Free Surface Flows Around Ships: Progress Toward Simulation Of High-Speed Flows And Motions

Abstract

A steady and unsteady single-phase level set method is being developed for the RANS code CFDSHIP-IOWA to simulate free surface flows around complex geometry with large amplitude motions and maneuvering. A structured overset grid approach is used to allow flexibility in grid generation, local mesh refinement, and to efficiently resolve incident waves. The overset interpolation coefficients are computed with the software packages Pegasus (from NASA) or Suggar (from HPC PET). Dynamic interpolation is achieved through interfacing CFDSHIP-IOWA with Suggar, allowing for the simulation of moving objects and enabling the computation of moving hulls, rudders, etc. while maintaining good grid quality in the far-field. We show examples of high speed-flows exhibiting breaking bow and transom waves and a high-amplitude rolling surface combatant. High-speed ships are of increasing interest for diverse applications including fast commuter services, fast ferries, fast cargo ships, and fast combatants requiring innovative hull designs and propulsion systems. The method is demonstrated for two high-speed hulls showing overturning waves: the surface combatant DTMB 5512 and the R/V Athena patrol boat. Comparison of numerical results with measurements shows that the method is able to accurately simulate the overturning bow wave, resulting free-surface vortices, and boundary layer. Several splash-ups can be captured if the grid refinement is appropriate. Dynamic overset grids are demonstrated for a coupled pitching and heaving bare hull surface combatant at medium and high Froude numbers in head waves.