  We introduce a modified and simplified version of the pre-existing fully
parallelized three-dimensional Navier--Stokes flow solver known as TPLS. We
demonstrate how the simplified version can be used as a pedagogical tool for
the study of computational fluid dynamics and parallel computing. TPLS is at
its heart a two-phase flow solver, and uses calls to a range of external
libraries to accelerate its performance. However, in the present context we
narrow the focus of the study to basic hydrodynamics and parallel computing
techniques, and the code is therefore simplified and modified to simulate
pressure-driven single-phase flow in a channel, using only relatively simple
Fortran 90 code with MPI parallelization, but no calls to any other external
libraries. The modified code is analysed in order to both validate its accuracy
and investigate its scalability up to 1000 CPU cores. Simulations are performed
for several benchmark cases in pressure-driven channel flow, including a
turbulent simulation, wherein the turbulence is incorporated via the large-eddy
simulation technique. The work may be of use to advanced undergraduate and
graduate students as an introductory study in computational fluid dynamics,
while also providing insight for those interested in more general aspects of
high-performance computing.
