University of Idaho - Research Portal

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The thesis of this paper is that cavitation in hydraulic spool valves involves large-scale vortical structures in an unsteady submerged jet. Current computational fluid dynamics approaches do not accurately predict these unsteady vortices, nor do they properly account for bubble-dynamics/flow-structure interactions. The large eddy simulation turbulence model was considered to overcome these deficiencifes. First, a commercial code was applied to study cavitation in a model spool valve, addressing the effects of including a cavitation model and the large eddy simulation turbulence model. Second, a research code was developed to study the effect of cavitation inception on vortex dynamics in a submerged planar jet. A previously developed cavitation model, which accounts for interactions between large-scale vortical structures and cavitation bubbles, was employed. Results were obtained which demonstrate that even low levels of cavitation have significant effects on the jet vortex dynamics, including vortex intensification and splitting. An analysis of the vorticity transport equation reveals the underlying mechanisms behind these effects.

SBD for ship hydrodynamics merges traditional fields of resistance and propulsion, seakeeping, and maneuvering, which with inclusion of environmental effects will revolutionize the design process and offers possibility for innovative out-of-the box concepts for future ships to meet the challenges of the 21st century. Development of SBD involves a new paradigm for hydrodynamics research in which CFD, EFD, UA are conducted simultaneously for benchmark geometries and conditions using an integrated approach along with optimization methods, all of which serve as internal engine guaranteeing simulation fidelity. Present paper describes research at IIHR in major components of SBD for ship hydrodynamics through overview the status of their application to traditional fields and future directions. Prognosis for realization practical applications is also discussed. 1. INTRODUCTION Rapid advancements in simulation technology are revolutionizing engineering practice, including ship design, as simulation-based design (SBD) and ultimately virtual reality are replacing current reliance on experimental observations and analytical methods. It is not unreasonable to expect a major shift in how scientific method forms its basis of conceptual truth, a shift from reliance on observations, based on experiments, to reliance on logic, based on simulation with profound similarities and differences to transition from Aristotelian to Galilean scientific methods, as occurred in 16th-18th centuries. SBD covers a broad range from computerized systems to solutions of physics based.

NOTE: Also presented at 8th International Conference on Numerical Ship Hydrodynamics (Busan, Korea, 2003)

Teaching modules for complementary computational and experimental fluid mechanics and uncertainty analysis were developed to integrate simulation technology into undergraduate engineering courses and laboratories. Engineering faculties from a range of public and private universities and the software partner Fluent, Inc. have collaborated to develop, implement, evaluate, and disseminate web-based teaching modules utilising simulation technology based on further development of the commercial software, FlowLab. The first two years' formative and summative student evaluation data identified successful leaning outcomes, as well as strategies for improvement, including the need for an efficient, hands-on, 'computational fluid dynamics educational interface' to better simulate engineering practice.

Development, implementation, and evaluation are described of hands-on student experience with complementary CFD educational interface and EFD and uncertainty analysis (UA) for introductory fluid mechanics course and laboratory at The University of Iowa, as part of a three-year National Science Foundation sponsored Course, Curriculum and Laboratory Improvement - Educational Materials Development project. The CFD educational interface is developed in collaboration with faculty partners from Iowa State, Cornell and Howard universities along with industrial partner FLUENT Inc. and designed to teach CFD methodology and procedures through interactive implementation that automates the “CFD process” following a step-by-step approach. Predefined active options for students’ exercises use a hierarchical system both for introductory and advanced levels and encourages individual investigation and learning. Ideally, transition for students would be easy from advanced level to using FLUENT or other industrial CFD code directly. Generalizations of CFD templates for pipe, nozzle, and airfoil flows facilitate their use at different universities with different applications, conditions, and exercise notes. Complementary EFD laboratories are also developed. Classroom and pre-lab lectures and laboratories teach students EFD methodology and UA procedures following a step-by-step approach, which mirrors the “real-life” EFD process. Students use tabletop and modern facilities such as pipe stands and wind tunnels and modern measurement systems, including pressure transducers, pitot probes, load cells, and computer data acquisition systems (Labview) and data reduction. Students implement EFD UA and use EFD data for validation of CFD and AFD results. Students analyze and relate EFD results to fluid physics and classroom lectures. The laboratories constitute 1 credit hour of a four credit hour 1 semester course and include tabletop kinematic viscosity experiment focusing on UA procedures and pipe and airfoil experiments focusing on complementary EFD and CFD for the same geometries and conditions. The evaluation and research plan (created in collaboration with a third party program evaluation center at the University of Iowa), focuses on exact descriptions of the implementations, especially as experienced by the students. Also discussed are conclusions and future work.

