3D-printed horizontal-axis micro wind turbine

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Objectives

Objectives of this project were deduced from two facts. The first one is that the renewable energies are more and more important in our society. They are one of the solutions we found at actual energetical and ecologial problems we have to deal with. The second one is that more and more Fab labs are created. These places allow everyone to realise self-designed objects. 3D printers are some machines among others that can be used to create these objets.

Based on these two facts, we defined the subject of our project: the design and test of a 3D-printed horizontal axis windturbine.

Design

In this part, we will explain the main design choices that we made

3D printer

The printer that we used is a Up Mini. We chose this printer because it has a good precision of printing and uses a thermoplastic, the ABS. The ABS possesses better mechanical properties than the others thermoplastics available on the other printers. The ABS is more ductile and more resistant. The main constraint we will have to deal with with this printer is the maximum size of the pieces to print. Indeed, the printing volume of the Up Mini is of 120 x 120 x 120 mm.

Generator

The generator that we chose is a Maxon EC-40. This generator is followed by a gearhead that allowed to increase the permitted maximum admission torque to 1.48Nm. It also enables some admission rotational speeds that are consistent with those of the hub untill 758.4rpm. An encoder connected to the generator allows to know at every moment its rotational speed.

Blades

Due to the printer choice, we were forced to create blades in several pieces. We decided to design two sets of blades. The first one has a 70cm diameter and blades are formed of 3 pieces. The second one possesses a 100cm diameter and blades are made of 4 pieces (see picture of assembly). To determine the shape of these blades, we used a matlab program that gives the form and the twist of the profiles as function of the radius. This matlab program takes as arguments: the type of profile used, the design wind speed, the design tip speed ratio and the desired rotor radius (for more details: see master's thesis). The implemented method is a improved version of the Blade Element Momentum method (BEM)

Hub

The hub has two main functions: to assure the blades position avoiding any rotation or unhooking of those, to transmit the torque to the generator. In our project, the different blades foots placed together form a cylinder. This one is then covered by the two parts of the hub. We maintain the assembly fixed with nuts and bolts. The first part, the nose, possesses also an aerodynamic function. The second part is resistant and fully printed because it transmits the torque to the generator. The assembly between the hub and the generator uses a key. A compression screw was added to press the key and maintain the rotor in place on the generator shaft.

Nacelle

The main function of the nacelle is to maintain the generator in position and to maintain all the assembly stable on the top of the tower. The tail fin is also fixed on the nacelle. It will orientate the hub en front of the wind. We decided to use the 3D printing to create an original shape. Indeed, 3D printing allows the design of pieces that would be extremely expensive to create with classic manufacturing means. The shape we designed uses the Venturi effect to create an air flux on the surface or the generator. It permits to cool it more efficiently and so to increase the general efficiency. The ABS is a thermoplastic and doesn't resist at high temperatures. In our project, the uses of this type of cooling turned out to be necessary. The assembly of the nacelle is shown on the hereby picture.

Tests

Test bench