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Marine propellers operate in turbulent flows, presenting a significant challenge for numerical analysis and design. Conventional linear and potential flow theories have limitations in predicting turbulent flows. Viscous flow methods, though capable of handling turbulence by incorporating a turbulence model, are often computationally intensive. The primary objective of this dissertation is to develop an efficient viscous numerical solver for simulating turbulent flows around propellers. The VIScous Vorticity Equation (VISVE) numerical solver was previously developed to handle laminar flow problems. This dissertation aims to extend this solver to allow for turbulence modeling and cavitation. The focus is on implementing the k − ω SST turbulence model in both 2-D and 3-D versions of the VISVE solver. The turbulence model is discretized using the Finite Volume Method (FVM), and a hybrid OpenMP/MPI parallelization strategy is adopted to fully leverage High-Performance Computing (HPC) resources. The developed method is first applied to 2-D hydrofoils in turbulent flow, showcasing excellent agreement with predictions from a Reynolds-Averaged Navier-Stokes (RANS) solver. The influence of Reynolds number (Re) on vorticity, velocity, and turbulent viscosity is studied across a range of Re values. The turbulent VISVE model is also successfully applied to a hydrofoil with a cupped trailing edge, capturing turbulent separated flow at high Reynolds numbers. The method is then extended to 3-D analysis, demonstrating consistency with RANS solver results for infinitely long hydrofoils and rectangular wings. The turbulent VISVE solver is further employed to study propellers in turbulent flow, with a focus on a 5-bladed propeller (e.g., the NSRCD propeller 4381) under various loading conditions. In addition to investigating 2-D and 3-D turbulent flow scenarios, the 2-D solver is extended to address turbulent cavitating conditions. A pressure calculation scheme is proposed for 2-D turbulent and cavitating flow, and multiphase and cavitation models are implemented in the 2-D turbulent VISVE solver, using the mixture model. Scalability tests are conducted to optimize computational resources, enhancing the solver’s efficiency. Notably, the VISVE method offers advantages such as a significantly smaller computational domain and post-processing pressure calculation. Moreover, the computational grid size, unknowns, and computation time for the propeller system are significantly reduced by considering the effects of all other blades using the key blade’s solution from an earlier time step. Overall, this research contributes to the development of a robust and efficient numerical solver for simulating turbulent flows around hydrofoils and propellers. The implementation of turbulence models and parallelization strategies advances the understanding and analysis of turbulent propeller flows, with potential applications in marine propulsion design and performance analysis.

Fishes must swim effectively to perform many behaviors that are important for evolutionary fitness. So, understanding how a fish’s body morphology, mechanical properties, and movements combine to enable swimming can provide insight into the evolution of their present body forms. Here, I use physical models and experimental fluid dynamics to study the relationships between fish body properties and swimming performance. The first section of this dissertation centers on the contributions the body’s flexural stiffness makes to overall swimming performance. In my previous work, I found that many swimming and flying animals, including fishes, bend their bodies and appendages in a similar way during steady locomotion in part due to non-uniform flexural stiffness in their propulsive structures. In Chapter 1, I use a simple physical modeling system to isolate the effects of flexural stiffness from the complexity of a fish body. Using versions of the simple model with different flexural stiffnesses, I show that having non-uniform stiffness along the body length leads to faster, more efficient swimming. I extend these results in Appendix I, where I compare several tuna-tail-shaped models of different stiffnesses and find that certain combinations of stiffness and fish-like movements improves swimming ability. The findings indicate that the non-uniform physical properties of different components of a fish’s body are paramount for maintaining high overall swimming performance, and I hypothesize that fish may be controlling their body stiffness and movements to achieve performance benefits. In the second section of my dissertation, I focus on how the fish’s body interacts with the surrounding water to create swimming forces. In the past, our understanding of these interactions has been limited by the difficulty of measuring forces in a fluid medium. Therefore, in Chapter 2, I develop and validate new tools that allow me to estimate these forces at high spatial and temporal resolution using a pressure-based approach. I then apply these tools in Chapter 3 to describe how carangiform swimmers – fishes swimming using only their bodies and caudal fins and undulate only the posterior portion of the body at large amplitudes – generate swimming forces. I find that both positive and negative pressure contribute to thrust and drag. Further, in contrast to previous hypotheses, I find that carangiform fishes generate both thrust and drag along much of the length of their bodies in complex temporal patterns. I conclude by describing how subtle differences between different carangiform swimmers’ movements and body shape lead to significant differences in force production. Taken together, my results suggest that fishes may simultaneously use a variety of mechanisms to produce swimming forces, and identifies specific body features and movements which dictate swimming abilities. Future work will continue to explore the relationships between body morphology, material properties, and swimming abilities, and to apply this knowledge to critically evaluate existing frameworks of hypotheses linking fish morphology to specific habitats and ecological roles.

Modern ships are usually designed for a broad range of sea conditions. In particular,much of the effort during ship design is focused on reduction of ship roll due to rough sea. Ship roll has always been of significant concern as it largely affects the ship performance. In order to mitigate the detrimental effects of ship roll, many kinds of ship stabilization systems havebeen tried and tested. One such system that is currently investigated in this work is the active-fin ship stabilization system. It consists of a system of dynamically oscillating hydrofoils, responding to cancel ship roll by producing counter acting lift. Below the dynamic stall angle,the lift force produced by hydrofoils is proportional to angle of attack. So ship stabilization systems are often operated between large angles of attack. However, at large angle of attack, aregion of low pressure forms over the suction side of the hydrofoil. The low pressure results in localized increase in cavitation. Cavitation affects the performance of fin stabilization systems,and it is therefore necessary to study and understand the flow physics involving cavitation,occurring over on oscillating fin stabilizers. In this study, the active fin stabilization system issimplified to a 2D NACA0015 hydrofoil geometry, and the aperiodic fin oscillation is simplified to a periodic hydrofoil oscillation and, to stay close to reality, a near trapezoidal hydrofoil oscillation profile is used. The present work is a contribution to the numerical simulation of cavitating flows over 2D NACA 0015 stationary and oscillating hydrofoils. The primary objective of this research is to establish a methodology to accurately identify the onset of cavitation, andto study and quantify the deleterious effects of cavitation on performance. In order to investigate and quantify the detrimental effects of cavitation on the present ship stabilization system, the commercial flow solver FLUENT v6.3 is employed. A detailed formulation of the numerical model is described, and its application to simulate cavitating flow over stationary and oscillating 2D NACA 0015 hydrofoils is demonstrated. Validation studies for the turbulence viscosity modifications for the RNG k epsilon equation have been presented. For both thestationary and oscillating cases, good agreement between the predictions and measurements is obtained. Simulation of cavitating flow over stationary hydrofoils is carried out, to understand the different steady and unsteady cavitating regimes, and to identify an approximate cavitation inception angle. The scillating hydrofoil analysis is carried out using a dynamic hybrid grid where the boundaries of the outer domain are fixed, and the hydrofoil and the inner domain surrounding the hydrofoil oscillate periodically according to a prescribed profile non sinusoidal.A user defined function (UDF) is coupled with the flow solver to oscillate the hydrofoil with its prescribed oscillation profile. A comparative study on effects of grid topology, flow regime and cavitation has been carried out at 5 Reynolds numbers.