Concorde engine intake "Thrust"

[goarnaut]

Crabman...maybe the word thrust is making it hard for you...

If you prefer... think of the inlet making a forward force...that's all it is...and that force is very real..the mechanism of it is that the diverging duct shape decreases flow speed and increases pressure...that increased pressure yields a forward force...after all force is pressure time area...


Since the outlet of a diverging duct has a bigger area than the inlet...and since the pressure is also increased...the result has to be a force pointing forward...there can be no other outcome in the physical world in which we live...


A converging duct...nozzle...is the opposite...I think you have stumbled on that “transferring” thrust part...that wording is unhelpful and does not actually have any place in this explanation...there is no transferring going on...the forward force is made right there in the duct...


Now of course it is true that the duct by itself cannot move the airplane forward...we need the entire engine and all of its bits...but the same is true for any other component...the gas generator without the nozzle will make no thrust...


So the bottom line is that if we look at the engine component by component...each of them makes either thrust or drag...doesn't change the fact that we still need each and every one of them...


I just pulled a good engine book off my shelf and looked this up...Aircraft Propulsion by Farokhi...Fluid Impulse is covered in chapter 2 and there is a whole section on it...with worked examples for each engine component...the inlet...compressor...burner...turbine and nozzle...there is a drawing that shows which components are making thrust and which ones drag...the inlet...compressor and burner all make thrust...while the turbine and nozzle make drag...


Now I agree with Clive that this is not hugely important to break things down in this way...but it is the physical reality and we must appreciate that...


As far as the Concorde inlet is concerned the goal was to have good aerodynamic performance...a diffuser is a difficult item...the flow is moving from low pressure to high pressure...an adverse pressure gradient...going uphill if you like...which can cause flow separation and the resulting turbulence eats up energy that we wish to recover as pressure...


So those were the design goals...I'm sure Clive and the team spent zero time thinking about how much “thrust” was going to be made in the inlet...that part we have no control over...it is just the way it works out if we do a proper job in recovering as much pressure as possible...


My aim here was just to shed a little light on this because it is fascinating...like many physical phenomena...it is another example that there is nothing for free in nature...when the air flow going at M2 gives up its momentum...it is the engine that gains...similarly if we inject cold fuel into a hot combustion chamber the fuel heats up and vaporizes...but the surrounding air loses the exact same amount of heat that the fuel gained...and the air temperature goes down...it is always a 2-way street...the action reaction thing...


I hope I have been able to help a little...if you still want to keep working through it I am certainly willing to help...


Regards,


Gordon.




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