[mario91]

false/numerical diffusion is a quite classical problem in CFD.

However I think that each simulation case should have more important corrections to handle that.I am having extreme numerical diffusion!

Briefly my case is this:

Fully developed flow along x direction. Free Atmospheric flow between ground and 150m high plane. Ground is flat so vy and vz are zero. I use orthogonal hexaedronds with r=1.07.
I am doing dispersion with species and varying schmidt number. Sct=0.7 gives high numerical diffusion, which increases even more with lower schmidt numbers (e.g. 0.4). vx velocity=(0,43m.s-1/0.4)*ln[(z+z0)/z0]. Z0=0.1m.

I am doing a point source emission and there is concentration of the emitted species even at upwind of its release!

Thanks for your ideas on this.

[Bernhard]

Where (which height) is your point source located?

[mario91]

i am doing different scenarios

point source (~1m3) at 10 m high or 30 m high.

Is that relevant for Numerical diffusion?
Numerical diffusion is higher near ground (e.g 1 meter high) because wind speed is slower?!


Thanks