In turbulent flow over an impervious solid walla)Viscous stress is zer...
Viscous stress and Reynolds stress in turbulent flow over an impervious solid wall
When fluid flow becomes turbulent, it is characterized by chaotic and irregular motion of fluid particles. This turbulent flow has a significant effect on the behavior of fluid near solid surfaces. In turbulent flow over an impervious solid wall, both viscous stress and Reynolds stress play important roles.
Viscous stress at the wall
Viscous stress is the resistance to flow within the fluid itself due to the internal friction between fluid layers. At the solid wall, viscous stress is not zero. In fact, it is highest at the wall and decreases as we move away from the wall. This is because the fluid in direct contact with the wall experiences a no-slip condition, which means that the fluid velocity is zero at the wall. The viscous stress at the wall is responsible for the creation of a thin layer of fluid known as the viscous sublayer.
Reynolds stress at the wall
Reynolds stress, on the other hand, is associated with the turbulent fluctuations of velocity in the flow. It is caused by the interactions between the various eddies and vortices present in the turbulent flow. Unlike viscous stress, Reynolds stress can be positive or negative, depending on the direction of the fluctuations. At the wall, the Reynolds stress is not zero. It is highest in the near-wall region, where the flow is most turbulent.
Comparison between viscous stress and Reynolds stress at the wall
In turbulent flow over an impervious solid wall, viscous stress and Reynolds stress both exist. However, the viscous stress is much smaller in magnitude compared to the Reynolds stress. This is because the turbulent fluctuations in the flow dominate the behavior of the flow near the wall. The Reynolds stress is responsible for the transfer of momentum between the different fluid layers and plays a crucial role in the overall turbulent flow dynamics.
Therefore, the correct answer is option D: Viscous stress is much smaller than Reynolds stress in turbulent flow over an impervious solid wall.
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