Characteristics of Flame Modes for a Conical Bluff Body Burner With a Central Fuel Jet

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Haojie Tang ◽  
Dong Yang ◽  
Tongfeng Zhang ◽  
Min Zhu
Keyword(s):  
High Speed ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Particle Image ◽  
Reynolds Numbers ◽  
Charge Coupled Device ◽  
Fuel Jet ◽  
Image Velocimetry ◽  
Intensified Charge Coupled Device ◽  
Turbulent Air Flow

Bluff body stabilized nonpremixed flames are usually used as pilot flames in lean-premixed combustors. Experiments are conducted to investigate the characteristics of the flame. Typical flame modes are investigated in both stable and unstable conditions. The flow structures, the reaction zone, and the dynamics of unstable flames are measured with particle image velocimetry (PIV), intensified charge-coupled device (ICCD) and a high-speed camera, respectively, based on which the inherent mechanisms that influence the configuration and stabilization of the flame are analyzed. Stable flames are apparently influenced by the mixing characteristics in the recirculation zone. Flame detachment, a typical phenomenon of stable flames in a turbulent air flow, can be explained by the distribution of fuel concentration in the recirculation zone. The Reynolds number of air has different effects on different parts of the flame, which results in three unstable flame modes at different Reynolds numbers of air. These results could be helpful for the design of stable burners in practice.

Characteristics of Flame Modes for a Conical Bluff Body Burner With a Central Fuel Jet

2013 ◽  
Author(s):  
Haojie Tang ◽  
Dong Yang ◽  
Tongfeng Zhang ◽  
Min Zhu
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Reynolds Numbers ◽  
Flow Structures ◽  
High Speed Camera ◽  
Fuel Jet ◽  
Turbulent Air Flow ◽  
Different Parts

Bluff body stabilised non-premixed flames are usually used as pilot flames in lean-premixed combustors. Experiments are conducted to investigate the characteristics of the flame. Typical flame modes are investigated in both stable and unstable conditions. The flow structures, the reaction zone, and the dynamics of unstable flames are measured with PIV, ICCD and a high speed camera, respectively, based on which the inherent mechanisms that influence the configuration and stabilisation of the flame are analysed. Stable flames are apparently influenced by the mixing characteristics in the recirculation zone. Flame detachment, a typical phenomenon of stable flames in a turbulent air flow, can be explained by the distribution of fuel concentration in the recirculation zone. The Reynolds number of air has different effects on different parts of the flame, which results in three unstable flame modes at different Reynolds numbers of air. These results could be helpful for the design of stable burners in practice.

Velocity distribution around a sphere descending in a linearly stratified fluid

2017 ◽  
Vol 826 ◽  
pp. 759-780 ◽  
Author(s):  
Shinya Okino ◽  
Shinsaku Akiyama ◽  
Hideshi Hanazaki
Keyword(s):  
Boundary Layer ◽  
Velocity Distribution ◽  
High Speed ◽  
Particle Image ◽  
Maximum Velocity ◽  
Reynolds Numbers ◽  
Stratified Fluid ◽  
Velocity Variation ◽  
Image Velocimetry ◽  
Wave Patterns

The flow around a sphere descending at constant speed in a salt-stratified fluid is observed by particle image velocimetry. A unique characteristic of this flow is the appearance of a thin and high-speed rear jet whose maximum velocity can reach more than five times the sphere velocity. In this study we have investigated how the velocity distributions, especially those in the jet and in the boundary layer of the sphere, vary when the Froude number $Fr(=W^{\ast }/N^{\ast }a^{\ast })$ or the Reynolds number $Re(=W^{\ast }(2a^{\ast })/\unicode[STIX]{x1D708}^{\ast })$ ($W^{\ast }$: vertical velocity of the sphere, $N^{\ast }$: Brunt–Väisälä frequency, $a^{\ast }$: radius of the sphere, $\unicode[STIX]{x1D708}^{\ast }$: kinematic viscosity of the fluid) is changed. The results show that the radius of the jet and the thickness of the boundary layer are comparable, and they decrease for smaller Froude numbers and larger Reynolds numbers. Both of them are estimated at moderate Reynolds numbers by the primitive length scale of the stratified fluid ($l_{\unicode[STIX]{x1D708}}^{\ast }=\sqrt{\unicode[STIX]{x1D708}^{\ast }/N^{\ast }}$), or in non-dimensional form by $l_{\unicode[STIX]{x1D708}}^{\ast }/2a^{\ast }=(Fr/2Re)^{1/2}$. The overall velocity distribution in the lee of the sphere is measured to identify the internal wave patterns and their effect on the velocity variation along the jet. Corresponding numerical simulation results using the axisymmetry assumption are in agreement with the experimental results.

