ORCID Profile
0000-0001-7664-306X
Current Organisations
Sharif University of Technology
,
University of Oxford
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Publisher: American Institute of Aeronautics and Astronautics (AIAA)
Date: 03-2018
DOI: 10.2514/1.B36569
Publisher: SAGE Publications
Date: 12-2013
DOI: 10.1260/1756-8277.5.4.309
Abstract: Acoustically excited lean premixed low-swirl flames were experimentally investigated to gain a better understanding of detrimental thermoacoustic couplings which can occur in applications like low-NO x gas turbines. Propane-air flames were imaged and analyzed at equivalence ratios of 0.6 to 0.8, mean flow velocities of 3.5 to 5.5 m/s and excitation frequencies of 135 Hz to 555 Hz. It was observed that with increasing excitation frequency, mean flame shape gradually became wider up to a Strouhal number of about 2.5 and then slowly reverted back to the unexcited flame shape. Such large changes in mean flame shape and possibly flow field under acoustic excitations can significantly affect flame dynamics. Increased heat release fluctuations were observed in the flame shear layer at Strouhal numbers from 1 to 2. Rolling up of the flame by vortices was suggested as a driving mechanism for these fluctuations which may lead to combustion instabilities.
Publisher: Elsevier BV
Date: 12-2021
Publisher: Elsevier BV
Date: 09-2023
Publisher: Elsevier BV
Date: 05-2023
Publisher: Springer Science and Business Media LLC
Date: 24-03-2021
Publisher: Elsevier BV
Date: 2021
Publisher: Cambridge University Press (CUP)
Date: 15-03-2021
DOI: 10.1017/JFM.2021.78
Publisher: Elsevier BV
Date: 04-2023
Publisher: Elsevier BV
Date: 11-2022
Publisher: AIP Publishing
Date: 04-2020
DOI: 10.1063/1.5133859
Abstract: This numerical study investigated the effects of the fresh mixture temperature on thermoacoustic instabilities in a lean premixed swirl-stabilized combustion chamber by utilizing high-fidelity, fully compressible large eddy simulations. At low fresh mixture temperatures, the side recirculation zone stabilized the premixed flame on the boundary of the burner rim, while the central part of the flame was detached from the burner due to the inability of the central recirculation zone to assist in flame stabilization. However, the central recirculation zone became stable enough to stabilize the central portion of the flame near the burner rim as the fresh mixture temperature increased. Moreover, the coherencies and penetration depths of the coherent structures and precessing vortex cores in the combustor increased with the fresh mixture temperature. Analyses showed that the limit cycle instabilities that occurred at low fresh mixture temperatures resulted from coupling between heat release fluctuations and the first tangential acoustic mode of the combustor. However, as the fresh mixture temperature increased, a combustor dynamics transition occurred, through which the coupling between heat release and pressure fluctuations shifted toward the mixed tangential and radial acoustical modes of the combustor. During this mode transition, limit cycle oscillations were replaced by burst oscillations. The results revealed that recirculation zones are the key features that trigger thermoacoustic instabilities at low fresh mixture temperatures, while coherent structures and precessing vortex cores are the main combustion instability drivers at high fresh mixture temperatures.
Publisher: AIP Publishing
Date: 09-2019
DOI: 10.1063/1.5118826
Abstract: In this study, simultaneous particle image velocimetry and planar laser induced fluorescence of hydroxyl radical, chemiluminescence imaging, and hot-wire measurements are utilized to study reacting low swirl flow dynamics under low to high litude acoustic excitations. Results show that a temporal weak recirculation zone exists downstream of the flame, which is enlarged in size under acoustic excitations. Investigations show that temporal behaviors of this recirculation zone play a significant role in flame movements and instabilities. As the acoustic wave litude increases, the flame lift-off distance changes drastically, resulting in flame instabilities (flashback and blowout) during the excitations. Prior to the flame blowout, although the flame lift-off distance responds periodically to the acoustic perturbations, heat release fluctuations display an aperiodic response. Flame dynamics are further studied by calculated power spectra of acoustic velocity and heat release fluctuations and reconstructed phase portraits of heat release fluctuations. Investigations show that increasing the forcing litude results in more deterministic features in the flame dynamics and lification of the higher harmonic modes in the heat release fluctuations. However, such regular patterns become scattered prior to the flame blowout due to the existence of nonlinearities induced by high litude excitations. It is speculated that flame blowout can be a symptom of such nonlinearities. The Rayleigh index is measured to study thermoacoustic couplings. At low litude excitations, various coupling patterns occur at the flame. However, such complex patterns are replaced by simple coherent patterns, when the flame is excited by high litude acoustic perturbations.
Publisher: Elsevier BV
Date: 07-2022
Publisher: Elsevier BV
Date: 11-2022
Publisher: Springer Science and Business Media LLC
Date: 22-11-2016
Publisher: Informa UK Limited
Date: 30-09-2023
Publisher: Elsevier BV
Date: 12-2022
Publisher: AIP Publishing
Date: 07-2019
DOI: 10.1063/1.5108856
Abstract: A comprehensive study on influences of hydrodynamic features of a swirling flow on thermoacoustic instabilities in a swirl stabilized combustor is performed by using large eddy simulations along with the dynamically thickened flame combustion model. The governing equations in full compressible form are solved by an in-house developed high-order numerical solver. The combustor is simulated in six different equivalence ratios to assess effects of equivalence ratio on the contributions of hydrodynamic features in inducing thermoacoustic instabilities. The obtained results show that the combustor suffers from combustion instabilities at equivalence ratios of 0.55, 0.6, 0.75, and 0.8, while it is stable at the midrange equivalence ratios (0.65 and 0.7). The results indicate that the instabilities are the result of the lock-in mechanism between heat release fluctuations induced by hydrodynamic features and the mixed first tangential and quarter wave longitudinal mode of the combustor. Investigations are carried out to evaluate contributions of central and side recirculation zones, precessing vortex core, and coherent structures in heat release fluctuations. The results show that contributions of hydrodynamic features highly depend on the combustor operating condition. At low equivalence ratios (0.55 and 0.6), coherent structures and side and central recirculation zones are the key features to induce heat release fluctuations in phase with the acoustic perturbations, while at equivalence ratios of 0.75 and 0.8, coherent structures and precessing vortex core play the main role in inducing combustion instabilities.
Publisher: Springer Science and Business Media LLC
Date: 04-07-2017
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Mohammad Shahsavari.