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| | style.org > The Strouhal Number in Cruising Flight |
 | | This dimensionless ratio is the Strouhal number, and evolution seems to favor efficient swimming motion with a Strouhal number in the range of 0.2–0.4. |
 | | In particular, although the authors of the Nature article provide a chart of Strouhal numbers for flapping flight and swimming along with their statistical analysis, I wanted to see what ratios of amplitude, frequency, and speed actually look like in winged flight, what the Strouhal number actually represents, and why it is dimensionless. |
 | | Assuming a symmetric flight motion, a normalized angle of attack, and a relative flight line, the wing tip descends in a smooth curve through the flapping stroke (red line), and rises through the recovery (gray line), tracing an even waveform. |
| www.style.org /strouhalflight (1501 words) |
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