Computational Fluid Dynamics Analysis of Moisture Ingress in Aircraft Structural Composite Materials

Moisture in composite materials has been proven to be an important issue leading to significant deterioration of commercial aircraft wing structures. Lingering problems associated with this issue that is initiated with defects during manufacturing and finishing include delamination, de-bonding, potential fracture, debris, etc. Despite extensive investigation and refinement in structural design, the water ingress problem persists as no general mitigation technique has yet been developed. Developing sustainable solutions to the water ingress problem can be very time-consuming and costly. The increasing use of composites in the aviation industry and in, for example, honeycomb sandwich components highlights the significant need to address the moisture ingress problem and develop deeper insights which can assist in combating this problem. Experimental testing, although the most dependable approach, can take months, if not years. Numerical simulations provide a powerful and alternative approach to experimental studies for obtaining an insight into the mechanisms and impact of moisture ingress in aircraft composites. The principal advantage is that they can be conducted considerably faster, are less costly than laboratory testing and furthermore can also utilize the results of laboratory studies to aid in visualizing practical problems. Therefore, the present study applies a computational fluid dynamics (CFD) methodology, specifically ANSYS finite volume software and the three fluid-based solvers, Fluent, CFX and ANSYS fluid–structure interaction, to simulate water ingress in composite aerospace structures. It is demonstrated that ANSYS Fluent is a satisfactory computational solver for fundamental studies, providing reasonably accurate results relatively quickly, especially while simulating two-dimensional components. Three-dimensional components are ideally simulated on CFX, although the accuracy achievable is reduced. The structural-fluid-based solver, ANSYS FSI (fluid–structure interaction), unfortunately does not fully implement the material studied leading to reduced accuracy. The simulations reveal interesting features associated with different inlet velocities, inlet fastener hole numbers, void number and dimensions. Pressure, velocity, streamline, total deformation and normal stress plots are presented with extensive interpretation. Furthermore, some possible mitigation pathways for water ingress effects including hydrophobic coatings are outlined.