Gravity Currents Simulation

Hi I am trying to simulate gravity current induced by saline water in freshwater in a laboratory scale. I have very fine grids and layers. The simulation shows high vertical fluctuations. Is it numerical fluctuation?

Hi Max,

High vertical fluctuations might be due the high horizontal eddy viscosity and vertical eddy viscosity/ molecular diffusivity. Make sure you decrease these values and try to rerun the model. Hopefully your vertical fluctuations be decreased.


I had decreased the vertical diffusion and ran the model. It didn’t help. Does horizontal molecular diffusivity value effect vertical fluctuation?

One possibility is that your time step may be too large. What is your CFL time step as computed by EE?

Thank you for your response.
The CFL timestep is around 0.0015 sec. The courant no. is in the range of 0.2 at the start of simulation to 3.5 at the end of simulation. The grid size are in the range of 0.01m, 0.01m and 0.005 m in x, y and z-directions. What are the best estimate for AVO and ABO?

With this kind of model a lot of detailed assessment is required and continual tweaking to obtain a stable model. Regarding the estimate for AVO (molecular kinematic viscosity) and ABO (molecular diffusivity), they are are somewhat domain dependent – but AVO could be anywhere from 1.0E-7 to 1.0E-3 m2/s . It is expected that ABO is less significant for your purposes.