Development described of an educational interface for hands-on student experience with computational fluid dynamics (CFD) for undergraduate engineering courses and laboratories. Project part of a three-year National Science Foundation sponsored Course, Curriculum and Laboratory Improvement - Educational Materials Development project with faculty partners from colleges of engineering at Iowa, Iowa State, Cornell and Howard universities along with industrial (commercial CFD code) partner FLUENT Inc, including complementary experimental fluid dynamics and uncertainty analysis. The design of the educational interface teaches students CFD methodology (modeling and numerical methods) and procedures through interactive implementation that automates the CFD process following a step-by-step approach. The CFD process mirrors actual engineering practice: geometry, physics, mesh, solve, reports, and post processing. Predefined active options for students’ exercises use a hierarchical system both for introductory and advanced levels and encourages individual investigation and learning. Ideally, transition for students would be easy from advanced level to using FLUENT or other industrial CFD code directly. Generalizations of CFD templates for pipe, nozzle, and airfoil flows facilitate their use at different universities with different applications, conditions, and exercise notes. Implementation based on results from site testing at faculty partner universities for an introductory fluid mechanics course at Iowa, for aerodynamics and gas dynamics laboratory courses at Iowa State, for a required fluid mechanics sequence at Cornell, and for an aerodynamics course at Howard. The evaluation and research plan (created in collaboration with a third party program evaluation center at the University of Iowa) is described, which focuses on exact descriptions of the implementations of the new interface at partner sites, especially as experienced by the students, including preliminary data on immediate student outcomes as documented from site testing for Fall 2003. Also discussed are conclusions and future work.

Flow over an Ahmed body is a key benchmark case for validating the complex turbulent flow field around vehicles. In spite of the simple geometry, the flow field around an Ahmed body retains critical features of real, external vehicular flow. The present study is an attempt to implement such a real life example into the course curriculum for undergraduate engineers. FlowLab, which is a Computational Fluid Dynamics (CFD) tool developed by Fluent Inc. for use in engineering education, allows students to conduct interactive application studies. This paper presents a synopsis of FlowLab, a description of one FlowLab exercise, and an overview of the educational experience gained by students through using FlowLab, which is understood through student surveys and examinations. FlowLab-based CFD exercises were implemented into 57:020 Mechanics of Fluids and Transport Processes and 58:160 Intermediate Mechanics of Fluids courses at the University of Iowa in the fall of 2004, although this report focuses only on experiences with the Ahmed body exercise, which was used only in the intermediate-level fluids class, 58:160. This exercise was developed under National Science Foundation funding by the authors of this paper. The focus of this study does not include validating the various turbulence models used for the Ahmed body simulation, because a two-dimensional simplification was applied. With the two-dimensional simplification, students may setup, run, and post process this model in a 50 minute class period using a single-CPU PC, as required for the 58:160 class at the University of Iowa. It is educational for students to understand the implication of a two- dimensional approximation for essentially a three-dimensional flow field, along with the consequent variation in both qualitative and quantitative results. Additionally, through this exercise, students may realize that the choice of the respective turbulence model will affect simulation prediction.