On the fluid side, interface with elastic solid means the fluid sticks or slips on the wall. But additionally, the force applied from the fluid to the wall is computed and acts as a boundary condition on the solid. The stick condition allows the application of zero velocity along the wall. Ansys Polyflow computes the force required to satisfy this condition. The default interpolation for that force is constant at the level of the elements. When a continuous interpolation is used, the method may need a stability coefficient in order to avoid numerical trouble at points where the velocity is already imposed.

This stability coefficient is dimensionless. When used, it must be small with respect to 1. If the stabilization coefficient is too big, it perturbs the solution all over the contact wall, and the velocity boundary condition will be not fully satisfied. For slip condition, a zero normal velocity component is imposed simultaneously with a relationship between the shear force and the tangential relative velocity. The relationship is the Navier’s law:

(8–16)

where is the tangential velocity, is the tangential velocity of the wall, and is a material parameter. In the frame of the fluid-structure interaction, = 0 and there is a penalty coefficient to guarantee the zero normal velocity. This coefficient must be large enough with respect to coefficient. If the penalty coefficient is too small, the zero normal velocity condition is not satisfied.

To define an interface with elastic solid on a boundary section, select Interface with elastic solid menu item in the list of boundary condition choices.

  Interface with elastic solid

The default is the stick condition. You can switch between the stick and the slip conditions by clicking one of the following:

  Switch to slip condition

  Switch to stick condition

You can specify various settings, depending on the condition you select: