Hi,
I am working on stationary wind-induced velocity profile (Coriolis
force neglected) in un-stratified box domains, constant turbulence
model and no thermal fluxes. I am comparing the numerical
results from boxes with different depths with the theoretical solution
for the steady state (Heaps 1984).
I verified that equilibrium is achieved (I am performing 60 days
simulations) and I found good agreement for shallow boxes (H = 10 m,
30 m, 50 m, see Fig.v_res100m.png in the attachments). A mismatch
between numerical and theoretical solution arises when I simulate deep
boxes (H = 300 m, H = 500 m, always in Fig.v_res100m.png).
As a first attempt I thought it was a time step problem and I reduced
it to meet the conditions in Table 10.1 (FLOW manual) but I didn’t get
any improvement.Then I tried changing the horizontal grid resolution
and I got the results in Fig.v_allres.png (in the attachments), where
I found that finer horizontal resolutions (DX = 20 m, 50 m, 100 m,
square cells) lead to worse results. I got the best match with DX =
2000 m but still I am not there. What if I choose DX = 5000 m?
Now, my questions are:
1. Why are coarser resolutions giving better result?
2. If the answer is the "ADI accuracy" in Table 10.1, why
is reducing time step not providing any change in the solution?
3. Is there a clear/formulated criterion for choosing the proper grid
size according to the depth of the basin?
4. How is it this criterion related to the choice of the background
vertical eddy viscosity (I am modeling with constant turbulence model,
nuz = 0.0373 m2/s)?
Thank you!
Marina
