Crashback Maneuvers

Propeller crashback simulations were performed under the 2006 Technology Insertion (TI) Capabilities Application Project (CAP) on the Naval Oceanographic Office Major Shared Resource Center (NAVO MSRC) 3,072 processor unclassified IBM POWERS+ system. Phase I of the CAP focused on fine-tuning communication and load-sharing protocols that improved the scalability of the flow solver used in the simulations. The Phase II effort simulated the crashback flow for a research propeller - a five-bladed open propeller recently investigated in high-fidelity experiments. The simulation was performed with a 949-block multiblock/overset grid and used a hybrid Reynolds-Averaged Navier-Stokes (RANS)/Large Eddy Simulation (LES) model. Consistent with experimental results, the simulated crashback flow is extremely complex and is dominated by chaotic variations of a large ring vortex generated by the flow recirculating around the propeller. Using 400-500 processors during Phase II allowed simulation of approximately 100 propeller revolutions. The paper discusses Phase I and II CAP results, including the solver scalability and comparisons of propeller thrust and side-force spectra with experimental results. Comparisons with experimental measurements demonstrate that the hybrid RANS/LES model provides an accurate means of calculating crashback flows.