I have a question about Reynolds Number and wind tunnel tests. Last semester a few students at my university were conducting wind tunnel tests on a small model of a truck, they were trying to find ways to reduce the drag in order to save fuel. I would guess they were testing at a Reynolds Number on the order of a few thousand which is no where near that of a full sized truck on a highway.
My question is, how valid are these tests if the Reynolds number is off a couple orders of magnitude?
When I brought it up they just said that they were only investigating the qualitative effects of various configurations. But based on my understanding even qualitative results may not be valid for very different reynolds numbers so I dont see how their results would be useful at all.