Turbine Engines

At the compressor outlet 

In the axial flow engine, the air is compressed while continuing in its original direction of flow, thus avoiding the energy loss caused by turns.

From inlet to exit the air flows along an axial path and is compressed at a ratio of approximately 1.25:1 per stage achieving highest pressure at the compressor outlet.

• This makes sense - the point of a compressor is to maximally compress the air prior to the combustion section.

Direct the flow of gases to strike the turbine blades at a desired angle 

The turbine assembly consists of two basic elements: turbine inlet guide vanes and turbine blades.

The stator element is known by a variety of names, of which turbine inlet nozzle vanes, turbine inlet guide vanes, and nozzle diaphragm are three of the most commonly used.

The turbine inlet nozzle vanes are located directly aft of the combustion chambers and immediately forward of the turbine wheel.

This is the highest or hottest temperature that comes in contact with metal components in the engine.

The turbine inlet temperature must be controlled or damage will occur to the turbine inlet vanes.

After the combustion chamber has introduced the heat energy into the mass airflow and delivered it evenly to the turbine inlet nozzles, the nozzles must prepare the mass air flow to drive the turbine rotor.

The stationary vanes of the turbine inlet nozzles are contoured and set at such an angle that they form a number of small nozzles discharging gas at extremely high speed; thus, the nozzle converts a varying portion of the heat and pressure energy to velocity energy that can then be converted to mechanical energy through the turbine blades.

The second purpose of the turbine inlet nozzle is to deflect the gases to a specific angle in the direction of turbine wheel rotation.

• Since the gas flow from the nozzle must enter the turbine blade passageway while it is still rotating, it is essential to aim the gas in the general direction of turbine rotation

• A reduced blade tip thickness
•                    or
• A cutout that reduces blade tip thickness 

Compressor rotor blades are usually made of stainless steel with the latter stages being made of titanium.

• The design of blade attachment to the rotor disk rims varies, but they are commonly fitted into disks by either bulb-type or fir-tree methods.
• The blades are then locked into place by differing methods. 

Compressor blade tips are reduced in thickness by cutouts, referred to as blade profiles. 

These profiles prevent serious damage to the blade or housing should the blades contact the compressor housing.

This condition can occur if rotor blades become excessively loose or if rotor support is reduced by a malfunctioning bearing.

Even though blade profiles greatly reduce such possibilities, occasionally a blade may break under stress of rubbing and cause considerable damage to compressor blades and stator vane assemblies.

• The blades vary in length from entry to discharge because the annular working space (drum to casing) is reduced progressively toward the rear by the decrease in the casing diameter.
• This feature provides for a fairly constant velocity through the compressor, which helps to keep the flow of air constant.

Please note that you may see the correct answer to this question either as "a cutout that reduces blade tip thickness" or "reduced blade tip thickness."

 low-pressure compressor 

In a jet engine, each major rotating section usually has a separate gauge devoted to monitoring its speed of rotation.

Depending on the make and model, a jet engine may have an N1 gauge that monitors the low pressure compressor section and/or fan speed in turbofan engines.

The gas generator section may be monitored by an N2 gauge, while triple spool engines may have an N3 gauge as well.

Each engine section rotates at many thousands of r.p.m.

• Their gauges therefore are calibrated in percent of r.p.m. rather than actual r.p.m., for ease of display and interpretation.

the total pressure at station No. 7

Pressures are measured at specific places in a turbine engine.

The locations are identified by their station. Pt7 refers to turbine discharge (exhaust) pressure.

Engine pressure ratio (EPR) is an indication of the thrust being developed by a turbofan engine and is used to set power for takeoff on many types of aircraft.

It is instrumented by total pressure pickups in the engine inlet (Pt2) and in the turbine exhaust (Pt7).

The reading is displayed in the flight deck by the EPR gauge, which is used in making engine power settings.

should be performed parallel to the length of the blade using smooth contours to minimize stress points 

When working on the inner half of the blade, damage must be treated with extreme caution.

Repaired compressor blades are inspected by either magnetic particle or fluorescent penetrant inspection methods, or they are dye checked to ensure that all traces of the damage have been removed.

All repairs must be well blended so that surfaces are smooth.

No cracks of any extent are tolerated in any area.

Whenever possible, stoning and local rework of the blade are performed parallel to the length of the blade.

