Flow Dynamics in Single and Multi-Nozzle Swirl Flames

2016 ◽  
Author(s):  
Travis Smith ◽  
Benjamin Emerson ◽  
Ianko Chterev ◽  
David R. Noble ◽  
Tim Lieuwen
Keyword(s):  
Reverse Flow ◽  
Transverse Velocity ◽  
Flow Dynamics ◽  
Stereoscopic Particle Image Velocimetry ◽  
Flame Spreading ◽  
Swirl Combustor ◽  
Flame Dynamics ◽  
Image Velocimetry ◽  
Planar Laser ◽  
Similar Growth

This paper describes an analysis of the unsteady flow structures in a single nozzle and triple nozzle swirl combustor (with nozzle spacing of s/D=2.9). It was motivated by a prior study by our group which compared the time averaged and unsteady features for a different swirling nozzle, and found that the single and triple nozzle flow dynamics were quite similar upstream of the jet merging region. This work is motivated by the fact that realistic hardware, whether in can or annular combustion systems, almost always contains several nozzles. However, it is common to use test facilities with a single nozzle to study flame dynamics, a key component of the combustion instability problem [1]. Simultaneous OH Planar Laser Induced Fluorescence (OH PLIF) and Stereoscopic Particle Image Velocimetry (sPIV) techniques were performed at 5 kHz on a swirl methane-air flame. Two transverse forcing configurations were applied, so that the flame nominally lies in a pressure node/transverse velocity antinode, and vice versa. The time averaged flow fields of the single and triple nozzle configurations are compared, and several key differences are identified. Most prominently, there are non-negligible differences in the recirculation zone reverse flow velocity and flame spreading angle. However, the spatial variation of the disturbance magnitudes along the shear layers exhibit quite similar growth and decay trends, and the convection speeds along the shear layer were nearly identical. These results corroborate the findings of Aguilar et al. [2] and Szedlmayer et al. [3], which show that despite differences in time average quantities, comparable flow dynamics occur in single and multi-nozzle flames. These results imply that useful insights into the dynamics of multi-nozzle systems can be gleaned from appropriately designed single-nozzle hardware, with appropriate accounting for the differences in time averaged flow/flame characteristics.

Blowoff and Reattachment Dynamics of a Linear Multi-Nozzle Combustor

2018 ◽  
Author(s):  
W. Y. Kwong ◽  
A. M. Steinberg
Keyword(s):  
Bluff Body ◽  
Random Order ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
The Other ◽  
Bluff Bodies ◽  
Coupled Flow ◽  
Flame Dynamics ◽  
Image Velocimetry ◽  
Planar Laser

This paper describes the coupled flow and flame dynamics during blowoff and reattachment events in a combustor consisting of a linear array of five interacting nozzles using 10 kHz repetition-rate OH planar laser induced fluorescence and stereoscopic particle image velocimetry. Steady operating conditions were studied at which the three central flames randomly blew-off and subsequently reattached to the bluff-bodies. Transition of the flame from one nozzle was rapidly followed by transition of the other nozzles, indicating cross-nozzle coupling. Blow-off transitions were preferentially initiated in one of the off-center nozzles, with the transition of subsequent nozzles occurring in a random order. Similarly, the center nozzle tended to be the last nozzle to reattach. The blowoff process of any individual nozzle was similar to that for a single bluff-body stabilized flame, though with cross-flame interactions providing additional means of re-stabilizing a partially extinguished flame. Subsequent to blowoff of the first nozzle, the other nozzles underwent similar blowoff processes. Flame reattachment was initiated by entrainment of a burning pocket into a recirculation zone, followed by transport to the bluff-body; the other nozzles subsequently underwent similar reattachment processes. Several forms of cross-nozzle interaction that can promote or prevent transition are identified. Furthermore, the velocity measurements indicated that blowoff or reattachment of the first nozzle during a multi-nozzle transition causes significant changes to the flow fields of the other nozzles. It is proposed that a single nozzle transition redistributes the flow to the other nozzles in a manner that promotes their transition.

