Accurate thermal simulations for the purpose of thermal or infrared signature management require accurate representation of all modes of heat transfer. For scenarios with complex fluid dynamics and convective heat transfer, traditional options have included very simple 0D methods or very computationally expensive 3D CFD simulations. Motivated by adding options between these extremes and tuning the method to a heat transfer focus, a 3D fluid dynamics solver is developed that is tightly integrated and automatically coupled with the MuSES thermal and EO/IR simulation software. Key applications of interest include wind flow around ground vehicles for the purpose of infrared signature management and HVAC air flow within cabins for the purpose of thermal management. The flow solver uses novel numerical techniques to simplify the standard Navier-Stokes equations and avoid calculations which may not be necessary for thermal simulations. Several domain meshing strategies, physics models, numerical approaches, and test models are developed with the goal of ease of use and minimal additional time investment for a thermal simulation.