Fluid-Structure Interaction over HAWT Turbine Vibration (two-way)

Description

In this project, we present a simulation of a Horizontal-Axis Water Turbine (HAWT) via ANSYS Fluent software.

Since the turbine blades are exposed to water flow, an interaction occurs between the water flowing and the turbine blades' structure. First, the water flow exerts a hydraulic force on the blades' body by hitting it. Subsequently, displacement or deformation appears on the turbine, which can lead to the water flow being affected. Therefore, we intend to perform a numerical simulation of the water turbine as a Fluid-Structure Interaction (called FSI).

The interaction between fluid and structure can be implemented as:

• One-way FSI

• Two-way FSI

In this project, we aim to analyze both the effect of fluid on the structure and the effect of the structure on the fluid. So, we choose Two-way FSI, which is a more accurate and realistic but more complex approach.

We modeled the geometry via Design Modeler software. The computational domain is a sample space for water flow, in which a distinct fluid region is defined around the turbine body. The turbine is of the horizontal-axis type and includes three blades.

We meshed the computational domain via ANSYS Meshing software. The mesh is of an unstructured type, and approximately 3,400,000 cells have been generated.

Methodology

Fluid-structure interaction can be performed in two general methodologies:

• In the ANSYS Workbench environment, using an external solver (specifically, system coupling)

• Only in the Fluent solver (in the form of an intrinsic FSI).

In this project, we implemented a two-way FSI in the ANSYS Fluent environment. In other words, the Fluent solver performs both fluid and solid calculations simultaneously.

For two-way FSI in Fluent solver, the Structure model is utilized. The structural model can be implemented in two ways:

• Linear elasticity: The deformation is proportional to the applied force. In this case, the deformations are usually small, and the calculation process is faster.

• Nonlinear elasticity: The deformation is not necessarily proportional to the applied force. In this case, the deformations are usually large, and the calculation process is more complex and time-consuming.

In this project, we considered fluid-structure interaction in the form of a Linear Elasticity state.

Since we were analyzing two-way FSI and considering the effect of structural displacement on the adjacent fluid, we used the Dynamic Mesh model. In other words, we establish a connection between the fluid and structural calculations with the Intrinsic FSI option. Then, we enabled the smoothing and remeshing methods to define a deformable mesh.

In addition, we used the Multiple Reference Frame (MRF) to define a rotational flow with a certain angular velocity in the region around the turbine body.

Results

We analyzed the results in two fluid and solid approaches:

In a fluid view, we studied the behavior of water flow around the turbine. For this, we obtained the distributions of the pressure and velocity of water near the blades. The results show that the water flow collides with the rotating blades' body and, as a result, exerts a hydraulic force on the turbine structure.

In a solid view, we studied the behavior of the turbine blades' body under the influence of the applied forces of the water flow. For this, we obtained the distribution of the von Mises stress and displacements (in all directions). The results confirm that the water flow affects the turbine blades' structure.

In conclusion, we can claim that we carried out the simulation project of a HAWT correctly and acceptably by using the two-way FSI method.