Question

Why wings of fan are usually rectangle or oval in shape?

Answer 1

Dear student,
I can see what you meant by oval shape is the leaves of turbine or airplane fans. By the way, good question. The oval shape that you call, has some peculiarities than just being oval. They are called aerofoils, that you will come across in higher classes. They are used to provide lift in aeroplanes. Their design is complicated, and hence, costly.

Aside from the extra cost to design and make a proper airfoil, it is not needed in those applications. The object is to simply move air, not create lift, thrust or air pressure differentials, as in a wing, propeller or turbine engine.

Yes, an airfoil shape would be more efficient, but of near zero value at the low rpm’s (low speeds compared to that of other applications of aerofoil) of a table or ceiling fan.
thank you.