GATE 2025 AE – Question 47
A rectangular wing of 1.2 m chord length and aspect ratio 5 is tested in a wind tunnel at an air speed of 60 m/s. The density and the dynamic viscosity of air are 1.3 kg/m$^3$ and $1.8 \times 10^{-5}$ kg/m-s, respectively. A second rectangular wing of the same span, but with an aspect ratio of 6, is to be tested in the same tunnel at the same Reynolds number. The air speed at which the second test should be performed is _______ m/s (answer in integer).
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: 72
Explanation
The span of the first wing is $b = AR \times c = 5 \times 1.2 = 6$ m. The second wing has the same span, so its chord is $\frac{6}{6} = 1$ m. The air in the tunnel is the same, so equal Reynolds number $\frac{\rho V c}{\mu}$ needs $V_2 = 60 \times \frac{1.2}{1} = 72$ m/s.