Investigation on Non-Premixed Swirling Flame in a Multi-Hole Burner

2011 ◽  
Vol 347-353 ◽  
pp. 2428-2431
Author(s):  
Bing Ge ◽  
Shu Sheng Zang ◽  
Pei Qing Guo
Keyword(s):  
Recirculation Zone ◽  
Reverse Flow ◽  
Swirl Burner ◽  
Mean Velocity ◽  
Swirling Jet ◽  
Swirl Combustion ◽  
Fuel Jet ◽  
Expansion Angle ◽  
Swirling Flame ◽  
Development And Validation

This paper focuses on investigating the flow structures in a multi-hole swirl burner. Using the Particle Image Velocimetry(PIV) technique, the experiment measured the velocity distributions of the swirling flame in a muti-hole burner. The experiments show that there is a central recirculation zone (CRZ) in the middle of the flow field, and two counter-rotating vortices exist along the centerline symmetrically. With fuel jet increase: the width of recirculating zone and axial mean velocity peaks changes little; length of recirculation zone and the biggest reverse flow velocity increases; the expansion angle of swirling jet increase at first, and then changes little; axial non-uniform coefficient of outlet reduces at first, and then increases. With airflow velocity increase: axial mean velocity peaks increase; the dimension of recirculating zone and the expansion angle of swirling jet are unchanged; axial non-uniform coefficient of outlet increases.The data from this experiment is helpful for optimization of the swirl burner design, and can be established as benchmarks for the development and validation of swirl combustion numerical simulations.

Experimental Investigation of the Confinement Effects in Radial-Radial Swirlers

2021 ◽  
Author(s):  
Fırat Kıyıcı ◽  
Mustafa Perçin
Keyword(s):  
Pressure Gradient ◽  
Flow Rate ◽  
Recirculation Zone ◽  
Reverse Flow ◽  
Adverse Pressure Gradient ◽  
The Other ◽  
Axial Position ◽  
Other Hand ◽  
Swirling Jet ◽  
Expansion Angle

Abstract This experimental study investigates the effect of confinement ratio (CR) on the flow field of a counter-rotating radial-radial swirler. Two-dimensional two-component (2D2C) particle image velocimetry (PIV) measurements are performed at the mid-plane of the jet. Four different confinement ratios (i.e., 10.4, 23.4, 41.6 and unconfined) are considered at a swirl number of 1.2. The results reveal the presence of a central toroidal recirculation zone (CTRZ) in all cases extending inside the jet which indicates the existence of an adverse pressure gradient. For the unconfined swirling jet, the recirculation zone is small in size and exists at the exit of the jet. For the CR = 41.6 case, on the other hand, there exist two separate recirculation zones with the first one being similar to the unconfined case in terms of size and axial position, while the second one being larger in size and positioned at a more downstream location. Variation of the axial velocity along the centerline of the jet for this case indicates the presence of an adverse pressure gradient only in the close-jet region correlated with the first recirculation zone. For the smaller CR values, a single massive CTRZ emerges. This leads to increase in the expansion angle of the swirling jet as the CR decreases. Correspondingly, the radial velocity at the jet exit increases. For the confined cases with a single recirculation zone, the length and the width to cross-section ratio increase with the CR. On the other hand, the ratio of the reverse flow rate to total mass flow rate decreases with increasing CR values.

Vortex Detachment and Reverse Flow in Pulsatile Laminar Flow Through Axisymmetric Sudden Expansions

1999 ◽  
Vol 121 (3) ◽  
pp. 574-579 ◽  
Author(s):  
S. Tavoularis ◽  
R. K. Singh
Keyword(s):  
Reynolds Number ◽  
Recirculation Zone ◽  
Reverse Flow ◽  
Flow Region ◽  
Vortex Rings ◽  
Mean Velocity ◽  
Zone Length ◽  
Deceleration Phase ◽  
Pulsatile Flows ◽  
Flow Through

Incompressible, steady and pulsatile flows in axisymmetric sudden expansions with diameter ratios of 1:2.25 and 1:2.00 have been simulated numerically over the ranges of time-averaged bulk Reynolds number 0.1 ≤ Re ≤ 400 and Womersley number 0.1 ≤ W ≤ 50. For steady flow, the calculated recirculation zone length increased linearly with an increase in Re, in good agreement with earlier experiments. For pulsatile flows, particularly at higher values of W, the recirculation zone length correlated strongly with the acceleration of the flow and not with the instantaneous Reynolds number; it increased during the deceleration phase and decreased during the acceleration phase. The computed mean velocity and reattachment length were in general agreement with published experimental data. At relatively low W, the computed near-wall, reverse flow region extended along the full domain over part of the cycle, similarly to that in the experiments. At low values of W, the vortex rings created at the expansion remained attached and oscillated back and forth; for an intermediate range of W, they detached and moved downstream; at relatively high W, these vortices became, once more, attached.

