Virtual reality aids understanding of fluid analysis results15 Mar, 2004 By: Kenneth M. Bryden Ph.D.
Virtual reality is beginning to have a major impact on engineering design by streamlining the process of converting analysis results into design solutions. Often, the person performing the analysis is not an expert on the design issues involved, while the engineers and customers who know the design best often have difficulty interpreting fluid flow results. Virtual reality can create a computer-generated world in which those who are not analysis experts can see the results in a context that they can easily understand. Even people who are familiar with interpreting analysis results can gain insights into the root causes of observed problems.
CFD (computational fluid dynamics) is a powerful tool that can determine fluid velocity, temperature, and other relevant variables for problems with complex geometries and boundary conditions. As part of the analysis, you can change the system geometry or the boundary conditions and view the effect on fluid flow patterns, temperatures, or the distributions of other variables. The ability of CFD to provide such complete information in much less time than would be required to build a physical prototype makes it the tool of choice for solving a wide range of design problems in the aerospace, automotive, power generation, chemical processing, and many other industries.
The most powerful CFD tools, such as FLUENT from Fluent (www.fluent.com), can analyze flow problems of great complexity within industrially relevant time scales. These flow problems include multiphase flows, complex combustion-related phenomena, intricate equipment geometries, and detailed, chemically reacting flowsThe question being asked now is not "What is CFD and how can it be used?" but "Why isn't CFD being applied to this flow problem?"The technical benefits to engineers and the financial benefits to managers are driving the phenomenal rise in the use of CFD, a trend that shows no sign of abating in the foreseeable future.
Traditional CFD postprocessing software requires users to interact with an analytical layer that focuses on manipulating model geometry relative to a fixed user position. This layer discourages discovery-analyst rely on previous knowledge to select views that show them what they expect to see. For the most part, the results are presented in isometric views that incorporate 2D section cuts. The analyst, who determines which section cuts are to be presented, is not often the best person to determine which ones are most important. Yet experts in the design or process, who are best suited to explore the analysis results, are often locked out by a user interface that prevents them from exploring anything other than the specific views of the data they are presented with.
VR's Working Environment
This obstacle can be overcome through the virtual reality experience. Virtual reality creates a safe and productive working environment in which to experience worlds too complex, too dangerous, or otherwise impossible or impractical to explore directly. Virtual reality enables close inspection of a component or activity whether the model is 50 meters high, as with a power boiler, or 5 mm wide, as with a channel in an electronic heat sink. The ultimate goal is to shift the user's mindset to focus purely on the problem with as little distraction as possible.
Figure 1. Top view flow through a reaction chamber.
True VR applications provide a first-person perspective in which you move around freely in a stationary virtual world. Simulator-style navigation in a virtual environment makes it easy to explore and discover unexpected but critical details about model behavior. Similarly, analytical tools and menus in a true virtual reality application need to be immersed in the environment so users can maintain focus on the problem at hand. A key aim of true virtual reality is to engage the human capacity for complex evaluation. A realistic visual experience activates creative, intuitive capabilities-the mind's eye. By creating a realistic experience from a computed simulation, and maintaining your focus within that experience, the fullest potential of human thought and skill can be brought to bear on the problem.
Figure 2. Flow in a mixing tank shows tightly packed starting points for animated streamlines beside a baffle.
How Real Is It?
Advances in affordable computing power and hardware now make fully immersive stereo cost effective and practical for routine use in many circumstances. However, more modest installations can also provide the benefits of virtual reality visualization. The more real a virtual world appears, the less distracted you are and the more discoveries you can make. VR environments can take many forms.
CFD Visualization Software
Software designed especially for visualizing CFD results is critical to the VR experience. Iowa State has had excellent results with Acuitiv visualization software from Fuel-Tech (www.acuitiv.com), which makes it possible to gain a quick, intuitive understanding of the critical flow, pressure, temperature, and species parameters that are driving a process. This understanding makes it possible to pinpoint flow characteristics in a fraction of the time required with traditional tools.
A basic but effective virtual reality experience is routinely accomplished with an ordinary, nonstereo monitor and standard desktop or workstation system. The CPU and graphics card performance on these systems now supports VR visualization, so high-performance machines are no longer a necessity. Computing power growth pushes through new milestones with predictable regularity. Recent breakthroughs in affordable high-performance graphics enable exciting new ways of handling complex and massive datasets.
Figure 3. Flow past a valve stem and seat.
You can add other hardware to augment the virtual reality experience. An emitter and a pair of stereoscopic glasses can enhance the sense of depth and realism of the VR world for under $300. A 3D input device such as the SpaceBall or SpaceMouse (3Dconnexion, http://www.3dconnexion.com/)lets you translate, rotate, and twist a ball or puck-shaped component on the device in the same way you would like to move inside the virtual world.
Projecting the virtual environment onto a wall provides a way to collaborate with customers. Designers can communicate visually what they have discovered and recommended to upper management for final decision-making and to customers for a greater probability of project approval and sale. Bringing the plant manager, the seasoned veteran, or the lead operator into the VR environment pays large dividends both in initial product design and final customer buy-in for the project.
Projectors for wall displays can support mono or stereo vision and use LCD or DLP technology. Companies such as FakeSpace Systems (formerly MechDyne Corp.; www.fakespace.com) provide a range of turnkey systems that include projectors and single or multiple screens in flexible configurations. Projection on multiple walls results in the creation of a VR theater, of which the CAVE, also from FakeSpace Systems, is a common example. Currently, the ultimate system is the six-sided, fully immersive VR environment in which several people can interact. Collaborative systems are also available so that people can interact in environments at multiple remote locations.
Head-mounted displays, boom-mounted devices, and VR 3-binoculars are all means by which a single user can explore a virtual world. These all work in roughly the same way. As you move the device, whether it's attached to your head or moved by controls, your perspective to the virtual world changes accordingly.
The VisionStation (elumens, www.elumens.com), the ImmersaDesk (FakeSpace), and other devices use a station format to present an enhanced virtual reality experience for multiple users. Other SE/VR resources include head-mounted displays, a Barco Baron stereo workbench, and access to an auditorium equipped for passive stereo-projection of one or multiple simulated environments on a 36' wide screen.
Iowa State's Solution
Companies that want to obtain the ultimate VR experience can work with facilities, such as the one at Iowa State, that provide a range of computing resources and interface devices such as the C6 (a 10' X 10' X 10' room with six display screens) and the C4-flex (a 12' X 12' X 9' room with four display screens that can also be configured as a 36' X 9' video display wall) where you are immersed in real-time stereo 3D image projections and full surround audio.
Figure 4. A tangentially fired boiler showing animated streamlines colored by velocity and isosurfaces of constant temperature.
Virtual reality-based engineering is emerging as a key technology to support scientific and industrial advancements in the 21st century. No other technology offers more potential for perfecting processes, improving products, reducing design-to-manufacturing cycle time, and cutting overall development costs. Without a powerful visualization tool, it's often difficult to recognize problems or inefficiencies. The virtual reality approach makes it possible to gain a quick, intuitive understanding of the critical flow, pressure, temperature, and species parameters that are driving a process.
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About the Author: Kenneth M. Bryden Ph.D.
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