Process-Resolved Attribution of Model-Choice Effects in Compressible Moving-Domain Flow: A Gas-Driven Launch System Study

In compressible moving-domain computations, similar terminal responses can mask energy-input and pressure-transport biases from different origins, preventing physical attribution of modeling differences. A process-resolved model-choice attribution (PMCA) framework is therefore constructed and applied to 28 controlled cases of a 45 mm combustion light gas gun. Flow closure and heat-source normalization volume are varied independently within a shared forward problem. Differences are tracked from energy input through pressure transport and base-pressure work to the ballistic endpoint, and their stability across heat-release amounts and projectile masses is tested. The laminar closure leaves the applied energy unchanged; the first difference arises in pressure transport. Base-pressure work increases by 9.37–10.84%, mainly because temporal coupling between the pressure history and projectile motion is enhanced, rather than because the overall pressure level rises. Fixed-volume normalization first changes energy input: the applied energy exceeds the prescribed value by 3.48–10.81%, controlled by gas-region expansion during heat release. Base-pressure work then increases by 2.49–6.90%, and the two biases are approximately proportional across common conditions. Cross-condition reconstruction shows that the applied energy, pressure histories, and base-pressure work reproduce these differences in held-out conditions, whereas local peak pressures do not exhibit comparable stability. Terminal responses of strongly coupled moving domains are therefore many-to-one mappings of distinct internal transfer processes; terminal agreement does not guarantee agreement in energy input or pressure transport. PMCA advances model comparison for moving-boundary flows with volumetric sources from terminal matching to physical-process consistency checks.