Visualising injector-coupled combustion instability in lox/H2 flames

Design, manufacture and test an experimental rocket combustor based on acoustic coupling and generate validation data considered essential in advancing the technology readiness level of predictive tools 

A recently completed technology activity (ESA-IPL-PTM-sfe-st-LE-2015-510) attempted to systematically test the capability of numerical tools in predicting injection-coupled combustion instability in lres. This type of instability is caused by the coupling of the acoustic pressure field in the combustion chamber to acoustic resonance modes in the injectors. The results demonstrated unsatisfactory predictive capability due to challenges in accurately capturing key aspects in the modelling, such as the distribution of fluid properties throughout the injector-chamber system. Further development of the tools for accurate prediction is hindered by a lack of experimental data suitable for validation.;The numerical tools will define the combustor?s stability characteristics. Optical access shall be maximised to capture the extent of the flame and instrumentation, to resolve the coupled acoustics. The proposed experiment will validate the low-order prediction of injection-coupled instability as well as high-fidelity simulation of flame-acoustic interaction response.;The activity encompasses the following tasks:1. Complete detailed design of an injector head and combustion chamber with a single shear-coaxial injector for LOX/H2 tests at pressures up to 6 mpa2. Manufacture the experiment and instrument the injector and chamber3. Perform tests at conditions relevant for industrial engines, at both sub- and supercriticalpressures, and both acoustically stable and unstable regimes (with acoustic forcing if required)4. Characterise the acoustic coupling of the injector and chamber for validation of acoustic models5. Characterise flame response with high-speed visualisation techniques (shadowgraphy amp; flame radiation), with quantitative measurements relevant for CFD model validation6. Derive flame describing functions for implementation in a low-order engine stability model7. Perform calculations of low-order modelling of injector coupling8. Perform calculations of unsteady CFD to reproduce dynamic flame response9. Identify model deficits from detailed experimental results and recommend further development;