Analysis of coolant flow and heat transfer in highly rough channels for LRE

The realization of thrust chambers for the new generation of liquid rocket engines is based on the increasingly popular additive layer manufacturing (ALM) techniques. Such techniques show advantages in terms of design flexibility, production costs and times, but at the same time, if used to manufacture tiny cooling channels lead to high relative surface roughness. In principle, the high roughness of channels is not necessarily unfavorable. In general, it is known to increase heat transfer at the cost of increased pressure loss. However, the correlation between the increase of friction and heat transfer changes at high roughness and the commonly used assumption for heat transfer prediction at low roughness may lead to order of magnitude errors if extended to high roughness channels. Therefore, special corrections must be introduced to have a reliable heat transfer prediction model, such as the one proposed in the present study for circular cross-section channels. The present correction of the Spalart-Allmaras one equation model for the closure of Reynolds averaged Navier-Stokes equations if of easy implementation and allows the user to predict realistic values of the convective heat transfer coefficient, in agreement with the correlations and experimental data reported in the literature.