Theoretical Innovations in Combining Analytical, Experimental, and Computational Combustion Stability Analysis

The occurrence of combustion instability has long been a matter of serious concern in the development of liquid-propellant rocket engines due to the high rate of energy release in a confined volume in which energy losses are relatively small. Shear layer instabilities and intermittent growth rates of the mixing layer cause fluctuations in the burning rates and result in acoustic waves triggering flow instabilities. These flow oscillations may grow uncontrolled if there is a positive feedback between the oscillatory heat release at the combustion front and acoustic waves within the combustion chamber. The proposed work will focus on shear layers and mixing around single and multiple jets under acoustic excitation. Conditions that lead to positive feedback between the acoustic waves and shear layers will be identified and the influence of amplitude and frequency of excitation on shear layer development will be quantified. BENEFIT: The study of shear layer development around fuel jets in the presence of acoustic excitation will furnish useful information concerning the instability mechanisms in rocket engines. It will extend experimental data and enable identification of cause and effect relationships between flow features evolving in three-dimensional, unsteady fields. The outcome of the proposed research has the potential to help build stable liquid propellant rocket engines. The proposed work will support the experimental investigation at AFRL. The experimental results will serve as a validation of the proposed methodology. The simulation will augment the experimental observations by providing a complete, three dimensional view of the evolving flow.