T1 fan blade sharpening - effects

[airschooled]

Hi Folks,

Anybody here ever run a Type 1 fan blade with sharpened blades?

I’m interested mostly in noise reduction; flow effects would be interesting too.

See you on the road,
Robbie
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[Chickensoup]

Me interested azwell interested me
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[PuddleRainbow]

From:

https://www.tandfonline.com/doi/pdf/10.1080/19942060.2010.11015339

Effects of Edge Geometry on Flow Driving of a
Stamped Metal Cooling Fan

Hongmin Li

From Conclusion:

".....The main advantages of the cooling fan with
sharp edges are in the noise reduction, air flow
rate improvement, and the reduction of power
consumption. Sharp edge cooling fans are
recommended for electric motors when any of the
following is true for the application. (1) The
broadband noise level is high. (2) The blade
passing frequency and vortex shedding frequency
spikes are big concerns. (3) The cooling fan
power consumption is a significant part of the
electric motor total power input."

[Chickensoup]

ok, next question... why hasnt anyone talked about doing this(well, at least here on the samba), and how should the be sharpened? What angle? what side? Would polishing the blades help too?
_________________
-'85 c10 5.3 LS, 222 cam, long tubes, x pipe, 3 inch spin tech's
-'05 B5.5 TDI Wagon 17in sport rims ;EGR + BSM + ASV Delete, Stage-2 Tune, straight pipe
'65 Tourist Delivery Build
'66 RIP
'69 RIP
Hosea 4:6 "My people are destroyed for lack of knowledge"

[airschooled]

PuddleRainbow, thanks for that reference!

This topic came up when I was discussing Type 1 noise with a turbine engineer last month, and we got on the topic of fan blade design. She suggested sharpening the leading and trailing edges of each fan blade, but I’m not sure what tools I would be able to do that with. Sharpening the outer (trailing) edges is simple enough... but the inners?

I doubt polishing the blades will help; my fan collects a fine layer of fuzz/grime as the miles pass by.
Robbie
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[txoval]

I don’t have this much time on my hands...the fans work as-built and probably the quietest part of the engine unless you have hydraulic lifters and a quiet muffler

[airschooled]

Yes, the fan works as built. Especially because they had to build six million of them for mere pennies.

If you spent 30,000 miles a year at 3,800rpm, you would know every single whine and whir too... The Type 1 fan is FAR from the quietest part of the engine. (Take your belt off and go for a drive if you don’t believe me.)

Another sound we can discuss is the 1:1.9 ratio of early bay fan to engine speed. (special belt/pulley setup different from all other Type 1 engines, which run a 1:1.8 or so.) The resulting “chord” of a pitch is a crunchy semi-tone relationship between the engine and fan, while the 1:1.8 is only slightly less irritating. This discussion is worth having if the fan blade sharpening does as described in the article. If the fan cools more, we can slow it down. Less speed is always quieter, but changing the ratio of engine to fan speeds will net subtle sonic success as well.

Robbie
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[Ohio Tom]

As one who has studied "some" fluid dynamics and airfoils, I can say that it's not as simple as just sharpening the tips.

Without empirical testing data, it is hard to be sure you are helping and not hurting.

The angle of the edge. The skewness of the edge. The blend radius, angle of attack: all can play a big part affecting "flow separation" in a flat airfoil.

I have found when VW fans get noisy, it's because they are loaded with debris, or have a flow restriction.

[Dan Ruddock]

[mark tucker]

yes dan is right, although some people dont think so. as for the fan blade and sharpening it, if you do you need to make a jig so all are the same,witch makes it much eaxer to do also. for the incomming side i wood do it this way,and for the outlet I wood do it that way. not a point from both sides. of coarse then come s the balancing....does ya have a balancer? stand it in the corner and see if it falls over?? I suppose a balanceer could be made somewhat simple if you wished to do so. but....balanced how? this way or that way? is it out on this side or that side of the fin? does it mater? I say MR dyno needs to do one and see what it does!!!! and finaly... is more hp less flow? or same or more flow& less pumping losses? and finaly what about cavatation??? eye wood think that doing the leading&trailing edges right should raise the cavatation rpm...but my eye woods can always see the florist through the trees& flowers. only real tested dayta would be reliable not well I done it any I got 50 more hp.... or a slails mans claims...and finaly the shape of the balde fin.... leave it alone or do some work to it?? and remember more flow may be less hp to the wheels...slower with a better blower so it last longer...or not

[raygreenwood]

[txoval]

I guess my smartass walked into that comment. Several factors can determine the “quietness” of the valve train. The point I was trying to make is that an Aircooled VW engine is not quiet (compared to a modern Honda Civic for example). I personally have never heard the VW fan over the exhaust or wind blowing in my windows...and in Houston, Texas we drive with the windows down 100% of the time.

Now, if this mod provided significantly better/more efficient cooling I could understand it.

[volksworld]

it should be much more efficient at shredding those mouse nests...and their residents

[Pruneman99]

[oprn]

There is no doubt in my mind that it would be possible to improve a stock fan but at what cost in time compared to gains? In my view the effort would be far more productive in designing a variable pitch or variable speed fan.

[Zundfolge1432]

Remembering years ago when balancing became a thing

[mark tucker]

aparently troxol hasent heard a quiet vw. yes they can be as quiet as a honda.

[petrol punk]

Might be doable with a file. A file as wide as the fan blades could sharpen the outer tips easily. The inner would be a pain but you could probably do it with a small file
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[txoval]

I would pay to hear VW with a stock pee-shooter exhaust be as quiet as a new honda civic, lol good luck with that. Change the exhaust to an A-1 merged header system and you'll need extra good luck. Now, perhaps if you ran the exhaust to the front of the car you could accomplish that

This is comical...post a video

[mark tucker]

what does exhaust have to do with engine noise? also good mufflers are very rare on vw's.