Hello,

Just a quick question. Does anybody know of a typical turbulence intensity on the inlet of an external flow domain? I am modeling vehicle aerodynamics and I want to specify a more realistic boundary condition. Does anybody know of a reliable reference for natural turbulence intensities on roads etc?

Best regards,

Carlos.

Hi Carlos,

The way I see it, you have two major possible situations:

- laminar, undisturbed flow in front of a car running at sufficient distance from other cars (hundreds of meters), when the level of turbulence intensity at inlet should be set, let's say to about 0.5-1%, and a turbulent viscosity ratio of 1;

- turbulent flow in front of a car running in the wake of another, in which case, if you really want a very realistic model, you should use an interpolated profile for velocity and turbulent quantities obtained from another simulation (taken at a proper distance), or if the car is running in highway-like conditions, with cars in front and behind, at approx. equal distances, you could use a translationally periodic condition for the inlet-outlet pair.

All the best,

Razvan

Hi Razvan,

Many thanks for your suggestions. At present I am only interested in laminar flow in front of my vehicle. I just feel that having no turbulence intensity there is too clinical and unreal. Obviously there is an atmospheric boundary layer and low levels of turbulence in the air on roads.

I will try your suggestion of 0.5-1%. I doubt it will change much of the solution but I am writing a paper and want to do it by the book. I cannot find much in the literature on natural turbulence intensity levels but if you know of one for your suggestion please let me know!

Best wishes,

Carlos.