Hi everyone and welcome to this new class in Engine Propulsion.
Today we will be discussing the design of inlets before describing what inlets are.
I created this slide so that each time we present the new components of the engine, we can easily identify
its location and function.
So the inlet is located at the front of the engine and enables the flow of air to be taken into the
engine.
Inlets do not increase the energy of the flow.
They can be thought of as passive.
Their only action is to direct the flow towards the engine by minimising disturbances of the flow.
It should be a smooth transition of wind from the outside to the inside of the engine.
The flow will smoothly enter the inlet at a specific temperature, pressure and velocity, which will
be then used to generate thrust.
In fact, due to the velocity of the aircraft, the wind will enter the engine at non static temperature
and pressure.
This is because the relative speed between the air and the aircraft will result in the air entering
the engine with noticeable kinetic energy.
This kinetic energy will be translated to higher pressure and temperature.
So in other words, the fact that the aircraft is moving results in an increase in temperature and pressure
of the flow.
For more information, though, you can look up the concepts of stagnation, pressure and temperature.
So in the image presented, this is a typical subsonic turbofan engine.
Right.
And as you can see, the inlet is the geometry of the outside of the engine.
Note that the flow needs to enter smoothly to the engine.
Therefore, one can see the smooth surfaces surrounding the engine.
Right.
These are called lips.
In addition, subsonic aircraft engines will be designed to intake as much as possible at low speeds,
while also avoiding all of the air to enter the engine at high speeds.
This design allows for a passive control of the amount of air entering the engine at all times.
Most of the commercial aircraft today will have this type of inlet because it is optimal for subsonic
regimes, meaning that it is optimal for flights below the speed of sound.
On the other hand, for supersonic aircraft, the design of the inlet would be completely different.
Here, the main objective is also for the flow to enter smoothly into the engines.
However, at speeds faster than the speed of sound, shock waves become a main consideration.
Note that at supersonic speeds, shock waves will appear thus making the flow heterogeneous and unbalanced.
Inlets for supersonic aircraft are typically long and are designed to cancel the effect of shock waves.
Supersonic inlets must destabilize these shock waves and homogenize the flow.
Right.
And by doing this, they will be able to avoid the shockwaves to damage the structural integrity of
the engine, which is, of course, a threat.
You know, unless shockwaves are mitigated.
So normal shockwaves are the consequence of such compression of the shock waves.
And as you can see in the images over here, it's what we can expect.
And it will be the way in which the flow is homogenized.
So.
These squared shapes on this f 18 supersonic.
Okay.
There are a good example of these type of geometries that are required for supersonic flight.
Four supersonic aircraft with a gas turbine engine.
The intake is ordered to compress the supersonic flow to a supersonic speed and provide a matched air
mass flow rate to the engine.
So this implies that the energy of the flow will be altered so that the engine can actually make productive
use of such conditions.
So of course, energy will be conserved, right?
But it will be altered.
It will be transformed in a way which is favorable to the movement of the flow and of course, is not
attacking or damaging the conditions of the engine.
Right.
So in the case of inlet cones, as you can see in this essay, our 71, for instance.
Right.
They push most of the flow outside of the engine by reducing the intake space and diverting the flow
using the current right.
And as you can see, this is the case of the S.R. 71 Blackbird, a well known military aircraft, which
could fly actually at speeds of three times the speed of sound, or, as it is known in airspace, typically,
one would say at Mach three.
Notice that the geometry of the inlet required to stabilize shock waves inside the inlet is really it
almost looks exaggerated.
It is a way to make sure that the shock waves move towards the outside of the engine and that the only
a certain amount of flow of air actually enters the engine.
In this image.
Actually, you can see the location, typical location of the turbojet engines.
Right.
Notice how they are located towards the back of the aircraft and inlets for this type of aircraft are
actually quite long.
These are some examples of subsonic and supersonic aircraft inlets.
Right.
Notice the smooth geometry around the turbofan.
In the Airbus A320, as opposed to this rectangular geometry found on the Eurofighter typhoon.
Clearly, aircraft designed for super flying flight are not at all similar to those specific supersonic
flight.
Right.
Particularly when compared to the inlets.
I also wanted to include a couple of images to visualize turboprop engines.
He had the right.
This is the Airbus A340 with its particular type of engines.
Right.
Notice that the propeller of each engine is key in generating the thrust for this type of aircraft.
On the left, the engine of the A400M is shown.
And as you can see, the shaft is not at the same axis as the propeller center.
Also importantly, notice the inlet below.
This type of engine has an inlet which intakes air from the outside into the engine, but does not do
it within the same axis of the engine, but rather using this open surface which is below.
And I think that this is a cool way to visualize how how turboprops actually differ from Turbo Jets
until the fans.
This is another image of the A400M where you can see the inlet below the engine, below the propeller
of the aircraft.
And of course, air is also key to the operation of turboprops.
To the propellers are also jet engines.
Nevertheless, the thrust is basically all particularly produced because of the force generated by the
propeller.
This is the main difference.
Okay, so this would be all in inlets.
We can now move to a next class.