A novel local-variable-based transition-turbulence model for underwater boundary layers with temperature gradient effects

Accurate prediction of boundary layer transition and turbulence phenomena is fundamental for assessing drag, heat flux and flow noise in underwater vehicles. While transition-turbulence prediction models for air have made encouraging progress over the past few decades, advancements for water-based boundary layers have been comparatively sluggish, with existing models for air often being directly applied to water. However, these models become invalid in the presence of a temperature gradient in the water medium. This is due to the fact that, in contrast to air, the trend of the temperature effect on the flow stability characteristics of water boundary layer is completely reversed. To address this critical gap, this study proposes a local-variable-based transition-turbulence prediction model specifically tailored for underwater boundary layers. This model is developed upon the flow stability analysis and is compatible with modern computational fluid dynamics (CFD) techniques, including unstructured grids and massively parallel computing. Validation of the model is achieved by comparing its predictions with experimental data for zero-pressure-gradient flat plates, an adiabatic axisymmetric body of Power [(1977). Drag, flow transition, and laminar separation on nine bodies of revolution having different forebody shapes (Tech. Rep.). David W. Taylor Naval Ship Research and Development Center], and an axisymmetric body of Lauchle & Gurney [(1984). Laminar boundary-layer transition on a heated underwater body. Journal of Fluid Mechanics, 144, 79–101. https://doi.org/10.1017/S0022112084001518] with a heated wall. The results demonstrate that the proposed model provides accurate predictions of transition locations in underwater flows with or without temperature gradients. This work establishes a reliable and scientifically sound foundation for advancing drag reduction, noise mitigation, and flow control research of underwater vehicles.