Effect of velocity on the Wind Turbine blade

Introduction

Windmills have been assisting mankind to convert the energy contained in wind to many other useful forms for the last two thousand years. Today’s wind turbines are capable of converting a great amount of energy in the wind into electricity. This is due to the blades which are developed using state of the art aerodynamics analysis and the other performance-enhancing equipment. If the blowing wind can turn the wing. We will receive electricity from the generator that is an attachment to it. The blade has a lot of aerofoils cross-sections consisting of different sizes and shapes from the root to tip. The simple aerofoil technologies make the wind turbine blade turn that means a lift force is produced when a fluid moves over an aerofoil the moving wind turbine blade also experiences the wind relatively. For the moving blade the relative wind velocities, therefore the wind turbine blade is positioned in a tilted manner in order to align with relative wind speed becomes more inclined towards the tip. So before connecting to the generator, the speed is increased in the gearbox. So before connecting to the generator, the speed is increased in the gearbox. The gearbox uses a planetary gear set arrangement to achieve the high-speed ratio (1:90). The wind turbine should face the wing normally for maximum power extraction. Wind turbine always is aligned with the wind direction by yaw mechanism. According to wind speed, the relative velocity angle of the wind also changes. A blade tilting mechanism tilts the blades and generators a proper alignment of the blade is always at the optimum angle of attack with the relative wind flow.

“A wind turbine absorbs 100% of the available kinetic energy only if the downstream wind speech becomes zero.

Blade Design

Rotor blade designs operate on either the principle of the lift or drag method for extracting energy from the flowing air masses. The lift blade design employs the same principle that enables airplanes, kites, and birds to fly producing a lifting force which is perpendicular to the direction of motion. The rotor blade is essentially an aerofoil, or wing similar in shape to an airplane wing. As the blade cuts through the air, wind speed and pressure differential are created between the upper and lower surfaces of the blade. The pressure at the lower surface is greater and thus acts to “lift” the blade upwards, so we want to make this force as big as possible. When the blades are attached to a central rotational axis, like a wind turbine rotor, this lift is translated into a rotational motion. Opposing this lifting force is a drag force which is parallel to the direction of motion and causes turbulence around the trailing edge of the blade as it cuts through the air. This turbulence has a braking effect on the blade so we want to make this drag force as small as possible. The combination of lift and drag causes the rotor to spin like a propeller.

Governing Eq.

The governing equations are the continuity and Navier-Stokes equations. These equations are written in a frame of reference rotating with the blade. This has the advantage of making our simulation not require a moving mesh to account for the rotation of the blade. 

Conservation of mass

The additional terms for the Coriolis force and the centripetal acceleration in the Navier-stokes equation

Boundary conditions

Inlet: Velocity varies from 3.5 to 20 m/s with turbulent intensity and turbulent viscosity ratio 10.

Outlet: Pressure of 1 atm

Velocity Vector Contour

Pressure Contour when Velocity 3.5 m/s

Pressure Contour when Velocity 5 m/s

Pressure Contour when Velocity 10 m/s

Pressure Contour when Velocity 12 m/s

Pressure Contour when Velocity 14 m/s

Pressure Contour when Velocity 15 m/s

Pressure Contour when Velocity 20 m/s

Pressure Contour at different plane of blade

Observation

The local blade velocity increases with radius.

The velocity at the tip, which is the highest velocity.

The pressure is lower on the back surface of the blade compared to the front surface of the blade.