September 15, 2022 at 1:05 amjms26Subscriber
I am running a 3D steady hypersonic simulation with sharp (90 deg) external expansion corners and am curious if anyone has experienced a similar phenomena I'm getting. I'm using Fluent's density-based, implicit solver with energy on and SST k-omega viscous model. My Reynolds # is ~9.2e6. Density follows ideal gas, viscosity set to Sutherland's law, and thermal conductivity follows a Pr = 0.71.
In order to converge, I needed to reduce the solution limit for pressure minimum to be 1e-3 Pa, and thus the timestep there is sadly on the order of 1e-12 (to maintain a CFL = 1.0).
I would like to use this steady solution as an IC for an unsteady simulation, but (as entirely expected) the timestep in the unsteady runs are on the order of 1e-12 when CFL is slightly below 1.0.
Is this something that's actually expected in this situation? Can pressure/timestep truly be on this very low order of magnitude? It just seems a bit unphysical for this to be occurring. While trying to dive deeper into this, I also have completed numerous additional simulations on highly refined 3D structured grids modeling just a cuboid-shaped trailing edge (see below images):
The inlets are the left side - I used a compressible laminar BL solution as a profile for it. I am able to easily reproduce it this pressure/timestep issue with this above
I also am extremely confident it's not a mesh refinement issue.
Any input is extremely appreciated!!
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