In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. In Poiseuille flow, for example, turbulence can first be sustained if the Reynolds number is larger than a critical value of about 2040; moreover, the turbulence is generally interspersed with the laminar flow until a larger Reynolds number of about 4000. Hence, the third hypothesis of Kolmogorov was that at a very high Reynolds number the statistics of scales in the range are universally and uniquely determined by the scaler and the rate of energy dissipation ε. Observations of Biologically Generated Turbulence in a Coastal Inlet". Bibcode:2007RSPTA.365..841N. doi:10.1098/rsta.2006.1949. ^ Kundu, Pijush K.; Cohen, Ira M.; Dowling, David R. (2012).
In fluid dynamics, laminar flow is characterized by fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing. At low velocities, the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. When a fluid is flowing through a closed channel such as a pipe or between two flat plates, either of two types of flow may occur depending on the velocity and viscosity of the fluid: laminar flow or turbulent flow. The specific calculation of the Reynolds number, and the values where laminar flow occurs, will depend on the geometry of the flow system and flow pattern. Optical transparency is then reduced or lost entirely. Laminar flow hoods are used to exclude contaminants from sensitive processes in science, electronics and medicine.
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