Richardson number, abbreviated as \(Ri\), a dimensionless number, in fluid dynamics that quantifies the relative importance of buoyancy forces to inertial (shear) forces in a stratified flow. It is used primarily in the analysis of atmosphere flows, oceanographic flows, and density-stratified engineering systems where velocity gradients and density gradients coexist. The parameter provides a stability criterion for shear flows subjected to density stratification.
Richardson Number formula |
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\( f \;=\; \dfrac{ Gr }{ Re^2 }\) (Richardson Number) \( Gr \;=\; f \cdot Re^2 \) \( Re \;=\; \sqrt{ \dfrac{ Gr }{ f } } \) |
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| Symbol | English | Metric |
| \( Ri \) = Richardson Number | \(dimensionless\) | \(dimensionless\) |
| \( Gr \) = Grashof Number | \(dimensionless\) | \(dimensionless\) |
| \( Re \) = Reynolds Number | \(dimensionless\) | \(dimensionless\) |
Richardson Number Interpretation
Low Richardson Number (Ri < 0.25) - The flow is dynamically unstable. Turbulence is likely to develop because the shear (mechanical mixing) dominates over buoyancy forces. This is often associated with the onset of Kelvin-Helmholtz instability, where waves and mixing occur.
Richardson Number (0.25 < Ri < 1) - This is a transitional range. The flow may still become turbulent under certain conditions, but buoyancy begins to play a more significant role in stabilizing the flow.
High Richardson Number (Ri > 1) - The flow is dynamically stable. Buoyancy forces dominate, suppressing turbulence and maintaining stratification. Mixing is inhibited, and the fluid tends to remain layered.
