Cloud computing facilitates end users to allow high performance computing applications by allocating resources on demand. This avoids large capital expenditure for small and medium sized enterprises having limited resources to obtain High Performance Computing(HPC). In this paper, we propose a new distributed HPC model in self-built OpenStack public cloud under SDN infrastructure. For partitioning any task in HPC, domain decomposition strategy is used. We analyse different parallel computation topologies and benchmark their performances. The public cloud constructed under OpenStack platform is integrated with OpenDaylight SDN controller for network controlling and monitoring. Also, we analyze and compare the performance of the OpenStack cloud with and without proposed distributed HPC system. The result shows that the speed performance of OpenStack cloud under SDN infrastructure is enhanced by implementation of our HPC system based on Hypercube algorithm and Mesh Algorithm.