The drag both between adjacent layers of fluid and between the fluid and its surroundings forms swirls and eddies, if the speed is great enough. First, any obstruction or sharp corner, such as in a faucet, creates turbulence by imparting velocities perpendicular to the flow. Streamlines are smooth and continuous when flow is laminar, but break up and mix when flow is turbulent. The lines that are shown in many illustrations are the paths followed by small volumes of fluids. When there is turbulence, the layers mix, and there are significant velocities in directions other than the overall direction of flow. Layers flow without mixing when flow is laminar. (credit: Creativity103)įigure 12.11 shows schematically how laminar and turbulent flow differ. If you watch the smoke (being careful not to breathe on it), you will notice that it rises more rapidly when flowing smoothly than after it becomes turbulent, implying that turbulence poses more resistance to flow. The smooth flow is called laminar flow, whereas the swirls and eddies typify turbulent flow.

Turbulent flow, or turbulence, is characterized by eddies and swirls that mix layers of fluid together.įigure 12.10 Smoke rises smoothly for a while and then begins to form swirls and eddies. Laminar flow is characterized by the smooth flow of the fluid in layers that do not mix. Before we can define viscosity, then, we need to define laminar flow and turbulent flow. The precise definition of viscosity is based on laminar, or nonturbulent, flow. In this section, we will investigate what factors, including viscosity, affect the rate of fluid flow.

In the previous sections we have considered ideal fluids with little or no viscosity. Juice has low viscosity, whereas syrup has high viscosity. We call this property of fluids viscosity. The difference is fluid friction, both within the fluid itself and between the fluid and its surroundings. But when you pour syrup on your pancakes, that liquid flows slowly and sticks to the pitcher. When you pour yourself a glass of juice, the liquid flows freely and quickly. Explain how pressure drops due to resistance.Calculate flow and resistance with Poiseuille’s law.Define laminar flow and turbulent flow.By the end of this section, you will be able to: Meilikhov, Physical Values, The Handbook (Energoatomizdat, Moscow, 1231).

Bird, Molecular Theory of Gases and Liquids (Wiley, New York, 1954). Cowling, The Mathematical Theory of Non-uniform Gases: An Account of the Kinetic Theory of Viscosity, Thermal Conduction, and Diffusion in Gases (Cambridge Univ. Zubarev, Nonequilibrium Statistical Thermodynamics (Nauka, Moscow, 1971). Bird, Molecular Gas Dynamics (Clarendon, Oxford, 1976).ĭ. Press, Oxford, 2005).Įncyclopedia of Microfluidics and Nanofluidics, Ed. Tabeling, Introduction to Microfluidics (Oxford Univ.

First person to test viscosity of gases