The Marriage Of Optical Tracer And Surface Indicator Techniques In Flow Visualization

The concept of uniting two or more flow visualization techniques is emphasized. Although this can be done, for a number of flow situations, using instrumentation and methods that have been available for many years, the use of modern technology and intruments makes such unions more easily realized. Some examples of this concept are discussed. Results are presented for a combined optical-(shadowgraph and schlieren) surface indicator (oil flow) technique; a versatile vapor screen technique using a CW laser; and a reversible dye technique. Whether used alone or united to the others the latter is especially valuable for use in a continuous wind tunnel since the surface flow patterns are erasable.

An ambitious vision for design based on the premise that data is material, not abstract. Data analysis and visualization are crucial tools in today's society, and digital representations have steadily become the default. Yet, more and more often, we find that citizen scientists, environmental activists, and forensic amateurs are using analog methods to present evidence of pollution, climate change, and the spread of disinformation. In this illuminating book, Dietmar Offenhuber presents a model for these practices, a model to make data generation accountable: autographic design. Autographic refers to the notion that every event inscribes itself in countless ways. Think of a sundial, for example—a perfectly autographic device that displays information on itself. Inspired by such post-digital practices of visualization and evidence construction, Offenhuber describes an approach to visualization based on the premise that data is a material entity rather than an abstract representation. Emerson wrote, “Every act of the man inscribes itself in the memories of his fellows, and in his own manners and face.” In Autographic Design, Offenhuber introduces a model for design that emphasizes traces, imprints, and self-inscriptions, turning them into sensory displays. In an age where misinformation is harder and harder to identify, Autographic Design makes an urgent and persuasive case for a different approach that calls attention to the production of data and its connection to the material world.

The subject is investigated with flow visualization techniques; the turbulent boundary layer on the wall of a continuous supersonic wind tunnel is used. Sizeable separated flow regions can be studied since the wall width is 38cm and the boundary layer is typically 2.5cm thick. The large scale of the experiment is required to resolve the fine details of the flow structure. The flow visualization techniques are discussed. The structure of the separated flow upstream of the obstacle is seen to change with relatively small changes in Reynolds number R; the number of vortices varies from 6 to 4 to 2 as R changes. Data are presented for large and small protuberances, but the latter are emphasized.