Modeling Fluid–Thermal Coupling in Gap Regions of High-Speed Control Surfaces

The gap region of all-movable control surfaces on high-speed vehicles involves complex flow conditions and extreme aerodynamic heating. This study models fluid–thermal coupling in such problems. A global–local decomposition procedure is implemented to manage disparate length scales in the gap region. The fluid–thermal coupling uses boundary condition exchange between a finite volume computational fluid dynamics solver and a finite element thermal solver. Two standard boundary conditions are considered: 1) direct heat flux from the fluid solver and 2) a film boundary condition that incorporates the heat transfer coefficient and adiabatic wall temperature. Results demonstrate that the common heat flux boundary condition can lead to unstable transient thermal solutions and degraded time accuracy if naively implemented with an implicit time integrator. Conversely, the film boundary condition maintains unconditional stability. Additionally, the impact of exchange frequency between fluid and thermal solvers is assessed in terms of computational expense and accuracy. Results highlight the coupled fluid–thermal response in the gap region, with peak surface heating rates up to 50 times baseline values and surface temperatures exceeding 1400 K. A long-duration thermal response of the gap region indicates peak temperatures in the substructure up to 700 K and strong thermal gradients.