Role of Azimuthal Flow Fluctuations on Flow Dynamics and Global Flame Response of Axisymmetric Swirling Flames

Abstract Gas turbine combustors are commonly operated with lean premix flames, allowing for high efficiencies and low emissions. These operating conditions are susceptible to thermoacoustic pulsations, originating from acoustic-flame coupling. To reveal this coupling, experiments or simulations of acoustically forced combustion systems are necessary, which are very challenging for real-scale applications. In this work we investigate the possibility to determine the flame response to acoustic forcing from snapshots of the unforced flow. This approach is based on three central hypothesis: first, the flame response is driven by flow fluctuations, second, these flow fluctuations are dominated by coherent structures driven by hydrodynamic instabilities, and third, these instabilities are driven by stochastic forcing of the background turbulence. As a consequence the dynamics in the natural flow should be low-rank and very similar to those of the acoustically forced system. In this work, the methodology is applied to experimental data of an industry-scale swirl combustor. A resolvent analysis is conducted based on the linearized Navier-Stokes equations to assure analytically the low-rank behavior of the flow dynamics. Then, these dynamics are extracted from flow snapshots using spectral proper orthogonal decomposition (SPOD). The extended SPOD is applied to determine the heat release rate fluctuations that are correlated with the flow dynamics. The low-rank flow and flame dynamics determined from the analytic and data-driven approach are then compared to the flow response determined from a classic phase average of the acoustically forced flow, which allow the research hypothesis to be evaluated. It is concluded that for the present combustor, the flow and flame dynamics are low-rank for a wider frequency range and the response to harmonic forcing can be determined quite accurately from unforced snapshots. The methodology further allows to isolate the frequency range where the flame response is predominantly driven by hydrodynamic instabilites.

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The role of the sinuses of valsalva in aortic root flow dynamics and aortic root surgery

The Thoracic and Cardiovascular Surgeon ◽

10.1055/s-2007-967320 ◽

2007 ◽

Vol 55 (S 1) ◽

Author(s):

F Schoenhoff ◽

C Loupatatzis ◽

FS Eckstein ◽

C Stoupis ◽

FF Immer ◽

...

Keyword(s):

Aortic Root ◽

Flow Dynamics ◽

Aortic Root Surgery

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System Level Analysis of Acoustically Forced Nonpremixed Swirling Flames

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4027297 ◽

2014 ◽

Vol 6 (3) ◽

Cited By ~ 3

Author(s):

Uyi Idahosa ◽

Saptarshi Basu ◽

Ankur Miglani

Keyword(s):

Heat Release ◽

Flow Rate ◽

Ccd Camera ◽

Time Dependent ◽

Fuel Flow Rate ◽

Fuel Flow ◽

Flame Response ◽

Rate Oscillations ◽

Swirling Flames ◽

Flame Sheet

This paper reports an experimental investigation of dynamic response of nonpremixed atmospheric swirling flames subjected to external, longitudinal acoustic excitation. Acoustic perturbations of varying frequencies (fp = 0–315 Hz) and velocity amplitudes (0.03 ≤ u′/Uavg ≤ 0.30) are imposed on the flames with various swirl intensities (S = 0.09 and 0.34). Flame dynamics at these swirl levels are studied for both constant and time-dependent fuel flow rate configurations. Heat release rates are quantified using a photomultiplier (PMT) and simultaneously imaged with a phase-locked CCD camera. The PMT and CCD camera are fitted with 430 nm ±10 nm band pass filters for CH* chemiluminescence intensity measurements. Flame transfer functions and continuous wavelet transforms (CWT) of heat release rate oscillations are used in order to understand the flame response at various burner swirl intensity and fuel flow rate settings. In addition, the natural modes of mixing and reaction processes are examined using the magnitude squared coherence analysis between major flame dynamics parameters. A low-pass filter characteristic is obtained with highly responsive flames below forcing frequencies of 200 Hz while the most significant flame response is observed at 105 Hz forcing mode. High strain rates induced in the flame sheet are observed to cause periodic extinction at localized regions of the flame sheet. Low swirl flames at lean fuel flow rates exhibit significant localized extinction and re-ignition of the flame sheet in the absence of acoustic forcing. However, pulsed flames exhibit increased resistance to straining due to the constrained inner recirculation zones (IRZ) resulting from acoustic perturbations that are transmitted by the co-flowing air. Wavelet spectra also show prominence of low frequency heat release rate oscillations for leaner (C2) flame configurations. For the time-dependent fuel flow rate flames, higher un-mixedness levels at lower swirl intensity is observed to induce periodic re-ignition as the flame approaches extinction. Increased swirl is observed to extend the time-to-extinction for both pulsed and unpulsed flame configurations under time-dependent fuel flow rate conditions.

