georgem2012
Topic Author
Posts: 7
Joined: Mon May 23, 2016 5:47 pm

Bypass Flow and Core Flow velocities

Sun Feb 11, 2018 6:28 pm

I realise the bypass Flow provides the larger proportion of the overall thrust, however, in say a high bypass ratio turbofan engine such as a GE90 or a Trent 900, what is the difference in speeds of the bypass and core airflows at maximum thrust?
 
Andre3K
Posts: 225
Joined: Tue May 30, 2017 10:11 pm

Re: Bypass Flow and Core Flow velocities

Mon Feb 12, 2018 1:27 am

 
BDQ2DXB
Posts: 4
Joined: Sat Feb 10, 2018 4:09 am

Re: Bypass Flow and Core Flow velocities

Mon Feb 12, 2018 3:04 am

Typically core flow exit velocity is in the vicinity of Mach 1 and bypass duct velocity is around Mach 0.3... Since the mass flow rate through the bypass duct is higher, it contributes a higher chuck of total thrust.
 
GalaxyFlyer
Posts: 541
Joined: Fri Jan 01, 2016 4:44 am

Re: Bypass Flow and Core Flow velocities

Mon Feb 12, 2018 10:48 pm

Are those numbers absolute or velocities above vehicle speed?

GF
 
PerVG
Posts: 10
Joined: Tue Jan 23, 2018 10:41 pm

Re: Bypass Flow and Core Flow velocities

Tue Feb 13, 2018 12:24 am

Can't be absolute. In order to produce thrust, bypass flow must be accelerated above the vehicle speed. I would guess the delta starts big at take off and then gradually shrinks as the plane picks up speed. But never reaches zero.

Core flow could produce thrust at absolute speeds equal or even a bit lower than vehicle speed due to the added mass of the fuel. But in practice, they are higher anyway, given the "low" speed of commercial aircraft.
 
BDQ2DXB
Posts: 4
Joined: Sat Feb 10, 2018 4:09 am

Re: Bypass Flow and Core Flow velocities

Tue Feb 13, 2018 1:05 am

Those are velocities measured at the exit of the core and bypass nozzles respectively. Those numbers usually apply to cruise conditions.

Its hard to give you real numbers in mph or m/s since these value depend on flow temperature at exit as well as the geometry of the nozzle & altitude.

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