In fluid dynamics, what does the term "viscous flow" refer to?

Viscous flow refers to the movement of a fluid in which the effects of viscosity are significant, resulting in the presence of internal friction within the fluid. This internal friction arises from the fluid’s resistance to motion, which is directly related to its viscosity. In the case of viscous flow, the fluid's layers slide past each other with substantial resistance, which impacts how the fluid behaves under different conditions.

Viscous flow is characterized by a predominance of viscous forces over inertial forces, often occurring in situations where the flow speed is relatively low compared to the fluid's viscosity. This relationship is key in defining whether a flow is laminar or turbulent. In laminar flow, which is a type of viscous flow, fluid moves in smooth paths or layers, while in turbulent flow, the viscosity effects are less dominant.

In contrast, flows described by other options may not emphasize viscosity's role in fluid movement. For instance, flow with low viscosity does not imply significant viscous effects, and high-velocity flows can often be dominated by inertial forces rather than viscous forces. Flow with low density does not necessarily correlate with viscosity and may involve different dynamics entirely. Hence, recognizing that viscous flow specifically pertains to a situation where friction