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Computational Modeling of Coupled Acoustic and Combustion Phenomena Inherent to Gas Turbine Engines


OBJECTIVE: Development and validation of a computational model to simulate combustion processes coupled with acoustic phenomena to quantitatively predict acoustic waves, i.e. screech and rumble, inherent to gas turbine engines. DESCRIPTION: There is a need for a validated computational model to simulate the combustion processes coupled with acoustic phenomena focus for military engine augmentors, i.e. afterburners, where coupled combustion and acoustic phenomena generate instabilities. Liquid fuel-injection combustion processes can stimulate strong acoustic waves inside hot sections of turbine engines. The origin of the acoustic waves can be traced, in some instances, to interactions of heat release combustion processes and geometric features of hot-section components. High-enthalpy heat release conditions inside the augmentor can stimulate strong longitudinal and circumferential standing acoustic waves, bounded in the axial upstream direction by the turbine exhaust case and downstream by the nozzle throat location. The amplitude of the waves can rapidly increase causing severe structural damage to the augmentor liner, which can limit the operability of the augmentor. These instabilities are known as"rumble"at low frequencies (<100 Hz) and"screech"at higher frequencies (100 to 500 Hz). Currently, many engine manufacturers utilize computer codes based on empirical correlations to qualitatively predict these effects. The qualitative correlations have limited use in augmentor design, and usually fail to predict rumble and screech when the operating conditions extend beyond the bounds of the empirical correlation parameters. Existing measurements from applicable combustion unit/rig experiments and/or augmentor development tests should be researched, identified and utilized to generate a more cogent understanding of the basic processes that contribute to instabilities in engine augmentors. The approach should incorporate a detailed sensitivity study of various turbine engine geometry configuration and performance parameters to be utilized in the model development such as pressure losses, flame holding, length of the combustion zone, geometry, wall heating and etc. Deliverables should include the source code. Reliance on licensed software should be identified, but avoided if possible. PHASE I: Perform a comprehensive evaluation and documentation of the current state-of-the-art technology, identify existing measurements applicable to this effort, and provide a rigorous description of the approach and methodology to be employed in developing and validating a high-fidelity numerical model. PHASE II: Development and validation of the high-fidelity, physics-based computational model optimized for high performance computational environments. PHASE III: Acoustic and combustion instability analysis is vital to military and commercial turbine engines to augment engine development and testing. REFERENCES: 1. Ebrahimi, Houshang. B."Overview of Gas Turbine Augmenter Design, Operation, and Combustion Oscillation,"AIAA 2006-4916, Joint Propulsion Conference, July 12, 2006. 2. Trinh, H.P., and Chen, C.P.,"Modeling of Turbulence Effects on Liquid Jet Atomization and Breakup,"AIAA 2005-0154, 43rd AIAA Aerospace Sciences Meeting and Exhibit, 10-13 January, 2004, Reno, Nevada. 3. Morgans, A. S., and Dowling, A.P.,"Model-Based Control of Combustion Instabilities,"Journal of Sound and Vibration, Vol. 299, No. 1-2, pp. 1-82.
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