I'm doing a university project on the GE90-115b engine and I'm having a hard time understanding this EASA type-certificate data sheet. In particular I can't figure out the air bleed extraction section (page 10 section 10). Is the stage number counted from the fan stage or from the LPC 1st stage?
Are there some specific reason for the choice of extraction air from "middle stages" instead of extracting it partially from low pressure stages and partially from high pressure ones?
The base engine (up -94B rating) has 10 stages HPC, the growth engine (up to -115B) has 9 (reference https://www.geaviation.com/commercial/engines/ge90-engine).
In both cases, the type certification is counting bleed starting from the first stage of the HPC (not the LPC).
The reference to "10th stage" bleed in the type certification is misleading. There is no 10th stage bleed in either engine. Rather it is "CDP" bleed. "CDP" stands for "compressor discharge pressure", i.e. right after the last stage of the compressor.
So in the base engine, the last bleed is extracted immediately after the 10th stage, and on the growth engine it's extracted right after the 9th stage.
Below is a diagram showing the bleed air flow that may (hopefully) clarify. The CDP bleed is in orange.
The stage number is counted from the front of the compressor the bleed is tapped from, in this case I'm assuming its the HP compressor so 4th, 7th and 10th stage HP air.
Extraction locations depend really on what you want the air to do, turbine cooling, cabin conditioning, anti ice, start/surge/stall control etc etc, Whilst there are bleed point on some LP stages (CFM56 LP booster for example) its just dumped overboard as it doesn't contain enough energy to do any useful work. And you couldn't really mix LP and HP air because, like people fluids under pressure like to take the easiest route so HP would always overcome the LP and you'd just end up recycling the air.
