The Aerodynamics Of The Wind Turbine Component 2

The Aerodynamics Of The Wind Turbine Component 3. WIND TURBINE BLADES BEHAVE IN THE SAME WAY Returning to wind turbine blade, just as within the situation for the cyclist, we can observe the aerodynamic and force diagrams in 3 different situations, when the wind turbine is stationary and when it is running at a normal operational speed. We molecule diagram an example the cross section near the blade tip of a Bonus 450 kW Mk III operating in a wind velocity v of 10 m or s. When the rotor is stationary, as shown in drawing A below, the wind. has a direction towards the blade, at a right angle to plane of rotation, that is the region swept by the rotor during the rotation regarding the blades.

The wind velocity of 10 m or s shall make a wind compression of 80 N or m2 of blade surface, just like the effect on our cyclist. The wind compression is roughly within the similar to direction as the wind and shall also be roughly perpendicular to flat side regarding the blade profile. The component regarding the wind compression blowing within the direction regarding the rotor shaft attempts to bend the blades and tower, while the smaller component regarding the wind compression blowing within the direction regarding the rotation regarding the blades produces a torque that attempts to begin the wind turbine. Once the turbine is in procedure and the rotor is turning, as is shown within the center diagram B, the blade encounters a head wind from its own forward movement in exactly the similar to method as the cyclist does. The strength of head wind u at any critical location on the blade depends partly on just how fast the wind turbine blade is rotating, and partly how distant out on the blade one is from the shaft.

In our example, at the normal operating velocity of 30 rpm, the head wind u near the tip regarding the 450 kW wind turbine is about 50 m or s. The meteorological wind v of 10 m or s shall thus release a resulting wind over the profile of about 51 m or s. This resulting wind shall have an effect on the blade surface with a force of 1500 N or m2. The force F shall not be within the direction regarding the resulting wind, but almost at a right angle to resulting wind. Within the drawing on the right C the force regarding the wind compression F is repeatedly split up into a component within the direction of rotation and another component at a right angle to this direction.

The force Fa at a right angle to plane of rotation attempts to bend the blade return against the tower, while the force Fd points within the direction of rotation and sends the driving torque. We shall notice 3 very important differences between the forces on the blade in these 3 different situations and forces on the cyclist within the 3 corresponding situations. One difference is that the forces on the blade grow to very huge during rotation. If vector arrows illustrating the forces within the diagrams were drawn in a scale that was indicative regarding the sizes regarding the different forces, then these vector arrows of a wind turbine in procedure should have been 20 times the volume regarding the vector arrows regarding the similar to wind turbine at rest. This huge difference is due to resulting wind velocity of 51 m or s striking a blade during operation, many times the wind velocity of 10 m or s when the wind turbine is at rest.

Just like the cyclist, the blade encounters head wind resulting from its own movement,however head wind is of distant greater importance on a wind turbine blade than for a cyclist in motion. The other important difference between a wind turbine blade and a cyclist is that the force on the blade is almost at a right angle to resulting wind striking the profile. This force is known as the lift and also produces a mini resistance or drag. The direction of this lift force is of best importance. A cyclist only feels the wind resistance like a burden, requiring him to push below extra hard on the pedals.

However with a wind turbine blade this extra wind resistance shall act like a kind of power booster, at fewest within the normal blade rotational velocity range. The reason for this difference is due to blades streamlined profile, which behaves aerodynamically completely differently as compared to irregular shaped profile of an lone on a bicycle. The wind turbine blade experiences. Experiences most lift and drag, while a cyclist only experiences drag. LIFT Lift is primary due to physical phenomena known as Bernoullis Law.

This physical law states that when the velocity of an space flow over a surface is increased the compression shall then drop. This law is counter to what most people skills development from walking or cycling in a head wind, where normally one feels that the compression increases when the wind also increases. This shall also be true when one sees an space flow blowing directly against a surface, but it is not the case when space is flowing over a surface. One can with no problems convince oneself that this is so by creating a mini experiment. Take 3 mini pieces of cardboard and bend them slightly within the middle.

Then hold them as shown within the diagram and blow in between them. The velocity regarding the space is higher in between these 3 pieces of cardboard than outside where of course the space velocity is about zero, so that is why the compression inside is decreased and regarding to Bernoullis Law the papers shall be sucked in towards each other. One should expect that they should be blown distant from each other, but in reality the opposite occurs. This is an interesting little experiment, that clearly demonstrates a physical phenomenon that has a completely different result than what one should expect. Just try for you and see.

The aerodynamic profile is formed with a rear side, that is many more curved than the front side facing the wind. 3 portions of space molecules side by side within the space flow moving towards the profile at spot A shall separate and pass around the profile and shall once repeatedly be side by side at spot Be subsequent to passing the profiles trailing edge. As the rear side is more curved than the front side on a wind turbine blade, this means that the space flowing over the rear side has to venture a detailed distance from spot A to Be than the space flowing over the front side. That is why this space flow over the rear side should hold a higher velocity if these 3 different portions of space shall be reunited at spot B. Greater velocity produces a compression drop on the rear side regarding the blade, and it is this compression drop that produces the lift.

The highest velocity is obtained at the rounded front edge regarding the blade. The blade is almost sucked forward by the compression drop resulting from this greater front edge speed. There shall also be a contribution resultingfrom a mini over-pressure on the front side regarding the blade. Compared to an idling blade the aerodynamic forces on the blade below operational conditions are very large. Most wind turbine owners have surely noticed these forces during a start-up in good wind conditions.

The wind turbine shall begin to rotate very slowly at first, but as it gathers velocity it begins to accelerate faster and faster. The change from slow to fast acceleration is a sign that the blades aerodynamic shape returns into play, and that the lift greatly increases when the blade meets the head wind of its own movement. The fast acceleration, near the wind turbines operational rotational velocity spots best demands on the electrical cut-in system that should capture and engage the wind turbine without releasing excessive peak electrical loads to grid.