How evolution builds the most efficient airfoils
June 29, 2018 by Christopher Packham, Phys.org report
Swimming and flying animals are optimally adapted for cruising through their environments, producing thrust via propulsors—wings for birds and caudal fins for fish. Over millions of years, the morphology of these animals evolved for maximally efficient cruising, and about 30 years ago, researchers proposed that most swimmers cruise within a narrow range of Strouhal numbers—these are dimensionless numbers describing oscillating flow. And more recently, researchers determined that flying animals cruise in the same range of Strouhal numbers.
Specifically, for swimming and flying animals, the Strouhal number is defined as St=f / U*A, where f is the oscillation frequency, U is the flow rate, and A is the oscillation amplitude. And the narrow range of Strouhal numbers in which swimming and flying animals cruise is 0.2 < St < 0.4.
Read more at:
https://phys.org/news/2018-06-evolution-efficient-airfoils.html#jCp
