Here are some photos of electric fans with variety of blade designs.
Traditional fan blades. Featuring round triangular blades with large surface area.
Westinghouse electric fan.
Holmes brand electric fan.
Spins clockwise.
Metal blades.
The back edge is straight, and has a fixed flap.
The cutting edge is convex, curved like a knife.
Holmes brand electric fans.
Patton's industrial fan.
Spins clockwise.
Notice that the cutting edge is concave, scythe-like.
Large fans usually use metal blades.
Vornado fan. Spins clockwise.
Vornado fan. Spins clockwise. This Vornado features flower-like, overlapping, thick, metal blades.
Vornado
fans tend to have a boat-propeller styled blades; fat and small with deep attack angle. The brand Vornado has always been making fans of this style. Its name makes one think of vortex and tornado. Its ads make-believe that the design can generate current that cycles the whole room without changing blow direction. Spins clockwise.
Airwave brand electric fan.
Spins clockwise.
Fancy curved penta-blades. Cutting edge is concave.
Airwave brand electric fan.
Bionaire electric fan.
Very different design. It has six thin scythe-like blades with concave edge, and with a rim that connects all blades.
Bionaire electric fan.
Ceiling fan, almost always having flat rectangular board as blade. The number of blades are usually from 3 to 5.
Ad for ceiling fans.
Particularly notable is the “Malibu
Star ceiling fan” that is selling for some seventeen hundreed dollars.
Its hub is ostensibly a bicycle sprocket, and its blade consists of silk
fabric made taut by the tension of bent fiber-glass rods. In this fan,
efficiency of looks is more important than the function of air-generation.
ceiling fan ad2
Exhaust fan. Notice the symmetry of the leafs, allowing the fan to spin both ways with equal effectiveness. (photo courtesy of http://electric-fan.com.)
This unusual fan has the rotation plane in a convex way. The blades are curved backwards, as if to blow wind not just straight-forward but outward like radiation. The edge of the blade that cuts air is concave. (the fan turns clockwise)
In general, i think that metal blades generate the most noise, and traditionally shaped fans that has wide area generate the most current (most efficient). Traditional shaped fans with their plastic blades tend to be the lightest and cheapest as well. I think all the fancily shaped blades are only for the looks.
Can any aerodynamics student or engineer summarize the blade design situation? That is, number of blades, attack angle, shape of blades (warped, flat), edge shape of blades (concave/straight/convex), surface area… what makes whiling blades noisy?
