Frequency response analysis of a (non-)reactive jet in crossflow

Sayadi, Taraneh; Schmid, Peter J.

doi:10.1017/jfm.2021.479

Cited by 6 publications

(5 citation statements)

References 57 publications

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“…(2019) characterized the spatial growth rate for RJICF conditions showing that combustion suppresses the growth of the windward shear layer structures. Further, Sayadi & Schmid (2021) used direct numerical simulation to demonstrate that combustion led to a reduction in the dominant frequencies associated with the shear layer structures in a jet with .…”

Section: Introductionmentioning

confidence: 99%

Combustion and flame position impacts on shear layer dynamics in a reacting jet in cross-flow

et al. 2022

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This study experimentally investigates reacting jets in cross-flow (RJICF), considering flame/shear layer offset, momentum flux ratio ( $J$ ) and density ratio ( $S$ ) effects. These results demonstrate that non-reacting JICF and RJICF can exhibit very similar or completely different dynamics and controlling physics, depending upon streamwise and radial flame location. Consistent with prior measurements of Getsinger et al. (Exp. Fluids, vol. 53 (3), 2012, pp. 783–801), spatial amplification rates of shear layer vortex (SLV) structures increased with decreasing $S$ for non-reacting cases. Similar $S$ dependencies exist for reacting cases in which the flame lay outside the jet shear layer, whose flow topology is also quite similar to non-reacting cases, albeit with reduced SLV growth rates. However, although the reacting cases have lower growth rates, these SLV structures ultimately reach approximately the same peak strength as in the non-reacting cases. Finally, the SLV decay rate in both non-reacting and reacting cases was found to similarly scale inversely with the initial SLV growth rate. As such, primarily inertial mechanisms govern SLV growth and decay for reacting cases where the flame lies outside the shear layer. In contrast, very different behaviour is exhibited by reacting cases where the flame lies inside the shear layer, where the locally increased viscosity exerts significant influences. In these reacting cases, SLV roll-up is completely suppressed and the entire jet column undulates over a long length scale relative to the jet diameter. As such, the relative roles of inertial and viscous mechanisms in controlling combustion influences on the SLV dynamics, changes markedly with shear layer–flame offset.

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Section: Introductionmentioning

confidence: 99%

Combustion and flame position impacts on shear layer dynamics in a reacting jet in cross-flow

et al. 2022

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“…(2016), Qadri et al. (2021) and Sayadi & Schmid (2021). Modal analysis has also been conducted for hot jets (Coenen et al.…”

Section: Introductionmentioning

confidence: 97%

“…In a recent study, we used resolvent analysis to identify the optimal forcing structures in a slot flame, leading to maximal heat release (Wang et al 2022). For linear analysis of diffusion jet flames, one may refer to Nichols & Schmid (2008), Qadri, Chandler & Juniper (2015), Moreno-Boza et al (2016), Qadri et al (2021) and Sayadi & Schmid (2021). Modal analysis has also been conducted for hot jets (Coenen et al 2017;Chakravarthy, Lesshafft & Huerre 2018) and in turbulent swirling flames with the presence of a precessing vortex core (Oberleithner et al 2015a,b).…”

Section: Introductionmentioning

confidence: 99%

Global linear stability analysis of a flame anchored to a cylinder

2022

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This study investigates the linear stability of a laminar premixed flame, anchored on a square cylinder and confined inside a channel. Many modern linear analysis concepts have been developed and validated around non-reacting bluff-body wake flows, and the objective of this paper is to explore whether those tools can be applied with the same success to the study of reacting flows in similar configurations. It is found that linear instability analysis of steady reacting flow states accurately predicts critical flow parameters for the onset of limit-cycle oscillations, when compared to direct numerical simulation performed with a simple one-step reaction scheme in the low Mach number limit. Furthermore, the linear analysis predicts a strong stabilising effect of flame ignition, consistent with documented experiments and numerical simulations. Instability in ignited wake flows is, however, found to set in at sufficiently high Reynolds number, and a linear wavemaker analysis characterises this instability as being driven by hydrodynamic mechanisms of a similar nature as in non-reacting wake flows. The frequency of nonlinear limit-cycle flame oscillations in this unstable regime is retrieved accurately by linear eigenmode analysis performed on the time-averaged mean flow, under the condition that the full set of the reacting flow equations is linearised. If, on the contrary, unsteadiness in the density and in the reaction rate are excluded from the linear model, then the congruence between linear and nonlinear dynamics is lost.

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“…exothermicity, stabilization location) that influence the transitional contour observed for non-reacting cases (figure 1 c ). Specifically for the case of an RJICF, Sayadi & Schmid (2021) demonstrated that a reacting jet shows lower characteristic frequencies compared to non-reacting jets across the same parameters ( and ), and also stronger responsivity to external forcing – hypothesized to be connected to a flame instability.…”

Section: Introductionmentioning

confidence: 99%

Near-field evolution and scaling of shear layer instabilities in a reacting jet in crossflow

et al. 2023

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This study analyses the stability characteristics of the shear layer vortices (SLV) in a reacting jet in crossflow, analysing effects of flame position, momentum flux ratio ( $J$ ) and density ratio ( $S$ ). It utilizes 40 kHz particle image velocimetry to characterize the dominant SLV frequencies, streamwise evolution and convective/global stability characteristics for three different canonical configurations, one non-reacting and two reacting (‘R1’ and ‘R2’). In the non-reacting case, both convective and global instability is observed, depending upon $S$ and $J$ . Qualitatively similar $S$ dependencies occur for the R1 reacting case where the radial flame position lies outside the jet shear layer, albeit with slower SLV growth rates. When the flame lies inside the jet shear layer, the R2 reacting case, a qualitatively different behaviour is observed, as vorticity concentration in the shear layers is suppressed almost completely. Finally, we show that frequency and stability characteristics of the non-reacting and R1 cases can be scaled in a unified manner using a counter-current shear layer model. This model relates these SLV behaviours to a vorticity layer thickness, a velocity scale and an effective density ratio (noting that there are three distinct densities associated with the jet, the crossflow and the burned gases). These parameters were extracted from the data and used to collapse the frequency scaling, and to explain the transition to self-excited oscillatory behaviour.

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Frequency response analysis of a (non-)reactive jet in crossflow

Abstract: Abstract

Cited by 6 publications

References 57 publications

Combustion and flame position impacts on shear layer dynamics in a reacting jet in cross-flow

Combustion and flame position impacts on shear layer dynamics in a reacting jet in cross-flow

Global linear stability analysis of a flame anchored to a cylinder

Near-field evolution and scaling of shear layer instabilities in a reacting jet in crossflow

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