Experimental Study on Flow Structure of Non-Premixed Swirl Burner Flows Using PIV

2011 ◽  
Vol 347-353 ◽  
pp. 2587-2592 ◽  
Author(s):  
Bing Ge ◽  
Shu Sheng Zang ◽  
Pei Qing Guo
Keyword(s):  
Flow Field ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Spatial Separation ◽  
Complex Flow ◽  
Image Velocimetry ◽  
Characteristic Modes ◽  
Swirling Flame ◽  
Development And Validation ◽  
Annular Jets

This paper focuses on investigating the characteristic modes and structures in non-premixed swirling methane/air flames. Using the Particle Image Velocimetry (PIV) technique, the experiment measured the velocity distributions of the swirling flame. Cold flow conditions have been included to provide a picture of the flow field and to demonstrate the modifications induced by combustion. The characteristic lengths, velocity vectors, streamlines, and velocity distributions are presented and discussed. The experiment shows that a large spatial separation at the exit between the central and swirling annular jets can expedite the formation of a recirculation zone. Complex flow structures are found in the recirculation zone. Moreover, the differences between cold swirling flow field and combustion swirling flow are analyzed at length. The data from this experiment is helpful for optimization of the non-premixed burner design, and can be established as benchmarks for the development and validation of combustion numerical simulations.

scholarly journals CFD predictions of Swirl burner aerodynamics with variable outlet configurations

2019 ◽  
pp. 31-43 ◽  
Author(s):  
Hesham Baej
Keyword(s):  
Recirculation Zone ◽  
Chemical Species ◽  
Swirl Burner ◽  
Low Velocity ◽  
Lean Premixed Combustion ◽  
Active Chemical ◽  
Lean Premixed ◽  
Swirling Flame ◽  
Recirculation Zones ◽  
Reduction Of Nox

Swirl stabilised combustion is one of the most widely used techniques for flame stabilisation in gas turbine combustors. Lean premixed combustion systems allow the reduction of NOx coupled with fair flame stability. The swirl mechanism produces an aerodynamic region known as central recirculation zone (CRZ) providing a low velocity region where the flame speed matches the flow velocity, thus anchoring the flame whilst serving to recycle heat and active chemical species to the root of the former. Another beneficial feature of the CRZ is the enhancement of the mixing in and around this region. However, the mixing and stabilisation processes inside of this zone have shown to be extremely complex. The level of swirl, burner outlet configuration and combustor expansion are very important variables that define the features of the CRZ. Therefore, in this paper swirling flame dynamics are investigated using computational fluid dynamics (CFD) with commercial software (ANSYS). A new generic swirl burner operated under lean-premixed conditions was modelled. A variety of nozzles were analysed using several gaseous blends at a constant power output. The investigation was based on recognising the size and strength of the central recirculation zones. The dimensions and turbulence of the Central Recirculation Zone were measured and correlated to previous experiments. The results show how the strength and size of the recirculation zone are highly influenced by the blend and infer that it is governed by both the shear layer surrounding the Central Recirculation Zones (CRZ) and the gas composition.

Gas Turbine Combustor Flow Structure Control Through Modification of the Chamber Geometry

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
B. S. Mohammad ◽  
J. Cai ◽  
San-Mou Jeng
Keyword(s):  
Flow Structure ◽  
Recirculation Zone ◽  
Reverse Flow ◽  
Rectangular Cross Section ◽  
Jet Impingement ◽  
Lessons Learned ◽  
Cross Sectional ◽  
Structure Control ◽  
Expansion Angle ◽  
Primary Jets

