Three-dimensional effects on flag flapping dynamics ; [and], Study and modeling of incompressible highly variable density turbulence in the bubbly wake of a transom stern

[摘要] Part II: Accurate prediction of the highly mixed flow in the near field of a surface ship is a challenging and active research topic in Computational Ship Hydrodynamics. The disparity in length and time scales recognizes the importance of accurate bubble source and mixed-phase flow models; whereas the current state of the art models are adhoc at best. Second part of the thesis details the air entrainment characteristics in the incompressible highly variable density turbulent flow-field behind a canonical stern with the inclusion of simple speed/geometry/Reynolds number effects. Using high-resolution two-phase flow data sets generated from high fidelity simulations of a canonical stern simulated down to the scales of bubble entrainment. The study details key variables for: (i) characterization of wake structure, near-wake air entrainment and the nature of incompressible variable density turbulence, underlining the major implications and dominant terms by studying the dynamics of the continuity equation, the momentum equation, the density variance equation, the turbulent mass flux and the turbulent kinetic energy; (ii) the role of non-Boussinesq effects and turbulent mass flux in the wake of the stern, identifying the breaking event to be related to the air-entrainment and subsequent generation of turbulent mass flux and establishing the density intensity as an effective metric; (iii) develop and a priori validate novel multiphase models for turbulent mass flux and turbulent kinetic energy using gradient hypothesis and measuring the model performance for varied geometry/speed/Reynolds number effects. The first part of the thesis advances our understanding in varying applications ranging from the biomechanics of snoring, to improving novel designs for flow energy harvesters. The second part presents a methodology, using high-fidelity simulations coupled to physics-based parameterization of near-field air entrainment about surface ships to help improve mixed-phase turbulent flow models in Computational Ship Hydrodynamics.

[发布机构] Massachusetts Institute of Technology