2.7 Fiber Grid Generation

The fibers penetrate the grid of the surrounding flow field arbitrarily. Both grids are treated distinctly from each other (see Figure  2.6.1).

The fiber grids are generated by defining fiber injections. The fibers are considered to be straight lines between injection points and a take-up point. Each fiber is divided into a number of volume cells.

For the grid generation, the following grid types are available:

equidistant   All cells of the fiber have the same length.

one-sided   The cells are graded near the injection point of the fiber and change their size according to a specified growth factor.

two-sided   In addition to the injection point the cells can also be graded at the take-up point by specifying a second growth factor at the end of the fiber.

three-sided   The second point where the fiber cells are graded at the end can be moved to a local refinement point laying between injection and take-up point. This generates fibers with a mesh graded at the injection point and at the local refinement point.

All grid types, except the equidistant grid type, require the specification of a growth factor $R$ which is the ratio of two subsequent fiber grid cells. It refines the mesh for values larger than 1 and coarsens the mesh for values smaller than 1.

If a finite fiber volume cell spans across several ANSYS FLUENT grid cells, a weighted average is used to estimate the corresponding variables of the surrounding flow. This averaging procedure considers the intersection point of each fiber volume cell with the boundaries of the ANSYS FLUENT grid cell.

When computing the source terms in an ANSYS FLUENT grid cell, only the part of each fiber volume cell that is inside the ANSYS FLUENT grid cell is taken into account. This provides a proper computation of ANSYS FLUENT fiber interactions even in hanging node adapted grids.

If the grid is adapted, the data structures that include information about neighbor cells are not updated automatically. For this you have to reinitialize all fibers to start a new search of the neighboring ANSYS FLUENT grid cells.