  The dynamics of an organ pipe's mouth region has been studied by numerical
simulations. The investigations presented here were carried out by solving the
compressible Navier-Stokes equations under suitable initial and boundary
conditions using parts of the open source C++ toolbox OpenFOAM. The focus of
the study is on the examination of the velocity field close to the jet. The
components of the velocity field sampled at a cross-section spanning the mouth
were analyzed by using methods of coarse-graining. It is shown that the
dynamics of the sampled velocity field can be separated into two fractions, a
velocity component mainly comprising the jet's flow velocity and a component
that essentially carries particle velocity caused by back-propagating sound
waves inside the resonator. The SPL-spectra calculated of the data sets of the
numerical simulations are compared with the measurements on real organ pipes.
The phase-space representations of sound pressure and particle velocity
indicate the presence of nonlinearities in the organ pipes's mouth region. The
numerical results are consistent with measurements on real organ pipes.
