The innovation proposed here is a computational framework for high performance, high fidelity computational fluid dynamics (CFD) to enable accurate, fast and robust simulation of unsteady turbulent, reacting or non-reacting flows involving real or ideal fluids in several applications. This framework will provide a state-of-the-art unsteady turbulent flow simulation capability employing Hybrid RANS-LES (HRLES) methods which are a blend of Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) approaches. Low-dissipation schemes will be employed which will enable high-fidelity modeling of unsteady flows as well as acoustic fields. Additionally, Lagrangian particle tracking and Eulerian multiphase models will be incorporated to enable simulation of multiphase combustion involving solid particles or liquid droplets. The work proposed here will result in a state-of-the-art design and analysis tool to enable the accurate modeling of: (a) multiphase combustion in solid and liquid rocket engines, (b) combustion stability analysis (c) acoustic fields of space propulsion syatems in near-ground operation, (d) small valves and turbopumps, etc. which constitute critical components of versatile space propulsion engines part of NASA's Constellation Program.