When Nektar++ is compiled with HDF5 support, solvers can select the format used for
output of .fld files. FieldConvert can be used to convert between these formats
using an option on the .fld output module. For example, if in.fld is stored in the
default XML format, it can be converted to HDF5 format by issuing the command
FieldConvert in.fld out.fld:fld:format=Hdf5