We introduce TPLS (Two-Phase Level Set), an MPI-parallel Direct Numerical Simulation code for two-phase flows in channel geometries. Recent developments to the code are discussed which improve the performance of the solvers and I/O by using the PETSc and NetCDF libraries respectively. Usability and functionality improvements enabled by code refactoring and merging of a separate OpenMP-parallelized version are also outlined. The overall scaling behaviour of the code is measured, and good strong scaling up to 1152 cores is observed for a 5.6 million element grid. A comparison is made between the legacy serial text-formatted I/O and new NetCDF implementations, showing speedups of up to 17x. Finally, we explore the effects of output file striping on the Lustre parallel file system on ARCHER, a Cray XC30 supercomputer, finding performance gains of up to 12% over the default striping settings.