Blowoff and Reattachment Dynamics of a Linear Multinozzle Combustor

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Wing Yin Kwong ◽  
Adam M. Steinberg
Keyword(s):  
Bluff Body ◽  
Random Order ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
The Other ◽  
Bluff Bodies ◽  
Coupled Flow ◽  
Flame Dynamics ◽  
Image Velocimetry ◽  
Planar Laser

This paper describes the coupled flow and flame dynamics during blowoff and reattachment events in a combustor consisting of a linear array of five interacting nozzles using 10 kHz repetition-rate OH planar laser-induced fluorescence and stereoscopic particle image velocimetry (S-PIV). Steady operating conditions were studied at which the three central flames randomly blew-off and subsequently reattached to the bluff-bodies. Transition of the flame from one nozzle was rapidly followed by transition of the other nozzles, indicating cross-nozzle coupling. Blow-off transitions were preferentially initiated in one of the off-center nozzles, with the transition of subsequent nozzles occurring in a random order. Similarly, the center nozzle tended to be the last nozzle to reattach. The blow-off process of any individual nozzle was similar to that for a single bluff-body stabilized flame, though with cross-flame interactions providing additional means of restabilizing a partially extinguished flame. Subsequent to blowoff of the first nozzle, the other nozzles underwent similar blow-off processes. Flame reattachment was initiated by entrainment of a burning pocket into a recirculation zone, followed by transport to the bluff-body; the other nozzles subsequently underwent similar reattachment processes. Several forms of cross-nozzle interaction that can promote or prevent transition are identified. Furthermore, the velocity measurements indicated that blowoff or reattachment of the first nozzle during a multinozzle transition causes significant changes to the flow fields of the other nozzles. It is proposed that a single-nozzle transition redistributes the flow to the other nozzles in a manner that promotes their transition.

Measurements of Periodic Reynolds Stress Oscillations in a Forced Turbulent Premixed Swirling Flame

2018 ◽  
Author(s):  
Christopher Douglas ◽  
Jamie Lim ◽  
Travis Smith ◽  
Benjamin Emerson ◽  
Timothy Lieuwen ◽  
...  
Keyword(s):  
Reynolds Stress ◽  
High Speed ◽  
Large Scale ◽  
Turbulent Transport ◽  
Stereoscopic Particle Image Velocimetry ◽  
Thermoacoustic Instability ◽  
Image Velocimetry ◽  
Planar Laser ◽  
Swirling Flame ◽  
Dynamics Simulations

This work is motivated by the thermoacoustic instability challenges associated with ultra-low emissions gas turbine combustors. It demonstrates the first use of high-speed dual-plane orthogonally-polarized stereoscopic-particle image velocimetry and synchronized OH planar laser-induced fluorescence in a premixed swirling flame. We use this technique to explore the effects of combustion and longitudinal acoustic forcing on the time- and phase-averaged flow field — particularly focusing on the behavior of the Reynolds stress in the presence of harmonic forcing. We observe significant differences between ensemble averaged and time averaged Reynolds stress. This implies that the large-scale motions are non-ergodic, due to coherent oscillations in Reynolds stress associated with the convection of periodic vortical structures. This result has important implications on hydrodynamic stability models and reduced order computational fluid dynamics simulations, which do show the importance of turbulent transport on the problem, but do not capture these coherent oscillations in their models.

Measurements of Periodic Reynolds Stress Oscillations in a Forced Turbulent Premixed Swirling Flame

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Christopher Douglas ◽  
Jamie Lim ◽  
Travis Smith ◽  
Benjamin Emerson ◽  
Timothy Lieuwen ◽  
...  
Keyword(s):  
Reynolds Stress ◽  
High Speed ◽  
Large Scale ◽  
Turbulent Transport ◽  
Stereoscopic Particle Image Velocimetry ◽  
Thermoacoustic Instability ◽  
Image Velocimetry ◽  
Planar Laser ◽  
Swirling Flame ◽  
Dynamics Simulations

This work is motivated by the thermoacoustic instability challenges associated with ultra-low emissions gas turbine (GT) combustors. It demonstrates the first use of high-speed dual-plane orthogonally-polarized stereoscopic-particle image velocimetry (PIV) and synchronized OH planar laser-induced fluorescence in a premixed swirling flame. We use this technique to explore the effects of combustion and longitudinal acoustic forcing on the time- and phase-averaged flow field—particularly focusing on the behavior of the Reynolds stress in the presence of harmonic forcing. We observe significant differences between ensemble-averaged and time-averaged Reynolds stress. This implies that the large-scale motions are nonergodic, due to coherent oscillations in Reynolds stress associated with the convection of periodic vortical structures. This result has important implications on hydrodynamic stability models and reduced-order computational fluid dynamics simulations, which do show the importance of turbulent transport on the problem, but do not capture these coherent oscillations in their models.

