turbine engine intake

TURBINE ENGINE

Aircraft Gas Turbine Power plants by Otis

FAA 12A

Aircraft Gas Turbine Engine Technology by Treager

Aircraft Power plant by Kroes& Wild

The Jet Engine by Rolls-Royce

TURBINE ENGINE

Gas turbine engine are considered to be of two types:-Gas turbine engine

Thrust Producing Engine

Torque Producing Engine

Turbojet Engine

Turbofan Engine

Turboprop Engine

Turbo shaft Engine

SECTIONS OF GAS TURBINE ENGINE

SECTIONS OF GAS TURBINE ENGINE

An aircraft gas turbine engine is divided into two sections:- Cold section Hot section

The cold section contains:- Air Inlet Duct Compressor Diffuser

The hot section contains:- Combustor Turbine Exhaust

ENGINE STATION DESIGNATION

To standardize the locations in gas turbine engines, a numbering system has been devised that allows a person to identify a location by numbers.

STUDY OF AIR INTAKE CONFIGURATION

NEED OF AIR INTAKE IN AN AIRCRAFT

• A widely used method to increase the thrust generated by the aircraft engine is to increase the air flow rate in the air intake by using auxiliary air intake systems.

• The air flow enters the intake and is required to reach the engine face with optimum levels of total pressure and flow uniformity hence need of an air intake system.

• Deceleration of airflow at high flight mach numbers or aerodynamic compression with help of air intake.

AIR INTAKE DESIGN REQUIREMENTS

• The air intake requires enormous effort properly to control airflow to the engine.

• The intake must be designed to provide the appropriate amount of airflow required by the engine.

• Furthermore this flow when leaving the intake section to enter the compressor should be uniform stable and of high quality.

• Good air intake design is therefore a prerequisite if installed engine performance is to come close to performance figures obtained at the static test bench.

• The engine intake must be a low drag, light weight construction ,that is carefully and exactly manufactures.

• These above conditions must be met not only during all phases of flight but also on the ground with the aircraft at rest and the engine demand maximum, thrust prior to take off

THE COLD SECTIONAIR INLET DUCTS

The air inlet duct is technically a part of the airframe, but it is so important in the development of thrust that it is included with the engine as a part of the clod section.

The air inlet duct must supply uniform flow of air to the compressor so that it can operate stall free.

It must produce as little drag as possible.

If taken only a small obstruction to the air flow inside the duct to cause a significant loss of efficiency.

Inlet cover must be installed to prevent damage or corrosion in this vital area.


Air Inlet Ducts

Single Entrance Duct

Divided Entrance Duct

AIR INLET DUCTS SINGLE ENTRANCE DUCT

Duct inlet is located directly ahead of the engine and aircraft in such a position that it scoops undisturbed air.

It is either straight configuration or with relatively genital curvatures.

Due to long shape there is a chance of pressure lost but that is offset by smooth airflow characteristic.

In multi engine installation a short straight duct results minimum pressure drop.

SINGLE ENTRANCE DUCT

AIR INLET DUCTS DIVIDED ENTRANCE DUCT

It is used in high speed, single engine aircraft where pilot sits low in the fuselage and close to the nose.

This divided duct can be either a wing root inlet or a scoop at each side of fuselage.

Create huge amount of drag

AIR INLET DUCTS DIVIDED ENTRANCE DUCT


Air Inlet Ducts

Subsonic Inlet Duct Supersonic Inlet Duct

THE COLD SECTION SUBSONIC AIR INLET DUCTS

The inlet duct is used in the multiengine subsonic aircraft is a fix geometry duct whose diameter progressively increases from the front to back. It is diverging duct and is also called an inlet diffuser because of the effect, it has the effect on the pressure of the air entering the engine.

As air enters the inlet at ambient pressure it beguns to defuse, or spread out, and by the time it arrives at the inlet to the compressor its pressure is slightly higher than the ambient pressure.

Usually the air diffuses in the front portion the duct and than it progresses along at a fairly constant pressure passes the engine inlet fairing and then into the compressor. This allows the engine to receive the air with less turbulence and at a more uniform pressure.

THE COLD SECTION SUBSONIC AIR INLET DUCTS

Turbojet Engine


Turbofan Engine


Turbofan Engine

AIR INLET DUCTS TURBOPROP ENGINE

The propeller reduction gears are located at the front of the engine and thus interfere with a smooth flow of air entering the compressor.

