Wells turbine
Encyclopedia
The Wells turbine is a low-pressure air turbine
Wind turbine
A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
that rotates continuously in one direction in spite of the direction of the air flow. Its blades feature a symmetrical airfoil
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
with its plane of symmetry in the plane of rotation
Plane of rotation
In geometry, a plane of rotation is an abstract object used to describe or visualise rotations in space. In three dimensions it is an alternative to the axis of rotation, but unlike the axis of rotation it can be used in other dimensions, such as two, four or more dimensions.Mathematically such...
and perpendicular to the air stream.
It was developed for use in oscillating-water-column wave power
Wave power
Wave power is the transport of energy by ocean surface waves, and the capture of that energy to do useful work — for example, electricity generation, water desalination, or the pumping of water...
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
Check valve
A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction....
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
Drag coefficient
In fluid dynamics, the drag coefficient is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment such as air or water. It is used in the drag equation, where a lower drag coefficient indicates the object will have less aerodynamic or...
than asymmetric ones, even under optimal conditions. Also, in the Wells turbine, the symmetric airfoil is used with a high angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
(i.e., low blade speed / air speed ratio), as it occurs during air velocity maxima in volatile flow. A high angle of attack causes a condition known as "stall
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
" in which the airfoil loses lift. The efficiency of the Wells turbine in oscillating flow reaches values between 0.4 and 0.7.
This simple but ingenious device was developed by Prof. Alan Arthur Wells
Alan Arthur Wells
-Early life:He was born in Goff's Oak, Hertfordshire to Arthur John Wells, a British Oxygen Company engineer and educated at the City of London School as a day boy. He left school in 1940 to become an apprentice fitter and studied for a London University external degree via day release and weekend...
of Queen's University Belfast in the late 1970s.
Annotation
Another solution of the problem of stream direction independent turbine is the Darrieus wind turbineDarrieus wind turbine
The Darrieus wind turbine is a type of vertical axis wind turbine used to generate electricity from the energy carried in the wind. The turbine consists of a number of aerofoils usually—but not always—vertically mounted on a rotating shaft or framework...
(Darrieus rotor).