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![Time sequence of instantaneous temperature fields at the lean blow-out condition carried out by [18].](publication/258391730/figure/fig3/AS:1088988332986368@1636646459238/Time-sequence-of-instantaneous-temperature-fields-at-the-lean-blow-out-condition-carried.jpg)
Time sequence of instantaneous temperature fields at the lean blow-out condition carried out by [18].
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In order to investigate effects of apex angle (α) on chemically reacting turbulent flow and thermal fields in a channel with a bluff body V-gutter flame holder, a numerical study has been carried out in this paper. With a basic geometry used in a previous experimental study, the apex angle was varied from 45° to 150°. Eddy dissipation concept (EDC)...
Citations
... In this case, the downstream flow recirculation takes place more strongly with higher velocities which prevail due to shortening of the bluff body horizontal length such that the intensity of turbulence increases in the downstream vortical region. This is responsible for reaching the greatest overall peak T. K. E. upon reducing the aspect ratio to its currently achieved minimum value of 0.3 (whereby the bluff body approaches the flat plate shape which induces the largest flow recirculation and turbulent kinetic energy, [6,45]. Before this takes place at the minimum aspect ratio, a local drop takes place as the aspect ratio decreases from 2.0 to 1.0 because of the reduction in the space available for turbulence. ...
... Such wake region was shown to be enlarged upon increasing the blockage effect. In this respect, Yang et al. [45] showed that as the V-gutter flame holder interior apex angle increases; the recirculation zone gets bigger, so does the backflow velocity magnitude and consequently the flame becomes wider. This consequently increases the heat release rate, thus extending the flame stability limits. ...
The combined effects of flow recirculation and preheating on the premixed flame stability limits were employed via two flow configurations. In the first configuration, the natural gas-air mixture was set to flow around a bluff body whose orientation, number of vertices and vertex angle were varied. In the second configuration, an innovative design was developed where the fuel–air mixture was set to flow inside the bluff body as two opposing jets whose resultant flow is redirected to pass around the bluff body. The peak turbulent kinetic energy (T. K. E.) decreased from 7.24 to 4.94 m²/s² with the star shape of 4 vertices as its orientation changed from 45 to 0° and such decrease was limited to 5.27 m²/s² upon having a smaller vertex angle. A smaller drop from 7.24 to 6.0 m²/s² was experienced when the 4 vertices were replaced by 5 vertices at 0° angle of orientation, while the drop continued to 4.3 m²/s² upon having 6 vertices due to the reduction in the space available for eddies. A smaller peak T. K. E. of 2.33 m²/s² was found with the star shape of 3 vertices because the sites for turbulence development were limited. With the star cross-section of 4 vertices at 45° angle of orientation, a maximum blow-off velocity as high as 51.5 m/s and a minimum lean limit as low as 0.40 were obtained. A further extension in the flame stability limits was provided via the second flow configuration due to the favorable effects of impingement and prolonged path of preheating. As the distance between the bluff body and the combustor separating wall decreased to 1.7 times the jet diameter, the blow-off velocity increased to 79.1 m/s; while the lean limit decreased to 0.31 with the star shape of 4 vertices at 45° angle of orientation.
... It can be detected that when the triangle apex angle increased, the size of walk region is increased and the turbulence intensity behind the cylinder is enhanced. This conclusion is compatible with the findings of Yang et al. [20] during the investigation of different apex angle effect on nonreactive and reactive flow in a channel with a V-gutter flame holder. ...
A numerical study has been provided to investigate the characteristics of PCM melting in triangular cylinder containers. Commercial paraffin wax has been selected as a PCM and a hot air stream is used as a source of heat energy for the melting process. The flow structure and convective heat transfer around the triangular cylinders have been determined and discussed. Three triangular cylinders of equal volume and different in apex angles (24°, 60° and 100°) have been investigated. The influence of apex angle variation on the flow behavior and on the mechanism of heat transfer to the cylinder walls is presented. Assessment of heat storage capacity is introduced for the various containers. The modeling of the flow field and heat transfer as well as the melting process has been carried out by using Ansys Fluent–CFD software. Finite volume technique is applied and SIMPLE algorithm is used. The results showed that the apex angle and the triangle base length have a remarkable effect on the container surface temperature and on the heat storage efficiency.
