I believe this is the function, much like the spinner on the hub of a prop plane. The blade attachment to the shaft takes a fairly large diameter, and to have just a flat plate would create a lot of drag. Older prop planes used to not have spinners, but they flew much slower and spinners were added to just about all of them that continued in production because it reduces drag. On a jet engine it is far more important.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
smartt1982 From United Kingdom, joined Nov 2007, 225 posts, RR: 0
Reply 7, posted (4 years 9 months 2 weeks 4 days 22 hours ago) and read 17773 times:
Quoting lightsaber (Reply 4): It also helps correct the velocity profile into the core. Having no 'spinner' would result in poor air feed to the core which would impact hot/high performance,
The main purpose is aerodynamic as part of the nacelle cowling diffuser into the fan. The ideal is a plug flow velocity into the fan.
It also helps control vibration. A flat plat at the hub would be a Karman pump. It would be inherently unstable for vortex shedding
lighsaber, can you just elaborate on this. I will be the first to admit my knowledge of this is is poor so would be very interested to hear how that works if you would be so kind. What is a Kaman pump and how does the spinner help or what is a plug type flow?
I have read a bit about jet engines, any suggestions on a book that would describe this also?
Quoting Stitch (Reply 5): And in the off chance you are referring to the white "blob" on said cone, smartt1982, as I understand it, it is designed to scare birds and keep them out of the fan.
I have heard that before aswell, has it ever been confirmed?
doug_Or From United States of America, joined Mar 2000, 3482 posts, RR: 3
Reply 10, posted (4 years 9 months 2 weeks 4 days 6 hours ago) and read 17416 times:
Quoting 26point2 (Reply 8): I thought the "blob" as well as the "swirl" was a safety design for ramp workers. Easy to see if the fan is rotating on a noisy ramp in low visibility.
yes, makes a running engine much more distinguishable from a non-running engine.
Not sure what it would do for birds. At any thrust setting it will just be a blur. The thing that scares birds will not be the spinning little painted bit. The thing that scares birds will be the 100 ton chunk of metal moving at 150+ mph while emitting 90+ decibels.
musang From United Kingdom, joined Apr 2001, 906 posts, RR: 6
Reply 22, posted (4 years 9 months 4 days 8 hours ago) and read 15916 times:
The other reason for the precise contouring of the spinner is to deflect foreign objects past the core intake. Stones, volcanic ash, bird wreckage etc. will do much less damage through the fan/bypass duct than if they go through the core. However I don't know why some are cone shaped and some domed.
I always thought the "blob" or "teardrop" shape painted on a spinner was intended for ground staff, as they'd only ever be near it when the engine was at or near idle speed, when such a design would be visible. The spiral stripe was intended for birds, as its still visible (i.e. not a blur) even when the engine is at take-off rpm.
Quoting 474218 (Reply 1): You have to attach the blades to something?
Close! That "something" is the hub, behind the spinner.
lightsaber From United States of America, joined Jan 2005, 14287 posts, RR: 100
Reply 24, posted (4 years 8 months 2 weeks 2 days 9 hours ago) and read 15236 times:
Quoting smartt1982 (Reply 7): What is a Kaman pump and how does the spinner help or what is a plug type flow?
Sorry for the late response...
Ok, we've already discussed that the spinner covers where the fan blades attach. Well... for optimum fan performance, it is best to have a 'reasonably high' mach number on the fan blades. There is no thrust (or more precisely pressure) generated at the hub of a fan anyway...
Now if there was no aerodynamic shape over the hub, it would be a flat circle. A spinning flat circle is a very primitive pump called a Karman pump. (Complex fluids). So the shape of the hub cover is based on:
1. aerodynamics (minimum pressure drop into the engine as that would be lost thrust)
2. Minimizing vortex shedding into the fan (noise oscillations that are both annoying to NIMBYS as well as likely to do high cycle fatigue wear on the engine).
"Plug flow" is idealized flow where everything is at the same velocity. In a jet engine 'plug flow' isn't quite the ideal... (I over-simplified.) One wants the bulk of the mass flow about 2/3rds of the radius out from the hub. But the engine has air coming in at the hub that needs to be moved outward to where the fan blades can do work on it, but not too much as the air still needs to flow into the core.
Quoting bikerthai (Reply 13): Has the "cone" shape spinner become the preferred configuration over the paraboloid shape?
What is the +/- of each design?
The cone is cheaper to make. Since the inlet part of the nacelle is becoming longer, the differences in shapes matters less than many would note. The inlet of the nacelle is shaped with the spinner. Most of the cost/work is on the nacelle... So the hubs have become more of an engine makers trademark than critical. Oh, there needs to be a spinner, but the exact are not as critical as the engineers designing them think they are.