Heat Transfer: Time step size sensitivity of transient heat transfer results with extruded elements
Issue
Transient thermal simulations with extruded mesh can show dramatically different thermal results when the time-step size is small.
In one particular case, a steady state analysis and a transient analysis with a time step size of 50 seconds both show a maximum temperature of 580 C. Reducing the time step to 1 second and re-running the same analysis produced lower maximum temperatures (220 C).
Solution
When an analysis with extruded mesh varies with time, diagonal terms dominate the thermal equations if the time step is sufficiently small. The equations that link the extruded mesh to non-extruded portions are not strong enough to capture the thermal connection adequately. The result is inadequate heat flow.
Increase the time step size.
Mesh such volumes using a standard tetrahedral mesh instead of an extruded mesh.
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