An experimental and numerical study of the structure and stability of laminar opposed-jet flows

Ciani, Andrea; Kreutner, W.; Frouzakis, Christos E.; Lust, Kurt; Coppola, Gianfilippo; Boulouchos, Konstantinos

doi:10.1016/j.compfluid.2009.07.006

Cited by 18 publications

(23 citation statements)

References 17 publications

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“…Second, current results can be used to explain the low-frequency irregular oscillations reported in the experiments 20,21 but absent in the simulation and stability analysis. 13,14 This discrepancy is due to the different boundary conditions, because the velocity inlet in the simulation is laminar and constant, while the flow fluctuations and other disturbance more or less exist in experiments. This discrepancy also occurred in the DNS of Icardi et al 31 and they suggested that some small excitation oscillations similar to the experimental ones should be introduced in inflow conditions in the simulation of opposed jets.…”

Section: Discussionmentioning

confidence: 89%

“…Simulations and bifurcation analyses of the structure and stability show that laminar axisymmetric opposed jets exhibit three steady states (two stable steady states and one unstable steady state) about at Re > 60, and no oscillatory instabilities were reported. 13,14 Unlike to the stagnation point offset, other researchers observed many types of oscillation behaviors for axisymmetric opposed jets. For the flow in RIM, the transition from stable laminar to chaotic oscillation have been reported at Re % 100 and the Strouhal number (St) is in the range of 0.004-0.06 at 100 < Re < 250.…”

Section: Introductionmentioning

confidence: 94%

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Experimental study of oscillation of axisymmetric turbulent opposed jets with modulated airflow

Guo-Feng

et al. 2013

AIChE Journal

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Oscillation behaviors of axisymmetric opposed jets with modulated airflow were experimentally studied. The oscillation frequency, the oscillation amplitude, and the movement velocity of the impingement plane at various nozzle separations, excitation frequencies, and exit turbulence intensities have been investigated by a hot-wire anemometer and flow visualization technique combined with a high-speed camera. Results show that the oscillation frequency of the impingement plane is nearly equal to the excitation frequency, whereas the oscillation amplitude decreases with the increase of the excitation frequency. The full-scale amplitude oscillation occurs at low excitation frequencies and 2 L/D 8 (where L is the nozzle separation and D is the diameter of the nozzle exit). With the increase of the exit turbulence intensity caused by a turbulence generating plate, the oscillation amplitude decreases remarkably. Flow regimes of axisymmetric opposed jets with excitations are analyzed and discussed based on the experimental results.

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Section: Discussionmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 94%

Experimental study of oscillation of axisymmetric turbulent opposed jets with modulated airflow

Guo-Feng

et al. 2013

AIChE Journal

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“…7,8,24 The "bouncing around" of the stagnation plane due to these instabilities may affect the statistics and specifically the velocity fluctuations even though it may not be strictly classified as part of the turbulent motion. Indeed, visual observation confirmed the presence of low-frequency ͓O͑100 Hz͒ or less͔ bouncing up and down and tilting of the stagnation plane.…”

Section: Resultsmentioning

confidence: 99%

“…5,7,24,25 A probable cause of the instability, similarly to sudden-expansion flows, [26][27][28][29] is the presence of strong recirculation bubbles and their dynamic coupling either in the vicinity of the turbulence generation plates within the nozzle or at the exit of the jets. One may question whether this instability is distinct from true turbulence, in which case it would artificially masks the turbulent features of these flows, as detected, for example, by rms measurements.…”

Section: Introductionmentioning

confidence: 99%

Experimental study of highly turbulent isothermal opposed-jet flows

Coppola

Gomez

2010

Physics of Fluids

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Opposed-jet flows have been shown to provide a valuable means to study a variety of combustion problems, but have been limited to either laminar or modestly turbulent conditions. With the ultimate goal of developing a burner for laboratory flames reaching turbulence regimes of relevance to practical systems, we characterized highly turbulent, strained, isothermal, opposed-jet flows using particle image velocimetry (PIV). The bulk strain rate was kept at 1250 s−1 and specially designed and properly positioned turbulence generation plates in the incoming streams boosted the turbulence intensity to well above 20%, under conditions that are amenable to flame stabilization. The data were analyzed with proper orthogonal decomposition (POD) and a novel statistical analysis conditioned to the instantaneous position of the stagnation surface. Both POD and the conditional analysis were found to be valuable tools allowing for the separation of the truly turbulent fluctuations from potential artifacts introduced by relatively low-frequency, large-scale instabilities that would otherwise partly mask the turbulence. These instabilities cause the stagnation surface to wobble with both an axial oscillation and a precession motion about the system axis of symmetry. Once these artifacts are removed, the longitudinal integral length scales are found to decrease as one approaches the stagnation line, as a consequence of the strained flow field, with the corresponding outer scale turbulent Reynolds number following a similar trend. The Taylor scale Reynolds number is found to be roughly constant throughout the flow field at about 200, with a value virtually independent of the data analysis technique. The novel conditional statistics allowed for the identification of highly convoluted stagnation lines and, in some cases, of strong three-dimensional effects, that can be screened, as they typically yield more than one stagnation line in the flow field. The ability to lock on the instantaneous stagnation line, at the intersection of the stagnation surface with the PIV measurement plane, is particularly useful in the combustion context, since the flame is aerodynamically stabilized in the vicinity of the stagnation surface. Estimates of the ratio of the mean residence time (inverse strain rate) to the vortex turnover time yield values greater than unity. The conditional mean velocity gradient suggests that, in contrast to the existing literature, the highest gradients are around the system centerline, which would result in a higher probability of flame extinction in that region under chemically reacting conditions. The compactness of the domain and the short mean residence time render the system well suited to direct numerical simulation, more so than conventional jet flames.

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“…The planar opposed jets can exhibit the feature of time-dependent deflection oscillation of two jets [3][4][5]. As for the axisymmetric opposed jets, multiple steady states of impinging plane in closely spaced axisymmetric opposed jets have been found by experimental way [6,7] and numerical way [3]. Li et al [4,8,9] experimentally studied the dynamic behavior of the impinging plane and found the phenomena of axial quasi-periodic oscillation of impinging plane and stagnation point offsets when L/D varied.…”

Section: Introductionmentioning

confidence: 94%

Numerical study of particle behavior in laminar axisymmetric opposed-jet flows

Liu

et al. 2015

Powder Technology

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An experimental and numerical study of the structure and stability of laminar opposed-jet flows

Cited by 18 publications

References 17 publications

Experimental study of oscillation of axisymmetric turbulent opposed jets with modulated airflow

Experimental study of oscillation of axisymmetric turbulent opposed jets with modulated airflow

Experimental study of highly turbulent isothermal opposed-jet flows

Numerical study of particle behavior in laminar axisymmetric opposed-jet flows

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