When the average flow is steady, which one of the following causes significant fluctuations in velocity, temperature and pressure ?
- AStreamlines in turbulent flow
- BMolecular diffusion in turbulent flow
- CEddy motion in turbulent flowCorrect
- DOrderly flow in turbulent flow
Solution
Concept
Eddies in turbulent flow
Step-by-step solution
1. In turbulent flow, random eddies carry fluid across layers. 2. This causes irregular fluctuations in velocity, pressure and temperature even when the mean flow is steady.
Explanation
Eddy motion is the characteristic cause of turbulent fluctuations.
Why the other options are wrong
Streamlines and orderly motion characterise laminar flow. Molecular diffusion is too weak to cause large fluctuations.
Shortcut
Turbulence = eddies.
Common mistake
Choosing molecular diffusion.
Correct answer: C) Eddy motion in turbulent flow