Frequently Asked Question

Engineering extraction

Post-processing converts fields into forces, moments, heat rates, profiles, averages, and balances. Define the surface or volume, direction, reference area, density, speed, averaging interval, and sign convention before calculating the result. A contour helps diagnose a mechanism, but an integrated balance is normally more defensible for a design decision. Sampling must also be fine enough to capture the variation relevant to the output.

F is force, p is pressure, n is surface normal, τ is viscous stress, and A_ref is the declared reference area.

Worked example

For F = 120 N, ρ = 1.2 kg/m³, U = 30 m/s, and A_ref = 0.5 m², C_F = 120/[0.5×1.2×30²×0.5] = 0.444. Recalculate if the reference area, force direction, or averaging definition changes.

Check: confirm surface closure, units, mesh sensitivity, and whether the average is area-, mass-, time-, or volume-weighted.

Engineering check

For Post-Processing Steady-State Results, report the governing output together with the reference condition, mesh or model assumptions, boundary data, convergence evidence, and sensitivity to the dominant input. Check a conservation balance or limiting case before comparing the result with a requirement. If the output changes materially under a reasonable refinement or input variation, the conclusion should be treated as conditional rather than final.

Engineering note

For Post-Processing Steady-State Results, state the intended use, input range, dominant mechanism, units, boundary conditions, acceptance criterion, and evidence owner. Use an independent balance, limiting case, repeat measurement, or sensitivity check to challenge the result. Document the configuration and uncertainty so another engineer can reproduce the reasoning and determine whether the result remains valid after a design, material, boundary, or process change.