Reynolds Number
Reynolds Number - Related Videos
01:10
Poiseuille's Law and Reynolds Number
0 Views •
2025
Any fluid in a horizontal tube can flow due to pressure differences—fluid flows from high to low pressure. The flow rate (Q) is the ratio of pressure difference and resistance through a horizontal tube. The greater the pressure difference, the higher the flow rate. The flow resistance is expressed as: When combined with the flow rate (Q), this relation gives Poiseuille's law for the laminar flow of an incompressible fluid in a tube. All factors that affect the flow rate, except pressure, are...
01:24
Reynolds Transport Theorem
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2025
The Reynolds transport theorem provides a framework to relate the time rate of change of an extensive property within a system to that in a control volume, which is crucial for analyzing fluid dynamics. Extensive properties, such as mass, velocity, acceleration, temperature, and momentum, can be expressed in terms of the mass of a fluid portion. These properties are called extensive because they depend on the system's size, while intensive properties are their corresponding values per unit mass.
13:21
Isolation and Expansion of the Adult Mouse Neural Stem Cells Using the Neurosphere Assay
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Cited by 113 •
2010
This video protocol demonstrates the neurosphere assay method to generate and expand neural stem cells from the adult mouse periventricular region, and provides technical insights to ensure one can achieve reproducible neurosphere cultures.
08:57
Cross Cylindrical Flow: Measuring Pressure Distribution and Estimating Drag Coefficients
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2023
Source: David Guo, College of Engineering, Technology, and Aeronautics (CETA), Southern New Hampshire University (SNHU), Manchester, New Hampshire The pressure distributions and drag estimations for cross cylindrical flow have been investigated for centuries. By ideal inviscid potential flow theory, the pressure distribution around a cylinder is vertically symmetric. The pressure distribution upstream and downstream of the cylinder is also symmetric, which results in a zero-net drag force.
09:23
Turbulence Sphere Method: Evaluating Wind Tunnel Flow Quality
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2023
Source: Jose Roberto Moreto and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, CA Wind tunnel tests are useful in the design of vehicles and structures that are subjected to airflow during their use. Wind tunnel data are generated by applying a controlled air flow to a model of the object being studied. The test model usually has a similar geometry but is a smaller scale compared to the full-sized object. To ensure accurate and useful data is collected...
FAQs
Choosing the characteristic length is essential because it sets the scale used in the Reynolds-number calculation. Engineers select a length that represents the relevant flow geometry, then use it consistently when comparing cases. Changing that reference length changes the numerical value, so comparisons are meaningful only when the selected length corresponds to the same physical feature or design scale.
Each variable changes the balance represented by Reynolds number in a predictable direction. Increasing density, velocity, or characteristic length raises Re, whereas increasing dynamic viscosity lowers it. Thus, faster or larger-scale flows tend to show stronger relative inertial effects, while more viscous fluids tend to show stronger relative viscous effects. These changes guide flow-regime expectations.
Reynolds number makes flows comparable even when their sizes, speeds, or fluids differ. Two cases with similar values can be evaluated using the same flow-regime framework because the relative importance of inertia and viscosity is similar. This comparison is particularly useful when engineers interpret experiments or assess whether observations from one configuration can inform another.
To calculate Reynolds number, identify the fluid density, characteristic velocity, characteristic length, and dynamic viscosity for the case being studied. Insert those quantities into Re = ρvL/μ, keeping the selected length and property values consistent. The resulting dimensionless value can then be used to classify the flow as laminar, transitional, or turbulent.
In pipe design, the value helps engineers anticipate whether flow conditions are likely to be laminar, transitional, or turbulent. That expectation supports decisions involving flow behavior and provides context for related engineering analyses, including drag estimation and heat-transfer analysis. The same calculation can therefore connect operating conditions and fluid properties with practical design evaluations.
For scaled experiments, Reynolds number provides a basis for judging whether a model flow is comparable with a larger or differently operated system. Engineers can compare the model and target using their respective density, velocity, length, and viscosity values. This helps determine whether the experiment represents the intended flow regime when interpreting observations from the design.