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Rolls Royce C30P inducer bleed port

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Rolls Royce C30P inducer bleed port

Old 19th Nov 2019, 15:17
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Rolls Royce C30P inducer bleed port

I have a simple question on how the inducer bleed port works for the suck/blow hole on the 206. Air escapes the inducer bleed port during startup to allow rapid acceleration and minimize compressor stall of the compressor and it sucks air In to allow for maximum efficiency of the compressor and engine once the engine is at a higher RPM. Although a novice question for most of you guys I can’t figure out how the inducer port is opened and closed? (I understand it’s a physical hole that’s not actually opened or closed)I know the inducer bleed port is just a slot machined at the top of the shroud housing (compressor lining) but how is air regulated entering and exiting the inducer bleed port. Thanks in advance!

Last edited by Weads; 19th Nov 2019 at 18:16.
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Old 20th Nov 2019, 00:31
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Not sure about the C30, and not sure if you are talking about the bleed valve either. The bleed valve is basically a hole in the compressor casing, about 1 1/2" across, with a flat disc that can close it off, and the disc is on a housing with a spring pulling it open. You can push the disc closed with your fingers, and wedge it shut for a compressor wash, to make sure the soapy mix goes down the spout and doesn't squirt out over the engine compartment.

On a C20, the bleed valve is spring-loaded to the open position. At startup, it allows excess air to vent overboard so the compressor can spin up easily, and there is not too much air going into the combustion chamber, to prevent a stall/surge.

As the engine accelerates, air pressure from further down the compressor pushes the valve slowly closed, until at about 92% N1 the valve is fully closed and all the air goes into the fire. The valve doesn't allow sucking, it only lets the air go one way, out. It can open when a sudden acceleration is needed, to reduce the back pressure.
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Old 20th Nov 2019, 13:23
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Originally Posted by Ascend Charlie View Post
not sure if you are talking about the bleed valve either. .
No, he's asking about the port on the front of the C30 compressor housing that usually has a hose connected to it and vents overboard through a small scoop on the engine cowl. In very simplistic terms, think of the inducer port as a calibrated bleed orifice that reduces compressor surge between ground/flight idle and increases compressor efficiency. Where the inducer provides both compressor intake and discharge, the bleed valve only controls compressor discharge air. However, the inducer port falls more under the internal magic of a turbine vs the any external scenario other than when you see oil misting out the inducer vent hose fitting. Then you got a problem.



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Old 20th Nov 2019, 13:26
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Originally Posted by Weads View Post
but how is air regulated entering and exiting the inducer bleed port. Thanks in advance!
If you google "turbine engine inducer port" or something similar it will most likely bring up some highly technical, long report on how the inducer port works.

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Old 20th Nov 2019, 13:27
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The inducer bleed port doesn't open and close, it is just an open hole that "sucks or blows" depending on the compressor speed/demand.
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Old 21st Nov 2019, 00:16
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During the Allison 250-C30 development program a localized dip in the surge line was encountered. Detailed analysis of the impeller inlet static pressures revealed that the surge line around the 80-85% speed line was influenced by inducer stall. The problem was resolved by adding an inducer bleed (see figure 2.14) and a bleed valve at the compressor discharge that would operate at low speeds. The inducer bleed would bleed air out at low speeds, increasing the airflow into the inducer, reducing blade incidence angles and possibly reducing the boundary layer thickness on the shroud. At high speeds, air flows in through the bleed, reducing inducer choking. The inducer bleed was found to increase the compressor efficiency by 1.5 - 3.2 % between the 85 % and 100% speed lines. LRP has defined its actuation.

https://core.ac.uk/download/pdf/4410583.pdf


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Old 21st Nov 2019, 01:30
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Thanks so much Megan that was very helpful
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Old 21st Nov 2019, 15:34
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To make things even clearer
To make things even clearer than just a drawing
a cut through the area
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Old 21st Nov 2019, 17:21
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Wrong engine FB.

C20 with an axial compressor before the centrifugal. Not an inducer as per C30 which does not have a bleed slot.

The C30 bleed valve is on the exit scroll. Close but no cigar!
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