Modeling liquid rocket engine coolant flow and heat transfer in high roughness channels

Abstract

The design of thrust chambers of modern liquid rocket engines is moving towards the use of additive layer manufacturing techniques, which are replacing traditional techniques because of its inherent advantages of customization and flexibility of design and prototyping phase that in the end leads to advantages in terms of production costs and times. In this framework, the realization of suitable cooling channels, which are characterized by tiny cross section, can lead to high relative surface roughness, as a result of the manufacturing process. Despite the increased friction loss, high roughness channels are considered often with interest because of the corresponding increase of heat transfer and thus cooling efficiency. However, the correlation between the increase of friction and heat transfer changes at high roughness. As a consequence, the commonly used assumption for heat transfer prediction at low roughness may lead to order of magnitude errors if extended to high roughness channels. To respond to the request of a reliable heat transfer prediction model, the correction introduced by Aupoix to the Spalart-Allmaras turbulence model to take into account for high roughness in external flows is extended and validated here for the application to high roughness channels. The implementation of the proposed correction allows to predict realistic values of the convective heat transfer coefficient, in agreement with the correlations reported in the literature.