Teaching:TUW - UE InfoVis WS 2007/08 - Gruppe 02 - Aufgabe 1 - Flow Visualization: Difference between revisions

Latest revision as of 15:01, 25 November 2009

Flow visualization is a process of making the physics of fluid flows visible in oder to analyse it.

Definition[edit]

To be able to recognize the motion of the fluid, one must therefore provide a certain technique by which the flow is made visible. Such methods are called flow-visualization techniques.

[Merzkirch, 1987]

Overview[edit]

Flow visualization is a modern technique to visualize motions and patterns of mostly invisible fluids, e.g. gas, air or water. Main target is to make flows in a specific context visible so that it can be analyzed.

Although the basic task for flow visualization is revealing the flow within fluids, it may offers an additional benefit. It does not only make flows visible, it can also be used as a method for simulating flows and the interaction of objects within fluids. So it is also a simulation technique and therefore, it can be classified as a method for Scientific Visualization.

Application areas for flow visualization are e.g. in aviation, aqua- or aerodynamic.

In fact, there are several ways how to do this. Generally we can divide into two main classes of methods:

Physical methods[edit]

Physical methods are an experimental approach on flow visualization. Basically these techniques can further be divided into three groups [Löffelmann, 1998]:

Adding foreign material

These methods work by adding small particles, e.g. smoke or oil, to the fluid to make it visible. Figure 1 gives an example for using smoke in a wind tunnel.

Optical techniques

These methods work e.g. with the refraction of the light or by working with light beams, where images with shadows and caustics indicate flows.

Adding heat or energy

These methods use e.g. gas, where the molecules have been excited by shooting electrons at them, to visualize motion patterns.

The main disadvantage of physical methods is that these techniques require a test system (e.g., a wind tunnel) and therefore, may be limited by physic constraints (e.g., the size of the tunnel) and costs.

Computational methods[edit]

In contrast to physic methods, the motion of fluids can also be expressed by mathematical equations which can be estimated numerically. Thus even supercomputers would take a long time to solve the equations and the solution would only be an estimation of the definite problem, more accurate methods needed to be discovered.

One approach is to discretize the spatial domain into small cells so every single cell can be computed separately. Using this method one gets a mesh grid of the definite fluid motion. Figure 2 shows how such a mesh grid looks like in practice. NASA is testing complex scenarios of its space shuttles like return-to-launch-site and transatlantic abort maneuvers by the use of computational fluid dynamics. The image shows the surface pressure distribution at the speed of Mach 15. Figure 3 shows another shape of how computers can be used for flow visualization.

References[edit]

[Merzkirch, 1987] Wolfgang Merzkirch. Flow Visualization, Second Edition. Academic Press Inc. Ltd., London, 1987.
[Devenport and Hartwell, 2006] W.J. Devenport and W.L. Hartwell, Experiment 1 - Flow Visualization. Last modified at: December 20, 2006. Retrieved at: November 9, 2007. http://www.aoe.vt.edu/~devenpor/aoe3054/manual/expt1/index.html.
[Löffelmann, 1998] Helwig Löffelmann , Visualizing Local Properties and Characteristic Structures of Dynamical Systems, Created at: November, 1998. Retrieved at: November 5, 2009 http://www.cg.tuwien.ac.at/~helwig/diss/

