Unstructured Grid Analysis for Computational Fluid Dynamics

Fluid Dynamics Case Study

The Scientific Visualization Group at CIRA, the Italian Aerospace Research Center, founded in 1985, is a critical contributor to research analysis efforts. It has been developing visualization systems for several years based on traditional approaches using proprietary graphics libraries, the C programming language, and public domain user interface toolkits. Choosing AVS/Express as our development tool has been a real revolution, says Paolo Leoncini, head of Scientific Visualization Group.

We can now focus on real visualization problems rather than on rendering, data management, interaction, or portability as we build our end-user applications, said Leoncini. With AVS/Express, our products will offer an actual scientific added value by incorporating innovative data representations and visualization techniques, properly developed by experts that concentrate mostly on research. Furthermore, AVS will easily enable us to keep our product up-to-date with new computer architectures, graphics platforms, and with computer techniques, technologies, as well as trends such as Web integration.

AVS/Express is the Launch Pad for Future Visualization Systems

CIRA Scientific Visualization Group develops innovative techniques and tools to aid researchers and engineers in the Italian and European aerospace industries. Moreover the group supports end-users (both CIRA researchers and industrial users) with application-specific software integration that provides for computational modules, user interfaces and data analysis graphics, resulting in user-friendly simulation systems.

CIRA for a long time has offered two visualization systems for fluid flow analysis using multiblock structured grids, both based on Silicon Graphics GL routines. FLOVIS is a general purpose 3D visualizer that offers most of the data representations and visualization techniques useful to researchers and engineers in fluid dynamics and in other computational disciplines. NOVA is specialized in particle tracing (stream lines and streak lines). It has been developed to investigate collaborative visualization between remotely-located scientists.

The next generation of these products is being created using AVS/Express. With greater flexibility, they will serve a wide range of applications. For one, they will introduce use of unstructured grids in Computational Fluid Dynamics (CFD). Traditionally, unstructured grids are used in finite element analysis, and the number of grid nodes is relatively low. In CFD, the number of grid nodes is very high, usually exceeding millions.

ãThe new version of FLOVIS will be used by a number of disciplines, not just aerospace, Leoncini said. It will be used for structural analysis and for manufacturing process simulations using animation. Using AVS/Express allows quick verification of ideas in a pre-development stage. Thus, a developer can choose from a variety of approaches for application development. Application building becomes really flexible with powerful, low-level control system mechanisms. At the same time, AVS/Express allows us to assemble modules and design the user interface almost interactively. This shortens development time and lets us more easily maintain our application code, Leoncini said.

Creating Unique, Effective Comparisons

The initial AVS/Express-based visualization system for unstructured grids was released for use in early 1997. It includes a module for implementing the Line Integral Convolution (LIC) technique for displaying the flow field over a surface in a natural, experimental-looking appearance.

Future developments include the ability to visualize multiblock structured grids as well as photographic and infrared images acquired from wind tunnel tests. CIRA plans to implement a variety of processing techniques for grids and images, making the visualization system flexible enough for direct numerical-experimental comparisons.

With World Wide Web-aware features, AVS/Express lets the CIRA visualization system be the central component for the integration between the CIRA Numerical Wind Tunnel simulation system and CIRA several wind tunnels. It will also be part of a complex system to allow remote access to CIRA wind tunnels. This is similar to a US program where NASA and a consortium of companies participate remotely in experimental tests. With AVS/Express, we can do this easily by customizing configurations and applications to balance data transfers Leoncini said.

Car image with fine-tuned display of vortex forces. Region of interest selected.

Close-up view of the vortex area.

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