Now could you please explain what you meant in your post#4 because as I said previously "I fail to see your point".
I meant it as complete, please. Youīre starting the engines with bleed air, bleed air is for getting the compressor of one (mostly the high pressure) stage out of pumping(TURIN: Hunting) into an stable environment.
(and yes, we in Germany see a difference between a compressor thatīs pumping(Hunting) and an compressor thatīs working good)
Now the bypass ratio: Air wonīt change its Direction on its own, if you ever built a turbine you know that. To manage a start with bleed air the compressor of the (high or low pressure)stage is often deactivated at the very beginning. When the compressor starts working it has to Pump enough air through its stages to provide the turbine with air and support the cooling system.
High bypass ratio guarantees higher massflow even at low speeds, so the air changes its direction properly. Low bpr has an lower massflow and an smaller diameter, anyhow the air will change its direction, but there is an danger that the air wonīt get into the compressor properly. (Two possibilities:
-Compressor gets no air: Turbine stops working when bleed air is off
-Compressor wont get enough air: Posibilities of rotating stall, definetively not enough air in the cooling system, Danger of destroying turbine and compressor!)
Often the reason for such an limitation is: "We havenīt tested it in this environment" But you can ask how much a single turbine blade costs and then think about trying it even in a 1 in a million chance to fail.
Greetings,