Rework must be accomplished by hand, using stones, files, or emery cloth.

Do not use a power tool to buff the entire area of the blade.

The surface finish in the repaired area must be comparable to that of a new blade.

• On centrifugal flow engines, it is difficult to inspect the compressor inducers without first removing the air inlet screen. After removing the screen, clean the compressor inducer and inspect it with a strong light. Check each vane for cracks by slowly turning the compressor

Combustion section 

During operation, air enters the front of the engine and is directed into the compressor at the proper angle by the variable inlet guide and variable stator vanes.

The air is compressed and forced into the combustion section.

• A fuel nozzle which extends into each combustion liner atomizes the fuel for combustion.
• Combustion section

pressure 

The principle used by a gas turbine engine as it provides force to move an airplane is based on Newton’s law of momentum.

This law states that for every action there is an equal and opposite reaction; therefore, if the engine accelerates a mass of air (action), it applies a force on the aircraft (reaction).

The turbofan generates thrust by giving a relatively slower acceleration to a large quantity of air.

The old pure turbojet engine achieves thrust by imparting greater acceleration to a smaller quantity of air.

This was its main problem with fuel consumption and noise.

The mass of air is accelerated within the engine by the use of a continuous-flow cycle. 

Ambient air enters the inlet diffuser where it is subjected to changes in temperature, pressure, and velocity due to ram effect. 

The compressor then increases pressure and temperature of the air mechanically.

The air continues at constant pressure to the burner section where its temperature is increased by combustion of fuel. 

• The energy is taken from the hot gas by expanding through a turbine which drives the compressor, and by expanding through an exhaust nozzle designed to discharge the exhaust gas at high velocity to produce thrust

At the higher engine speeds, thrust increases rapidly with small increases in RPM 

The relationship between thrust and RPM is such that the amount of thrust increases rapidly as the engine speed increases.

A small change in speed at low RPM will not produce nearly as much increase in thrust as the same amount of change at high RPM.

 low-pressure rotor will increase in speed as the compressor load decreases in the lower density air 

In a two spool compressor, the high pressure rotor is governed for speed, while the low pressure compressor is free to run at its own best speed.

• As the density of the air decreases, the load on the compressor decreases and it turns at a higher speed.

increase the velocity of the heated gases flowing past this point 

The stator element is known by a variety of names, of which turbine nozzle vanes, turbine guide vanes, and nozzle diaphragm are three of the most commonly used.

The turbine nozzle vanes are located directly aft of the combustion chambers and immediately forward of the turbine wheel.

The function of the turbine nozzles is twofold.

First, after the combustion chamber has introduced the heat energy into the mass airflow and delivered it evenly to the turbine nozzles, it becomes the job of the nozzles to prepare the mass air flow for driving the turbine rotor. 

The stationary blades or vanes of the turbine nozzles are contoured and set at such an angle that they form a number of small nozzles discharging the gas at extremely high speed; thus, the nozzle converts a varying portion of the heat and pressure energy to velocity energy which can then be converted to mechanical energy through the rotor blades.

The second purpose of the turbine nozzle is to deflect the gases to a specific angle in the direction of turbine wheel rotation.

Since the gas flow from the nozzle must enter the turbine blade passageway while it is still rotating, it is essential to aim the gas in the general direction of turbine rotation.

The turbine nozzle assembly consists of an inner shroud and an outer shroud between which are fixed the nozzle vanes.

The number of vanes employed vary with different types and sizes of engines

In the entrance of the burner section 



The highest gas pressure in a turbojet engine is in the entrance of the burner section which is the exit of the compressor section.

In the axial flow engine, the air is compressed while continuing in its original direction of flow, thus avoiding the energy loss caused by turns.

From inlet to exit the air flows along an axial path and is compressed at a ratio of approximately 1.25:1 per stage achieving highest pressure at the compressor outlet.

• This makes sense - the point of a compressor is to maximally compress the air prior to the combustion section.

 increase and the velocity to decrease 

The exhaust cone collects the exhaust gases discharged from the turbine buckets and gradually converts them into a solid jet.

In performing this, the velocity of the gases is decreased slightly and the pressure increased.

• This is due to the diverging passage between the outer duct and the inner cone; that is, the annular area between the two units increases rearward.