Boundary layer transition models for CFD: contributions to naval hydrodynamics applications

Boundary layer transition is a complex phenomenon that involves multiple physical mechanisms. In naval hydrodynamics applications, it can have considerable effects on skin friction, noise, propulsion efficiency, and maneuverability, especially for model-scale experiments and small craft operating at moderate Reynolds numbers.

This thesis presents three main contributions: a) implements several boundary layer transition models into the computational naval hydrodynamics code REX, and investigates capabilities and limitations to solve several canonical and naval hydrodynamics problems, b) recalibrates and improves the crossflow model to extend the range of conditions in which it works, and c) adds a roughness model to the recalibrated crossflow transition model, validates it and demonstrates for a model scale generic submarine.

The implemented transition models are added to one- and two-equation Reynolds-Average Navier-Stokes (RANS) turbulence models. Extensions to consider the effect of surface roughness, which can simulate boundary layer tripping in model-scale calculations, are also included. Extensive validation is conducted for 2- and 3-dimensional geometries against experimental data.

Simulation results presented show that the accuracy of each model is highly dependent on the mechanism involved in the transition. Since it is unlikely that a single model can cover all transition mechanisms, knowledge on the specific mechanism of interest for a naval hydrodynamic application is required, and recalibration and modification of the models are proposed. These modifications are then applied to a relevant case, the computation of straight and static drift self-propulsion of the generic submarine Joubert BB2 in model scale.