Abstract Time-dependent Navier–Stokes equations are solved in conjunction with the radiative transfer equation by coupling a previously developed direct numerical simulation-based computational fluid dynamics code to an existing radiation code, both based on the method of lines approach. The temperature profiles predicted by the coupled code are validated against steady-state solutions available in the literature for laminar, axisymmetric, hydrodynamically developed flow of a gray, absorbing, emitting fluid in a heated pipe. Favorable comparisons show the predictive accuracy and reliability of the coupling strategy employed. Transient solutions for a more realistic heat transfer problem are also demonstrated for simultaneous hydrodynamic and thermal development.