scholarly journals Experimental Investigation of Vortex Structures in Wake of Hyperboloid-Shaped Model by Means of 2D Particle Image Velocimetry Measurement

2018 ◽  
Vol 180 ◽  
pp. 02004
Author(s):  
V. Barraclough ◽  
J. Novotný ◽  
P. Šafařík
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Wind Tunnel ◽  
Atmospheric Boundary Layer ◽  
Bluff Body ◽  
Particle Image ◽  
Reynolds Numbers ◽  
High Rate ◽  
Incoming Flow ◽  
Image Velocimetry

This paper deals with flow around a bluff body of hyperboloid shape. It consists of results gathered in the course of research by means of Particle Image Velocimetry (PIV). The experiments were carried out by means of low-frequency 2D PIV in a range of Reynolds numbers from 40000 to 50000. A hyperboloid-shaped model was measured in a wind tunnel with a modelled atmospheric boundary layer (and additionally, in a low-speed wind tunnel with low turbulence). The model was tested in a subcritical range of Reynolds numbers and various planes in a wake of the model were captured with the intention of getting an estimation of 3D flow structures. The tunnel with the modelled atmospheric boundary layer has a high rate of turbulence, so the influence of the turbulence of incoming flow on the wake could be outlined. The ratio of the height of the model to a thickness of the modelled boundary layer in the tunnel was 1/3, meaning the turbulence in the boundary layer strongly influenced the flow around the model; it suppresses the wake which leads to a lot shorter area of recirculation than low turbulence incoming flow would cause.

The Flow Around an Impulsively Started Square Prism

2010 ◽  
Author(s):  
Nelson Tonui ◽  
David Sumner
Keyword(s):  
Circular Cylinder ◽  
Recirculation Zone ◽  
Particle Image ◽  
Reynolds Numbers ◽  
Temporal Development ◽  
Near Wake ◽  
Towing Tank ◽  
Streamwise Location ◽  
Square Prism ◽  
Image Velocimetry

The flow around a square prism impulsively set into motion was studied experimentally using particle image velocimetry (PIV). The experiments were conducted in an X-Y towing tank for Reynolds numbers from Re = 200 to 1000 and dimensionless acceleration parameters from a* = 0.5 to 10. The temporal development of the near-wake recirculation zone, and its pair of primary eddies, was examined from the initial start until the wake became asymmetric. When considering the time elapsed from the start of motion, the temporal development of the wake was sensitive the initial acceleration. “Impulsively started” conditions were effectively attained for a* ≥ 3. However, when considering the distance traveled from the start of motion, the wake parameters were sensibly independent of a* for a* ≥ 0.5. Concerning the temporal development of the recirculation zone, the length of the recirculation zone, the streamwise location of the primary eddies, and the strength of the primary eddies increased with time following the impulsive start, while the cross-stream spacing of the eddy centres remained nearly constant. The recirculation zone of the square prism was longer than that of the impulsively started circular cylinder but shorter than an impulsively started flat plate. For t* > 2, the primary eddy strength, maximum vorticity, and cross-stream spacing of the primary eddies were the same for both the square prism and circular cylinder.

scholarly journals Experimental investigation of flow behind a cube for moderate Reynolds numbers

2014 ◽  
Vol 750 ◽  
pp. 73-98 ◽  
Author(s):  
L. Klotz ◽  
S. Goujon-Durand ◽  
J. Rokicki ◽  
J. E. Wesfreid
Keyword(s):  
Numerical Simulation ◽  
Experimental Investigation ◽  
Particle Image Velocimetry ◽  
Bluff Body ◽  
Particle Image ◽  
Reynolds Numbers ◽  
Laser Induced Fluorescence ◽  
Basic Flow ◽  
Water Tunnel ◽  
Image Velocimetry

