Hydrodynamics. Fluid kinematics Presentation

How does submarine work?

Learning objectives

Learners be able to:
describe laminar and turbulent flow of liquids;
distinguish between laminar and turbulent flow characteristics;
describe the behaviour of fluids in motion;
define viscosity of a fluid.

Glossary

Hydrodynamics

a branch of physics that deals with the motion of fluids and the forces acting on solid bodies immersed in fluids and in motion relative to them

An ideal fluid

Fluid motion is usually very complicated. However, by making a set of assumptions about the fluid, one can still develop useful models of fluid behaviour. An ideal fluid is:
• Incompressible – the density is constant
• Irrotational – the flow is smooth, no turbulence
• Nonviscous– fluid has no internal friction (η= 0)
• Steady flow – the velocity of the fluid at each point is constant in time.

Work in pairs

Laminar flow

Laminar flow occurs when the fluid flows in infinitesimal parallel layers with no disruption between them. In laminar flows, fluid layers slide in parallel, with no eddies, swirls or currents normal to the flow itself. This type of flow is also referred to as streamline flow because it is characterized by non-crossing streamlines

Turbulent flow

Turbulent flow, type of fluid (gas or liquid) flow in which the fluid undergoes irregular fluctuations, or mixing. In turbulent flow the speed of the fluid at a point is continuously undergoing changes in both magnitude and direction

Viscous and non-viscous fluids

1. In viscous flow, fluid moves in adjacent layers without slip. Non-viscous or turbulent flow is characterized by random, erratic, unpredictable motion of fluid particles which results in eddy currents.
2. Viscous flow occurs at low velocity while non-viscous occurs at higher velocities.
3. In viscous shear stresses are of small magnitude. In non-viscous flow shear stresses are much greater.

Viscosity

Viscosity is the property of a fluid which opposes the relative motion between two surfaces of the fluid that are moving at different velocities.
In simple terms, viscosity means friction between the molecules of fluid.
A simulation of liquids with different viscosities. The liquid on the right has higher viscosity than the liquid on the left.

Applications 

In flowing rivers, when going from deep to shallow, the flow speed increases (often becoming turbulent) "still water runs deep".
A river flows slowly and languidly through a meadow where it is broad, but speeds up to torrential speed when passing a narrows.
In the circulatory system of the blood there is a branching effect. When a fluid flows past a Y-junction made up of pipes of the same diameter, the total cross-sectional area after the branch is twice that before the branch, so the flow speed must fall to half. Conversely, if it is important to keep the flow speed up, the pipes after the branch must have half the cross-sectional area of those before. (Note: blood will clot if its speed falls too low.)
Blood flow – blood flows from the heart into the aorta then into the 32 major arteries. These branch into smaller arteries (arterioles) that branch into a myriad of tiny capillaries and then the blood returns to the heart via the veins.
Air conditioning systems must also be built with consideration for the branch effect.
Also the tube structure of the respiratory system is remarkably similar to that of the circulatory system.

Questions

How is blood flow measured in a vessel?  [3]
How can you predict whether a certain vessel will be bright or dark on an MR image?   [2]
Question 3 related to football. What is magnus effect in football? What causes a soccer ball to curve when kicked?

Feedback

What do I know before?
What has been learned?
What remained unclear
What is necessary to work on
Students have to answer one of above questions in brief. If student prefers to write, they can use different stickers

Thank you!