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Research > Fluid Dynamics

    Computational Fluid Dynamics
    Preservation of environment is indispensable for the realization of stable and comfortable human life. In the atmospheric environment, fluid turbulence plays an important role in the dispersion of contaminants. The turbulence phenomena are quite complex and their study is challenging. Recent technological developments have enabled us to holistically represent both the fine and large-scale turbulent flow structures on a computer by directly solving the Navier-Stokes equation, which expresses the first principle of fluid dynamics. This kind of computation refers to Direct Numerical Simulation (DNS). One group of the Holistic Computational Science Research Centre (HOLCS) has been conducting the largest class of DNS in the world.

    One of the world's largest Direct Numerical Simulation Under the present project, these activities will be extended, and DNS will be carried out for turbulent flows including the effects of system rotation and heat transfer, which are critical to the evaluation of atmospheric turbulence. Through the research, the relationships between flow velocity and the thermal fields, the characteristics of heat and mass transfer, and the influence of system rotation on the turbulent flow field will be clarified. The numerical data obtained will be analyzed, and used to calculate more practical problems. HOLCS maintains the DNS database that is open to the public access through its Web page. The database is used by researchers worldwide, accessed over 1000 times every year to compare their experimental and computational results, and to construct their turbulence models. Moreover, this database will contribute to the development of an environment simulation system in the present project.

    Water pollution in urban rivers and lake basins In urban rivers and lake basins, water pollution has been an environmental problem for a long time. Individual countermeasures for each river and lake in a city are not sufficient to overcome the water pollution. The contaminant generation, advection and diffusion processes in an environmental system will be investigated by holistically considering the "basin-river-lake" inter-connected environmental system. As part of the present project, a monitoring system for an urban river and lake will be constructed. Furthermore, through utilization of the environmental information as the input, a real-time prediction system for the urban river and lake environments will be established. Teganuma Lake and its related rivers are selected as the observation field. The data obtained through the field experiments will be open to the public on the Web site. The final purpose of this research is to contribute to the maintenance of a regional environment.

    Experiment and simulation of sand particle and dune movements in the Taklamakan desert

    Our university provides a research exchange agreement with the Xinjiang University in Xinjiangweiwuerz, China. The governmental region includes the Taklamakan desert. Over there, sand particle and dune movements cause severe environmental problems. Each sand particle moves or flies due to the interaction between the wind and the sand particle. As a result, a large-scale dune can shift downwind. To simulate the phenomena, a holistic approach is necessary. In the present project, through the cooperation between our university and the Xinjiang University, the critical velocity of sand movement, the relationship between wind and dune will be investigated. In addition, the large-scale sand movement, the generation, growth and movement of wind pattern in the sand and dune will be measured in field experiments. The sampling and analysis of sand particle movements at several points in the Taklamakan desert will also yield valuable insights. The wind effect on sand movements will be clarified experimentally, and a phenomenological model of wind and sand movement will be developed. The model will be modified, comparing the numerical results with the field observations. Furthermore, comparing the large-scale simulation with the field observations, we aim to generate a practical prediction and thus to provide protection against dune movements.

    Molecular dynamics is very effective in a number of flow phenomena. Flow phenomenon for which surface tension is dominant is a typical example of representing the interaction between microscopic fluid particles affects macroscopic behavior. Surface tension-induced flow plays an important role in material processing. The present project focuses on Marangoni convection, induced by surface tension, and the contact line formed among the solid, liquid and gas interface. Holistic simulations will be carried out by adopting the molecular dynamics approach as well as the macroscopic method using Navier-Stokes equations. Furthermore, by simultaneously conducting fundamental experiments, an advanced simulation methodologies will be verified. To our further understanding of surface-tension induced flow, we are going to take part in an International Space Station micro-gravity experiment, which targets surface tension- induced flow. Integrating these results, we will contribute to the understanding of surface-tension induced flows for the production of new thin film and other novel materials.

    A great amount of research on environmental comfort is being performed worldwide. However, although much research has been conducted on thermal environments, there have been few studies of acoustic environments. Sound is transferred to all persons in a spatial domain, and thus information transferred in this manner is quite different from that by paper-based or electric media. This is preferable in some cases, but not in other cases. In the present project, we develop a new technology to transfer acoustic information to a selected person in a spatial domain, and work to realize a more acoustically comfortable and convenient environment. For example, this technology would enable us to transfer different sounds to each person in a classroom, a sickroom, a car compartment, and so on. To establish the technology, holistic simulations for three-dimensional acoustic fields are to be conducted. In such simulations, we have to consider the geometries, dimensions, arrangements, surface characteristics and material of every object in the environment. Moreover, by performing the reference experiments in parallel, we will verify and establish the new technology.