A few questions about the design of a common table fan, such as below.
- Does the round disc (silver in the image) in front of the blades serve any functional purpose?
- Does the metal casing around the blades serve any functional purpose except protecting the blades?
- What exactly are the sources of noise in a well-designed fan? Does the metal casing in a well-designed fan have an impact on the noise level?
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Answer
To the last comment - I disagree. Wind turbines operate in a fairly different flow regime, and compare the table fan to the prop of a ship, they are about the same shape. The key difference is moving fluid volume. The larger blades push against the fluid more strongly, which is desirable in the fan case and in the ship case. Wind turbines are different as the builder cares nothing about the exhaust wind.
Anyway... 1. I don't think it's 'functional' in any sense other than the fact that the motor is behind it. 2. I don't believe so and I agree with other commentators that the fan would be more simple and less noisy without them. I'll withhold comment on the obvious safety considerations. 3. Everything dealing with pumping or pushing a fluid makes noise, and it is quite considerable. You could remove the blades and listen to the electric motor itself and you would find it constitutes only a small fraction of the noise. Noise minimization for fans is a major engineering topic and it's more or less impossible to reduce it. Obviously, the faster you get the bigger of a problem it is. I believe we're talking about turbulent flow in general, I don't think many pumps are actually laminar. The metal bars will have an influence, but I could not say how much.
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