The NASA Langley stability wind tunnel [0] is now part of Randolph Hall at Virginia Tech. You can visit it in Blacksburg, VA. Beautiful campus, btw. The stability tunnel is the biggest, they also have smaller hypersonic tunnels and

I worked there as a work-study student. Part of the job was wiping down the tunnel chamber after their test runs. The smoke you see used in wind tunnel videos is not actually smoke, but a white oil. And for a FWS job the pay wasn't bad, had to put on a bunny suit and crawl around tight spaces, LOL.

[0] https://en.wikipedia.org/wiki/Virginia_Tech_Stability_Wind_T...