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Laminar flow, turbulent flow and Reynold’s number. Chan Wei Lim Zhong Hui Tan Hong You M4. Laminar flow. Also known as streamline flow Occurs when the fluid flows in parallel layers, with no disruption between the layers The opposite of turbulent flow (rough). Laminar flow.
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Laminar flow, turbulent flow and Reynold’s number Chan Wei Lim Zhong Hui Tan Hong You M4
Laminar flow • Also known as streamline flow • Occurs when the fluid flows in parallel layers, with no disruption between the layers • The opposite of turbulent flow (rough)
Laminar flow • In fluid dynamics (scientific study of properties of moving fluids), laminar flow is: • A flow regime characterized by high momentum diffusion, low momentum convection, pressure and velocity independent from time. *momentum diffusion refers to the spread of momentum (diffusion) between particles of substances, usually liquids
Laminar flow Turbulent Flow • Laminar flow over a flat and horizontal surface can be pictured as consisting of parallel and thin layers • Layers slide over each other, thus the name ‘streamline’ or smooth. • The paths are regular and there are no fluctuations Laminar Flow
Laminar flow • 3 Conditions • fluid moves slowly • viscosity is relatively high • flow channel is relatively small • Blood flow through capillaries is laminar flow, as it satisfies the 3 conditions • Most type of fluid flow is turbulent • There is poor transfer of heat energy!
Turbulent flow • Usually occurs when the liquid is moving fast • The flow is ‘chaotic’ and there are irregular fluctuations • Includes: • Low momentum diffusion • high momentum convection • rapid variation of pressure and velocity of the fluid • Good way to transfer thermal energy
Turbulent Flow • The speed of the fluid at a point is continuously undergoing changes in both magnitude and direction.
Examples of turbulence • Oceanic and atmospheric layers and ocean currents • External flow of air/water over vehicles such as cars/ships/submarines • In racing cars, e.g. leading car causes understeer at fast corners • Turbulence during air-plane’s flight • Most of terrestrial atmospheric circulation • Flow of most liquids through pipes
Reynold’s number • A dimensionless number in fluid mechanics • Dynamic Pressure : Shearing Stress • Thus, it quantifies the relative importance of these two types of forces for given flow conditions. • Arises when performing analysis of fluid dynamics • Can be used to determine dynamic similitude in such cases. Concept used in the testing of models, e.g. testing miniature airplanes/submarines
Dynamic Pressure + Shearing Stress • Dynamic Pressure • The pressure of a fluid which results from its motion • Formula: • Shearing Stress • Measure of the force of friction from a fluid acting on a body in the path of that fluid • Formula: Fluid Density Weight Density of Water Fluid Velocity Water Surface Slope Average water depth
Reynold’s numberFlow in a pipe or liquid • p is the density of the fluid • V is the mean fluid velocity • D is the diameter • Q is the volumetric flow rate Dynamic Pressure • μ is the dynamic viscosity of the fluid • v is the kinematic velocity of the fluid • A is the pipe cross-sectional area. Shearing Stress
Reynold’s number • The Reynold’s number can be used to determine if a flow is laminar, transient or turbulent • Laminar when Re < 2300 • Turbulent when Re > 4000 • Transient when 2300 < Re < 4000
Acknowledgements • http://www.geo.wvu.edu/~jtoro/geol101/streams/laminar%20flow.jpg • http://www.britannica.com/EBchecked/topic/328742/laminar-flow • http://en.wikipedia.org/wiki/Laminar_flow • http://www.answers.com/topic/laminar-flow • http://www.cosmosmagazine.com/files/imagecache/feature/files/20071217_physics.jpg • http://en.wikipedia.org/wiki/Turbulent_flow#Examples_of_turbulence
Acknowledgements • http://anordinarymom.files.wordpress.com/2008/11/airplane-turbulence-copy.gif • http://www.engineeringtoolbox.com/reynolds-number-d_237.html • http://en.wikipedia.org/wiki/Dynamic_similitude • http://www.engineeringtoolbox.com/reynolds-number-d_237.html