Global Sensitivity and Trade-Off Analyses for Multi-Objective Liquid Rocket Injector Design

This paper presents sensitivity and trade-off analyses for the design of a gaseous injector used for liquid rocket propulsion whose geometry (hydrogen flow angle, hydrogen and oxygen flow areas and oxygen post tip thickness) is sought to optimize performance (combustion length) and life/survivability (temperatures at three different locations). The analyses are conducted using data available from surrogate models of the design objectives, and the multi-objective optima (Pareto optimal front, POF) generated with the aid of multi-objective genetic algorithm and local search method. The trade-offs among objectives are estimated in different clusters (identified through a hierarchical clustering algorithm) along the POF. Sensitivity analyses are conducted using a variance-based non-parametric approach over the whole design space as well as on the clusters at the POF. The former analysis help identify the contribution of the design variables to the objective variability. The latter analysis highlights: the variability of the design variables and the objectives within a cluster of the POF (using box plots), and the relationship between the design variables and the objectives (using partial correlation coefficients). Additionally, the trade-offs between selected pairs of objectives are also analyzed.