CFD modeling of moisture accumulation in the insulation layers of an aircraft

Abstract

Modern commercial airplanes operate in an extreme atmospheric environment, where they can easily acquire a large amount of moisture within the porous insulation layers. The accumulated moisture may increase the aircraft’s weight, induce corrosion, and degrade thermal and sound insulation performance. This investigation proposes a numerical model to predict moisture and heat transfer within porous insulation blankets. To capture natural convection flows of gases within the porous material, the volumetric-based Navier–Stokes equations were solved. The moisture in three phases was considered and the phase change rates between any two phases were predicted. The latent heat of absorption or release during phase changes is balanced with the heat conduction in the mixture and the heat convection of the gaseous substances. To validate the model, the moisture gain in a reduced-scale aircraft mockup was measured by placing the mockup inside an altitude psychrometric chamber. Then the validated model was applied to predict the moisture accumulation in a rectangular insulation block from a Boeing 777 airplane. The results reveal that the flight altitude and cabin humidity are the two key parameters determining the moisture accumulation rates. A high outer shell surface temperature is helpful for reducing moisture gain in the insulation blankets.