This Guidebook is a work in progress. Complete draft expected Fall 2023. Comments welcome
Both science and art are fundamentally based in our perception of the world around us. In science, clear observations lead to understanding, particularly in physics, which is a prerequisite to successful engineering. In art, creating and influencing perception of the work, whatever it may be, is the whole point. Art may also be defined as an execution of a vision — an instantiation of an idea, ‘making it so’. In this guidebook, accompanying the Flow Vis course, we will focus on making the physics of fluid flow more available to perception — specifically, in a word, visible. You may find in reading this text that your perception of fluid flow in everyday life is sharpened. In the process we will be creating both art and science.
Flow visualization is particularly suited to the interface between art and science. Many fluid physicists are motivated not only by the important scientific and engineering goals of their work, but also by a visceral fascination with their subject. That fascination is reflected in several (scientific) venues for displaying of fluid flow art. Foremost among these venues is the Gallery of Fluid Motion , a poster and video competition which is held in conjunction with the American Physical Society Division of Fluid Dynamics (APS-DFD) annual fall meeting. Gallery entries are judged “based upon criteria of scientific merit, originality, and artistry/aesthetic appeal.” (Some winners were works from this course.) Additional examples include the seminal Album of Fluid Motion , which can be found on the bookshelf of nearly every fluid dynamics researcher, and the popular blog FYFD , which celebrates all aspects of fluids, including their beauty. In each of these examples, the sheer beauty of fluid flow is revealed and, to some extent, acknowledged. With this course I hope to encourage engineering students to gain a deeper perception of fluid flow by capitalizing on this aesthetic and creative motivation for doing science, that is, for aesthetic and creative purposes. In the case of art and other non-engineering students, my goal is to introduce students to the simple beauty and fascination of fluid flow, as well asprovide some exposure to the discipline of documented experimentation.
This guidebook will address capturing the visual aspects of fluid physics. We’ll cover both still photography and videography. There is no broadly accepted term to refer to both of them, so I’ll just use ‘visuals’ to refer to both photos and videos.
This guide is designed to be broadly accessible by anybody with an interest in flow visualization. It was initially conceived as a textbook for the Flow Visualization course at the University of Colorado Boulder, which welcomes students from both engineering and fine arts. Although I am an engineering professor, I want to keep this accessible to non-engineers, with little math and lots of physics. I am also casting it as more of a guide than a textbook, in that it can be used as a spot reference. I hope students will find it useful although they may prefer instructional videos; someday I will try to produce some. Meanwhile, I plan to record and publish my lectures. Faculty, on the other hand, are voracious readers, and I hope that having a textbook will make Flow Visualization a more attractive course to teach. So, although the content is hopefully accessible to non-engineers, the factual accuracy should stand up to rigorous scrutiny.
A word about pronouns: I’ll use ‘I’ to refer to me, Jean Hertzberg, the author of this text and instructor of the Flow Vis course. ‘You’ is the reader, students, and the person attempting to do flow visualization. ‘We’ will mean me and the students, and me and you, the readers.
The content follows my lecture notes, developed over the nearly 20 years I’ve been offering Flow Vis. I believe in an iterative approach to learning, so we start with an overview of flow vis techniques. Next is an introduction to photography including ray optics and digital imaging. Students are encouraged to make both still images and videos, although a good still is much more easily managed by most students. The next topic is the physics of clouds, as an example of flow visualization accessible to all. Then the specific flow visualization techniques are covered in more depth, beginning with boundary techniques: heavy seeding with dyes and particles, including rheoscopic fluids. Light and matter interactions are covered in this context. Refractive index techniques including shadowgraphy and schlieren follow. Depending on the pace of the semester, additional topics are covered such as vorticity, critique, team behaviors and art-science relationships. The Course Info page has links to the Assignments and Schedule pages from the most recent semester, which show how the course content is integrated with assignments over the semester.
Activities are set in boxes throughout the text to engage the reader or to be used in class. If you are reading the text, take a minute to consider the question being posed before expanding the answers. This will either whet your appetite for the following material and help you retain it, or tell you that you already know it, and can skim it. If you are teaching this material in a class, use these activities to engage your students. It makes the class more fun, interesting and useful when they can talk about the material with their peers. They will appreciate being able to contribute to the flow of the lecture. You’ll get a break from talking nonstop, and you can gauge how much the students know so you can adjust your speed or depth accordingly. You might want to give ‘points’ to reward participation, but keep the stakes low so the motivation remains with learning, not points. I’ve found that just a whiff of credit is sufficient.
Students critique each other’s work throughout the semester. During an in-person semester, there are three to four 50 minute critique sessions for each of the six assignments. During COVID, we’ve decreased the total number of assignments.
I’ve been using Liz Lerman’s Critical Response Process . This is a moderated 4 step process that provides a framework for live critiques. Engineering students are very reluctant to criticize each other, but this process provides them with tools to make inquiries rather than attack with criticism. Since applying this method I’ve found that I can trust students to call attention to the work’s strengths and weaknesses in an appropriate and respectful way. Students do a good job critiquing the photographic and artistic aspects, but don’t have a lot of context to cover the fluid physics. I try to attend all critiques to offer insight on the fluid mechanics. In particular I give keywords (e.g. Kelvin-Helmholtz instability, mountain waves, impinging jets, etc.) to help students understand what physics they’ve revealed, so they can research background information for their reports. Since students are doing a wide range of projects, they are exposed to a wide range of fluid physics during critique sessions.
Since this text is being offered as an Open Educational Resource, with a Creative Commons license, all illustrations require a similarly public copyright. I’ve chosen sources such as previous work by Flow Vis students, for which I have explicit copyright for educational purposes, public sources such as Wikimedia Commons and government websites (NASA, NOAA etc). Finally, I’ve created my own illustrations when necessary, using tools such Blender for the 3D motion graphics animations.