Amplitude-Dependent Damping and Driving Rates of High-Frequency Thermoacoustic Oscillations in a Lab-Scale Lean-Premixed Gas Turbine Combustor
| Autor: | Thomas Hofmeister, Thomas Sattelmayer |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
Gas turbines
Physics business.industry Mechanical Engineering Lab scale Energy Engineering and Power Technology Aerospace Engineering Mechanics Dissipation Computational fluid dynamics Vorticity Physics::Fluid Dynamics Fuel Technology Amplitude Nuclear Energy and Engineering Combustor Combustion chamber business |
| Zdroj: | Volume 3A: Combustion, Fuels, and Emissions. |
| Popis: | This paper presents the numerical investigations of amplitude-dependent stability behavior of thermoacoustic oscillations at screech level frequencies in a lean-premixed, atmospheric, swirl-stabilized, lab-scale gas turbine combustor. A hybrid Computational Fluid Dynamics / Computational AeroAcoustics (CFD / CAA) approach is applied to individually compute thermoacoustic damping and driving rates for various acoustic amplitude levels at the combustors’ first transversal (T1) eigenfrequency. Harmonically forced CFD simulations with the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations mimic the real combustor’s rotating T1 eigenmode. A slow and monotonous increase of the forcing amplitude over time allows observation of the amplitude-dependent flow field and flame evolution. In accordance with measured OH*-chemiluminescence images, a pulsation amplitude-dependent flame contraction is reproduced in the CFD simulations, where acoustically induced backflow at the combustion chamber inlet is identified as the root-cause of this phenomenon. At several amplitude levels, period-averaged flow fields are then denoted as reference states, which serve as inputs for the CAA part. There, eigenfrequency simulations with linearized flow equations are performed with the Finite Element Method (FEM). The outcomes are damping and driving rates as a response to the amplitude dependency of the mean flow field, which combined give the net thermoacoustic growth rate. It is found that driving due to flame-acoustics interactions only governs a weak amplitude dependency, which agrees with prior, experimentally based studies at the authors’ institute. This disqualifies the perception of heat release saturation as the root-cause for limit-cycle oscillations — at least in this high-frequency thermoacoustic system. Instead, significantly increased dissipation due to the interaction of acoustically induced vorticity perturbations with the mean flow is identified, which may explain the formation of a limit-cycle. |
| Databáze: | OpenAIRE |
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