14.5 Fluid Dynamics
The wind blowing through your hair, a white-water river, and oil gushing from an oil well are examples of fluids in motion. We’ve focused thus far on fluid statics, but it’s time to turn our attention to fluid dynamics.
Fluid flow is a complex subject. Many aspects, especially turbulence and the formation of eddies, are still not well understood and are areas of current science and engineering research. We will avoid these difficulties by using a simplified model. The ideal-fluid model provides a good, though not perfect, description of fluid flow in many situations. It captures the essence of fluid flow while eliminating unnecessary details.
MODEL 14.2 Ideal fluid
Applies to liquids and gases. A fluid can be considered ideal if
The fluid is incompressible.
The fluid is nonviscous.
Viscosity, a fluid’s resistance to flow, is analogous to kinetic friction.
Nonviscous flow is analogous to friction-free motion.
The flow is laminar.
Laminar flow occurs when the fluid velocity at each point in the fluid is constant. The flow is smooth; it doesn’t change or fluctuate.
Limitations: The model fails if
the fluid has significant viscosity.
the flow is turbulent rather than laminar.
Workbook Exercise 19
The rising smoke in the photograph of FIGURE 14.24 begins as laminar flow, recognizable by the smooth contours, but at some point undergoes a transition to turbulent flow. A laminar-to-turbulent transition is not uncommon in fluid flow. The ideal-fluid model can be applied to the laminar flow, but not to the turbulent flow.
FIGURE 14.24 Rising smoke changes from laminar flow to turbulent flow.
