Variable bleed valve, bleed valve and Ordinary Guide Vane

[Futureng]

Hi all,

I have got 3 different questions for you. I wanna know the difference between variable bleed valve and normal bleed valves. What are their function? Also I want to learn the Function of OGV.

Thanks a lot.

[spannersatKL]

No doubt another college project looking for answers here.....try the Rolls Royce book!!
An OGV is an outlet guide vane.....usually on the outlet of the Fan Flow.

They all do as they say on the tin.....VBV variable Bleed Valve varies opening or closing, a Bleed Valve is open or closed, both maintain the surge margin of the compressor.

Guide Vanes.....Inlet guide vanes or Variable Inlet Guide Vanes, VIGVs? You don't say which.
Never heard of an ordinary Guide Vane.
May be you mean Variable Stator Vanes? VSVs?
All manage the airflow in to a compressor to ensure optimum airflow with RPM and Temperature.

[Futureng]

I am specifically talking about cfm56-3 engine. I heard that outlet guide vanes are in the LP section and they have important role while thrust changes from idle to full . It allows air to pass to the secondary flow inlet that supplies oppsite force to prevent buckling in engine due to rotational force. if it is right, I want to learn what really happens theoretically . if it is not, thanks for your helps anyway :)

[rmm]

If your talking about the OGV's in the by-pass duct (secondary) they're just airflow straighteners. These vanes are set and do not move. There are from memory 8 steel struts in the by-pass duct to support the fan case.

There are also 12 VBV's located in this area as well. They dump air from the LP compressor to the secondary air flow for surge protection.

[Terry McCassey]

Google . . Google . . Google, works a zillion times out of a zillion !

[spannersatKL]

'oppsite force to prevent buckling in engine due to rotational force'

Please note....There is no rotary torque felt external to the engine, so no need to oppose any 'buckling' etc!!!!