H-Type VAWT (Vertical Axis Wind Turbine): Mesh Motion

H-Type Vertical Axis Wind Turbine (VAWT), Mesh Motion — ANSYS Fluent CFD Simulation

Description

This project presents a CFD simulation of an H-type vertical axis wind turbine (VAWT) using ANSYS Fluent's Mesh Motion method. Turbines are a reliable, clean source of electricity generated by wind-induced rotation, but wind farms face challenges such as the low efficiency of horizontal axis turbines (HAWTs) at smaller diameters, the disruption of natural landscape views, and low wind conditions. Vertical axis turbines (VAWTs) address these issues: they avoid the very large diameters (up to 200 m) common in HAWTs, are widely used offshore where they don't disrupt valley views, and benefit from the more predictable, reliable wind of offshore sites. The H-type turbine analyzed here has six blades, with three positioned closer to the center of rotation.

Methodology

The geometry is drawn in Design Modeler and meshed in ANSYS Meshing with an unstructured grid of 1,546,624 cells. In this simulation, the rotational motion of the turbine blades must be defined — but rather than applying rotation to the blades themselves, the rotation is applied to the field around them, which requires separating a distinct moving zone from the overall computational domain. Because a vertical axis turbine's flow is time-dependent, as the blade positions vary over time, the Mesh Motion method is used in the cell zone conditions, with the rotation axis and rotation speed defined. The turbine rotates in the −Z direction at an angular velocity of 14.17 rad/s, and the air enters the domain at 5.3 m/s. The simulation is carried out as an unsteady (transient) analysis.

Analysis

After the simulation, contours of velocity and pressure are obtained, along with velocity vectors and pathlines around the turbine blades. The results show that the airflow around the blades has a rotational movement, dominated by the turbine's rotation, with a maximum air velocity of 45 m/s captured downstream of the turbine and an inlet air mass flow rate of 272.685 kg/s. The blade tip speed ratio (TSR) is almost 6, with a tip speed of 30 m/s against a free-stream velocity of 5.3 m/s. A stagnation point forms in the −Y direction of the turbine — the maximum pressure zone — set by the combination of rotation and free-stream direction. The combined effect of the free-stream flow and the rotation-induced flow differs between the inner and outer blades: the pressure difference is smaller on the inner blades than on the outer ones, a result of the outer blades' higher linear velocity. By the end of this project, you'll be able to set up a transient Mesh Motion simulation of an H-type VAWT, define a rotating zone around the blades with the correct axis and speed, and interpret the velocity, pressure, TSR, and mass-flow results that characterize vertical-axis turbine aerodynamics.