|MLA Citation:||Bloomfield, Louis A. "Question 152"|
How Everything Works 19 Jan 2018. 19 Jan 2018 <http://howeverythingworks.org/print1.php?QNum=152>.
A turbofan engine contains two separate rotating assemblies or "spools," each of which is powered by hot exhaust gases flowing out of the combustion chamber through some turbine discs and each of which spins some compressor disc that push air toward the combustion chamber. The shorter of the two spools is hollow and the lower spool passes through its center.
The shorter spool, which spins at about 12,000 rpm, derives its power from high speed gas flowing through its turbine blades just after the combustion chamber and it powers a high pressure compressor just in front of the combustion chamber. The longer spool, which spins at about 4,000 rpm, derives its power from low-pressure gas flowing out of the high-pressure turbine and it powers both a low-pressure compressor in front of the high-pressure compressor and the actual turbofan blades. Overall, there is a rapidly turning hollow spool right around the combustion chamber and a more slowly spinning solid spool that extends both in front of and behind the high-speed spool. It's the low speed spool that spins the turbofan itself.