Improving validation of predictive tools for injector-coupled combustion instabilities

Abstract

This paper summarises work conducted within an ESA TDE project addressing the development of predictive tools for the avoidance of injector-coupled combustion instabilities during the design phase of cryogenic rocket engines. A new experimental combustion chamber was operated for the first time to generate validation data for numerical tools. The chamber was operated at pressures from 40 to 70 bar, at load points both sub- and supercritical for oxygen. The single injection element is representative of those found in number in lower stage engines in terms of dimension and propellant flow rate. Tests have been performed in the frame of the current project with LOX and hydrogen at cryogenic temperatures. The chamber is well instrumented with pressure and temperature sensors, and extraordinarily large optical access windows facilitate the application of highspeed visualisation techniques to resolve the spatial and temporal response of the flame. Achieved experimental conditions were modelled to benchmark existing numerical tools. Different modelling approaches were compared, including the industrial state-of-the-art in hybrid combination of lower order methods, and unsteady CFD of the reacting. flow field. While the hybrid approach is efficient and fast with acceptable accuracy for design purposes, CFD allowed the nature of the coupled modes to be studied in detail, and the dynamic flame response to be predicted.