Answers - Turbine Engine

1. c
As air enters the compressor section of a turbine engine, it is compressed. The air then leaves the compressor at its highest pressure and lowest volume. From here, the air passes through a diffuser which causes a slight decrease in pressure.

2. c
When high energy gases leave the combustion section of a turbine engine, they enter the turbine section. The turbine section is made up of stationary and rotating airfoils, or vanes. The stationary vanes, sometimes called a nozzle diaphragm, direct the high energy gases leaving the combustor into the rotating turbine blades. The nozzle diaphragm also increases the velocity of the gases.

3. b
When looking at the profile of a compressor blade you will see that the tip of each blade is cut out to reduce tip thickness. This shape allows the blade to wear rather than break if the blade tip should come in contact with the case.

4. a
On a dual axial or dual spool turbofan engine, the forward fan is typically bolted to the first compressor making the fan part of the low-pressure compressor.

5. c
The abbreviation P stands for pressure, and subscript t7 indicates a total at station 7 which is immediately aft of the last turbine stage. Therefore, Pt7 is the total pressure aft of the turbine.

6. b
Minor damage to turbine engine blades and vanes can usually be repaired if the damage can be removed without exceeding the allowable limits established by the manufacturer. However, all repairs must be well blended so that the blade's surface is smooth. Blending is almost always done by hand using crocus cloth, fine files, and stones. Furthermore, whenever possible, blending is performed parallel to the length of the blade to minimize stress points. Cracks are normally not allowed, in any area.

7. a
The combustion section of a turbine engine is where the fuel and air are mixed and then burned. The compressor section (answer B) compresses the inlet air and the diffuser section (answer C) directs the compressed air to the burner cans.

8. b
During the combustion process in a turbine engine, burning fuel provides heat to expand the compressed air coming from the compressor. Throughout this process the pressure remains relatively constant.

9. b
In a typical turbine engine, a small increase in rpm produces a relatively proportional increase in thrust when operating at low engine speeds. However, at high engine speeds a small increase in rpm produces a large increase in thrust.

10. a A two-spool or dual spool turbine engine is one in which there are two independently rotating units. The front compressor is called the low-pressure compressor, and the rear compressor is called the high-pressure compressor. This type of engine has more operating flexibility than a single spool engine because the two compressors are free to find their own optimum rpm. This allows the low pressure compressor to increase in rpm at altitude because of the reduction in drag caused by the decrease in air density.

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