Real Fluids

Head losses, boundary layers, vortex shedding, and viscous dissipation in real flows.

General idea of the topic

Real fluids have viscosity and, in many cases, turbulence, so the ideal model describes only part of what happens. There are energy losses to friction at the walls, drag forces on submerged bodies and flows that depend strongly on geometry.

The topic brings together the cases where those differences matter: pipe flow, with its pressure drop; basic aerodynamics, with drag and lift; the hydrodynamics of bodies and vessels; and engineering applications that combine everything above.

What you will truly understand

By the end you will be able to estimate losses in an installation, compute the drag force on a body in a fluid and recognize when lift or the wake conditions the design.

You will also be able to judge the error involved in applying the ideal model.

Recommended learning route

1. Pipe Flow: flow rate, head loss and pumping power in pipelines.
2. Basic Aerodynamics: drag and lift forces on bodies in air.
3. Hydrodynamics: motion of bodies and flows in water.
4. Engineering Applications: design examples that integrate these effects.

Physical criterion you must acquire

The essential criterion is to choose the dimensionless quantity that governs the problem, such as the Reynolds number, and use it to decide which simplifications are acceptable. The drag force increases with the square of the velocity in turbulent regime, whereas in laminar regime it does so in proportion to it.

Connection with real problems

• water networks and pipelines.
• aeronautics and automotive engineering.
• ships and marine structures.
• ventilation and air conditioning.

Final goal of the topic

The final goal is to model flow in installations and the interaction of fluids with bodies realistically, quantifying losses and forces.