C2 (Compressors)

Question 1

Purpose of Compressors.

Answer 1

To give pre-determined pressure rise throughout the compressor.

Question 2

Whats two basic types of compressor?

Answer 2

a).Centrifugal flow Compressor

b). Axial flow compressor (straight-through flow)

Question 3

On an axial flow compressor, what constitutes a stage.

Answer 3

-Rotor
-Stator

Question 4

Explain the principle of operation for Centrifugal flow compressor

Answer 4

To raise the pressure of the air, divergent duct is used. The impeller is rotated at high speed by the turbine and air is continuously induced into the center of the impeller(the eye).

Centrifugal action causes it to flow radially outwards along the divergent vanes to the impeller tip, thus accelerating the air and also causing a rise in pressure to occur.

Question 5

Diffuser section

Answer 5

The air leaving the impeller, passes into the diffuser section where the passages form a divergent nozzles that convert most of the kinetic energy into pressure energy.

Question 6

To maintain the efficiency of the compressor, it is necessary to prevent excessive air leakage between the impeller and the casing; how is this achieved.

Answer 6

By keeping their clearances as small as possible.

(If too close will cause buffeting)

Question 7

The last row of stator vanes usually acts as air straighteners to remove _________ from air prior to entry into the ______________ at a reasonably uniform axial velocity.

Answer 7

Swirl
Combustion system

Question 8

The impeller shaft rotates on ________ and ________ and is either common to the turbine shaft or spilt in the centre with a coupling connection, which is usually designed for ease of detachment.

Answer 8

-Ball
-Roller bearings

Question 9

Advantages of centrifugal compressors

Answer 9

-Robust, cheap and simple to make
-low surge tendency
-flexible relatively efficient
-withstands icing/ FOD fairly well
-balancing is relatively easy
-simple to maintain

Question 10

Disadvatage of centrifugal compressors.

Answer 10

-low compression ratio
-large frontal area
-high impeller tip speeds
-no straight through airflow

Question 11

A stage consists of a set of ________ followed by a set of ________.

Answer 11

Rotors
Stators

Question 12

Cascade effect

Answer 12

Drum and outer casing forming a convergent duct.