The startup Ronamic has designed an innovative low-head water turbine. We cooperated in developing the design to achieve the highest possible efficiency. We also investigated other flow-related topics such as maximum pressures and expected forces. The design is optimized for use in a dam application and open water (free flow). Ultimately, the idea turned out to be so successful that it received budget from the Shell Gamechanger program to have the feasibility of the design assessed by an external party, DNV-GL. The text below gives a summary of the process we went through during this project.
First, the design of the rotor has been optimized for various applications.
We have been involved in this project almost from the start. The first simulation has been performed for a very simple rotor. Unfortunately, the rotor turned out not to be very efficient for a free flow application, the water would rather flow around the rotor than through it. However, for applications in free flow, such as the sea, many rotors will be placed next to each other, which might increases efficiency.
With 10 rotor sets next to each other, the efficiency was approximately 10x higher. We concluded that for an application in which the water flow is not confined (such as with a dam), a larger obstruction by using more rotors, causes more water to flow through the turbine instead of around it, which increases efficiency.
In addition to the free flow, the performance of the turbine in a dam application has been investigated. With this application the water pressure is higher and water simply cannot pass by the turbine. The first design had straight blades, then more streamlined blades were designed.
The design became more efficient, but it could be even better. Ultimately, the idea came up to use a traditional rotary lobe pump as a rotor because there is little leakage and therefore maximum efficiency.
The lobe shape appeared to work very well and provides a high efficiency.
However, there is always room for improvement. We thereby took up a challenge to run a series of optimization simulations in order to really understand the operation of this turbine. However, the rotor shape is extremely challenging to simulate. The calculation grid in particular is a challenge as two rotating parts rotate through each other’s space. To solve this problem, we collaborated with CFX Berlin. They have developed a tool TwinMesh and with the aid of this tool calculation grids for such complicated inter-penetrating shapes could be easily generated. Therefore, making it possible to run a series of optimization simulations and make the design better.
In order to find the best operating point, the efficiency, torque and power have been calculated for many rpms.
With the support of our final report, the Shell Gamechanger program was convinced and Shell made a budget available to test the entire design for feasibility. This feasibility study was carried out by DNV-GL and was not only a check of the performance of the turbine, but included much more aspects such as the manufacturability, robustness and cost price. The analysis of DNV-GL did not reveal any major flaws or other unforeseen problems. They recommended to go to the testing phase. Unfortunately, this is costly and no investor has yet been found.
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