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GATE 2022 AE – Question 39

Aerodynamics · Basic fluid mechanics: kinematics, conservation laws, dimensional analysis, incompressibility and Newtonian fluids · 2 marks · Multiple choice

A 900 mm cylinder moves axially in air at 60 m/s. A half-scale water model has drag 2280 N. Air has μ=$1.86\times10^{-5}$ Pa s and ρ=1.2 kg/m³; water has μ=$1.01\times10^{-3}$ Pa s and ρ=1000 kg/m³. With flow similarity, full-scale drag (nearest integer N) is

  1. 322
  2. 644
  3. 1288
  4. 2576

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Correct answer: (C) 1288

Explanation

Reynolds similarity gives model speed 7.82 m/s. Equal drag coefficients give $D_p/D_m=(1.2/1000)(60/7.82)^2(2)^2$, yielding 1288 N.