@@ Line 1: / Line 1: @@
-== Brief definition ==
+Flow visualization is a process of making the physics of fluid flows visible in oder to analyse it.
-{{Quotation|TextTextTextTextTextTextText|[Author, Year]}}
-== What is flow visualization? ==
+== Definition ==
-As we are human beings who live on earth, we are familiar with all the elements and forces that affect our lives constantly. Thus most of us roughly know some things about fluids too. Everyone has at least once seen how water whirls in a bathtub when it runs out or how wind blows leaves around in autumn forming kind of a small vortex. We all know pictures of a cloud formed like a mushroom after the explosion of an atomic bomb. Obviously we are acquainted with the flow of fluids though we can’t actually see many of them because they are transparent, i.e. air, water or gas. We do also know how to describe the fluid motion by mathematical equations but the problem is that these are far too difficult to be computed by humans. We can only try to solve these equations via using numerical calculators, i.e. very fast computer algorithms. But even the numerical results are only estimations and may not correspond to natural processes until they have been approved by physical experiments. So, in order to understand what is going on we need to find ways to make visible what cannot be actually perceived by the human eye.
+{{Quotation|To be able to recognize the motion of the fluid, one must therefore provide a certain technique by which the flow is made visible. Such methods are called flow-visualization techniques.|[Merzkirch, 1987]}}
+== Overview ==
+Flow visualization is a modern technique to visualize motions and patterns of mostly invisible fluids, e.g. gas, air or water.
+Main target is to make flows in a specific context visible so that it can be analyzed.
+Although the basic task for flow visualization is revealing the flow within fluids, it may offers an additional benefit. It does not only make flows visible, it can also be used as a method for simulating flows and the interaction of objects within fluids. So it is also a simulation technique and therefore, it can be classified as a method for [[Scientific Visualization]].
+Application areas for flow visualization are e.g. in aviation, aqua- or aerodynamic.
-In fact, there are several ways how to do this. Generally we can divide into two main methods:
+In fact, there are several ways how to do this. Generally we can divide into two main classes of methods:
 [[Image:e398-inflatable.jpg|right|thumb|150px|Figure 1]]
 [[Image:2-01-AERO-Papodopoulos.jpg|right|thumb|150px|Figure 2]]
 [[Image:HyFish.jpg|right|thumb|150px|Figure 3]]
-* Physical method. By the use of wind in a tunnel combined with small particles, i.e. smoke, oil, etc. one can make the motion of a fluid, i.e. air visible. Figure 1 shows how such a windtunnel works. From a definite source wind is imitated by fans and directed at the airfoil. In this case small smoke particles are used to make the flow of the air visible. We can actually perceive how the air moves around the airfoil and forms vortices at the bottom and the back of it. These method is very useful in designing aircrafts and especially airfoils.
+=== Physical methods===
-* Computational method, i.e. computational fluid dynamics. As already mentioned above, the motion of fluids as a whole can be expressed by mathematical equations which can be estimated numerically. Thus even supercomputers would take a long time to solve the equations and the solution would only be an estimation of the definite problem, more accurate methods needed to be discovered. One approach is to discretize the spatial domain into small cells so every single cell can be computed separately. Using this method one gets a mesh grid of the definite fluid motion. Figure 2 shows how such a mesh grid looks like in practice. NASA is testing complex scenarios of its space shuttles like return-to-launch-site and transatlantic abort maneuvers by the use of computational fluid dynamics. The image shows the surface pressure distribution at the speed of Mach 15. Figure 3 shows another shape of how computers can be used for flow visualization. With an accurate software packet, i.e. FieldView, streamlines around a solid surface can be computed virtually without the use of a windtunnel.
+Physical methods are an experimental approach on flow visualization. Basically these techniques can further be divided into three groups [Löffelmann, 1998]:
+* Adding foreign material
+:These methods work by adding small particles, e.g. smoke or oil, to the fluid to make it visible. Figure 1 gives an example for using smoke in a wind tunnel.
+* Optical techniques
+:These methods work e.g. with the refraction of the light or by working with light beams, where images with shadows and caustics indicate flows.
+* Adding heat or energy
+:These methods use e.g. gas, where the molecules have been excited by shooting electrons at them, to visualize motion patterns.
+The main disadvantage of physical methods is that these techniques require a test system (e.g., a wind tunnel) and therefore, may be limited by physic constraints (e.g., the size of the tunnel) and costs.
+=== Computational methods ===
+In contrast to physic methods, the motion of fluids can also be expressed by mathematical equations which can be estimated numerically. Thus even supercomputers would take a long time to solve the equations and the solution would only be an estimation of the definite problem, more accurate methods needed to be discovered.
+One approach is to discretize the spatial domain into small cells so every single cell can be computed separately. Using this method one gets a mesh grid of the definite fluid motion. Figure 2 shows how such a mesh grid looks like in practice. NASA is testing complex scenarios of its space shuttles like return-to-launch-site and transatlantic abort maneuvers by the use of computational fluid dynamics. The image shows the surface pressure distribution at the speed of Mach 15. Figure 3 shows another shape of how computers can be used for flow visualization.
-== Definition ==
-{{Quotation|The insight into a physical process is always improved if a pattern, produced by or related to this process, can be observed by visual inspection. This becomes obvious if we think of a fluid-mechanical process where a fluid is flowing in a channel or around a solid obstacle. By observing such a flow pattern, which might be stationary or variable with time, one can get an idea of the whole development of the flow. However, most fluids, gaseous or liquid, are transparent media, and their motion remains invisible to the human eye during a direct observation. To be able to recognize the motion of the fluid, one must therefore provide a certain technique by which the flow is made visible. Such methods are called flow-visualization techniques.|[Merzkirch, 1987]}}
-{{Quotation|In general, flow visualization is an experimental means of examining the flow pattern around a body or over its surface. The flow is "visualized" by introducing dye, smoke or pigment to the flow in the area under investigation. The primary advantage of such a method is the ability to provide a description of a flow over a model without complicated data reduction and analysis.|[Devenport and Hartwell, 2006]}}
 == References ==
 *[Merzkirch, 1987] Wolfgang Merzkirch. ''Flow Visualization, Second Edition''. Academic Press Inc. Ltd., London, 1987.
 *[Devenport and Hartwell, 2006] W.J. Devenport and W.L. Hartwell, Experiment 1 - Flow Visualization. Last modified at: December 20, 2006. Retrieved at: November 9, 2007. [http://www.aoe.vt.edu/~devenpor/aoe3054/manual/expt1/index.html http://www.aoe.vt.edu/~devenpor/aoe3054/manual/expt1/index.html].
+* [Löffelmann, 1998] Helwig Löffelmann , Visualizing Local Properties and Characteristic Structures of Dynamical Systems, Created at: November, 1998. Retrieved at: November 5, 2009 http://www.cg.tuwien.ac.at/~helwig/diss/
 == External Links ==
 *[http://en.wikipedia.org/wiki/Flow_visualization http://en.wikipedia.org/wiki/Flow_visualization]
 *[http://en.wikipedia.org/wiki/Computational_fluid_dynamics http://en.wikipedia.org/wiki/Computational_fluid_dynamics]
+*[http://www.ilight.com/ FieldView, a software for simulating, streamlines around a solid surface]