As combustors are put in service, problems such as erosion, hot spots, and liner oxidation occur, and a solution based on lessons learned is essential to avoid similar problems in future combustor generations. In the present paper, a combustor flow structure control via combustor geometry alteration is investigated using laser Doppler velocimetry. Mainly, three configurations are studied. The first configuration is that of a swirl cup feeding a dump (rectangular cross section) combustor. The rectangular chamber is configured with a width to breadth (w/b) ratio of 85%. The second configuration is similar to the first one, but a combustion dome is installed. The dome is configured with a 9 deg difference in the expansion angle on both sides (asymmetric dome). The third configuration is that of a swirl cup and a combustion dome installed in a prototype combustor (single annular combustor (SAC) sector), with both primary and secondary dilution jets blocked. The SAC is configured with a cross sectional area that decreases toward the exit through the tilting of the inner combustor liner. The results show that the combustion dome eliminates the corner recirculation zone and the low velocity region close to the combustor walls. The combustion dome asymmetry results in a significant asymmetry in the velocity magnitude, as well as the turbulence activities and the tilting of the central recirculation zone (CRZ) toward the surface with the higher expansion angle. The liner tilting results in a 40% reduction in the length of the CRZ. However, once the primary jets are open, they define the termination point of the CRZ. The chamber w/b ratio results in a CRZ with the same diameter ratio (85%) in all configurations. Interestingly, the maximum reverse flow velocity is roughly constant in all measurement plans and configurations up to a downstream distance of 1R (R is the flare radius). However, with open primary jets, the CRZ strength increases appreciably. It appears that the confinement dictates both the flow field outside the CRZ and the size of the CRZ, while the swirl cup configuration mainly influences the strength of the CRZ. Regarding turbulence activities, the presence of the dome damps the fluctuations in the expanding swirling jet region. On the other hand, the primary jets increase the turbulence activities appreciably in the jet impingement region, as well as the upper portion of the CRZ (60% increase).

Effect of the Flare Expansion Angle on the Mean and Dynamic Behavior of Swirling Flow Generated by a Counter Rotating Radial-Radial Swirler Using a Water Test Rig

2015 ◽  
Author(s):  
Wessam Estefanos ◽  
Samir Tambe ◽  
San-Mou Jeng
Keyword(s):  
Dynamic Behavior ◽  
High Speed ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Flow Instability ◽  
Reverse Flow ◽  
Test Rig ◽  
Expansion Angle ◽  
Water Test ◽  
The Mean

A series of experiments have been conducted to study the effect of the flare expansion angle on the mean and unsteady behavior of the non-reacting swirling flow using a water test rig. The flow was examined in water using a 3X model of a counter rotating radial-radial swirler. Three flares having expansion angles of 30.9°, 35.9° and 40.9° with respect to the swirler centerline were tested. 2D high speed Particle Image Velocimetry (PIV) measurements were employed to study the instantaneous and mean velocity fields. Tests were conducted at a Reynolds number equivalent to an air pressure drop of 4% for the corresponding 1X model of the swirler under atmospheric conditions. The flare expansion angle was found to have a clear impact on the mean, turbulent and dynamic behavior of the swirling flow. With the increase in the flare expansion angle, the width of the Center Toroidal Recirculation Zone (CTRZ) increased. The length and width of the Corner Recirculation Zone decreased with increasing the flare angle. For the 30.9° flare, the high turbulence regions extended further axially compared to the other two flares. Strong flow instability was observed on the boundaries of the reverse flow zones. A temporal FFT approach was used to obtain the dominant frequencies of flow instability based on the instantaneous velocity data. The dominant frequency of this instability was slightly lower for the 30.9° flare angle. High turbulent kinetic energy (TKE) was located in the vicinity of the unstable shear layers originating from the CTRZ and CRZ. The TKE reached its maximum near the center for the 30.9° flare and near the walls for the 35.9° and 40.9° flares. The phase angle difference between the high TKE regions was 3.14 radians, indicating a circumferential mode of instability. The obtained results give a clear explanation on the mechanisms driving the flow instability and how these mechanisms change with the change in the flare angle. These results also serve as a tool to validate CFD models.

A Meanline Model for Impeller Flow Recirculation

2008 ◽  
Author(s):  
Xuwen Qiu ◽  
David Japikse ◽  
Mark Anderson
Keyword(s):  
Flow Rate ◽  
Recirculation Zone ◽  
Reverse Flow ◽  
Low Flow ◽  
Suction Surface ◽  
Blade Loading ◽  
Flow Recirculation ◽  
Impeller Outlet ◽  
Active Flow ◽  
Low Flow Rate

Flow recirculation at the impeller inlet and outlet is an important feature that affects impeller performance, especially the power consumption at a very low flow rate. Although the mechanisms for this flow phenomenon have been studied, a practical model is needed for meanline modeling of impeller off-design performance. In this paper, a meanline recirculation model is proposed. At the inlet, the recirculation zone acts as area blockage to relieve the large incidence of the active flow at a low flow rate. The size of the blockage is estimated through a critical area ratio of an artificial “inlet diffuser” from the inlet to throat. The intensity of the reverse flow can then be calculated by assuming a linear velocity profile of meridional velocity in the recirculation zone. At the impeller outlet, a recirculation zone near the suction surface is established to balance the velocity difference on the pressure and suction sides of the blade. The size and the intensity of the outlet recirculation zone is assumed related to blade loading, which can be evaluated based on flow turning and Coriolis force. A few validation cases are presented showing a good comparison between test data and prediction by the model.

