The first step is to generate a mesh that is readable by Nektar++ . The files necessary in this section can
be found in $/NEKTUTORIAL/Channel/Geometry/. To achieve this task we use Gmsh in conjunction with
the Nektar++ pre-processing utility called $NEK/MeshConvert. Specifically, we first generate the mesh in
figure 1 using Gmsh and successively we convert it into a suitable Nektar++ format using
$NEK/MeshConvert.
Channel.msh can be generated using Gmsh by running the following command:
gmsh -2 Channel.geo
Channel.xml can be generated using the $NEK/MeshConvert pre-processing tool:
$NEK/MeshConvert Channel.msh Channel.xml
Channel-al.xml can be generated using the module peralign available with the
pre-processing tool $NEK/MeshConvert:
$NEK/MeshConvert -m peralign:surf1=2:surf2=3:dir=x Channel.xml
Channel-al.xml
where surf1 and surf2 correspond to the periodic physical surface IDs specified in Gmsh
(in our case the inflow has a physical ID=2 while the outflow has a physical ID=3) and dir
is the periodicity direction (i.e. the direction normal to the inflow and outflow boundaries
- in our case x).
Examine the Channel.xml and Channel-al.xml files you have just created. Only the mesh and
default expansions are defined at present and the only difference between the two files is the ordering
of the edges in the section composite ID=3 which has been re-ordered in order to apply periodic
boundary conditions correctly.
$NEKTUTORIAL/Channel/Stability/Coupled.