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GATE 2022 CH – Question 16

Fluid Mechanics and Mechanical Operations · Turbulent flow, boundary layer and flow past immersed bodies · 1 mark · Multiple choice

Consider turbulent flow in a pipe under isothermal conditions. Let $r$ denote the radial coordinate and $z$ denote the axial flow direction. On moving away from the wall towards the center of the pipe, the $rz$-component of the Reynolds stress

  1. Increases and then decreases
  2. Decreases and then increases
  3. Remains unchanged
  4. Only increases

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Show answer and explanation

Correct answer: (A) Increases and then decreases

Explanation

The Reynolds stress is zero at the wall (the fluctuations vanish there), rises to a maximum in the turbulent region close to the wall and then falls to zero again at the centre line, where the total shear stress is zero.