Dissertation
Scale-resolving simulations of the Japan bulk carrier
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2026
Abstract
This thesis investigates the application of hybrid Scale-Resolving Simulation (SRS) methods for the prediction of ship resistance and turbulence characteristics, using the Japan Bulk Carrier (JBC) as the test case and CFDShip-Iowa as the computational framework. Simulations are performed at model scale (Re = 7.46 × 10⁶, Fr = 0.142), evaluating two code versions — V4.5 and V5.5 — across isotropic and anisotropic RANS formulations and scale-resolving approaches, with particular emphasis on the Improved Delayed Detached-Eddy Simulation (IDDES) methodology.The thesis establishes a systematic framework for assessing SRS capability, contributing to the JBC turbulence test case at the W2025 CFD Workshop on Ship Hydrodynamics. The overarching hypothesis is that accurate prediction of energy-containing-range macro scales, turbulence anisotropy, and organized oscillations requires sufficient resolution of the inertial subrange to simultaneously capture both the temporal and spatial Taylor micro- (λf) and macro- (Λf) scales. Based on the overall results of the JBC test case submissions, it is also hypothesized that a measure of accurate resolution of the Taylor macro and micro scales is that their spatial and temporal macro and micro estimates are in close agreement.
CFDShip-Iowa V4.5, employing a single-phase level-set interface formulation, demonstrates computational efficiency but overpredicts resistance by 12% in RANS and 36% in IDDES, whereas V5.5, incorporating a Volume-of-Fluid based two-phase formulation, corrects this deficiency and achieves improved resistance predictions of 5.83% (SST) and 7.34% (IDDES). This is attributed to insufficient pressure recovery in the wake, indicating the necessity of two-phase simulations to obtain improved resistance predictions. The dominant vortical structures are the primary Afterbody Vortex (ABV1), originating at x/L ≈ 0.9 through crossflow separation, and the secondary ABV2, originating on the propeller hub cap. IDDES predicts a larger reverse-flow separation bubble than RANS and resolves over 99% of the turbulent kinetic energy at the vortex cores as unsteady fluctuations. These resolved levels of turbulent kinetic energy (TKE) exceed both RANS predictions and experimental measurements, revealing an excess generation of resolved turbulence at the vortex cores that is consistent across both solver versions and is identified as the primary deficiency of the scale-resolving approach for this configuration.
The W2025 workshop results indicate that CFDShip-Iowa V4.5 is one of only three acceptable hybrid SRS submissions among nine entries. While isotropic RANS remains the most reliable and cost-effective tool for industrial applications, it lacks the fidelity to capture complex turbulence anisotropy and time-dependent oscillations. In contrast, hybrid SRS methods exhibit significant scatter and turbulence overprediction at vortex cores, suggesting they are not yet mature for routine use. To bridge this gap, a numerical benchmark is being developed in collaboration with the Shipbuilding Research Center of Japan (SRC), based on a Wall-Resolved LES (WRLES) method. Establishing this benchmark requires a standardized framework for demonstrating statistical convergence across refined grids and time steps, ultimately providing the reference data necessary to validate and improve hybrid scale-resolving models for ship hydrodynamics. While experiments remain indispensable in the near term as the primary validation reference for model-scale turbulence, CFD — and SRS in particular — represents the more realizable long-term framework for the comprehensive characterization of ship wake physics.
Future research will focus on carrying out additional analysis of the vortical structures of the current solutions and continuing the ongoing collaboration with SRC to improve the scale-resolving capabilities for ship hydrodynamics.
Details
- Title: Subtitle
- Scale-resolving simulations of the Japan bulk carrier
- Creators
- Christian Milano
- Contributors
- Frederick F. Stern (Advisor)Shanti Bhushan (Committee Member)George Constantinescu (Committee Member)Ching-long Lin (Committee Member)Cong Wang (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Mechanical Engineering
- Date degree season
- Spring 2026
- Publisher
- University of Iowa
- Number of pages
- xix, 169 pages
- Copyright
- Copyright 2026 Christian Milano
- Language
- English
- Date submitted
- 04/28/2026
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (page 157-169).
- Public Abstract (ETD)
Large cargo ships moving through water create complex swirling flow patterns around their hulls, particularly near the stern. These swirling structures, known as vortices, significantly influence how much fuel a ship consumes and how efficiently it moves through water. Understanding and predicting these flow patterns accurately is essential for designing more efficient and environmentally friendly ships.
This thesis investigates whether advanced computer simulations can accurately capture these complex flow patterns. Using the Japan Bulk Carrier — a standard cargo ship hull used in international workshops as a benchmark — two versions of a state-of-the-art simulation tool developed at the University of Iowa (CFDShip-Iowa V4.5 and V5.5) are evaluated and compared against experimental measurements from towing tank tests.
The results show that while standard simulation methods reliably predict overall ship resistance and large-scale flow features, capturing the fine details of turbulence — the chaotic, small-scale fluid motions that ultimately govern energy dissipation — remains a significant challenge. The study identifies the key limitations of current simulation approaches and proposes practical strategies to overcome them, including targeted improvements in computational grid resolution and turbulence modeling.
The findings of this thesis contribute to a roadmap for the development of simulation tools capable of replacing costly physical model testing, ultimately supporting the advancement of simulation capabilities for the design of cleaner, more fuel-efficient ships.
- Academic Unit
- Mechanical Engineering
- Record Identifier
- 9985177173102771
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