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Beginner's Guide to Propulsion
Turbine Engine Identification
Answers


Answers will vary. Suggested answers are shown below:


Gas Turbine parts
  1. Use the Gas Turbine Parts section located in the Propulsion Index of the Beginner's Guide to Propulsion to match the correct letter from above with the listed part. Write the corresponding letter for each part in the space to the right of the word.

    Nozzle

    F

    Turbine

    E

    Compressor

    B

    Shaft

    C

    Burner

    D

    Inlet

    A

  2. Answer the following questions about Turbine Engine Parts and Engine Component Analysis using the Beginner's Guide to Propulsion.

 

  1. Why is the inlet lip of a supersonic airplane's engine sharper than the inlet lip of a subsonic airplane?
    The inlet lip is sharpened to minimize the performance losses from shock waves that occur during supersonic flight.
  2. What is the purpose of the central cone in the "Axisymetric Supersonic" engine?
    Some supersonic inlets, like the one at the upper right, use a central cone to shock the flow down to subsonic speeds.
  3. What is the purpose of the stators in the compressor? Other rows, called stators, are fixed and do not rotate. The job of the stators is to both increase pressure and to keep the flow from spiraling around the axis by bringing the flow back parallel to the axis.
  4. What is the advantage of having a rectangular nozzle on a jet engine?
    This allows the exhaust flow to be easily deflected. Changing the direction of the thrust with the nozzle makes the aircraft much more maneuverable.
  5. What is "spillage drag?" Spillage drag, as the name implies, occurs when an inlet "spills" air around the outside instead of conducting the air to the compressor face. The amount of air that goes through the inlet is set by the engine and can change with altitude and throttle setting. The inlet is usually sized to pass the maximum airflow that the engine can ever demand and, for all other conditions, the inlet will spill the difference between the actual engine airflow and the maximum air demanded. As the air is spilled over the external cowl lip, the air is accelerated and the pressure decreases. This produces a lip suction effect, which partially cancels out the drag due to spilling.
  6. What is meant by "distortion" in reference to inlet performance? As the air is brought from free stream to the compressor face, the flow may be distorted by the inlet. At the exit of the inlet (the compressor face), one portion of the flow may have a higher velocity, or higher pressure, than another portion. The flow may be swirling or some section of the boundary layer may be thicker than another section because of the inlet shape. The rotor blades of the compressor move in circles around the central shaft. As the blades encounter distorted inlet flow, the flow conditions around the blade change very quickly. The changing flow conditions can cause flow separation in the compressor (a compressor stall) and can cause structural problems for the compressor blades.
  7. What is the difference between an axial compressor and a centrifugal compressor? The flow through the axial compressor travels parallel to the axis of rotation. The flow through the centrifugal compressor is turned perpendicular to the axis of rotation.
  8. Why did designers change from centrifugal compressors to axial compressors? An average, single-stage centrifugal compressor can increase the pressure by a factor of 4. A similar, single-stage axial compressor increases the pressure by only a factor of 1.2. But it is relatively easy to link together several stages and produce a multistage axial compressor. In the multistage compressor, the pressure is multiplied from row to row (8 stages at 1.2 per stage gives a factor of 4.3). It is much more difficult to produce an efficient multistage centrifugal compressor because the flow has to be ducted back to the axis at each stage. Because the flow is turned perpendicular to the axis, an engine with a centrifugal compressor tends to be wider (greater cross-sectional area) than a corresponding axial. This creates additional undesirable aircraft drag. Centrifugal compressors are also less efficient than axial compressors.
  9. At what point in the turbojet engine is the pressure the highest?
    diagram of turbojet engine

     

  10. How does the nozzle produce thrust? The nozzle converts the high pressure and temperature into high velocity. Because the exit velocity is greater than the free stream velocity, thrust is created.  

Related Pages:
Standards
Worksheet
Activity
Propulsion Activity Index
Propulsion Index

 

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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: Thu, Jun 12 04:39:33 PM EDT 2014

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