Structural analysis of a 1kW Darrieus turbine spoke

A structural study of a 1 kW Darrieus turbine spoke was performed in order to study stress distribution on the piece and make it more light. The VAWT turbine, originally intended for urban operation, is provided with 3 blades and 6 spokes. Since turbine initial tests showed relevant balancing issues, the main analysis target was to reduce the rotor weight. A detailed analysis of the involved forces (both inertial and aerodynamic) was performed in order to evaluate the most significant loads affecting the structure. A finite element approach was adopted to simplify the structure composed by one blade and two spokes. A first finite element model was implemented to extract force reactions at the spoke tip. Reactions were then used in a second more refined and experimentally validated finite element model, representing only the spoke, in order to evaluate stress distribution. In this model, the spoke was considered rotating at the maximum admitted rotational speed, since centrifugal forces were observed to be much more remarkable than others loads. Original steel configuration and different architectures with shaped holes made along the spoke were simulated, but stress value was found to exceed inevitably yield stress at most critical cross section. Therefore, the final spoke was designed in aluminum. This implied a remarkable weight reduction as well as a notable stress value reduction.