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

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:

${{0.997 g/cm³ * 0.668 m/s * 18 cm} \over {8.9e-4 Pa s}} = 134702$

For roughly the same Re 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):

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

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?

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

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:

${{0.997 g/cm³ * 0.668 m/s * 18 cm} \over {8.9e-4 Pa s}} = 134702$

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):

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

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?

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

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.

For roughly the same Re and the full car size of 4.5 m in air I come up with a speed of 0.45 m/s (1.62 km/h).

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?

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

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:

${{0.997 g/cm³ * 0.668 m/s * 18 cm} \over {8.9e-4 Pa s}} = 134702$

For roughly the same Re 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):

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

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?