scholarly journals Flow and wake characteristics associated with large wood to inform river restoration

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Isabella Schalko ◽  
Ellen Wohl ◽  
Heidi M. Nepf
Keyword(s):  
Habitat Suitability ◽  
River Restoration ◽  
Recirculation Zone ◽  
Habitat Diversity ◽  
Turbulence Level ◽  
Large Wood ◽  
River Ecosystem ◽  
Mean Velocity ◽  
Physical Model Tests ◽  
Channel Center

AbstractWood is an integral part of a river ecosystem and the number of restoration projects using log placements is increasing. Physical model tests were used to explore how the wood position and submergence level (discharge) affect wake structure, and hence the resulting habitat. We observed a von-Kármán vortex street (VS) for emergent logs placed at the channel center, while no VS formed for submerged logs, because the flow entering the wake from above the log (sweeping flow) inhibited VS formation. As a result, emergent logs placed at the channel center resulted in ten times higher turbulent kinetic energy compared to submerged logs. In addition, both spatial variation in time-mean velocity and turbulence level increased with increasing log length and decreasing submergence level. Submerged logs and logs placed at the channel side created a greater velocity deficit and a longer recirculation zone, both of which can increase the residence time in the wake and deposition of organic matter and nutrients. The results demonstrate that variation in log size and degree of submergence can be used as a tool to vary habitat suitability for different fish preferences. To maximize habitat diversity in rivers, we suggest a diverse large wood placement.

scholarly journals On the structure of the self-sustaining cycle in separating and reattaching flows

2018 ◽  
Vol 857 ◽  
pp. 907-936 ◽  
Author(s):  
A. Cimarelli ◽  
A. Leonforte ◽  
D. Angeli
Keyword(s):  
Shear Layer ◽  
Rectangular Plate ◽  
Large Scale ◽  
Reverse Flow ◽  
Leading Edge ◽  
Streamwise Velocity ◽  
The Self ◽  
Small Scale ◽  
Spectral Evolution ◽  
Mean Velocity

The separating and reattaching flows and the wake of a finite rectangular plate are studied by means of direct numerical simulation data. The large amount of information provided by the numerical approach is exploited here to address the multi-scale features of the flow and to assess the self-sustaining mechanisms that form the basis of the main unsteadinesses of the flows. We first analyse the statistically dominant flow structures by means of three-dimensional spatial correlation functions. The developed flow is found to be statistically dominated by quasi-streamwise vortices and streamwise velocity streaks as a result of flow motions induced by hairpin-like structures. On the other hand, the reverse flow within the separated region is found to be characterized by spanwise vortices. We then study the spectral properties of the flow. Given the strongly inhomogeneous nature of the flow, the spectral analysis has been conducted along two selected streamtraces of the mean velocity field. This approach allows us to study the spectral evolution of the flow along its paths. Two well-separated characteristic scales are identified in the near-wall reverse flow and in the leading-edge shear layer. The first is recognized to represent trains of small-scale structures triggering the leading-edge shear layer, whereas the second is found to be related to a very large-scale phenomenon that embraces the entire flow field. A picture of the self-sustaining mechanisms of the flow is then derived. It is shown that very-large-scale fluctuations of the pressure field alternate between promoting and suppressing the reverse flow within the separation region. Driven by these large-scale dynamics, packages of small-scale motions trigger the leading-edge shear layers, which in turn created them, alternating in the top and bottom sides of the rectangular plate with a relatively long period of inversion, thus closing the self-sustaining cycle.

Aerodynamic Behavior of Asymmetric Jets in 3-D Furnaces

1994 ◽  
Author(s):  
F. M. El-Mahallawy ◽  
M. A. Hassan ◽  
M. A. Ismail ◽  
H. Zafan
Keyword(s):  
Numerical Simulation ◽  
Flow Pattern ◽  
Numerical Experiments ◽  
Recirculation Zone ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Region ◽  
Stabilization Method ◽  
Flow Features

The purpose of this paper is to present and evaluate numerical experiments illustrating the flow features in a 3-D furnace utilizing unconventional asymmetrical jet that creates natural recirculation zone. The numerical simulation of this aerodynamic stabilization method have unveiled the three-dimensional nature of the flow pattern which possesses a quite large reverse flow region. The size and strength of the built recirculation zone would be capable of stabilizing the burning of low-quality fuels.

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