Complexity of the Configuration

Depending of the complexity of the computational domain, the user should use CFD software capable of treating different types of grids. There are two different types of grids, structured and unstructured. An unstruc­tured grid (see Fig. 11.5) allows the most complex geometries to be ade­quately represented. Grids around most types of furniture could be created, as well as grids around persons. An unstructured grid also allows local grid refinement in geometrically complex regions, or in regions where the grid needs to be fine due to strong velocity gradients. The drawback is that the numerical solver usually is less efficient than a solver based on structured grids, which means that more computer time is needed.

A

19

Ial

Multizone model

Zonal division of parcel distribution

FIGURE

0.4 m/s

0.3 m/s

0.2 m/s

0. 1 m/s

I

FIGURE 11.6 Example of a Cartesian grid.

For the structured grid, there are at least four subtypes:

1. Cartesian grid (Fig. 11.6).

2. Boundary-fitted (curvilinear) grid (Fig. 11.7).

3. Multiblock, either with Cartesian or boundary-fitted grid; in Fig. 11.8, a two-block Cartesian grid is shown.

4. Multiblock, either with Cartesian or boundary-fitted grid, where the interface of the blocks does not need to be a one-to-one relation; i. e. one cell in one block can meet two cells of the adjacent block (see Fig. 11.9).

When flow in empty rooms is to be computed, a Cartesian grid is suffi­cient. If the ceiling, floor, or walls of a room are inclined or curved, a bound­ary-fitted grid should be used. For computing the flow in an apartment or a building with multiple rooms, a multiblock grid should be used. With a grid as

I FIGURE I 1.8 Example of a multiblock grid.

Described in item 4 above, local grid refinement can be used in geometrically complex regions or in regions where large (velocity) gradients prevail.

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