Modeling of Gaseous Reacting Flow and Thermal Environment of Liquid Rocket Injectors.

Abstract

Reacting flow and thermal fields around the injector critically affect the performance and life of liquid rocket engines. The performance gain by enhanced mixing is often countered by increased heat flux to the chamber wall, which can result in material failure. A CFD based design approach can aid in optimization of competing objectives by providing detailed flow field data and an ability to feasibly evaluate a large number of design configurations. To address issues related to the CFD analysis of such flows, various turbulence and combustion modeling aspects are assessed.

Laminar finite-rate chemistry and steady laminar flamelet combustion models are adopted to facilitate individual assessments of turbulence-chemistry interactions (TCI) and chemical non-equilibrium. Besides the experimental wall heat transfer information, assessments are aided by evaluations of time scales, grid sensitivity, wall treatments and kinetic schemes. Several multi-element injector configurations are considered to study element-to-element interactions. Under the conditions considered, chemical non-equilibrium effect is found to be unimportant. TCI is found to noticeably alter the flow and thermal fields near the injector and the flame surface. In the multi-element injector case, due to proximity of the outer row injector elements to the wall, wall heat flux distribution is also significantly affected by TCI. The near wall treatment is found to critically affect wall heat flux predictions. A zonal treatment, blending the low-Reynolds number model and the law-of-the-wall approach is shown to improve the accuracy significantly.

Porous materials such as Rigimesh are often used as the injector face plate of liquid rocket engines. A multi-scale model, which eliminates the empirical dependence of conventional analysis methods, is developed. The resulting model is tested using experimental information showing excellent agreement.

The model development and assessment presented for both injector flows and transport in porous materials will be valuable for advancement of computational tools aiding design and analysis of liquid rocket engine flows. Towards this end, further challenges such as the modeling of liquid propellants and the atomization process, detailed characterization of the Rigimesh material and more rigorous validation need to be addressed.