Just as the thread says, I am looking for some good flow visualization techniques at low Reynolds numbers. I am working on the design of a small recirculating water tunnel that I think can be built for ~$100. I cannot get a specific RE at the moment as I am still doing a preliminary feasibility survey. So far things are looking up. I'm going to look up some technical papers later, but for now if anyone knows of some methods off hand that would be great.