A Log-Gaussian Scale-Space Limiter for Hybrid Continuum--Ballistic Gas Dynamics

Abstract

We propose a log-Gaussian scale-space limiter for hybrid continuum-ballistic gas dynamics. The method defines complementary continuum and ballistic weights as Gaussian cumulative probabilities in logarithmic Knudsen-number space. This construction gives a smooth numerical transition between Navier-Stokes-Fourier and kinetic/free-molecular fluxes and suppresses asymptotically invalid correction branches in the continuum and free-molecular limits. The limiter is incorporated into a conservative finite-volume interface flux by blending a Navier-Stokes-Fourier flux with a half-range Maxwellian kinetic flux. Numerical tests using one-dimensional DVM/BGK Fourier and Couette benchmarks show that rarefaction corrections improve macroscopic profiles relative to NSF. A parameter scan over the transition center and width gives a DVM/BGK-calibrated pair K0=0.03 and sigma=2.5, reducing the combined mean profile error by about 40% for the tested planar wall-bounded flows. The paper is intended as a proof-of-concept numerical method and calibration study.