Laminar and Turbulent Flow

SPH4C

Learning Goals and Success CriteriaToday I will be able to…

describe factors affecting laminar flow, and explain how the design of an item or organism responds to these factors.

Fluid DynamicsFluid dynamics is the study of the

factors that affect fluids in motion.

Computational fluid dynamics can simulate the flow of air around a vehicle.

Internal FrictionAs a fluid flows, the forces of attraction

between the molecules cause internal friction, or resistance to the flow.

Some fluids have more resistance than others.

ViscosityThe resistance of a fluid to flow is called its

viscosity.Water has a low viscosity. Syrup has a higher

viscosity.

Temperature DependenceAs temperature increases, the viscosity of a

liquid generally decreases because the particles of the liquid have more energy and flow more easily.

However, gases generally increase in viscosity as the particles collide more often making it more difficult for them to flow in one direction. Choosing the right oil

viscosity grade for your vehicle requires consideration of the temperatures in which your vehicle will be operating.

External FrictionAs fluids flow, their particles also interact with

their surroundings and experience external friction.

In a pipe the water flowing close to the sides is almost not moving while the water in the middle of the pipe can be moving quickly.

Laminar FlowIf the speed of a flow is slow and

adjacent regions flow smoothly over one another, the flow is called laminar flow.

This term can also be applied to air flow over a smooth object.

EddiesLaminar flow is difficult to achieve

because as the fluid flows past the object, the flow becomes irregular, resulting in whirls called eddies or vortices.

Turbulent FlowEddies are common in turbulent flow, a

fluid flow with a disturbance that resists the fluid’s motion.

Turbulent FlowEddies are common in turbulent flow, a

fluid flow with a disturbance that resists the fluid’s motion.

Turbulent flow decreases kinetic energy as some of the energy is converted into thermal and sound energy.

VelocityTurbulence increases with the velocity

of the fluid.

Reducing TurbulenceOne mechanism of reducing

turbulence in liquids is introducing small amounts of liquid plastic.

Blood flow in arteries is typically turbulent. The introduction of liquid plastic into the bloodstream can help people who have problems with blood flow.

Turbulence and DesignEngineers consider the effects of

turbulence when designing structures.

For example, high rise buildings can direct strong gusts of air down to street level.The circular

podium between the towers of Toronto City Hall was placed there to reduce winds.

More PracticeRead: Pg. 278-281Practice Problems: Pg. 280 #2, 6 and pg. 281 #2, 3 Laminar and Turbulent Flow Lab Activity