Turbofan Inlet Diffuser

[smjmitchell]

Hi,

Can anyone tell me what are the typical design conditions for the inlet diffuser on a turbofan engine for an airliner, for example a JT9D as used on the 747-200.

By design condition I mean what flight condition (i.e. static, takeoff, climb, cruise etc) is the main design point used to define the geometry of the diffuser. I imagine that this is probably the takeoff or climb condition because of the larger mass flow and lower airspeed is this the case ?

Can anyone recommend any good references on the design of inlet diffusers ?

Thanks,

Stephen

 

[ferdo]

Hi,

Maybe FAQ wil help you to find some references.

Main design is at take-öff.

Regards
Fernando

 

[borjame]

Hello, I've never designed an inlet diffuser BUT I would imagine the flt pt is cruise, the aero folks design the gaspath (and hence the shape of the inlet diffuser) at the point they want max efficiency. For commercial applications like the JT9D you would want max eff. at the flt pt you sit at the longest, namely cruise. If the engine was for a short haul regional jet, you might design for take-off b/c more fuel was sonsumed there than the cruise portion of the mission. To re-cap: the intended mission of the aircraft/engine defines what flt pt aero design occurs at.

 

[ferdo]

Hi,

The response for this question is not so simple. Basically, you have right to consider the take-off as main design point exactly for those reasons you said.

Anyway, after this minimal condition you have to do a lot of other compromises because of other reason as fuel consumption due to drag resistance, a.s.o.

For different types of aircrafts you have different conditions as you can see in following links.

http://142.26.194.131/aerodynamics1/High-Speed/Page7.html

http://www.alt-accel.com/pogo/pogapndc.htm

http://www.aeronautics.ru/nws001/ai014.htm

Regards
Fernando