Vortex Phase-Jitter in Acoustically Excited Bluff Body Flames

Shanbhogue, Santosh J.; Seelhorst, Michael; Lieuwen, Tim

doi:10.1260/175682709789141528

Cited by 20 publications

(7 citation statements)

References 33 publications

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“…Wake vortices are formed at slightly different downstream locations in different cycles, a feature known as "phase jitter" [49]. When multiple bluff bodies are placed in parallel, this leads to further intermittency and jitter caused by interactions between adjacent flows.…”

Section: Variations In Time-averaged Flow Topologymentioning

confidence: 99%

Flow dynamics in a variable-spacing, three bluff-body flowfield

2018

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This work explores the wake dynamics of systems with three bluff bodies with variable spacing. Studies of single-wake systems have shown that coherent wake vortices have a regular, and predictable, periodicity. A growing literature of dual-wake studies has shown that multi-wake systems are more stochastic than single-wake systems, and their dynamics are highly dependent on the spacing between the wakes. Here, we expand on this literature by investigating three-wake systems, and find that the coherent dynamics of the wakes are highly intermittent. We use proper orthogonal decomposition to extract the most energetic modes of the three-wake system at six bluff-body spacings that span a range of dynamical "regimes." After describing the time-dependent behavior of the interacting wakes in these regimes, we use a statistical approach to describe the relative phase between oscillations in each of the wakes, identifying regimes where oscillations are more or less random. Interestingly, the wake oscillations are less random when the bluff bodies are positioned very close and relatively far from each other. In between these two extremes, an intermediary regime is identified where the wake oscillations are almost completely random; this finding parallels data from the dual-wake literature. Finally, we discuss the implications of the observed behaviors and possible future directions for this work. I. INTRODUCTION The goal of this paper is to characterize transitions in flow development and stability characteristics with variations in bluff-body spacing in a three bluff-body flow field. The applications of this work are far reaching, from flame holders in jet engine augmentors, to air moving though power transmission lines, to flows through heat exchangers, to piers supporting trusses in unsteady waters. In each of these applications, adjacent flow fields, or a series of individual wakes, experience a significant level of interaction. The interaction can change both the time-averaged and dynamical characteristics of

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Section: Variations In Time-averaged Flow Topologymentioning

confidence: 99%

Flow dynamics in a variable-spacing, three bluff-body flowfield

2018

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Section: Overview Of Space-only Pod and Permuted Pod Propertiesmentioning

confidence: 99%

“…To emulate turbulent flow data and prevent rank deficiencies, these advecting structures are superimposed onto a background of low-intensity noise sampled from a uniform distribution with ±20 % relative amplitude. Additionally, the centre locations of the high-intensity squares are randomly perturbed in order to simulate 'phase jitter' effects (Shanbhogue, Seelhorst & Lieuwen 2009). These perturbations correspond to spatial shifts of ±1.75 pixels in both s and n. To illustrate, three consecutive temporal snapshots of the disturbance scalar fields are displayed in figure 1, where the advecting structures travel along the nominal trajectory indicated by the red dotted line oriented at an angle α with respect to the s coordinate axis.…”

Section: Model Problem With Advecting Structuresmentioning

confidence: 99%

Permuted proper orthogonal decomposition for analysis of advecting structures

Nair

Douglas

et al. 2021

J. Fluid Mech.

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Flow data are often decomposed using proper orthogonal decomposition (POD) of the space–time separated form, $\boldsymbol {q}'\left (\boldsymbol {x},t\right )=\sum _j a_j\left (t\right )\boldsymbol {\phi }_j\left (\boldsymbol {x}\right )$ , which targets spatially correlated flow structures in an optimal manner. This paper analyses permuted POD (PPOD), which decomposes data as $\boldsymbol {q}'\left (\boldsymbol {x},t\right )=\sum _j a_j\left (\boldsymbol {n}\right )\boldsymbol {\phi }_j\left (s,t\right )$ , where $\boldsymbol {x}=(s,\boldsymbol {n})$ is a general spatial coordinate system, $s$ is the coordinate along the bulk advection direction and $\boldsymbol {n}=(n_1,n_2)$ are along mutually orthogonal directions normal to the advection characteristic. This separation of variables is associated with a fundamentally different inner product space for which PPOD is optimal and targets correlations in $s,t$ space. This paper presents mathematical features of PPOD, followed by analysis of three experimental datasets from high-Reynolds-number, turbulent shear flows: a wake, a swirling annular jet and a jet in cross-flow. In the wake and swirling jet cases, the leading PPOD and space-only POD modes focus on similar features but differ in convergence rates and fidelity in capturing spatial and temporal information. In contrast, the leading PPOD and space-only POD modes for the jet in cross-flow capture completely different features – advecting shear layer structures and flapping of the jet column, respectively. This example demonstrates how the different inner product spaces, which order the PPOD and space-only POD modes according to different measures of variance, provide unique ‘lenses’ into features of advection-dominated flows, allowing complementary insights.

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“…2014). Additionally, turbulence can cause phase jitter, which causes cycle-to-cycle variations in the location of a coherent vortex, lowering phase-averaged vorticity (Shanbhogue, Seelhorst & Lieuwen 2009 b ). In this study we do not attempt to discern between these two effects, like we have in previous work (Karmarkar et al.…”

Section: Introductionmentioning

confidence: 99%

Interaction between coherent and turbulent oscillations in non-reacting and reacting wake flows

Karmarkar

O’Connor

2023

J. Fluid Mech.

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The presence of large-scale coherent structures can significantly impact the dynamics of a turbulent flow field and the behaviour of a flame stabilized in that flow. The goal of this study is to analyse how increasing free-stream turbulence can change the response of the flow to longitudinal acoustic excitation of varying amplitudes. We study the flow in the wake of a cylindrical bluff body at both non-reacting and reacting conditions, as the presence of a flame can significantly alter the global stability of the flow. The frequency of longitudinal acoustic excitation is set to match the natural frequency of anti-symmetric vortex shedding for this configuration and we vary the free-stream turbulence using perforated plates upstream of the bluff body. The results show that varying the level of free-stream turbulence can influence not only the amplitude of the coherent flow response, but also the symmetry of vortex shedding in the presence of longitudinal acoustic excitation. Increasing the turbulence intensity can fundamentally change the structure of the time-averaged flow and can directly impact the coherent flow response in two ways. First, increasing turbulence intensity can enhance the amplitude of the natural anti-symmetric vortex shedding mode in the wake. Second, increasing turbulence intensity weakens the symmetric response of the flow to the longitudinal acoustic excitation. In the non-reacting and reacting conditions, both symmetric and anti-symmetric modes are present and are characterized using a spectral proper orthogonal decomposition. We see evidence of interaction between the symmetric and anti-symmetric modes, which leads to an interference pattern in the coherent vorticity response in the shear layers. We conclude by presenting a conceptual model for the influence that turbulence has on these flows.

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Vortex Phase-Jitter in Acoustically Excited Bluff Body Flames

Cited by 20 publications

References 33 publications

Flow dynamics in a variable-spacing, three bluff-body flowfield

Flow dynamics in a variable-spacing, three bluff-body flowfield

Permuted proper orthogonal decomposition for analysis of advecting structures

Interaction between coherent and turbulent oscillations in non-reacting and reacting wake flows

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