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 ar0cketman rated 17 months ago - Some very good tips for improving aerodynamics of small wind turbines, with references.
From the page: "Simple improvements
The simplest way to improve aerodynamic efficiency for the current 2 metre three bladed turbine would be to select an airfoil that is well suited to the operating co...
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- ar0cketman rated 17 months ago
- Some very good tips for improving aerodynamics of small wind turbines, with references.
From the page: "Simple improvements
The simplest way to improve aerodynamic efficiency for the current 2 metre three bladed turbine would be to select an airfoil that is well suited to the operating conditions, improve the pitch distribution by using the helical + angle of attack distribution and change the tip to a simple Hoerner shape. This is a minimum effort approach that should produce a noticeable performance improvement. The steps are:
1. Use the airfoil data or a wing section analysis program to select a blade airfoil that is a good match with operating conditions along the whole blade, bearing in mind that the majority of the work is done nearer the tip than the root. Martin Hepperle's MH30 section looks like a good starting point.
2. Determine the angle of attack of the airfoil at its maximum Cl/Cd using published wind tunnel data or an airfoil analysis program.
3. Subtract the airfoil angle of attack from the helical pitch calculated from wind speed and design rotational speed. Use the result to set the geometric pitch distribution along the blade. This is the 'helical + angle of attack' pitch distribution.
4. Use a the conventional, straight tapered, blade shape but rake the tip at 30 degrees and round off the point where the leading edge meets the tip. Thin the end of the blade by curving the rear surface down to meet the front surface in a smooth three-dimensional curve. If the curve is smooth it will be easy for wetted-out glass cloth to follow it. Leave the edge of the tip about twice the thickness of the FRP blade skins. The resulting blade shape is shown below.
5. Lay out the blade, taking account of the revised angles at each station. Use the method described in Rubber model propellers from 1/2" balsa sheet to determine the dimensions of the blank and to draw the leading and trailing edge lines on the blank.
6. Carve a new master blade. Use accurate airfoil templates to verify the accuracy of the blade section. Make templates for the root and tip at the minimum and use a metal straight edge to check the blade accuracy at intermediate points. Pay particular attention to leading edge radius. Use templates to check it; carving an accurate leading edge radius is surprisingly hard. Section accuracy will have a big effect on performance so its worth taking extra care over the master blade.
7. The remainder of the blade construction process is unchanged; the current method is to make female moulds from the hand-carved master blade and to form the upper and lower blade skins in them. These are joined in a separate operation to make a set of hollow blades with solid block infill at the root mounting points."
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