Turbofan thrust Vs bypass ratio...?

[Turbofan]

Howdy all.

As most of you know, thrust from a turbofan engine is produced partly from exhaust gases and partly from the acceleration of air through the fan section of the low pressure compressor (the bypass section).

So let's say we have a turbofan engine with a bypass ration of 5:1. Does that mean that the thrust from the fan is 5 times that of the exhaust?

I do realise that the bypass ratio is a measure of differing volumes of air and their respectivfe passage through the engine, but I was just wondering if there was any direct relation of bypass ratio to thrust produced.

Cheers,

Turbofan

[3holelover]

Nope, well, not really... The bypass ratio is just that, in your example there will be 5x volume of air coming from the fan for every 1x volume coming from the turbine.
The typical high-bypass turbofan gets about 80% of it's thrust from the fan at take off.
A relation does exist, but it won't be directly proportional, won't be constant, and will depend on things like number of stages of compression, number of spools, number of stages of turbine etc.

Cheers.

[411A]

Turbofan works best at takeoff for airfield performance (and noise). TurboJET works best at "high" altitudes.

[EchoTango]

The thrust ratio (that is, bypass thrust / exhaust thrust) will equal the bypass ratio if each flow gets the same acceleration as it goes thru the engine. Thrust is a force, and force = mass x acceleration.

But we know that is not so, for all the reasons already given.

[Turbofan]

Thanks for the replies, makes it much clearer.