Description

The problem simulates the water flow around a vertical axis water turbine (VAWT) submerged in water using the Dynamic Mesh method in ANSYS Fluent software.

The water turbine is from the category of vertical axis turbines and is of the Darrieus type, So the turbine's axis is perpendicular to the direction of water flow.

For this simulation, a vertical axis turbine with three blades is designed within a relatively large computational area in which the computational area has only water flow.

The boundary conditions are also defined in such a way that the incoming water flow enters the computational domain with an average flow velocity of 1 m/s in the direction of the horizon (x-axis). The water flow exits the computational domain with a pressure equal to atmospheric pressure.

We design the present model in three dimensions using Design Modeler software. The model includes a computational domain, and we design a water turbine within this domain.

A darrieus-type water turbine is a category of vertical axis turbines. This turbine has three blades with a height of 0.5 m. This computational area is defined so that the center of the turbine is 3 m far from the inlet section, 10 m from the outlet section, and 0.75 m from the top and bottom surfaces.

We carry out the meshing of the model using ANSYS Meshing software, and the mesh type is Hybrid. Thus, the meshing in the areas around the turbine body is unstructured and structured in other areas of the model. The element number is 7422668.

Darrieus Methodology

In this simulation, it is assumed that the vertical turbine is rotating in the water flow, and therefore, this rotational motion of the turbine blade body affects the surrounding meshing. Therefore, the dynamic mesh model defines the change of meshing around the rotating turbine blades.

To better define the dynamic mesh, a cylindrical area is separated from the entire computational domain so that this area includes the turbine blades. Now, to define the areas under the dynamic mesh, the walls of the turbine blade body and the differentiated area around the turbine blades are defined as Rigid Bodies.

Two methods can be used to define the motion with several degrees of freedom for turbine blades; You can either use a UDF to define this motion, or you can define it manually in fluent software. Since this current model is a turbine, it only has a rotational motion, and on the other hand, this rotational motion can only take place around an axis.

Therefore, to define the type of motion of a rigid body, a rotational motion with one degree of freedom (1-DOF) should be specified; Thus, the mass of the blades was considered equal to 1 kg, and the moment of inertia of the blades was considered equal to 3.09 kg.m2.

The symmetry-type boundary condition also defines the upper and lateral surfaces of the computational area.

Due to the main nature of the model based on the use of dynamic mesh, the simulation process should be defined as Transient (Unsteady) that in the present model, the simulation process is performed in 50 seconds with a time step of 0.05 seconds.

Darrieus Conclusion

At the end of the solution process, we obtain two-dimensional contours relating to velocity, pressure, and kinetic turbulence energy, as well as path lines and velocity vectors on a plane passing through the center of the turbine. Turbine Torque and other turbine performance characteristics are also analyzed.