POWEPLANTS ATA 70 – 80 Part 1

In the next articles we will present the powerplant and the important elements which played a major role and which enabled the creation of the Concorde.

To be as complete as possible and especially given the scale of the task, we will divide this article into several parts:

-           The general presentation.

-           Air inlet.

-           The turbojet.

-           The nozzle.

-           The thrust reverser.

The general presentation.

Concorde is equipped with four powertrains arranged in pairs under the wing and composed of Rolls-Royce Olympus engines.

Each powertrain includes:

-           An air intake with variable geometry.

-           A ROLLS ROYCE OLYMPUS 593 Mark 610 engine equipped with reheats. This engine is contained in a housing consisting of a central wall, inspection doors, afront firewall separating this housing from the air intake structure.

-           A primary nozzle with variable section in the form of petals, for a first variation of the output flow.

-          a secondary nozzle consisting of a structure ensuring the assembly of the eyelids (also called « buckets » in English) which have two functions, to make a second variation of the output flow, and to allow thrust reversal.

These two nozzles work in unison.

LThis engine is of the subsonic type, like all current engines. It cannot therefore be satisfied with a flow at supersonic speed.

Devices, formed by convergent-diverging elements placed at the front and rear of the engine, making it possible to adapt the air flow to the engine in any aircraft configuration.

These convergers-divergers are not only designed for flight at Mach 2, but also for any speed in between.

These devices have variable geometry in order to obtain optimal performance throughout the flight range of the aircraft.

At the front of the engine:

-           Variable geometry air intake.

At the rear of the engine:

-           The primary nozzle which forms the converging device.

-           The secondary nozzle which forms the divergent device.

These last two devices cannot be dissociated from the engine, in particular, the primary nozzle which also allows, by opening or closing, to vary the pressure directly downstream of the turbine and thus to control the compressor speed N1.

But before going any further, IT IS IMPORTANT to try to give some explanations which, we hope, will clarify the rest a little.

CONVERGENT DIVERGENT THEORY

Subsonic flow.

Some definitions on the convergent-diverging theory.

In the converging part of a venturi, the air accelerates and the pressure decreases. In the divergent part, the phenomenon is reversed: the speed decreases and the pressure increases.

At the pass, the speed is maximum, the pressure minimum.

This principle remains valid for any speed lower than that of sound measured at the pass.

Sonic flow.

When the flow at the neck reaches M = 1, the flow is maximum, the conditions in the convergent no longer vary whatever the shape of the flow through the divergent.

We say that there is a sonic pass or sonic obstruction.

In the divergent part, there is supersonic expansion; the pressure continues to decrease and the speed to increase.

How it works on Concorde.

The engine is subsonic and, throughout the flight envelope up to Mach 2, the air flow past the compressor must not be greater than M 0.5.

It is therefore the role of the air intake to control the flow at this speed.

This principle only applies to an air intake at subsonic speed.

If the air intake is supersonic, the principle is reversed.

For a supersonic admission we obtain, through the venturi effect, an internal deceleration in the convergent part up to Mach 1 at the neck and then further deceleration in the divergent part.

This deceleration will be evident, accompanied by an increase in pressure.

This principle is not in fact acceptable in this ideal form because such a flow can be ensured only by various delicate technological artifices involving a significant variation of the geometry of the air intake, in order to obtain in all aircraft and engine configurations, optimal efficiency.

This is why the solution of external supersonic compression air intake was adopted.

Its principle is to ensure the compression of the supersonic flow by an external deflection using a ramp of progressively increasing slope.

The compression waves thus generated make it possible to reduce the Mach number at the pass to around unity.

Let us now observe that the transformation of this flow.

From Mach 2, we see for the air intake:

-           The speed decreases from 2,300 km/h at entry (which is equivalent to local Mach 2) to 700 km/h at exit.

-           The pressure increases.

Regarding the Mach,

-           Upstream of the air intake we have Mach 2. 

-           At the outlet we only have Mach 0,5.

In the engine, this flow is treated in a conventional manner:

-           Increase in pressure and temperature in compressors where the flow speed is minimum at the last stage.

-           Significant increase in temperature in the combustion chamber.

-           Expansion of this flow in the turbines which drive the compressors.

At the turbine exit, the gas speed is 700 km/h, which corresponds to local Mach 0.5.

- Crossing of the heating system, which allows possibly obtaining a significant and momentary additional thrust in the take-off and transonic acceleration phases.

- Then, ejection by the convergent-divergent formed of the primary and secondary nozzle.

The flow speed is then, in the exit plane, 3,600 km/h, or M • 2.35 local.

Thrust distribution:

The thrust developed on take off by each element is as follows:

-           AIR INLET                  + 21%

-           REACTOR                 + 82%

-           NOZZLE %                 + 6 %

The thrust developed in cruise by each element is as follows:

-            AIR INLET                 + 75%

-           REACTOR                 + 8%

-           NOZZLE %                 + 29%

There is a 12% loss at the front of the nacelles due to the reduction in airflow caused by the nacelle.

Air flows:

There are 3 main airflows passing through the power package:

-          Primary air is the air flow used in the engine.

-          Secondary air taken from the air intake, circulating around the engine to ensure ventilation.

-          Tertiary air: this is the outside air which enters the nozzle at the level of the eyelids, through openings located on the upper and lower surfaces at the rear of the nacelles.

And now if you have reached the end of these explanations, we can continue with the rest which is easier to describe in the next articles which will be devoted to:

-           The air inlet.

-           The turbojet.

-           The nozzle.

-           The thrust reverser.

To be continued…