FSI Analysis for a Ball in Water Flow, ANSYS Fluent CFD Simulation Training

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The present problem simulates a spherical ball’s behavior in water flow using ANSYS Fluent software using FSI method.

This product includes a Mesh file and a comprehensive Training Movie.

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Project Description

The present problem simulates a spherical ball’s behavior in water flow using ANSYS Fluent software using FSI method. We perform this simulation using FSI (fluid-solid interaction) method. In this simulation, a computational area is designed in the form of a horizontal tube filled with water flow; So that a solid or spherical object in the shape of a ball is immersed in it. In such models, there is a need for instantaneous and time-dependent change in modeling the model based on the type of displacement at the mesh adjacent boundaries. In the determination of dynamic mesh methods, smoothing and remeshing methods have been used.

According to the smoothing method, the number of nodes does not change and only adjusts the mesh of an area by moving or deforming the boundaries. However, the remeshing method is used when the displacement of the borders is large compared to the size of the local cells in order to regenerate the destructive cells of the critical size limit. To define areas with dynamic mesh, the pipe area is defined as stationary, and the wall around the ball is determined by system coupling with transient structural software. This means that the water flow location inside the pipe is constant relative to the ball, and the ball has no movement or rotation within the water flow.

Project Description (FSI)

The flow of water enters the tube at speed equal to 0.001 m.s-1 and exits it at a pressure equal to atmospheric pressure. In the settings section of structural analysis software, the spherical body wall boundary is defined as fluid and solid interaction (fluid-solid interaction), ie this solid boundary can be affected by water flow behavior. Then, it describes the type of data transfer between fluid and structural software in the system coupling section settings. The definition of data transfer is defined from one boundary as a source in Fluent software to the same boundary as a target in transient structural software or vice versa in the form of a variable. For this simulation, two data transmissions are defined.

Thus, force is transferred from the fluid part to the structural part and displacement is transferred from the structural part to the fluid region. This means that the flow of water hits the spherical body with its movement, and the spherical body can also move inside the pipe.

FSI Geometry & Mesh

The present model is designed in three dimensions using Design Modeler software. The model consists of a horizontal tube with a length of 0.02 m and a diameter of 0.001 m in which a spherical solid or ball with a diameter of 0.00009 m is placed.


We carry out the model’s meshing using ANSYS Meshing software, and the mesh type is unstructured. The element number is 20192. The following figure shows the mesh.


CFD Simulation

We consider several assumptions to simulate the present model:

  • We perform a pressure-based solver.
  • The simulation is unsteady. Because the current model has a dynamic mesh and variable with time.
  • We ignore the gravity effect on the fluid.

The following table represents a summary of the defining steps of the problem and its solution:

Models (FSI)
Viscous k-epsilon
k-epsilon model standard
near-wall treatment standard wall function
Dynamic Mesh Active
mesh methods smoothing & remeshing
tube stationary
wal-solid system coupling
Boundary conditions (FSI)
Inlet Velocity Inlet
velocity  magnitude 0.001 m.s-1
Outlet Pressure Outlet
pressure gauge 0 Pascal
Wall-tube & Wall-soild Wall
wall motion stationary wall
Methods (FSI)
Pressure-velocity coupling SIMPLE
pressure second order
momentum second order upwind
turbulent kinetic energy first order upwind
turbulent dissipation rate first order upwind
Initialization (FSI)
Initialization methods Satandard
gauge pessure 0 Pascal
x-velocity & y-velocity 0 m.s-1
z-velocity 0.001 m.s-1

Results & Discussions

After the solution process, two-dimensional contours related to the pressure and shear stress on the surface of the body of the spherical body and two-dimensional contours related to the speed and pressure around the spherical body in the middle plate of the tube are obtained. These contours correspond to the last second of the simulation process. Contours related to deformation and elastic strain are also obtained in the structural analysis section.

There are a Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.


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