twistedenginestarter
Some of this ground has been covered recently on another thread. Should you wish to read that thread, then click
here.
Briefly, the design of the intake and exhaust systems of a supersonic engine is absolutely critical, and plays a major part in the efficiency of the engine. On Concorde they generate a large percentage of the total thrust required at M 2.0, although not quite as much as reported in the article where it said:
<font face="Verdana, Arial, Helvetica" size="2">The Olympus engines, with the thundering 38,050 pounds of thrust on takeoff, are now producing only nine percent of the total thrust.</font>
The core engine in fact produces about half the total thrust required at M 2.0.
If I may use part of a recent post by
John Farley, quoting from an article by Paul Crickmore on the A12/YF-12/SR71 story, as published in Wings of Fame Vol. 8.
<font face="Verdana, Arial, Helvetica" size="2">The inlet system created internal pressures which reached 18 psi when operating at M 3.2 and 80,000ft, where the ambient pressure is only 0.4psi. This extremely large pressure differential led to a forward thrust vector which resulted in the forward inlet producing 54 per cent of the total thrust. A further 29 per cent was produced by the ejector, while the J58 engine contributed only 17 per cent of the total thrust.</font>
The relevant figures for Concorde’s intakes, at M 2.0 and 60,000 ft, are an engine intake pressure of 8 psi, up from an ambient pressure of 1 psi, with an intake temperature of +125°C, up from an ambient temperature of -56.5°C.
At the exhaust end, the exhaust gas has to be accelerated to very high speed to produce the required thrust, which is done by a system of primary and secondary nozzles forming an efficient convergent/divergent nozzle system.
Bear in mind when considering supersonic airflow that a convergent nozzle will slow and compress a supersonic airflow whereas a divergent nozzle will slow and compress a subsonic airflow.
Under these conditions, approximately 25% of the thrust required is produced by the intake system, another 25% is produced by the exhaust system, leaving the core engine needing to produce only around 50% of the total thrust required in the cruise.