Evaluation of the overset method applied to an active lift turbine

In the current context of energy transition, the development and improvement of energy recovery systems is essential. These system are numerous and some of them use turbines to convert flow kinetic energy into electricity. For a long time, vertical-axis turbines were considered less efficient than horizontal-axis ones. However, they are still better suited to urban areas. Thus, they are now being studied again and new turbine concepts are emerging that can works differently from today's turbines. The entire dynamics of these new -generation turbines can be completely different from those of conventional turbines. The active lift turbine, for example, changes the trajectory of the blades (by varying the turbine radius) to convert the normal forces applying on them into torque. This particularity hinders the use of conventional rotation methods for turbines (Arbitrary Mesh Interface (AMI), Rotating Frame of Reference (RFR), ... ) in Computational Fluid Dynamics (CFD) and an innovative method such as overset could be an alternative. The purpose of this work is to evaluate the overset method for these new-generation turbines modelling. It enables the motion of a structure in its environment to be controlled at will. Various modelling parameters are being tested. The impact of the mesh size (mesh convergence), the turbulence modelling approach (RANS/LES) and the interpolation method between the background mesh and the overset mesh (Cell Volume Weight/Inverse distances) are evaluated and compared. The overset method is first validated on a conventional turbine (Darrieus turbine). The results obtained for the conventional turbine are close to those expected, with a relative error (numerical/experimental) between 3% and 8% depending of the Tip Speed Ratio (TSR) with an averaged error around 7%. Then overset method is extended to an active lift turbine to assess the potential of this new technology. The overset method proves its worth for this type of problem, which cannot be solved by conventional CFD methods of setting structures into motion. It provides control over blade motion without loss of information. Overall, this study demonstrates the interest and applicability of the overset method to the Active Lift Turbine or other kind of turbines that have a specific motion.

Automated summary

This study evaluates the applicability of the overset method in modeling new-generation turbines, demonstrating its potential for solving problems that cannot be addressed by conventional CFD methods. The overset method allows for controlled blade motion without loss of information.