Vertical Axis Wind Turbine : H-Type VAWT, Mesh Motion

Description

This project simulates airflow around an H-type vertical axis wind turbine (VAWT) using ANSYS Fluent. VAWTs offer a practical alternative to horizontal axis turbines (HAWTs) in several respects: they avoid the low efficiency HAWTs suffer at smaller diameters, don't require the roughly 200 m diameters common to HAWT installations, and don't disrupt the natural skyline the way large horizontal turbines do, making them especially well suited to offshore wind farms where wind conditions are also more consistent. The turbine modeled here has six blades, three positioned closer to the rotation axis, rotating in the −Z direction at 14.17 rad/s under an inlet air velocity of 5.3 m/s. The geometry is built in Design Modeler and meshed in ANSYS Meshing with an unstructured grid of 1,546,624 cells.

Methodology

Rather than physically rotating the blades, the simulation applies rotational motion to the fluid zone surrounding them, requiring a distinct moving zone to be separated from the rest of the computational domain. Because the blade positions change over time, relative to the surrounding flow, the problem is inherently time-dependent, and this is captured using the Mesh Motion method under cell zone conditions, with a defined rotation axis and rotation speed governing how that zone moves.

Analysis

The resulting velocity and pressure contours, along with velocity vectors and pathlines around the blades, confirm that the airflow develops a rotational pattern driven by the turbine's motion, with a maximum air velocity of 45 m/s appearing downstream of the turbine and an inlet mass flow rate of 272.685 kg/s. The blade tip speed ratio works out to about 6, based on a tip speed of 30 m/s against the 5.3 m/s free-stream velocity. A stagnation point, and correspondingly the peak pressure zone, appears on the minus-Y side of the turbine, consistent with how the free-stream flow and rotational flow combine there. That combination also affects the inner and outer blades differently: the outer blades, moving at higher linear velocity, experience a larger pressure differential than the inner blades, which sit closer to the rotation axis and move more slowly.