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Competing Fluid Forces Control Endothelial Sprouting in a 3-D Microfluidic Vessel Bifurcation Model

Micromachines ◽

10.3390/mi10070451 ◽

2019 ◽

Vol 10 (7) ◽

pp. 451 ◽

Cited By ~ 8

Author(s):

Ehsan Akbari ◽

Griffin B. Spychalski ◽

Kaushik K. Rangharajan ◽

Shaurya Prakash ◽

Jonathan W. Song

Keyword(s):

Shear Stress ◽

Fluid Flow ◽

Bifurcation Point ◽

Flow Dynamics ◽

Laminar Shear Stress ◽

Local Flow ◽

Fluid Forces ◽

Sprouting Angiogenesis ◽

Laminar Shear

Sprouting angiogenesis—the infiltration and extension of endothelial cells from pre-existing blood vessels—helps orchestrate vascular growth and remodeling. It is now agreed that fluid forces, such as laminar shear stress due to unidirectional flow in straight vessel segments, are important regulators of angiogenesis. However, regulation of angiogenesis by the different flow dynamics that arise due to vessel branching, such as impinging flow stagnation at the base of a bifurcating vessel, are not well understood. Here we used a recently developed 3-D microfluidic model to investigate the role of the flow conditions that occur due to vessel bifurcations on endothelial sprouting. We observed that bifurcating fluid flow located at the vessel bifurcation point suppresses the formation of angiogenic sprouts. Similarly, laminar shear stress at a magnitude of ~3 dyn/cm2 applied in the branched vessels downstream of the bifurcation point, inhibited the formation of angiogenic sprouts. In contrast, co-application of ~1 µm/s average transvascular flow across the endothelial monolayer with laminar shear stress induced the formation of angiogenic sprouts. These results suggest that transvascular flow imparts a competing effect against bifurcating fluid flow and laminar shear stress in regulating endothelial sprouting. To our knowledge, these findings are the first report on the stabilizing role of bifurcating fluid flow on endothelial sprouting. These results also demonstrate the importance of local flow dynamics due to branched vessel geometry in determining the location of sprouting angiogenesis.

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The role of the arterial prestress in blood flow dynamics

Medical Engineering & Physics ◽

10.1016/j.medengphy.2005.04.013 ◽

2006 ◽

Vol 28 (1) ◽

pp. 6-12 ◽

Cited By ~ 4

Author(s):

Giuseppe Pontrelli

Keyword(s):

Blood Flow ◽

Flow Dynamics ◽

Blood Flow Dynamics

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CFD Comparison of Steady and Unsteady Flow Through a Human Nasal Passage

ASME 2009 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2009-206673 ◽

2009 ◽

Author(s):

Brian Savilonis ◽

Kalen Smith

Keyword(s):

Unsteady Flow ◽

Steady Flow ◽

Flow Behavior ◽

Flow Dynamics ◽

Nasal Passage ◽

Normal Breathing ◽

Flow Through ◽

Nasal Flow

Understanding of the transnasal pressure and flow behavior during normal breathing conditions has been a subject of much discussion and research. In particular we are interested in testing the hypothesis of quasi-steady flow as well as the role of turbulence on nasal flow dynamics.

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Role of upslope soil pore pressure on lateral subsurface storm flow dynamics

Water Resources Research ◽

10.1029/2003wr002139 ◽

2004 ◽

Vol 40 (12) ◽

Cited By ~ 53

Author(s):

Taro Uchida ◽

Yuko Asano ◽

Takahisa Mizuyama ◽

Jeffery J. McDonnell

Keyword(s):

Pore Pressure ◽

Flow Dynamics ◽

Storm Flow

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Competing Fluid Forces Control Endothelial Sprouting in a 3-D Microfluidic Vessel Bifurcation Model

10.1101/626531 ◽

2019 ◽

Author(s):

Ehsan Akbari ◽

Griffin B. Spychalski ◽

Kaushik K. Rangharajan ◽

Shaurya Prakash ◽

Jonathan W. Song

Keyword(s):

Shear Stress ◽

Fluid Flow ◽

Bifurcation Point ◽

Flow Dynamics ◽

Laminar Shear Stress ◽

Local Flow ◽

Fluid Forces ◽

Sprouting Angiogenesis ◽

Laminar Shear

AbstractSprouting angiogenesis, the infiltration and extension of endothelial cells from pre-existing blood vessels, helps orchestrate vascular growth and remodeling. It is now agreed that fluid forces, such as laminar shear stress due to unidirectional flow in straight vessel segments, are important regulators of angiogenesis. However, regulation of angiogenesis by the different flow dynamics that arise due to vessel branching, such as impinging flow stagnation at the base of a bifurcating vessel, are not well understood. Here we used a recently developed 3-D microfluidic model to investigate the role of the flow conditions that occur due to vessel bifurcations on endothelial sprouting. We observed that bifurcating fluid flow located at the vessel bifurcation point suppresses the formation of angiogenic sprouts. Similarly, laminar shear stress at a magnitude of ∼3 dyn/cm2 applied in the branched vessels downstream of the bifurcation point, inhibited the formation of angiogenic sprouts. In contrast, co-application of ∼1 µm/s average transvascular flow across the endothelial monolayer with bifurcating fluid flow and laminar shear stress induced the formation of angiogenic sprouts. These results suggest that transvascular flow imparts a competing effect against bifurcating fluid flow and laminar shear stress in regulating endothelial sprouting. To our knowledge, these findings are the first report on the stabilizing role of bifurcating fluid flow on endothelial sprouting. These results also demonstrate the importance of local flow dynamics due to branched vessel geometry in determining the location of sprouting angiogenesis.

