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Summary
The thrust of a propeller is calculated using
where Á is the fluid density, n is the rotational rate of the propeller, and D is the propeller diameter. The thrust
coefficient CT is a function of the advance ratio V0/nD. The efficiency of a propeller is the ratio of the power
delivered by the propeller to the power provided to the propeller.
An axial-flow pump, or blower, consists of an impeller, much like a propeller, mounted in a housing. In a
radial-flow, or centrifugal pump, on the other hand, fluid enters near the eye of the impeller, passes through the
vanes, and exits at the edge of the vanes. The head provided by a pump is quantified by the head coefficient, CH,
defined as
where "H is the head across the pump. The head coefficient is a function of the discharge coefficient, which is
where Q is the discharge. Pump performance curves show head delivered, power required, and efficiency as a
function of discharge. The specific speed of a pump can be used to select an appropriate pump for a given
application. Axial-flow pumps are best suited for high-discharge, low-head applications, whereas radial-flow
pumps are best suited for low-discharge, high-head applications.
Turbines convert the energy associated with a moving fluid to shaft work. The impulse turbine consists of a
liquid jet impinging on vanes of a turbine wheel or runner. A reaction turbine consists of a series of rotating
vanes where liquid enters from the outside and exits at the center. The pressure on the vanes provides the torque
for the power. Wind turbines consist of the conventional horizontal-axis design, the Darrieus turbine, or
Savonius rotor. The maximum power derivable from a wind turbine is
where A is the capture area of the wind turbine (projected area from direction of wind) and V0 is the wind speed.
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