Victor Kaplan (Figure 1.26) created the Kaplan turbine, a propeller-type machine, in 1913. It was an evolution of the Francis turbine but revolutionized the ability to develop low-head hydro sites.
A modern water turbine is a device that converts the energy in a stream of fluid into mechanical energy by passing the stream through a system of fixed and moving blades and causing the latter to rotate (Electrical Engineering Tutorials, 2008).
Turbines may be classified according to the direction of the water flow into four groups (cf. Chapter 3):
1. Tangential or peripheral turbines have flow along the tangential direction, such as the Pelton wheel.
2. Inward radial-flow turbines have flow along the radius, such as the crossflow turbine.
3. Mixed flow turbines have a radial inlet and axial outlet, such as the Francis turbine.
4. Axial-flow turbines have flow along the shaft axis, such as the Kaplan turbine.
Turbines are also classified into impulse turbines and reaction turbines:
• Impulse turbines change the direction of the flow of a high-velocity fluid jet. The resulting impulse spins the turbine and reduces the kinetic energy of the flow. There is no pressure change of the fluid in the turbine rotor blades. Before reaching the turbine, the fluid’s pressure head is changed to a velocity head by accelerating the fluid with a nozzle. Pelton wheels use this process exclusively. Impulse turbines do not require a pressure casement around the runner, since the fluid jet is prepared by a nozzle prior to reaching the turbine.
• Reaction turbines develop torque by reacting to the fluid’s pressure or weight. The pressure of the fluid changes as it passes through the turbine rotor blades. A pressure casement is needed to contain the working fluid as it acts on the turbine stage(s), or the turbine must be fully immersed in the fluid flow. The casing contains and directs the working fluid and, for water turbines, maintains the suction imparted by the draft tube. Francis and Kaplan turbines are different types of reaction turbine. For compressible working fluids such as gases, multiple turbine stages may be used to harness the expanding gas efficiently.
Although the connection between the tides and the Moon had been recognized by Aristotle, three centuries before Christ, Earth-centred astronomy persisted. Newton wrote the equilibrium theory in the late seventeenth century, and this was developed by Laplace who recognized that the response functions would have the same frequencies as the astronomical drivers. Kelvin took these forward, applied harmonic analyses, and introduced the naming convention for the constituents.
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The harmonic current equation might be rewritten as
The first two constituents are the lunar semi-diurnal constituent, with a symbol MU2 and a period of 12.4206012 h, and the solar semi-diurnal SU2, with a period of 12.00 h.
