I recently stumbled across the water tunnel videos by this guy:

[![enter image description here][1]][1]

https://youtu.be/quDLzxmJl5I?t=838

He states that for his "high flow" experiments the water speed is at 0.668 m/s. The car model is about 18 cm long. From what I understand about Reynolds numbers this equates to [Re = 134702][2]:
 
${{0.997 g/cm³ * 0.668 m/s * 18 cm} \over {8.9e-4 Pa s}} = 134702$

For roughly the same Re in air and the full car size of 4.5 m in air I come up with a [speed of 0.433 m/s (1.56 km/h)][3]:

${{134702 * 1.8448e-5 Pa s} \over {0.001275 g/cm³ * 4.5 m}} = 0.433 m/s$

I like to believe that my thinking here is wrong, as the flow lines in his experiments look "to scale". But from my calculations above it seems that his 0.668 m/s seem to low to represent typical driving speeds at scale?

So to make this a question:

(edited) How are water tunnel experiments equivalent to wind tunnel experiments if, from my napkin calculations above, it seems that to simulate air flow at x km/h you need about the same flow velocity in water?


  [1]: https://i.sstatic.net/EHXco.jpg
  [2]: https://www.wolframalpha.com/input?i=reynolds%20number%20in%20water&assumption=%7B%22F%22%2C%20%22ReynoldsNumber%22%2C%20%22l%22%7D%20-%3E%2218%20cm%20%22&assumption=%7B%22FS%22%7D%20-%3E%20%7B%7B%22ReynoldsNumber%22%2C%20%22Re%22%7D%7D&assumption=%7B%22F%22%2C%20%22ReynoldsNumber%22%2C%20%22v%22%7D%20-%3E%220.668%20m%2Fs%22&assumption=%7B%22F%22%2C%20%22ReynoldsNumber%22%2C%20%22eta%22%7D%20-%3E%220.00089%20Pa%20s%22
  [3]: https://www.wolframalpha.com/input?i=reynolds%20number%20in%20air&assumption=%7B%22F%22%2C%20%22ReynoldsNumber%22%2C%20%22l%22%7D%20-%3E%224.5%20m%22&assumption=%7B%22FS%22%7D%20-%3E%20%7B%7B%22ReynoldsNumber%22%2C%20%22Re%22%7D%7D&assumption=%7B%22F%22%2C%20%22ReynoldsNumber%22%2C%20%22v%22%7D%20-%3E%220.45%20m%2Fs%22&assumption=%7B%22F%22%2C%20%22ReynoldsNumber%22%2C%20%22eta%22%7D%20-%3E%220.0000184481%20Pa%20s%22