Is there an aerodynamicist in the house?

[widebody911]

Some company has come out with a PC fan with blades that are dimpled like a golf ball.

http://www.sharkoon.com/enghtml/fans_se.htm

[kach22i]

If it sells more fans................it works per the rules of the free market.

[Moses]

With a golf ball, the dimples break up air flow, limiting your hook or slice. I suppose the disrupted airflow might make a fan more quiet.

[Moses]

Originally posted by Moses
With a golf ball, the dimples break up air flow, limiting your hook or slice. I suppose the disrupted airflow might make a fan more quiet.

Actually I just looked it up. I was completely wrong. About the golf balls.

[BlueSkyJaunte]

Time for an E-Ram style test!

[kach22i]

Dimples are for round surfaces. If the blades are curved such that air would not cling to the air blade/foil because of it's steep curve, then maybe. Those blades look pretty flat to me. GMICK!

http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml

Before explaining the purpose of dimples, we first need to understand the aerodynamic properties of a sphere.

[gaijindabe]

So. You are saying cellulite is important on a big round ass?

[Moses]

Originally posted by gaijindabe
So. You are saying cellulite is important on a big round ass?

They would definitely travel faster through space. Important skydiving consideration.

[arcsine]

It is all about boundary layers which are major players in determining friction between moving and static surfaces. As a surface moves through a medium (air or water), there will be a layer of the medium that will move with the moving surface (static layer). Father away from the moving surface will be layer where the flow is laminar. In between the static layer and the laminar layer is the turbulent boundary layer. Dimples on the golf ball make the boundary layer thinner and therefore reduce aerodynamic friction and the ball flies farther. Americas Cup sailboats have a "rough" surface, much likes sharks, that thins the boundary layer, reducing hydrodynamic friction and the boat sails faster.

[Tim Hancock]

I know a guy who dimpled his leading edge on his prop on an experimental airplane and he claims it helped. Supposedly it helps keep the airflow stay attached further back on the airfoil shape for a given angle of attack. The further back that it stays attached, the less turbulence will result after the airflow separates near the trailing edge.

The golf ball drawing above shows this.

Basically you get more lift (or thrust on a propellor) with less drag.

[arcsine]

Folks on sailbots have messed with the same idea as what Tim mentions. You disturb the air on the leading edge (luff) and get better attachment through the rest of the sail (and hence more lift)

[island911]

inducing turbulence on a blade!? . . .when trying to create lift? WTF?

I'm always amazed at what can be sold.

[red-beard]

this is a classic...

It says that the fan is quieter. There is nothing that says the fan is more effective.

[notfarnow]

Originally posted by arcsine
Americas Cup sailboats have a "rough" surface, much likes sharks, that thins the boundary layer, reducing hydrodynamic friction and the boat sails faster.

So you mean the osmosis on my sailboat is making it FASTER?!?

[Flatbutt1]

Right, all very impressive. . . but is the fan quieter due to a thinner boundary layer. That is if the blade shape induces such layering.

[island911]

Boundary layer -- yish

dimlpes on a golfball surrond the ball be cause it is always changing its orientation w.r.t. the air stream.

IF you know the direction of air flow you design for it.

Is that whats happening here?

[kach22i]

Ever hear a gold ball whiz by your head? They make sound, all that swrilling air does make noise. Guess it depends on a lot of factors, my guess is this fan will never spin fast enough to have the dimples affect it one way or the other.

[Rex Walter]

As the fan spins faster and faster, the angle of attack of the fan blades, relative to the airflow, increases. If the fan spins too fast, the angle becomes too great, and the airflow will separate off the trailing edge of the blade. This separation makes noise. The dimpled surface will cause a turbulent boundary layer, that will help keep the airflow attached longer (arcsine has this pretty much correct) - so in theory, the dimples should work. But for a fan that spins at a set speed, why not just design a blade that works well at that speed?

Rex

[red-beard]

Funny how the power consumption doesn't change....

Silent Eagle
1000 Silent Eagle

Rated voltage 12 V (DC)
Power consumption 1.44 W
Fan speed 1000 rpm
Airflow 11.4 CFM
Noise level 8.9 dB(A)
Dimensions (mm) 80 x 80 x 25
Connector universal

Silent Eagle 2000
Rated voltage 12 V (DC)
Power consumption 1.44 W
Fan speed 2000 rpm
Airflow 22.7 CFM
Noise level 17.8 dB(A)
Dimensions (mm) 80 x 80 x 25
Connector universal

1.6 in radius

1000 rpm = 16.67 rps

2*pi*1.6=10 inches

166.7 inches per second

13.9 feet per second, tip velocity

1.6 in radius

2000 rpm = 33.33 rps

2*pi*1.6=10 inches

333.3 inches per second

28.8 feet per second, tip velocity

I agree with Kach (did I say that?) that the velocity is pretty darn low and most likely will not have much effect on the noise.

[red-beard]

Originally posted by Rex Walter
As the fan spins faster and faster, the angle of attack of the fan blades, relative to the airflow, increases. If the fan spins too fast, the angle becomes too great, and the airflow will separate off the trailing edge of the blade. This separation makes noise. The dimpled surface will cause a turbulent boundary layer, that will help keep the airflow attached longer (arcsine has this pretty much correct) - so in theory, the dimples should work. But for a fan that spins at a set speed, why not just design a blade that works well at that speed?

Rex

loss of cool looking marketing gimmick for the unwashed masses?