Kroll, Thomas2023-02-162023-02-162022-12https://hdl.handle.net/11299/252535University of Minnesota Ph.D. dissertation. December 2022. Major: Aerospace Engineering and Mechanics. Advisor: Krishnan Mahesh. 1 computer file (PDF); xxiii, 142 pages.Maneuvering marine vehicles are often characterized by high Reynolds numbers ($Re$) and complex geometries with the propeller being an essential component. Studying marine propeller flows computationally or experimentally, requires overcoming the challenges presented by the high Reynolds number and the complex geometries. This dissertation is the first application of a novel unstructured overset method developed by \citet{WyattAssembly,WyattMethod} to perform large-eddy simulation (LES) of marine propeller flows. This method enables experimentally validated LES that provides insight into multiple aspects of propeller flows. First, water tunnel interference effects for a marine propeller in both design conditions or forward mode and the off-design condition known as crashback are investigated. Next, the complex, unsteady flow field and resulting loads of a ducted propeller in crashback are deciphered and elucidated. And lastly, the complex vortex interactions in the blade tip region of a ducted propeller in the forward mode of operation are investigated. Past experiments by \citet{jessup2004, jessup2006} studied the marine propeller David Taylor Model Basin (DTMB) 4381 in the open jet test section of the 36-inch variable pressure water tunnel (VPWT). In this dissertation, we perform large-eddy simulation (LES) at design conditions (advance ratio $J=0.889$) and propeller diameter based Reynolds number $Re=894,000$ including the VPWT geometry, and demonstrate that interference effects are negligible. In crashback, we explain the significant discrepancy that exists between the mean propeller loads from the VPWT and open-water towing tank (OW) experiments by \citet{ebert_2007}. We perform LES at $Re=561,000$ and advance ratios $J=-0.50$ and $-0.82$ with the VPWT geometry and compare to an unconfined case at $Re=480,000$ and $J=-0.50$. Comparison of the LES to the experiments shows good agreement. The water tunnel interference effects responsible for the discrepancy are identified and delineated. It is demonstrated that these effects resemble those of a symmetric solid model or bluff body. Two primary interference effects are identified: solid blockage due to jet expansion and nozzle blockage due to proximity to the tunnel nozzle. Though theoretical correction methodologies exist for forward mode, the impact of interference effects in crashback varies with $J$, as solid blockage increases for higher $|J|$ while nozzle blockage increases for lower $|J|$, complicating the possibility of a generalized theoretical correction. Crashback flow of a ducted marine propeller presents a complex, unsteady flow field with resultant unsteady loads. LES results for the marine propeller David Taylor Model Basin (DTMB) 4381 with a neutrally loaded duct are compared to experiments, showing good agreement. The simulations are performed at the propeller diameter based Reynolds number $Re=561,000$ and an advance ratio $J=-0.82$. The complex flow field around the different components (duct, rotor blades, and stator blades) and their impact on the unsteady loading are examined. The side-force coefficient $K_S$ is mostly generated from the duct surface, consistent with experiments. The majority of the thrust and torque coefficients $K_T$ and $K_Q$ are found to arise from the rotor blades. A prominent contribution to $K_Q$ is also produced from the stator blades. Tip-leakage flow between the rotor blade tips and duct surface is shown to play a major role in the local unsteady loads on the rotor blades and duct. The physical mechanisms responsible for the overall unsteady loads and large side-force production are identified as globally, the vortex ring and locally, leading-edge separation as well as tip-leakage flow which forms blade-local recirculation zones on the duct surface. The flow of a ducted propeller in forward mode is often characterized by complex vortex interactions of the tip-leakage vortex (TLV) and trailing-edge vortex (TEV). The resulting tip-vortex interactions that occur downstream of the propeller blade tips have been shown to be essential to the flow phenomenon known as cavitation. To study these vortex interactions, two geometrically similar three-bladed propellers P5407 (smaller) and P5206 (larger) were studied in the experiments by \citet{judge2001tip,chesnakas2003tip,Oweis_TL_1,Oweis_TL_2} at different propeller tip Reynolds numbers. LES is used to study these complex interactions for a ducted marine propeller P5407 at an advance ratio $J=0.98$ and tip Reynolds number $Re_{tip}=1.4\times 10^6$. Good agreement is obtained with the experiment for loads and velocity field. Matching the experimental configuration and boundary conditions is shown to be essential for proper validation. Sensitivity of propeller loads to duct inflow is demonstrated. The TEV is found to be composed of co and counter-rotating small-scale vortices and is not coherent enough to be identified by low-pressure regions. The TLV is revealed to interact with the duct wall boundary layer, inducing upstream, secondary, and counter-rotating vortices. The interaction and merger of these vortices with the TLV forms a complex flow field with increased unsteadiness and pressure fluctuations past $50\%$ chord length downstream of the blade tip, supporting the observations of downstream cavitation inception in the experiments.enThesis or Dissertation