Inlet Values for the Turbulence Length Scale and Turbulent Intensity
If inlet data for the turbulence variables are not available, crude approximations for k, ε, ω and ζ can be obtained from the following formulas:
(3-142)
where IT is the turbulent intensity and LT is the turbulence length scale.
A value of 10−3 (0.1%) is a low turbulent intensity IT. Good wind tunnels can produce values as low as 5·10−4 (0.05%). Fully turbulent flows usually have intensities between 0.05 (5%) and 0.1 (10%).
The turbulence length scale LT is a measure of the size of the eddies that are not resolved. For free-stream flows these are typically very small (on the order of centimeters). The length scale cannot be zero, however, because that would imply infinite dissipation. Use Table 3-5 as a guideline when specifying LT (Ref. 3) where lw is the wall distance, and
LT
0.07L
0.09L
0.08L
0.075L
Boundary layer (p / ∂x = 0)
0.09L
0.07L