Vertical Axis Wind Turbine (VAWT) Validation — ANSYS Fluent CFD Simulation

Description

This project simulates the airflow over a vertical axis wind turbine (VAWT) using ANSYS Fluent, with the results validated against a reference paper. The simulation is based on the study "Wind tunnel and numerical study of a small vertical axis wind turbine," and its results are compared with and validated against those in the article. The turbine studied is a Darrieus type — a VAWT consisting of several curved airfoil blades mounted on a vertical rotating shaft or framework, with the main rotor positioned vertically so it can be installed near the ground. Being a validation study, the project's central aim is to reproduce the published results and confirm the accuracy of the CFD setup.

Methodology

The model is designed in SpaceClaim and consists of a rectangular domain containing the rotating domain. Meshing is carried out in ANSYS Meshing with a structured grid of 1,650,940 elements, and the transient solver is enabled to accompany the Mesh Motion option. The airflow enters the domain at 5.07 m/s, and the RNG k-epsilon model solves the turbulent flow equations, as specified in the paper. The Mesh Motion option is enabled to simulate the rotating motion of the blades, which turn at 42.25 rad/s. The study considers a three-blade turbine with a tip speed ratio (TSR) of 2.5, a free-stream velocity of 5.07 m/s, and a blade length (turbine radius) of 0.3 m.

Analysis

At the end of the simulation, the present results are compared with and validated against those of the reference paper, using the diagram of the torque coefficient over time for each rotor blade (figure 14 of the paper). The pressure contours show that the load on the blades changes continuously as their position and angle of attack vary through each rotation — the source of the dynamic stall that challenges VAWTs, and of the wide force variation that makes the blades fatigue-prone. The results also reveal the tip vortices generated at the top of the blades, whose strength varies with each blade's phase angle: a stronger tip-vortex core corresponds to a stronger lift force on that blade, as the lift changes through the rotation, with a small delay expected between the maximum lift and the maximum tip-vortex strength as the flow responds to the changing lift. By the end of this project, you'll be able to set up a transient Mesh Motion simulation of a Darrieus VAWT, validate the results against a published reference through the torque-coefficient history, and interpret the pressure and tip-vortex behavior that governs vertical-axis turbine aerodynamics.