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Laser doppler flowmetry assessment of microcirculation in children of 6–7 years old

Regional blood circulation and microcirculation ◽

10.24884/1682-6655-2021-20-3-46-53 ◽

2021 ◽

Vol 20 (3) ◽

pp. 46-53

Author(s):

V. I. Kozlov ◽

V. N. Sakharov ◽

O. A. Gurova ◽

V. V. Sidorov

Keyword(s):

Blood Flow ◽

Laser Doppler Flowmetry ◽

Laser Doppler ◽

Lower Limbs ◽

Doppler Flowmetry ◽

Flow Modulation ◽

Left Hand ◽

Flow Fluctuations ◽

Ongoing Development

Introduction. The state of the blood flow within the capillaries and close blood vessels is highly important in practice for the revealing of pathogenetic mechanisms of both systemic and local circulatory disorders. Aim of the study was to define the parameters of microcirculation and the level of blood flow fluctuations (flux) in the distal segments of upper and lower limbs (in fingers of hands and toes of feet) in children of 6–7 years old; and to describe the possible differences in the mechanisms of blood flow modulation in boys and girls. Materials and methods. Skin microcirculation was assessed in middle fingers of hands and great toes of feet in children of 6-7 years old (14 girls and 7 boys in prone position) by means of laser doppler flowmetry. Results. The ranges for parameters of microcirculation (PM) for distal segments of upper and lower limbs in children of mentioned age group were defined, also it was shown that the PM are significantly lower in the lower limbs comparing to those of the upper limbs (both in groups of girls and boys). Asymmetry of PM in the feet was not found; the features of right hand-left hand asymmetry for PM in girls and boys are described. The analysis of modulation of blood flow fluctuations (fluxmotions) of different frequencies showed the profound role of vasomotor (myogenic) rhythm for regulation of microcirculation. Conclusion. Increased neurogenic influences on the modulation of fluxmotions in girls of 6-7 years old may be an evidence of the ongoing development of the mechanisms of blood flow regulation, particularly the association with the growth rate of girls is possible.

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Investigation on Effect of Inlet Flow Turbulence on the Combustion Instability Using Simultaneous PIV and CH* Chemiluminescence in a Backward Facing Step Combustor

Volume 4B: Combustion, Fuels, and Emissions ◽

10.1115/gt2019-92022 ◽

2019 ◽

Author(s):

Pankaj Pancharia ◽

Vikram Ramanan ◽

Baladandayuthapani Nagarajan ◽

S. R. Chakravarthy

Keyword(s):

Turbulence Intensity ◽

Equivalence Ratio ◽

Large Scale ◽

Combustion Instability ◽

Flow Dynamics ◽

Airflow Rate ◽

Backward Facing Step ◽

Time Resolved ◽

Flame Holder

Abstract The present study investigates the role of inlet turbulence intensity on the stability characteristics of a lab scale backward facing step combustor (BFS). Turbulence generator placed upstream of the flame holder is used to vary the turbulence levels. The present study utilizes simultaneous chemiluminescence, particle image velocimetry (PIV) and unsteady pressure fluctuation measurement are done in a time-resolved manner to study the role of inlet turbulence intensity on the flame-flow dynamics and identify different modes of combustion instability as a result of the same. The bifurcation plot with airflow rate, in terms of step-based Reynolds number (Re) as the control parameter, indicates a counterintuitive picture, whereby higher turbulence intensity postpones the onset of instability. The finding has been reported in the past by Nagarajan et. al [30], with the present work extending it. It is shown that the flow-flame structures at high (∼1000 Pa) and very high (>4000 Pa), conditions, the dynamics are significantly different across the same turbulence intensity at different equivalence ratio as well as at different turbulence intensities for the same equivalence ratio. Analysis of the flame-flow dynamics reveals the role of the extent of vortex initiated by acoustics and its orientation in forming an unsteady loop, whereby the vortex span and strength aids the flame to propagate upstream of the step, and the flame in-turn being responsible to sustain the large-scale vortex. This phenomenon is distinct from the conventional vortex sustained combustion instability, whereby the vortex is of the lower span and does not influence the upstream flow. The role of inlet turbulence intensity is seen to be more pronounced in the extent of the flame propagating upward, which then completes the fore-mentioned loop.

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