Modeling Breaking Ship Waves for Design and Analysis of Naval Vessels Challenge Project C1V

Abstract

One of the remaining challenges involved in modern Naval ship design and analysis is to account for the effects of breaking waves, spray and air entrainment on various performance measures of a surface ship. The near field flow about a surface ship is characterized by complex physical processes such as: (i) spray sheet and jet formation; (ii) strong free-surface turbulence interactions with (large-amplitude) breaking waves; (iii) air entrainment and bubble generation; and (iv) postbreaking turbulence and dissipation. The challenges associated with this task are twofold. The first is robustly simulating the large-scale problem of the near-field flow of an entire surface ship. The second is the development of physics-based closure models for steep breaking waves in the presence of turbulence. To wit, a two-pronged approach consisting of developing a strong foundation for closure model development and applying cutting-edge parallel computing capabilities has been developed to accurately simulate the free-surface flow around naval combatants which includes these phenomena. Using high-resolution direct numerical simulation of the Navier-Stokes equations using the level set method, we have successfully simulated an ensemble of unsteady breaking waves (currently 36) at Reynolds numbers O(10^3^4). This breaking-waves database includes both spilling and plunging breaking waves of varying intensity and is being used as a first step in evaluating closure models for inclusion in existing LES and off-the-shelf RANS capabilities. Using NFA (Numerical Flow Analysis), simulations of a gun-ship were performed at a range of speeds. The numerical results show wave overturning at the bow and flow separation at the transom. Air is entrained along the side of the hull and in the rooster-tail region behind the stern. This marks the first time that NFA has been used to simulate an entire ship hull. The numerical simulations were performed on the AHPCRC Cray T3E using 256 processors. Approximately, 90 million grid points were used in the simulation.