compressor, select the statements that are TRUE.

Diagram for Aerospace Engineering question 28

Your answerSelect all correct options. You can choose more than one.

In comparison to point B, point A is closer to the surge point

In comparison to point A, point B is closer to the choke point

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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 C and W, respectively. The subscripts 1 and 2 refer to the locations before and after the rotor, respectively. The blade velocity is denoted by U. Select the CORRECT statement(s) for this device.

Diagram for Aerospace Engineering question 46

Your answerSelect all correct options. You can choose more than one.

The axial velocity is constant across the rotor

The flow coefficient is 0.6

The blade loading coefficient is 0.6

If the acoustic velocity at the rotor inlet is 350 m/s, then the inlet relative Mach number is 0.333

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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,

J/kg/K and specific heat ratio,

. The rotor blade angle at the outlet is ____ degrees (rounded off to two decimal places).

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A multistage axial compressor, with overall isentropic efficiency of 0.83, is used to compress air at a station 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

and

for air. How many stages are there in the compressor?

Your answerChoose one option.

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

Your answerSelect all correct options. You can choose more than one.

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)

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)

Keeping the mass flow rate constant, if the blade RPM is increased, the compressor may experience surge

At the same blade RPM, if the mass flow rate is increased, the compressor may experience surge

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In a single-spool aviation turbojet engine, which of the following is the correct relationship between the total work output

of a 2-stage axial turbine and the total work required

by a 6-stage axial compressor, neglecting losses?

Your answerChoose one option.

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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?

Your answerSelect all correct options. You can choose more than one.

Blade cooling

Variable angle stator vanes

Blow-off valves

Multi-spool shaft

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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,

is 0.55 for each stage. For air, use

J/(kg-K),

J/(kg-K) and

If the compression is isentropic, the number of stages required is __________ (rounded off to the next higher integer).

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At the design conditions, the velocity triangle at the mean radius of a single stage axial compressor is such that the blade angle at the rotor exit is equal to 30°. The absolute velocities at the rotor inlet and exit are equal to 140 m/s and 240 m/s, respectively. The flow velocities relative to the rotor at inlet and exit of the rotor are equal to 240 m/s and 140 m/s, respectively.

The blade speed (

) at the mean radius of the rotor is __________ m/s (round off to two decimal places).

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Air enters the rotor of an axial compressor stage with no pre-whirl (

) and exits the rotor with whirl velocity,

m/s. The velocity of rotor vanes,

is 200 m/s. Assuming

J/(kg K), the stagnation temperature rise across the rotor is ______ K (round off to one decimal place).

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GATE AE concept:axial-compressors PYQs

How to practice concept:axial-compressors

Question 28

Question 46

Question 65

Question 40

Question 50

Question 20

Question 30

Question 65

Question 46

Question 23