AbstractThe wake behind a cube with a face normal to the flow was investigated experimentally in a water tunnel using laser induced fluorescence (LIF) visualisation and particle image velocimetry (PIV) techniques. Measurements were carried out for moderate Reynolds numbers between 100 and 400 and in this range a sequence of two flow bifurcations was confirmed. Values for both onsets were determined in the framework of Landau’s instability model. The measured longitudinal vorticity was separated into three components corresponding to each of the identified regimes. It was shown that the vorticity associated with a basic flow regime originates from corners of the bluff body, in contrast to the two other contributions which are related to instability effects. The present experimental results are compared with numerical simulation carried out earlier by Saha (Phys. Fluids, vol. 16, 2004, pp. 1630–1646).

A particle image velocimetry study on the pulsatile flow characteristics in straight tubes with an asymmetric bulge

2000 ◽  
Vol 214 (5) ◽  
pp. 655-671 ◽  
Author(s):  
S C M Yu ◽  
J B Zhao
Keyword(s):  
Particle Image Velocimetry ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Condition ◽  
Particle Image ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Flow Conditions ◽  
Image Velocimetry

Flow characteristics in straight tubes with an asymmetric bulge have been investigated using particle image velocimetry (PIV) over a range of Reynolds numbers from 600 to 1200 and at a Womersley number of 22. A mixture of glycerine and water (approximately 40:60 by volume) was used as the working fluid. The study was carried out because of their relevance in some aspects of physiological flows, such as arterial flow through a sidewall aneurysm. Results for both steady and pulsatile flow conditions were obtained. It was found that at a steady flow condition, a weak recirculating vortex formed inside the bulge. The recirculation became stronger at higher Reynolds numbers but weaker at larger bulge sizes. The centre of the vortex was located close to the distal neck. At pulsatile flow conditions, the vortex appeared and disappeared at different phases of the cycle, and the sequence was only punctuated by strong forward flow behaviour (near the peak flow condition). In particular, strong flow interactions between the parent tube and the bulge were observed during the deceleration phase. Stents and springs were used to dampen the flow movement inside the bulge. It was found that the recirculation vortex could be eliminated completely in steady flow conditions using both devices. However, under pulsatile flow conditions, flow velocities inside the bulge could not be suppressed completely by both devices, but could be reduced by more than 80 per cent.

scholarly journals Aerodynamics of manoeuvring flight in brown long-eared bats ( Plecotus auritus )

2018 ◽  
Vol 15 (148) ◽  
pp. 20180441 ◽  
Author(s):  
Per Henningsson ◽  
Lasse Jakobsen ◽  
Anders Hedenström
Keyword(s):  
Particle Image Velocimetry ◽  
Wind Tunnel ◽  
High Speed ◽  
Particle Image ◽  
Future Studies ◽  
Image Velocimetry ◽  
Mechanistic Basis

In this study, we explicitly examine the aerodynamics of manoeuvring flight in animals. We studied brown long-eared bats flying in a wind tunnel while performing basic sideways manoeuvres. We used particle image velocimetry in combination with high-speed filming to link aerodynamics and kinematics to understand the mechanistic basis of manoeuvres. We predicted that the bats would primarily use the downstroke to generate the asymmetries for the manoeuvre since it has been shown previously that the majority of forces are generated during this phase of the wingbeat. We found instead that the bats more often used the upstroke than they used the downstroke for this. We also found that the bats used both drag/thrust-based and lift-based asymmetries to perform the manoeuvre and that they even frequently switch between these within the course of a manoeuvre. We conclude that the bats used three main modes: lift asymmetries during downstroke, thrust/drag asymmetries during downstroke and thrust/drag asymmetries during upstroke. For future studies, we hypothesize that lift asymmetries are used for fast turns and thrust/drag for slow turns and that the choice between up- and downstroke depends on the timing of when the bat needs to generate asymmetries.

scholarly journals Dual-camera system for high-speed imaging in particle image velocimetry

2012 ◽  
Vol 15 (3) ◽  
pp. 193-195 ◽  
Author(s):  
K. Hashimoto ◽  
A. Hori ◽  
T. Hara ◽  
S. Onogi ◽  
H. Mouri
Keyword(s):  
Particle Image Velocimetry ◽  
High Speed ◽  
Particle Image ◽  
High Speed Imaging ◽  
Camera System ◽  
Image Velocimetry
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