As part of their doctoral research at TU Munich, the Anovion founders designed, commissioned and operated a megawatt class thermofluid-dynamic test rig. The research behind this project was motivated by the need to predict thermoacoustic stability of novel combustor designs in power generating gas turbines. With the created test environment, spatially and temporally resolved measurements of the heat release and acoustic pulsations in an unstable combustion were conducted. Main research achievements were a reconstruction of high-frequency thermoacoustic modulation phenomena and analytic models with which thermoacoustic stability prediction is improved.
Key figures
The conditions in the test stand were harsh, so special equipment was designed to enable measurements at high temperatures and with the required resolution.
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Flame temperature in which we measured acoustic fluctuations with special microphones
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Thermal power release of the two staged combustion which we sensibly controlled
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Thermal power density of the reheat flame to which we designed optical access for high resolution measurements
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High-amplitude thermoacoustic limit cycle pulsations occured in the combustor
Project summary
Modern, low-emission gas turbines present a crucial component for building a power grid that predominantly relies on renewable sources.
Specifically, such gas turbine are used to compensate for load fluctuations induced by the unpredictable availability of the primary renewable source, i.e. wind and solar energy. Thus, besides high-efficiencies, gas turbines need to be highly dynamic and responsive. For this reason, lean-premixed combustion is utilized to power the gas turbines, which achieves the latter requirements, yet, renders the systems prone to developed thermoacoustic instabilities.
These instabilities are understood as high-amplitude pressure pulsations at distinct frequencies that are driven by oscillating heat release rates of the flame in a positive feedback. Their occurrence can be detrimental for the low emissivity of the combustion process or even damage the system. Thus, their avoidance or suppression is of paramount importance for developing and operate novel combustion systems for power generating gas turbines.
“We have succeeded in designing a thermoacoustic experiment that exhibits high-frequency thermoacoustics in a gas turbine-like reheat flame. The development of such an experiment is a great challenge and has led to unprecedented insights.”
Frederik BergerCo-Founder, Anovion
The greatest challenge was to establish an auto-ignition reheat flame at atmospheric conditions and to modify the system in such a way that it generates thermoacoustic pulsations at high frequencies.
As part of their doctoral research at the Technical University of Munich, Anovion’s founders engineered, build, and commissioned a mega-watt class thermo-fluiddynamic test-stand from scratch. The test-stand required to reproduce two-staged premixed combustion as occurs in modern gas turbine systems. The primary purpose of the test-stand was to experimentally investigate high-frequency thermoacoustic instabilities. The associated research objectives were to gain physical understanding, generate measurement data for model development and validation, and derive best-practice guidelines on how to avoid or suppress the occurrence of thermoacoustic instabilities.
The engineering design work was guided by model-based principles, which consisted of the following steps:
- Thermal-fluid calculations as basis for an initial 1D conceptual design.
- Derivation of 3D CAD design of important components (combustion chambers, injection and mixing system, cooling system, exhaust, control, measurement, and diagnostic setup) from the conceptual design.
- Execution of high-fidelity numerical analyses and design studies by means of computational acoustics, computational fluid dynamics and conjugate heat transfer simulations.
- Working out the detailed design of the test-stand in an iterative approach with the numerical analyses until performance targets were met.
- Development of controlling algorithms and implementation of controlling software for the rig operation
- Generation of manufacturing and assembly documentation upon design approval
Then, the test-stand was built and commissioned. Highly precise control capabilities of air, fuel and coolant fluid streams were required, which was realized by utilizing real-time equipment to ensure a robust operationability. This was accompanied with the development of the control system for operating the test-stand, which was required to be capable of synchronously sampling and processing measurement data.
The greatest design challenges for the test-stand were (1) to establish a representative auto-ignition flame at atmospheric conditions as occurring in real gas turbine systems, (2) to controllably generate thermoacoustic pulsations in order to measure the acoustic and heat release quantities in close vicinity to the flame. For the latter measurements, image intensified high-speed cameras and special high-temperature resistant microphones in the flame zone were used to synchronously obtain data of the flame and acoustic oscillations.
The test-stand exhibited the following key features and performance values:
- Realistic reproduction of gas turbine combustion by means of a two sequentially arranged combustion chambers. The first and second chamber hosted an aerodynamically and self-ignition stabilized flame, respectively.
- Operational thermal power ratings were up to 0.7MW at maximum local thermal power densities of 20 MW/m³ (at 1bara) and temperatures of up to 2000K.
- Spatially and temporally resolved measurement and diagnostics capabilities for: dynamic fluid pressures, static and dynamic heat release rates, flow meters, temperatures of gas and coolant flows
- Controllably generating thermoacoustic oscillations at distinct frequencies the second chamber with self-ignition stabilized combustion