Converts a mean velocity, a turbulence intensity and a turbulence length scale into the k, epsilon, omega and eddy-viscosity values that RANS inlets need.
Inputs
Conditions at the inlet plane. Defaults suit a 5 m/s duct flow with moderate turbulence.
Bulk velocity at the inlet.
Percent. 5 is a common default.
Eddy size. Try 7 to 10 percent of the duct diameter for internal flow.
Results
Turbulent kinetic energy k
-
Dissipation rate ε
-
Specific dissipation ω
-
Turbulent viscosity νt
-
For internal flows a length scale near 7-10% of the hydraulic diameter is a common starting point; for external flows choose from ambient conditions.
How it works
Most two-equation RANS models do not accept intensity directly: they need the turbulent kinetic energy and either the dissipation rate or the specific dissipation rate. This calculator builds those quantities from the intensity definition and a single length scale, using the standard model constant Cμ = 0.09.
Convert the intensity to a fraction and compute the turbulent kinetic energy k = (3/2)(U I)^2.
Compute the dissipation rate from the length scale: ε = Cμ k^(3/2) / l.
Compute the specific dissipation rate ω = ε / (Cμ k).
Compute the turbulent kinematic viscosity νt = k / ω.
Turbulent kinetic energy
k = (3/2) (U I)^2
Dissipation rate
ε = Cμ k^(3/2) / l ; Cμ = 0.09
Specific dissipation rate
ω = ε / (Cμ k)
Turbulent kinematic viscosity
νt = k / ω
U
Mean velocity at the inlet, m/s
I
Turbulence intensity as a fraction
l
Turbulence length scale, m
k
Turbulent kinetic energy, m2/s2
ε
Turbulent dissipation rate, m2/s3
ω
Specific dissipation rate, 1/s
νt
Turbulent kinematic viscosity, m2/s
Cμ
Model constant, 0.09
References
Wilcox, D. C., Turbulence Modeling for CFD, 3rd ed., DCW Industries, 2006.
Versteeg, H. K. and Malalasekera, W., An Introduction to Computational Fluid Dynamics, 2nd ed., Pearson, 2007.