... The effect of apex angle (α) on the combustion process inside bluff body V-gutter flame holder has been numerically studied by Yang et al. [2] with apex angle was varied from 45 o to 150 o . While Ma and Harn [3] study the same effect numerically with different combustor configuration. ...
In this paper, CFD analyses using Reynold Stress Model (RSM) approaches are being adopted to study the effect of bluff body apex angle, stream inlet velocity and thermal conditions of the combustor wall on the velocity and thermal fields inside a lean premixed bluff body stabilized gas turbine combustor. The numerical simulation is performed under a steady state condition utilizing the commercial software ANSYS-FLUENT. Four various apex angles (α) including 30, 60, 90 and 120 degree and five different inlet velocities namely 10, 15, 20, 25 and 30 m/s were compared. It was found that the size of the recirculation zone formed behind the bluff body is increased with the increase in apex angle and inlet velocity which can help in achieving a more stable flame. In addition, applying the proper thermal conditions of combustor wall improved the accuracy of predicted temperature field, especially inside the recirculation zone near to the bluff body.
... Research on flame stabilization using various techniques including gutters have been done over the years. Experimentation on bluff bodies under cold and hot flows were carried out by Fujii et al and Yue et al [1]. Numerical studies on the same were done by Gelan yang , Huixia Jin and Na Bai [2] . ...
... Increase in wake width and recirculation zone length with increase in gutter apex angle is listed in the tabulation. The magnitude of increase in width and length in the experimental data can be validated with numerical results of reference [1]. In the paper "A Numerical Study on Premixed Bluff Body Flame of Different Bluff Apex Angle." ...
The Present experimental study focuses on the flame stabilization using V Gutter Bluff Bodies for afterburner applications. Maximum wake formation and minimum loss in total quantities are the prime requirements for flame stabilization. Cold Flow studies are carried out in the prototype combustor test rig. The experimental setup comprises of a constant area dump type combustor of dimensions 8.5 x 8.5 x 86cm. Air is fed through a radial blower whose speed can be varied from 3.5m/s to 7.5 m/s by a belt and pulley arrangement. Experiments are carried out using three gutters of apex angles 60, 90 and 120 with each gutter at different speeds from 3.5 to 7.5m/s .Pressure readings are measured using a 15 port pressure rake from the exit plane of combustor to immediately behind the gutter. The parameters of interest in the cold flow studies are recirculation zone length and wake width. Plots are drawn between normalized velocity values and normalized positions. It is observed that at a given speed, the wake width of a 120 V gutter and 90 V gutter is 1.467 times and 1.267 times respectively that of a 60 V gutter. It is also observed that at a given speed, the recirculation zone length of a 120 and 90 gutter is 1.667 and 1.333 times respectively that of a 60 V gutter. As the speed is increased the wake width and recirculation zone length also increases for a particular gutter. It can thus be inferred that, the optimum apex angle with maximum wake formation and minimum loss in total quantities occur between 90 and 120 degrees. NOMENCLATURE L Recirculation zone length[mm] P Pressure [N/m 2 ] T Temperature of flow [Kelvin] V Velocity of flow [m/s 2 ] W Wake width [mm] LPM Air flow rate α Gutter apex angle [degrees]
... Research on flame stabilization using various techniques including gutters have been done over the years. Experimentation on bluff bodies under cold and hot flows were carried out by Fujii et al and Yue et al [1]. Numerical studies on the same were done by Gelan yang , Huixia Jin and Na Bai [2] . ...
... Increase in wake width and recirculation zone length with increase in gutter apex angle is listed in the tabulation. The magnitude of increase in width and length in the experimental data can be validated with numerical results of reference [1]. In the paper "A Numerical Study on Premixed Bluff Body Flame of Different Bluff Apex Angle." ...
