The FSI model in Ansys Polyflow allows you to take into account the elasticity of a solid region coupled to the flow in your simulation. Even very small geometry deformations can affect the flow. During die design, for example, for a thin die such as coat hanger the balance of the die can be sensitive to die deformation. Temperature has an effect on die deformation, and thus on the flow. The result is that the elastic model can produce unwanted stresses on the solid part that must be considered.