A Simple Empirical Method for Estimating Extreme Air Velocities from CFD Mean-Flow Statistics: Validation Using ISS Columbus and CASA Ventilation Data

Computational Fluid Dynamics (CFD) simulations based on Reynolds-Averaged Navier-Stokes (RANS) models are widely used for spacecraft cabin ventilation design; however, they primarily provide mean-flow quantities and often underestimate velocity extremes relevant to crew comfort, ventilation effectiveness, and stagnation-zone assessment. This study presents a simple empirical post-processing framework for estimating extreme air velocities from CFD mean-flow statistics. The proposed approach expresses the upper velocity envelope as a function of the local mean velocity and standard deviation through a single empirical coefficient, Kc. The method is calibrated using published velocity-field data from International Space Station (ISS) Crew Quarters studies and subsequently examined against independent ISS ventilation datasets, including the Columbus module and Crew Alternative Sleeping Area (CASA) configurations. Analysis of digitized experimental and CFD-derived velocity distributions yields a robust median coefficient of approximately Kc = 4.5, while external datasets indicate p99-equivalent values generally within the range Kc ≈ 4–6. Independent validation evidence from Columbus ventilation studies demonstrates that accounting for velocity fluctuations substantially improves agreement with experimental observations, reducing distribution mismatch by approximately 83% compared with uncorrected mean-velocity predictions. The results suggest that a simple statistical correction applied to standard CFD outputs can provide practical estimates of extreme ventilation velocities without the computational cost of Large Eddy Simulation (LES). While the proposed framework should be regarded as a conservative upper-envelope estimator rather than a universal turbulence closure, the consistency observed across multiple ISS ventilation datasets indicates that it offers a useful engineering tool for preliminary spacecraft cabin ventilation assessment and design.