Theory of Wind Energy
The principles concerned with converting the potential energy of fluids into useful power relies on three basic fundamentals: conservation of mass, energy and momentum, so it is useful to discuss these before examining the operation of wind turbines.
Conservation of Mass:
The continuity equation applies the principle of conservation of mass to fluid flow. Consider a fluid flowing through a fixed conduit having one inlet and one outlet.
If the flow is steady i.e no accumulation of fluid within the control volume, then the rate of fluid flow at
entry must be equal to the rate of fluid flow at exit for mass conservation. If the flow cross-sectional area A (m2), and the fluid parcel travels a distance dL in time dt, then the volume flow rate (Vf, m3/s) is given by:
Vf = A.dL/dt
but since dL/dt is the fluid velocity (V, m/s) we can write: Vf = V x A The mass flow rate (m, kg/s) is given by the product of density and volume flow rate. Between any two points within the control volume, the fluid mass flow rate can be shown to remain constant:
or 91A1V1 = p2A2V2
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