HPC realization of a controlled turbulent round jet using OpenFOAM
  The present paper investigates high performance computing abilities of OpenFOAM for a low Reynolds number ($Re_D=2000$) axisymmetric jet subject to multiple zero net mass flux (ZNMF) actuators. First, parallel performance of OpenFOAM is tested by performing a scaling study up to $2048$ processors on a supercomputer of Flemish Supercomputer Center(VSC). Then, a method to improve the parallel efficiency is proposed. The method is based on developing a hybrid concept to calculate the statistical moments. This new concept combines ensemble and time averaging in order to allow data sampling in parallel. The motivation is obtaining a reduction in the walltime to collect turbulent statistics which is observed to be the dominating part in the ZNMF controlled jet flow. Employing this parallel statistical averaging approach in combination with regular grid partitioning parallelism, allowed us conducting DNS cases on $P=624$ processors with an overall speed-up of $S_e=540.56$ and a parallel efficiency of $E_e=0.87$. The parallelization using only grid partitioning exhibited inferior performance with $S_e=423.94$ and $E_e=0.68$. In addition to develop a methodology to increase the parallel performance, we reduced the time step cost of the existing unsteady solver as well. To this end, an incremental projection method is implemented into OpenFOAM and a performance gain above $30\%$ is realized. 
Asim \"Onder and Johan Meyers
physics.flu-dyn