Wind power systems for heat supply of settlements: The basis of classical wind power technologies

Macroscopic wind power technologies and wind power engineering are based on the use of energy of directed macroscopic air flows (wind), interaction of these wind flows one with other and action of these flows on the other bodies without regarding deeply the structure of matter. Wind energy is work performed by moving air. Another sign (feature) of macroscopic wind power technologies is the use of massive elements (wind turbines) for intermediate conversion of mechanical (kinetic) energy of the air flow into the mechanical (kinetic) energy of the rotors. Mass, as known, is a measure of body inertia and energy is a measure of its motion.

Aeromechanics. Theoretical basis for macroscopic wind power technologies and wind power engineering is aeromechanics (aerostatics and aerodynamics) - a part of mechanics exploring the balance and flow of gaseous environments, interaction between them and solids submerged into the gases. The equations of aerostatics and aerodynamics define the parameters of wind turbines, wind loads onto buildings and structures. The aerodynamics explores the movement not a single molecule of gas, but the whole element, which consists of a large number of molecules, and this element is considered as a gas piece or a point. Such idealization allows finding and formulating the equation of motion. For a complete description of the gas state it is enough to set three components of velocity v = v (x, y, z, t), pressure p = r (x, y, z, t) and density ρ = ρ(x, y, z, t). The variable parameter x, y, z, t characterize the coordinates and the time for the appropriate point of space filled with gas (fig. 4.8).

At fixed time t = t0 the function v = v(x, y, z, t) describes a field of velocities, in other words, it gives total image of gas velocity distribution for any point of space. The field of velocities can be presented graphically by the lines of current. Their density is proportional to the velocity of gas particles in a given point. All the space occupied by gas can be divided into the tubes of current (part of gas limited by the lines of current). If the tube of current has very small cross section area, it is possible to consider that gas velocity is identical for all points of tube and directed along its axis.

The motion of the body in a gas causes aerodynamic force. Aerodynamic force is determined by the gas pressure on the surface of the body immersed into the air gas mixture, and by viscosity (friction). Pressure acts perpendicular to the surface. This aerodynamic force includes drag force component parallel to the direction of relative motion, and lift force component perpendicular to the direction of relative motion (fig. 4.8). According to KuttaJoukowski theorem the lift force Fl is calculated by imposing a «circulation» (the integral of velocity of the air in a closed loop around the boundary of thin airfoil):

 

Fl = 0, 5ρАpсlva2,                                 

 

where ρ is air density, v is air velocity, A is specific area of airfoil, and сl is the lift coefficient.

The basic system of classic macroscopic wind power technologies that are widely used in world practice is wind power plant (WPP) that consists of row of wind turbines with a horizontal axis of rotation and two or three blades, fixed to the rotor.

 

By Vasil Sidorov on October 10, 2012 

Technopark QUELTA, Queltanews from

Nizhyn Laboratories of Scanning Devices

sidorovvasil@gmail.com

 


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