Open cbegeman opened 4 years ago
A few more figures for the same case
@cbegeman one other possibility besides altering K_max is to allow the Poincare constant to have a length scale that is a function of stratification (similar to what Schuman did for Smagorinsky), which would limit SGS fluxes in high stratification scenarios.
@vanroekel Per our conversation yesterday, I looked into the l_stable
variable currently used in PALM (Deardorff, 1980) and it is a function of the SGS TKE, which we do not solve for with AMD. Are you aware of other mixing length scales that are a function of stratification without a dependence on e
?
shoot of course, I forgot that. Let me think about this some more.
One idea is to limit the mixing length to l_wall
as in PALM's closure, without the stratification dependence. This could help somewhat.
It might be worth a shot, I worry though that we may find ourselves continually lowering the influence for different tests.
Summary of our conversation yesterday: The stratification term is only dominant when TKE is low, and in that case the viscosity is unrealistically high. Cat Vreugdenhil has found that in a stratified Couette flow, the stratification term is not dominant. It could be the case that the stratification term is not important when the flow is well-resolved by LES but is important for these simulations with dz >= 0.25m. In the absence of more information we proceed with simulations in which AMD is used but the stratification term is removed (see PR https://github.com/xylar/palm_les_lanl/pull/72). The scale-dependent Lagrangian dynamic model of Bou-Zeid et al. (2005) is a good candidate for an alternate sub-grid scheme.
@xylar @vanroekel @katsmith133 I'm running into high
km
values in the second grid level below melting ice interfaces as a result of high buoyancy gradients. This problem was noted here, at which time the problem seemed limited to just the first grid level below the interface.I'd like to get your thoughts on possible remedies, whether that's in code changes to AMD, a more restrictive km_max or different simulation configuration. Thanks! Note, km_max = 0.1. Namelist file here: /lustre/scratch3/turquoise/cbegeman/palm/jobs/test_ocean_amd_mcphee_lowres_disturb5h_cd1e-2_rotation