The Present experimental study focuses on the flame stabilization using V Gutter Bluff Bodies for afterburner applications. Maximum wake formation and minimum loss in total pressures are the prime requirements for flame stabilization. Cold flow studies are carried out in the prototype combustor test rig. The experimental setup comprises of a constant area dump type combustor of dimensions 8.5 x 8.5 x 86 cm. Air is fed through a radial blower whose speed can be varied from 3.5 m/s (940 lpm) to 7.5 m/s (1570 lpm). Experiments are carried out using three V gutters of apex angles 60, 90 and 120. Pressure readings are measured with scanivalve pressure transducers using a 15 port pressure rake from the exit plane of combustor. The parameters of interest for flame stabilization in the cold flow studies are recirculation zone length and wake width. Plots are drawn between normalized velocity values obtained from the pressure data and normalized positions. It is observed that for a given speed, the wake width of a 120 V gutter and 90 V gutter is 1.467 times and 1.267 times respectively that of a 60 V gutter. It is also observed that for a given speed, the recirculation zone length of a 120 and 90 gutter is 1.667 and 1.333 times respectively that of a 60 V gutter. As the speed is increased the wake width and recirculation zone length also increases for a particular apex angle gutter. It is inferred that, the optimum apex angle with maximum wake formation and minimum loss in total pressures occurs between 90 and 120 degrees. It is recommended based on the experiments that, the apex angle of 90 to 120 degrees of V gutters are best suited for flame stabilization for afterburner applications. NOMENCLATURE L Recirculation zone length [mm] P Pressure [N/m 2 ] T Temperature of flow [Kelvin] V Velocity of flow [m/s] W Wake width [mm] lpm Air flow rate α Gutter apex angle [degrees] 1.INTRODUCTION The combustion environment in turbulent combustion flames is highly complex, making the prediction of flame ignition and stability conditions a big challenge. In spark ignition engines, no provision for flame stabilization is required since the flame freely propagates in a sealed chamber, and the concepts of flashback, lift-off and blow-off do not exist. Gas burners, gas turbines and turbojet afterburners require flame stabilizing mechanism as combustion does not occur as like in SI engines. In such circumstances, a stable flame is one that is anchored at a desired location and is resistant to flashback , lift-off and blow-off over the device " s operating range.
The results of computer simulation of the heat state of the combustion zone and the burnup rate of fuel for stabilizer burners with asymmetric fuel distribution are presented. The features of temperature fields in this zone that are characteristic of the conditions under study are revealed. The analysis of these features in the aspect of their conditionality by the two-stage combustion of fuel gas is carried out.
The combustion at high speed reactants requires a flame holding characteristics to sustain the flame in the afterburner. The flame holding characteristics of the combustor is carried out by the bluff-body stabilizers. The range of conditions of parameters influencing the flame stabilization is to be identified and the effects on the flame sustainability have to be investigated. DeZubay used the concept of DeZubay number and flame stability envelope to determine the stabilization and blowout range. In the present work, the effect of air pressure and the angle of apex of the V-gutter on flame stabilization and blowout mechanism have been experimentally investigated for six different apex angles and four different air pressure conditions. The value of DeZubay number at each condition has been calculated and verified with DeZubay stability chart for flame stabilization. The results show that stable flame is obtained for the entire pressure range when the apex angle of the V gutter is in 60° and 90°.
Рассматривается влияние способа задания характеристик турбулентности на входной границе на результаты расчёта параметров потока за уголковым стабилизатором пламени при использовании метода крупных вихрей и подсеточной модели турбулентности – Смагоринского-Лилли. Исследование проводится для пропановоздушной смеси с температурой 300 К в канале квадратного сечения с расположенным в нём плохообтекаемым телом, в основании которого лежит равносторонний треугольник с длиной ребра 25 мм. Среднемассовая скорость потока на входе – 10 м/с. Рассматривались несколько способов задания граничных условий на входной границе. Два варианта без турбулентности на входе (равномерное распределение скорости по входному сечению и трубный профиль скорости) и два варианта с искусственно смоделированной турбулентностью (вихревой метод и спектральный синтезатор турбулентности). В результате исследования были получены значения интенсивности потока в области до стабилизатора, распределение скорости, кинетической энергии в поперечных и продольных сечениях за стабилизатором. Также приведены графики спектра энергетической плотности пульсаций скорости.
