Advanced questions for jetfighter design

R

rousseau

Новичок
Is rectangular section nozzles really superior than circular section nozzle?
No matter your answer is yes or no, please tell me why?
 
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310

310

Сторожил
It depends of what you want to get out of this nozzle.
Rectangle shapes used to dissiminate heat and make nozzle less "attractive" for missile. (F117, B2...) Round shapes are more economical in terms of engine cost and less power loss in the nozzle. (All the rest non-STELTH and non-military planes)
 
R

rousseau

Новичок
yeah? less IR signature you mean?

putting the same quantity of 100°C water to a quadrate cup that temperature of cup's surface will be lower than a rounded cup if the cups quality are same?
 
Ultranomad

Ultranomad

G-NODE
rousseau, if you fix the cross section of a nozzle (which determines the gas flow in the first approximation), then among all different shapes the round one has the least perimeter, which translates into the least surface available to dissipate heat - therefore the jet out of a round nozzle is hotter.
 
R

rousseau

Новичок
rousseau, if you fix the cross section of a nozzle (which determines the gas flow in the first approximation), then among all different shapes the round one has the least perimeter, which translates into the least surface available to dissipate heat - therefore the jet out of a round nozzle is hotter.

Dear Sir:

Your statement is right, which only based on the condition that section of rectangular nozzle is same as that section of circular nozzle. But have you ever seen there is no way to make equal section on rectangluar nozzle and circular nozzle to both up to now. The F119's rectangular nozzle is an excircle or say the engine is circumscirbed by the rectangualr nozzle. So the perimeter of the rectangualr nozzle is longer than original one.
So your stand is untanable.:oops:
 
Ultranomad

Ultranomad

G-NODE
rousseau, following the same line of thought, you will easily understand that in this case the jet will cool down even more. Of course, this is a very rough approximation anyway.