Measurements of Turbulent Swirl Flame Dynamics in an Ethylene-fuelled Gas Turbine Model Combustor at Elevated Pressure

The present paper compares the flow structure and flame dynamics during combustion of methane and syngas in a model gas-turbine swirl burner. The burner is based on a design by Turbomeca. The fuel is supplied through injection holes between the swirler blades to provide well-premixed combustion, or fed as a central jet from the swirler’s centerbody to increase flame stability via a pilot flame. The measurements of flow structure and flame front are performed by using the stereo particle image velocimetry and OH planar laser-induced fluorescence methods. The measurements are performed for the atmospheric pressure without preheating and for 2 atm with the air preheated up to 500 K. The flow Reynolds numbers for the non-reacting flows at these two conditions are 1.5 × 103 and 1.0 × 103, respectively. The flame dynamics are analyzed based on a high-speed OH* chemiluminescence imaging. It is found that the flame dynamics at elevated conditions are related with frequent events of flame lift-off and global extinction, followed by re-ignition. The analysis of flow structure via the proper orthogonal decomposition reveals the presence of two different types of coherent flow fluctuations, namely, longitudinal and transverse instability modes. The same procedure is applied to the chemiluminescence images for visualization of bulk movement of the flame front and similar spatial structures are observed. Thus, the longitudinal and transverse instability modes are found in all cases, but for the syngas at the elevated pressure and temperature the longitudinal mode is related to strong thermoacoustic fluctuations. Therefore, the present study demonstrates that a lean syngas flame can become unstable at elevated pressure and temperature conditions due to a greater flame propagation speed, which results in periodic events of flame flash-back, extinction and re-ignition. The reported data is also useful for the validation of numerical simulation codes for syngas flames.

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Numerical Study of Unsteady Flow-Field and Flame Dynamics in a Gas Turbine Model Combustor

Volume 4A: Combustion, Fuels and Emissions ◽

10.1115/gt2014-25784 ◽

2014 ◽

Cited By ~ 3

Author(s):

Moresh J. Wankhede ◽

Ferry A. Tap ◽

Philipp Schapotschnikow ◽

Wilhelmus J. S. Ramaekers

Keyword(s):

Flow Field ◽

Unsteady Flow ◽

Gas Turbine ◽

Swirling Flow ◽

Numerical Study ◽

Swirl Flow ◽

Detached Eddy Simulation ◽

Flame Dynamics ◽

Flamelet Generated Manifold ◽

Turbine Model

In swirl-stabilized gas turbine combustors, interaction between unsteady flow-field and flame dynamics play a key role in driving several types of combustion instabilities, establishing flame location and its structure and influencing heat release rates. This is challenging to understand and computationally expensive to resolve in detail. In this study, a highly turbulent and swirling flow-flame dynamics in a gas turbine model combustor is characterized numerically using unsteady Reynolds-averaged Navier Stokes (URANS) and detached eddy simulation (DES) based computational fluid dynamics (CFD) methods. From flame representation point of view, the Flamelet Generated Manifold (FGM) method is used to reduce combustion chemistry (which still includes detailed reaction kinetics and species diffusion in reaction layers) and hence computational requirements. The helical precessing vortex core (PVC) instability and its influence on downstream flow/flame dynamics is captured. Further insight is gained into URANS and DES methods capabilities in simulating various coherent swirl flow structures such as central toroidal recirculation zone (CTRZ) and outer recirculation zones (ORZ) as well as fuel-air mixing patterns. NOx emission, which is currently a high-priority design objective due to stringent pollutant regulations, is also computed. The results show that the numerically captured swirling flow-flame dynamics is in accordance with the experimental observations and measurements.

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