Wells turbine

It was developed for use in Oscillating Water Column wave power plants, in which a rising and falling water surface moving in an air compression chamber produces an oscillating air current.

The use of this bidirectional turbine avoids the need to rectify the air stream by delicate and expensive check valve systems.

Its efficiency is lower than that of a turbine with constant air stream direction and asymmetric airfoil.

One reason for the lower efficiency is that symmetric airfoils have a higher drag coefficient than asymmetric ones, even under optimal conditions.

Also, in the Wells turbine, the symmetric airfoil runs partly under high angle of attack (i.e., low blade speed / air speed ratio), which occurs during the air velocity maxima of the oscillating flow.