Question

What is the physical mechanism that causes the friction factor to be higher in turbulent flow?

Short answer

Short Answer: The friction factor is higher in turbulent flow compared to laminar flow due to the increased interaction between the fluid and the wall caused by chaotic, disordered fluid motion. Turbulent flow generates higher wall shear stress, pressure fluctuations, and a more chaotic flow pattern, leading to greater resistance to fluid flow, as represented by a higher friction factor.

Step-by-step solution

Define Laminar and Turbulent Flow

Laminar flow and turbulent flow are two types of fluid flow, each with distinct characteristics. Laminar flow is a smooth, orderly flow in which fluid particles move in parallel layers, or "laminae." There is little to no mixing of particles between layers, and the flow is characterized by low fluid velocities and gentle gradients in velocity and fluid properties. Turbulent flow, on the other hand, is characterized by chaotic, disordered fluid motion, in which fluid particles move in irregular and swirling patterns. This results in rapid mixing of particles and greater fluctuations in velocity and other fluid properties.

Explain Friction Factor

The friction factor is a dimensionless quantity that represents the resistance to flow caused by the interaction of a fluid with its surroundings, such as the walls of a pipe or other conduit. In fluid flow through a pipe, it is the ratio of the wall shear stress to the dynamic pressure of the fluid. A higher friction factor indicates greater resistance to fluid flow, which can result in a higher pressure drop along the pipe and an increased energy requirement to maintain a given flow rate.

Describe the Physical Mechanism of Friction Factor in Turbulent Flow

In turbulent flow, fluid particles are constantly moving and mixing randomly, leading to higher velocities, greater fluctuations in velocity, and a more chaotic flow pattern. This results in an increased interaction between the fluid and the wall, which causes the wall shear stress to be higher in turbulent flow compared to laminar flow. Additionally, turbulent flow causes higher pressure fluctuations, which can result in larger forces acting on the walls and an increased pressure drop along the pipe. This turbulent mixing also increases the transport of momentum from the fluid's core to the wall, which further contributes to a higher wall shear stress and friction factor.

Conclusion

The physical mechanism that causes the friction factor to be higher in turbulent flow is the increased interaction between the fluid and the wall due to the chaotic, disordered fluid motion. Turbulent flow results in higher wall shear stress and pressure fluctuations, which in turn lead to a greater resistance to fluid flow, represented by a higher friction factor.