scholarly journals Measurements of turbulent diffusion in uniformly sheared flow

2014 ◽  
Vol 754 ◽  
pp. 488-514 ◽  
Author(s):  
Christina Vanderwel ◽  
Stavros Tavoularis
Keyword(s):  
Stereoscopic Particle Image Velocimetry ◽  
Turbulent Diffusivity ◽  
Relative Significance ◽  
Advection Diffusion Equation ◽  
Image Velocimetry ◽  
Planar Laser ◽  
The Mean ◽  
First Time ◽  
Diffusivity Tensor ◽  
Good Agreement

AbstractThe diffusion of a plume of dye in uniformly sheared turbulent flow in a water tunnel was investigated using simultaneous stereoscopic particle image velocimetry (SPIV) and planar laser-induced fluorescence (PLIF). Maps of the mean concentration and the turbulent concentration fluxes in planes normal to the plume axis were constructed, from which all components of the second-order turbulent diffusivity tensor were determined for the first time. Good agreement between the corresponding apparent and true diffusivities was observed. The turbulent diffusivity tensor was found to have strong off-diagonal components, whereas the streamwise component appeared to be counter-gradient. The different terms in the advection–diffusion equation were estimated from the measurements and their relative significance was discussed. All observed phenomena were explained by physical arguments and the results were compared to previous ones.

Experimental Investigation of Boundary Layer Instabilities on the Free Surface of Non-Turbulent Jet

2012 ◽  
Author(s):  
Matthieu A. Andre ◽  
Philippe M. Bardet
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
High Speed ◽  
Particle Tracking Velocimetry ◽  
Capillary Waves ◽  
Wave Growth ◽  
Image Velocimetry ◽  
Planar Laser ◽  
Surface Visualization ◽  
The Waves

Shear instabilities induced by the relaxation of laminar boundary layer at the free surface of a high speed liquid jet are investigated experimentally. Physical insights into these instabilities and the resulting capillary wave growth are gained by performing non-intrusive measurements of flow structure in the direct vicinity of the surface. The experimental results are a combination of surface visualization, planar laser induced fluorescence (PLIF), particle image velocimetry (PIV), and particle tracking velocimetry (PTV). They suggest that 2D spanwise vortices in the shear layer play a major role in these instabilities by triggering 2D waves on the free surface as predicted by linear stability analysis. These vortices, however, are found to travel at a different speed than the capillary waves they initially created resulting in interference with the waves and wave growth. A new experimental facility was built; it consists of a 20.3 × 146.mm rectangular water wall jet with Reynolds number based on channel depth between 3.13 × 104 to 1.65 × 105 and 115. to 264. based on boundary layer momentum thickness.

scholarly journals Turbulent drag in a rotating frame

2016 ◽  
Vol 794 ◽  
Author(s):  
Antoine Campagne ◽  
Nathanaël Machicoane ◽  
Basile Gallet ◽  
Pierre-Philippe Cortet ◽  
Frédéric Moisy
Keyword(s):  
Large Scale ◽  
Scaling Law ◽  
Stereoscopic Particle Image Velocimetry ◽  
Turbulence Theory ◽  
Water Tank ◽  
Wave Interactions ◽  
Turbulent Drag ◽  
Image Velocimetry ◽  
Weak Turbulence Theory ◽  
Large Scale Flow

What is the turbulent drag force experienced by an object moving in a rotating fluid? This open and fundamental question can be addressed by measuring the torque needed to drive an impeller at a constant angular velocity ${\it\omega}$ in a water tank mounted on a platform rotating at a rate ${\it\Omega}$. We report a dramatic reduction in drag as ${\it\Omega}$ increases, down to values as low as 12 % of the non-rotating drag. At small Rossby number $Ro={\it\omega}/{\it\Omega}$, the decrease in the drag coefficient $K$ follows the approximate scaling law $K\sim Ro$, which is predicted in the framework of nonlinear inertial-wave interactions and weak-turbulence theory. However, stereoscopic particle image velocimetry measurements indicate that this drag reduction instead originates from a weakening of the turbulence intensity in line with the two-dimensionalization of the large-scale flow.

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