Design and Analysis of Low Reynolds Number Marine Propellers with Computational Fluid Dynamics (CFD) Transition Modeling

Small-scale marine propellers operate at low Reynolds numbers, where laminar-turbulent transition of the boundary layer can impact the distributions of pressure and shear stress on the blade surface. Marine propellers operating at low Reynolds numbers are subject to laminar-turbulent transition of the boundary layer, which impacts the distributions of pressure and shear stress on the blade surface. To design efficient propellers for operation at low Reynolds numbers, transitional effects must be included in the evaluations of propeller performance. In this work, transition modeling techniques in Reynolds Averaged Navier-Stokes computational fluid dynamics (RANS CFD) are utilized to evaluate and design propellers operating at low Reynolds numbers. The Galilean invariant γ transition model with an extension for crossflow transition is coupled to the SSG (Speziale, Sarkar, Gatski) /LRR (Launder, Reece, Rodi) -ω Reynolds stress transport turbulence model, with validation cases performed for flate plate boundary layers, 2-dimensional airfoils, a 3-dimensional wing, and 6:1 prolate spheroids. The performance of the coupled SSG/LRR-ω-γ Reynolds stress transition model for propellers with flow transition is then evaluated using experimental surface streamline and force data from four model-scale marine propellers. A method for the design of low Reynolds number marine propellers is presented using a transition-sensitive lifting line method coupled with the panel method code XFOIL. Initial geometries generated using the lifting-line method are then optimized in RANS CFD using the 2 equation γ-Reθ transition model and an adjoint method to warp the propeller shape to improve the efficiency. Two design studies are performed, including an open water propeller, and a propeller designed for a small autonomous underwater vehicle.