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I am looking for specifics of building and the operation of low speed wind tunnels, but most diy wind tunnels on internet are improved versions of science fair projects at best.

What would I need to keep in mind if I decide to make one myself? Image for size reference.

enter image description here

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    $\begingroup$ Start with roundly a million dollars... $\endgroup$
    – Zeiss Ikon
    Jul 15 at 16:29
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    $\begingroup$ How many square feet of floor space? How low a Reynolds number? What budget for maintenance? For how many years? $\endgroup$ Jul 15 at 16:47
  • $\begingroup$ @CamilleGoudeseune 60ft*40ft space, low reynolds number from 200k to 1 million or more, 65k-100k usd budget... mostly aimed at mid size UAV testing of upto 5 metre wingspans and some other research $\endgroup$ Jul 15 at 17:04
  • $\begingroup$ You want to put a complete 5 meter UAV inside this, or test on scale models? $\endgroup$
    – Zeiss Ikon
    Jul 15 at 17:07
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    $\begingroup$ For a project you'll spend $65,000+ on, working from plans that didn't come from a professional with experience designing wind tunnels seems like an opportunity for an expensive mistake or lessons learned. At some point, "you get what you pay for". $\endgroup$
    – Ralph J
    Jul 16 at 2:17
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This question sets forth a project of considerable undertaking. Nevertheless, a relatively small wind tunnel is feasible, particularly for low-speed work (i.e. low Reynolds number), if there is willingness to use care and understand the technical issues in smoothing airflow and eliminating turbulence in the free stream flowing through the model test section (about 1/16th the area or even smaller, compared to the test section pictured in the question). This link here will show the similarities between a large engineering wind tunnel, and a much smaller version used at the same facility. The smaller version has been ideal for low-speed work, and has been used advantageously in that realm. A description of the main facility for the associated large, engineering wind tunnel is found here. In the United States, much work has been done with intermediate sized wind tunnels capable of reproducing results of equivalent quality to those obtained in the large wind tunnel mentioned herein. These wind tunnels are located at a) Princeton University, b) University of Illinois Urbana Campus, and c) Notre Dame University. These wind tunnels, although relatively small, are quite substantial. The wind tunnel used at the University of Illinois Urbana has produced engineering results of the highest quality in the study of airfoils, and in comparison of those results with computational methods available from various sources.

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It depends on the cross-section and speed of airflow. The tunnel itself is just a duct. Is the power usage for fan that makes it expensive

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You also require a means of smoothing out all the velocity gradients and eddies in the flow before it enters your test section. This is done my filtering the incoming air through a series of 10 or so screens with the fineness of a window screen, completely spanning the inlet cross-section, and set about 4 inches apart.

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