Gambit -- MODELING A COMBUSTION CHAMBER (3-D)

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The problem to be considered is shown schematically in Figure 4-1. The geometry consists of a simplified fuel injection nozzle that feeds into a combustion chamber. You will

only model one quarter of the burner geometry in this tutorial, because of the symmetry of

the geometry. The nozzle consists of two concentric pipes with radii of 4 units and 10

units respectively. The edges of the combustion chamber are blended on the wall next to

the nozzle.

In this tutorial, you will create a combustion chamber geometry using the “top-down”

construction method. You will create volumes (in this case, bricks and cylinders) and use

Boolean operations to unite, intersect, and subtract these volumes to obtain the basic

geometry. Finally, using the “blend” command, you will round off some edges to complete the geometry creation.

For this model, it is not possible to simply pick the geometry and mesh the entire domain

with hexahedral elements, because the Cooper tool (which you will be using in this tutorial) requires two groups of faces, one group topologically parallel to a sweep path, and

the other group topologically perpendicular. However, the rounded (blended) edges fit in

neither group. See the GAMBIT Modeling Guide for a more detailed description of the

Cooper tool. You need to decompose the geometry into portions that can be meshed using

the Cooper tool. There are several ways to decompose geometry in GAMBIT. In this

example, you will use a method whereby portions of the volume around the blend are split

off from the main volume. A detailed description of the decomposition strategy for the

combustion chamber is given below.

Note that there are several faces in the geometry for which the default meshing scheme is

the Pave scheme; most of these faces are perpendicular to the z direction. There are also

geometrical protrusions in the z direction, so this should be chosen as the main direction

for the Cooper meshing scheme. To make this possible, the paved faces in the x and y

directions (the two symmetry planes in the geometry shown in Figure 4-2) must be

changed to use the Submap or Map meshing scheme.