Research

4-2. Multi Rotor Turbine

Wind turbines have been growing considerably in size in the last two decades. From 50m rotor diameter in 1995 to 124 m rotor diameter of a standard 5 MW turbine in 2005, now the size reached a diameter of 164 meters with the 8 MW turbine from Vestas. Innovative materials allowed for manufacturing of longer blades. With increasing the power capacity of one turbine it was possible to reduce the cost of energy.

マルチロータレンズ風車(クラスタードレンズ風車)

マルチロータレンズ風車(クラスタードレンズ風車)

To further increase the power of turbine researchers are looking for ways to further increase the length of the blades. An alternative approach is to use the latest blade manufacturing technology for multiple rotors in a single structure also called the multi-rotor concept.

マルチロータレンズ風車(クラスタードレンズ風車)

Based on the concept that many small turbines are cheaper than one big turbine if installed in the same structure the multi-rotor concept promises reduced weight, cost (theoretically by 2/3) and higher capacity factors amongst other advantages.

マルチロータレンズ風車(クラスタードレンズ風車)

The wind lens turbine, developed by Kyushu University, has a brimmed diffuser surrounding the rotor. The diffuser has a curved shape that leads into a vertical brim at the exit.
In the Wind Engineering Section at RIAM we study the effect of closely spaced turbines on their performance. In the boundary layer wind tunnel, the wind lens turbines are tested in in side-by-side arrangements to evaluate the aerodynamic performance. We started with 2 turbines and measured the power output at different gap width. Next we modified the brim height of the wind lens to find out what the effect will be on the power output. We were able to measure a power increase of up to 5 % with two turbines side-by-side and even up to 9% with three turbines side-by-side. The highest power increase was achieved with 10% brim height. ( brim height referred to the throat diameter of the wind lens )
Two turbines side-by-side
マルチロータレンズ風車(クラスタードレンズ風車)


Three turbines side-by-side
マルチロータレンズ風車(クラスタードレンズ風車)


After the wind tunnel experiment we are modelling the turbines to calculate the flow around them. In a computational fluid dynamics (CFD) analysis we calculate the power output of the turbines and compare the results with the experiment. If there is good agreement between simulation and experimental results, we can analyze the flow to find flow patterns that cause the variations in power output.

マルチロータレンズ風車(クラスタードレンズ風車)

CFD simulation of three bare turbines side-by-side, gap 0.025D (left) and three wind lens turbines side-by-side, gap 0.1D (right). In the case of bare turbines the power output does not increase significantly at any gap width. In the case of wind lens turbine we can observe increased flow speed in the gap and reverse flow behind the brim of the turbines.

マルチロータレンズ風車(クラスタードレンズ風車)

The promising results from the wind tunnel let us to start a field experiment. A Multi-Rotor Turbine, comprising three 1-kW wind lens turbines was installed in December 2014 at the campus of Kyushu University in Fukuoka. Since then we are collecting data which will be analyzed later.
<< back to Research page
│ Home │ Research │ Resources │ People │ Publications │ Access │ Links │