Exploring Turbulent Wakes in a Non-Uniformly Stratified Environment for Submarine Detection

• Ano de defesa: 2022
• Autor(a) principal: Nadaf, Elias de Castro
• Orientador(a): Timour Radko
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Naval Postgraduate School (NPS), Monterey, EUA
• Palavras-chave em Português: wake dynamics; non-linear stratification; kinetic energy; thermal energy; dissipation rate of kinetic energy; dissipation rate of thermal variance; epsilon parameter; chi parameter; variations in temperature field; numerical modeling; openfoam; submarine detection; no acoustic means detection; internal waves reflection; Froude number; high-resolution numerical simulation; wake core position
• Link de acesso: https://www.repositorio.mar.mil.br/handle/ripcmb/846481

This study aims to explore the behavior of turbulent wakes generated by a spherical submerged body propagating with constant speed in a non-uniformly stratified fluid. The investigation is based on a series of high-resolution numerical simulations in which the background stratification is systematically varied. We consider one linear and five non-linear temperature profiles and two sets of Froude numbers (Fr), Fr = 1.0 and Fr = 3.2. The analysis of dissipation of thermal variance (χ) shows that the shape of the wake for non-uniform profiles is more horizontally spread, and internal waves are much stronger than in linear stratification. Experiments with Fr = 1.0 show a rather asymmetric energy distribution caused by internal wave reflections from low-gradient regions. An idealized model demonstrates that internal waves emitted at horizontal angles shallower than roughly 64 degrees are reflected. For Fr = 3.2, internal waves are radiated at steeper angles and transmitted more. Using decay rates of χ, the maximum detection time of the wake can be estimated, showing that for Fr = 3.2, the thermal signal lasts four to five times longer than for Fr = 1.0. Furthermore, concave profiles produce signals lasting approximately twice as long as those for linear profiles, whereas low-gradient types have half the duration. This research is expected to assist in the development of non-traditional detection algorithms for undersea warfare.