**3. Wind tunnel design**

In an engineering paper on wind tunnel design [48], the author stated that "the design of blower-driven air tunnel…is a combination of art, science, and common sense, the last being the most essential. It is difficult and unwise to predict firm rules for tunnel design." In addi‐ tion to the power source, fan or blower, flow conditioning section, and working section, flow tripping fences and spires are often used to deepen the boundary layer thickness [49, 50], abrader feeders and regulators are used to initiate a saltation cloud, and sediment sam‐ plers to quantify the rate of erosion and dust emissions are often included in the design. In‐ strumentation such as anemometers of many designs and particle impact sensors are often used to monitor wind tunnel performance and to set operating parameters. In almost all cas‐ es, portable field wind tunnel designs are somewhat unique and highly influenced by their intended use.
