Entropy and Vorticity Wave Generation in Realistic Gas Turbine Combustors

Abstract

Understanding the nature of the unsteady flow at the combustor exit is required to accurately simulate time dependent phenomena in the turbine entry, such as indirect noise generation. Using Large Eddy Simulations of the combustion process in a realistic geometry, we analyse the flow at its exit. Two realistic, near-ground certification operating conditions are considered. Different mechanisms for large-scale flow and thermal structure generation are described, which are ejected into the turbine. Modal decomposition methods are used to extract the spatial and temporal scales at the turbine entry. We find that, depending on the operating condition, the entropy waves convect as elongated streaks in the core of the combustor annulus or the proximity of the walls. The dominant unsteady character of the fluctuations exhibits different spectral properties, i.e. low-frequency in the core and high-frequency towards walls. At the combustor exit, the vortical field is dominated by the swirl in the air inlet, which is found to have little influence on the entropy perturbations. Further, the importance of considering the interaction of multiple fuel injectors and combustion zones in an annular combustor is investigated. It is shown that pulsating circumferential vorticity modes can occur in multi-sector annular combustors but these, however, do not affect the entropy wave distribution.

Design and Commissioning of a Combustor Simulator Combining Swirl and Entropy Wave Generation

“…Sattelmayer [9] states that entropy waves are diffused by the flow turbulence, whereas in [10], the authors demonstrate that entropy wave dispersion from combustor to turbine is weak and the entropy wave strength is preserved at the combustor exit. Furthermore, Semlitsch et al [11] have demonstrated by means of a computational study that swirl also persists at the combustor exit.…”

A posteriori assessment of consumption speed correction for LES with tabulated methods

“…On the other hand, the intricate balance between heat release, turbulence and mixing in this configuration poses challenges for the numerical modeling and a more stable, V-shape configuration can be observed instead (Langella et al, 2020). The expected M-shape was predicted by Semlitsch et al (2019) for this configuration using model C of Table 1 with a dynamic evaluation of the combustion model constant; however, whether this shape was a result of an optimised value of the model constant (via dynamic evaluation) in the SDR model was not investigated. Additional simulations using the subgrid SDR models A and B of Table 1 are carried out in this study and observed to lead respectively to a too-weak M-flame and a strong V-flame near the pilot, regardless of the value used for the model constant within the range indicated in Table 1.…”

Scattering of entropy waves into sound by isolated aerofoils

“…Entropy generation has been the subject of recent investigations using low-order models (Chen, Bomberg & Polifke 2016), numerical simulations (Semlitsch et al. 2019) and experimental measurements (Wang et al. 2019; Weilenmann et al.…”

“…Yoon (2020) found that the entropic cutoff frequency is inversely proportional to the flame residence time. Entropy generation has been the subject of recent investigations using low-order models (Chen, Bomberg & Polifke 2016), numerical simulations (Semlitsch et al 2019) and experimental measurements (Wang et al 2019;Weilenmann et al 2020a).…”