Gas Turbine Engine Components
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Questions and Answers

What is the primary function of the diffuser in a gas turbine engine?

  • To convert velocity energy into pressure energy (correct)
  • To increase the velocity of the air
  • To deliver air to the combustion chambers
  • To change the airflow direction

    • What is the purpose of the turning vanes or cascade vanes in the manifold?

  • To distribute air to the combustion chambers
  • To increase the airflow velocity
  • To reduce air pressure losses (correct)
  • To change the airflow direction

    • What is the function of the compressor outlet elbow?

  • To change the airflow direction
  • To act as an air duct (correct)
  • To distribute air to the combustion chambers
  • To increase the air pressure

    • What is another term for a single-entry impeller?

    <p>Single-sided</p> Signup and view all the answers

    What is the purpose of the manifold in a gas turbine engine?

    <p>To deliver air to the combustion chambers</p> Signup and view all the answers

    What is a disadvantage of the single-stage dual-sided impeller?

    <p>Turbulent side air entry</p> Signup and view all the answers

    What material is the diffuser typically made of?

    <p>Steel alloy</p> Signup and view all the answers

    What is the function of the outlet ducts in the compressor manifold?

    <p>To act as an air duct</p> Signup and view all the answers

    What is the purpose of inlet guide vanes?

    <p>To impart a whirl motion in the direction of impeller rotation</p> Signup and view all the answers

    What replaces the single-stage dual-sided impeller?

    <p>Single-entry two-stage centrifugal compressors</p> Signup and view all the answers

    What is the purpose of stationary pre-swirl vanes?

    <p>To ease the change of airflow from axial to radial direction</p> Signup and view all the answers

    Where are inlet guide vanes sometimes formed?

    <p>At the front of the impeller</p> Signup and view all the answers

    What is the direction of airflow and compression in an axial compressor?

    <p>Parallel to the rotational axis</p> Signup and view all the answers

    What is a common drawback of single-spool compressors?

    <p>The forward stages are typically overloaded while the rear stages operate at a fraction of their capacity</p> Signup and view all the answers

    What is the main difference between a single-spool and a dual-spool engine?

    <p>The mechanical connection between the rotors</p> Signup and view all the answers

    What type of axial flow compressor is typically used in small turboshaft and turboprop engines?

    <p>Single-spool</p> Signup and view all the answers

    What is a characteristic of a triple-spool engine?

    <p>It is used in some large and medium-sized turbofan engines</p> Signup and view all the answers

    What is an advantage of dual-spool engines over single-spool engines?

    <p>They respond more quickly to control input changes</p> Signup and view all the answers

    What happens to the kinetic energy of the air as it passes through the stator vanes?

    <p>It is converted to potential energy (pressure)</p> Signup and view all the answers

    What determines the velocity of the airflow in each stage of the compressor?

    <p>The speed of the rotor</p> Signup and view all the answers

    What is the secondary function of the stator vanes?

    <p>To direct airflow to the next stage of compression at the desired angle</p> Signup and view all the answers

    What are the blades typically made of?

    <p>Stainless steel alloy or titanium alloy</p> Signup and view all the answers

    What is a blisk?

    <p>A one-piece blade and rotor unit</p> Signup and view all the answers

    What is the material used to make the discs?

    <p>Nickel steel alloy or titanium alloy</p> Signup and view all the answers

    What is the operating zone between the ‘normal operating line’ and the ‘surge stall line’?

    <p>Surge-stall margin</p> Signup and view all the answers

    At what point does the engine operate during most of its service life?

    <p>During cruise speed, at altitude</p> Signup and view all the answers

    What may occur when a stall or surge causes a momentary stagnation of mass airflow followed by an over-rich condition in the combustor?

    <p>Exhaust flames</p> Signup and view all the answers

    What is the purpose of the compressor anti-stall bleed system?

    <p>To unload the compressor during starting and low power operation</p> Signup and view all the answers

    Why is the compressor anti-stall bleed system necessary?

    <p>To maintain AOA and air velocity within desired limits</p> Signup and view all the answers

    What is dumped directly back into the atmosphere by the compressor surge/stall bleed air valve system?

    <p>Air not used for aircraft systems</p> Signup and view all the answers

    Study Notes

    Impellers

    • Impellers can be referred to as single-entry (single-sided) or dual- or double- entry (dual-sided)
    • Single-stage dual-sided impeller provides the same compressor ratio and mass air flow with a smaller impeller diameter
    • Single-entry two-stage centrifugal turbo-propeller replaced the single-stage dual-sided impeller due to its disadvantages

    Impeller Components

    • Impellers incorporate inlet guide vanes called rotating guide vanes or inducers
    • Inlet guide vanes induce rotation of the air into the eye of the impeller
    • Inlet guide vanes may be part of, or attached to, the impeller
    • Inlet guide vanes can be formed by inclining the front sections of the impeller vanes to impart a whirl motion in the direction of impeller rotation

    Diffuser

    • High-velocity air from the impeller is slung into divergent ducts within the diffuser
    • The purpose of the diffuser is to convert velocity energy into pressure energy
    • Diffusers are typically made from aluminum alloy or steel alloy

    Manifold

    • The purpose of the manifold is to change the airflow direction and deliver air to the combustion chambers
    • Turning vanes, or cascade vanes, within the manifold straighten the airflow
    • Manifold distributes the air in a smooth flow to the combustion section

    Axial Flow Compressors

    • Axial flow compressors have airflow and compression occurring parallel to the rotational axis
    • There are three types of axial flow compressors: single-spool, dual-spool, and triple-spool
    • Single-spool axial flow compressors are commonly used in small turboshaft and turboprop engines

    Rotor Blades

    • Each rotor consists of a set of blades fitted into a disc, which move air rearwards through each stage
    • The speed of the rotor determines the velocity present in each stage
    • Kinetic energy is transferred to the air with increased velocity
    • Stator vanes receive the air at high velocity and act as a diffuser, changing kinetic energy to potential energy (pressure)

    Blisks

    • Blisks are one-piece blade and rotor units
    • Blisks are commonly used in small turboprop and turboshaft engines
    • Blisks are being applied to many smaller fans, compressor rotors, and stators, and to some turbine components

    Surge-Stall Margin

    • The surge-stall margin is the operating zone between the 'normal operating line' and the 'surge stall line'
    • The margin decreases as compressor efficiency deteriorates
    • Design point is the point on this line at which the engine operates during most of its service life

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    Description

    Test your knowledge of gas turbine engine components and their functions, including diffusers, turning vanes, compressor outlet elbows, and manifolds.

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