Using Large-Eddy Simulation to Study Water Tunnel Confinement Effects for a Marine Propeller in Crashback

We discuss water tunnel confinement effects for a marine propeller in the off-design mode of operation known as crashback. In crashback, the propeller rotates in the reverse direction while the vessel moves in the forward direction, yielding highly unsteady loads. The experiments by Jessup et al. [25th Symposium of Naval Hydrodynamics (2004)] studied marine propeller David Taylor Model Basin (DTMB) 4381 in the 36-inch variable pressure water tunnel (VPWT). In the crashback mode of operation, these experiments acknowledge a large difference between the propeller loads measured in the water tunnel and previous tow tank (open water conditions) experiments. Water tunnel confinement effects in the open-jet test section are hypothesized to be one of the contributors. Large-eddy simulation is used to study the confinement effects of the 36--inch VPWT for the marine propeller (DTMB) 4381 in both forward and crashback modes of operation. The simulations use a novel, unstructured grid methodology, developed by Horne & Mahesh [J. Comput. Phys (2019) 376:585-596].