Ram Pressure Rewrites the Rules: How Suppressed Turbulent Folding Explains Da Scaling in Astrophysical Plasmas

Numerical experiments on turbulent radiative mixing layers (TRMLs) reveal a transition in cooling luminosity scaling once the Damköhler number Da = t_eddy / t_cool exceeds unity. The arXiv preprint (2026) demonstrates that the shift from Ė_cool ∝ Da^{1/2} to Ė_cool ∝ Da^{1/4} arises because ram pressure of inflowing gas exceeds turbulent pressure, flattening the fractal interface and limiting surface area available for radiative losses. This preprint remains unreviewed and relies on idealized hydrodynamic simulations without magnetic fields or cosmic-ray feedback, limiting direct applicability to magnetized interstellar or intracluster media. Related work by Fielding et al. (MNRAS 2020) on galactic wind entrainment similarly identifies cooling-layer regulation of mass loading but attributes discrepancies to resolution rather than explicit ram-pressure suppression. A 2022 ApJ study of supernova remnant interfaces further shows observed filamentary structures whose surface brightness saturates at high cooling rates, consistent with the preprint’s mechanism yet lacking the Da parameterization. Together these indicate that fast-cooling mixing layers across scales—from circumgalactic gas to cluster plasmas—share a common dynamical bottleneck where inflow ram pressure caps turbulent folding, thereby setting observable emission measures and structure lifetimes.