Numerical and Experimental Flame Stabilization Analysis in the New Spinning Combustion Technology Framework

Abstract

Global warming, climate change and pollution are burning environmental issues. To reduce the carbon footprint of the aviation sector, aeronautical companies have been striving to lower engine emissions via the development of reliable lean combustors. In this context, effort has been devoted to the better understanding of various flame dynamics with emphasis on thermoacoustic instabilities, lean blow-off and extinctions. In line with this effort, Safran Helicopter Engines has recently developed and patented the revolutionary spinning combustion technology (SCT) for its next generation of combustors. This technology has indeed great flexibility when it comes to ignition and blow-off capabilities. To better understand the various physical mechanisms occurring in a SCT combustor, a joint numerical and experimental analysis of the flame stabilization in this spinning combustion technology framework has been devised. On the experimental side, the NTNU atmospheric annular combustor has been modified to introduce a relevant azimuthal component of velocity while operating under premixed fuel conditions, following the SCT concept. Note that to reduce temperature at the backplane of the chamber, film cooling is incorporated to avoid fuel injector damage. On the numerical side, high fidelity Large Eddy Simulations of the test bench have been carried out with the

Impact of wall heat transfer in Large Eddy Simulation of flame dynamics in a swirled combustion chamber

“…typically the Biot number 3 is much lower than unity [7,65]). However, this feature cannot be correctly reproduced by the HRT approach which assigns a single thermal resistance value for the whole surface 4 .…”

“…In the current operating conditions, the convective heat transfer at the backplane is low due to low velocity (∼ 2 m/s) in the ORZ, making the conduction heat transfer more efficient. 4 Although imposing a spatial distribution of thermal resistances for each surface is possible, it is in practice difficult to validate due to the marginal EXP LES been fixed, case P30 W is simulated to tune the thermal resistance at the combustion chamber walls. Bénard et al [28] conducted a similar tuning on the same case to find the temperature profile to be imposed at walls with a Dirichlet boundary condition.…”

“…Large Eddy Simulation (LES) is a powerful method to investigate flow physics in complex geometries, including swirling reacting flows often present in gas-turbine combustors [1][2][3][4] and complex multi-physics phenomena such as the coupling between the flame and acoustics as experienced in thermoacoustic combustion instabilities [5,6]. Nevertheless, such simulations are often performed with simple boundary conditions on walls, where temperature is either imposed or adiabaticity is assumed, although these thermal boundary conditions control the heat transfer between the flow and the combustor walls [7].…”

“…3. Imposed local thermal resistance: the local heat flux Φ q can be computed from a reference temperature T re f , the temperature of the fluid at the wall T f provided by the simulation and a suitable thermal resistance R which takes into account the conduction through the solid [6,38] and the external convection and radiation [4]: Φ q = (T f − T re f )/R. 4.…”

Static mesh adaptation for reliable large eddy simulation of turbulent reacting flows

“…Nowadays, thanks to the progress in computer technology and the significant advances in flow modeling (e.g. SGS models 2,3 , near-wall models), LES has become a reference method also for simulating flow physics in complex geometries, including swirling reacting flows in combustors [4][5][6][7] . In the aeronautical sector, together with experiments, because of its ability to accurately predict the interactions between turbulence, acoustic, spray and flame, the LES approach has been widely used 8,9 to study unsteady combustion thermoacoustic instabilities 10,11 , lean blow-off 12,13 , extinctions 14,15 or even to address pollutant emissions 16,17 .…”