Generally 3 types of inlet duct is used:-

i) Ducted spinner inlet ii) Conical spinner inlet iii) Under scoop inlet

AIR INLET DUCTS TURBOPROP ENGINE

AIR INLET DUCTS TURBO SHAFT ENGINE

BELLMOUTH COMPRESSOR INLET

Bellmouth inlet are converging in shape, found primarily on helicopter.

It provides an inlet with very thin boundary layers and corresponding low pressure losses.

Actually duct lost is so slight that it is considered zero.

SUPERSONIC INLET DUCT

The air approaching the compressor inlet must always be at speed below the speed of sound.

when an aircraft is flying at supersonic speed, the inlet air must be slowed down to subsonic speed before it reaches the compressor. This is done by :-

Using a convergent-divergent or CD inlet duct

Raising a Wedge or Spike or Plug inlet


Convergent-divergent or CD inlet duct


Using movable wedge inlet

FLOW CONDITIONS OVER WEDGE AND CONE

In the design of supersonic air intakes flow conditions over wedge and cone are of the greatest importance as these are simple geometric bodies and relatively easy to manufacture.

COMPARISON OF SUPERSONIC FLOW OVER CONE AND WEDGE

The major advantage of a (supersonic) conical flow is a smaller total pressure loss (when compared to a wedge of the same half-angle), together with the fact that a conical shock sustains lower mach numbers until it becomes detached to form a high loss bow shock.

A major disadvantage of conical flows is that it is less tolerant to asymmetric flow conditions which cause distortion to the intake flow. As combat aircraft are frequently required to maneuver at higher angles of attack, the flow inevitably gets asymmetric- hence a performance for the (horizontally arranged) wedge in all modern combat aircraft, despite its reduced efficiency.


Using movable spike inlet

Using movable Plug inlet

EXAMPLES OF USE OFF OBLIQUE SHOCK DIFFUSERS

Mirage ||| fighter with side mounted oblique-shock diffuser

Two dimensional oblique shock diffuser (Northrop F-5 with vertical ramp)

SUPERSONIC AIR INTAKE CASE STUDIES F-16 intake

characteristics


Inlet Buzz:- The buzz is an airflow instability which occur when a shock

wave is alternately slowed and irregular flow occur at the inlet.

In increasing condition it can cause violent fluctuations in pressure through the inlet, which occur when a shock wave is alternately swallowed and regulate by the inlet.

This condition also cause damage to the inlet structure or possibly to engine itself.

A suitable variable geometry duct is used to eliminate the buzz by increasing of airflow within the inlet duct.

INTAKE CONFIGURATION AND OPERATION

Present-day turbine aero engines require subsonic flow at the entry to the compressor, even if the aircraft is flying at supersonic speed. The task of air intake is therefore to decelerate the supersonic external flow to a subsonic speed acceptable to the compressor. As intake discharge mach number are required to be in range of mach 0.4 to 0.7 great care must be exercised when decelerating the flow in order to keep total pressure losses to a minimum .

Normal shock diffuser For aircraft operating at a maximum speed equivalent to

mach 1.5 a normal shock diffuser is generally sufficient to decelerate the supersonic airflow efficiently to the speed needed by the compressor.

NACA SUBMERGED INLET IN A EURO FIGHTER

The NACA submerged type intake is not very efficient for use with propulsion

installations. However, they are frequently used as intakes of auxiliary

systems (auxiliary power unit, heating and avionics bay cooling) as seen in

Fig above

Various types of supersonic inlets

RAM RECOVERY

When a turbine engine is operated there is a negative pressure in the inlet because of the high velocity of the airflow. As the aircraft moves forward in the flight, air rams in to the inlet duct and ram recovery takes place. This ram pressure rise cancel the pressure drops due to friction inside the duct and the inlet pressure return to ambient. Ram recovery occur above about 160 miles/hrs or 0.1 mach to 0.2 mach in most of the aircraft.

From this point the pressure continue to increases with aircraft speed and additional thrust is created by the engine with less expenditure of fuel.

PRESSURE RECOVERY AND NOSE SUCTION FORMATION

BLOW-IN -DOOR

It is used to prevent compressor stall.

It is installed in the side of inlet duct and are spring loaded to hold them closed.

But when the inlet pressure becomes a specified amount lower than that of the ambient air, the pressure differential forces then open and furnishes additional air to the compressor inlet.