Rolls Royce C30P inducer bleed port

[Weads]

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 regulated? (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!

[Eric Hunt]

You've got an answer on Proon

[Weads]

Thank you I saw it but specifically I’m referring to the slot in the liner of the compressor for the suck/blow hole

[iChris]

On 11/19/2019 at 8:46 AM, Weads said:

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 regulated? (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!

The 250-C30 compressor bleed air system permits rapid engine response. The system consists of a bleed control valve located on the front face of the scroll and an inducer bleed manifold which encases the slotted compressor shroud housing.

The inducer bleed system is composed of circumferential slots on the impeller
inducer shroud, a circumferential collecting plenum, and a bleed port which is located 
clockwise from the top dead center.

At low speed, the inducer bleed system bleeds air out, increasing air flow rate at the
face of the impeller, which reduces inducer angle of attack and decreases the chance of
inducer stall. This improves part speed stability, especially near 85 % N1, where the
At high speed, the bleed system sucks in air from outside, which reduces inducer choking. On the standard operating line, bleed direction changes between 95% to 100% N1.

The compressor receives air at the center of the impeller in an axial direction and accelerates the air outward by centrifugal reaction to its rotational speed. At the lower rotational speed some air bleeds off via the inducer bleed port. As rotational speed increases and the air continues its acceleration, the static pressure decreases according to Bernoulli’s Principle. This continuing reduction is static pressure at the impeller, versus outside ambient pressure, works to eventually choke off the inducer bleed air and allows air flow in through the bleed.  

Quote

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 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.

 Ref:  Chapman, Dennis C., Model 250-C30/C28B Development, AGARD-CP-282, 7-9 May 1980, pp. 20-1 to 20-6

Edited November 20, 2019 by iChris

[Weads]

Thank you so very much for your answer it was exactly what I was looking for! I knew since it was literally a hole in the impeller inducer shroud then pressure had to play a part someway and somehow in whether air was taken in or blown out. I just couldn’t figure out where and how the pressure came from and thankfully you provide a great answer to my question! I appreciate the time and thoroughness that you put into my answer! Thanks again!