Laminar and Turbulent Flow SPH4C

Learning Goals and Success Criteria Today 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 Dynamics Fluid 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 Friction As 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.

Viscosity The resistance of a fluid to flow is called its viscosity. Water has a low viscosity. Syrup has a higher viscosity.

Temperature Dependence As 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 Friction As 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 Flow If 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.

Eddies Laminar 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 Flow Eddies are common in turbulent flow, a fluid flow with a disturbance that resists the fluid’s motion.

Turbulent Flow Eddies 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.

Velocity Turbulence increases with the velocity of the fluid.

Reducing Turbulence One 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 Design Engineers 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 Practice Read: Pg. 278-281 Practice Problems: Pg. 280 #2, 6 and pg. 281 #2, 3 Laminar and Turbulent Flow Lab Activity