GE90 and Trent 900 supposedly have low SFC because they have higher bypass ratio than Trent 800 and other older high-bypass turbofans.
But the original high bypass turbofan, TF39, is supposed to have a bypass ratio as big as 8:1.
Why were next turbofans like TF39 derivative CF6 designed with low bypass ratios like 5:1…6:1? What was wrong with TF39?
By: Rocketeer - 2nd November 2008 at 20:10
dunno, but probaby down to that old engineering answer…compromise….high bypass ratio are cool as they give decent SFC (specific fuel consumption for those that dont know) and a good whack of thrust from the cool bypass air. The rest goes into the combustion/turbine stage to give ‘hot’ thrust and run the compressor of course.
My old tutor said it was easier to compress a cold gas than a hot gas! Bless him….anyhoo, the design will have a load of factors, not least of which are installed thrust out put, customer bleed requirements and the design of the blades/stages etc come in to……having said all this, not sure this is a historic subject?!
By: ZRX61 - 2nd November 2008 at 20:04
huh?
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November 2, 2008 at 7:39 pm