Статті в журналах: "Low-swirl"

1

Xiao, Yinli, Zhibo Cao, and Changwu Wang. "Flame stability limits of premixed low-swirl combustion." Advances in Mechanical Engineering 10, no. 9 (September 2018): 168781401879087. http://dx.doi.org/10.1177/1687814018790878.

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The objective of this study is to gain a fundamental understanding of the flow-field and flame behaviors associated with a low-swirl burner. A vane-type low-swirl burner with different swirl numbers has been developed. The velocity field measurements are carried out with particle image velocimetry. The basic flame structures are characterized using OH radicals measured by planar laser-induced fluorescence. Three combustion regimes of low-swirl flames are identified depending on the operating conditions. For the same low-swirl injector under atmospheric conditions, attached flame is first observed when the incoming velocity is too low to generate vortex breakdown. Then, W-shaped flame is formed above the burner at moderate incoming velocity. Bowl-shaped flame structure is formed as the mixture velocity increases until it extinct. Local extinction and relight zones are observed in the low-swirl flame. Flow-field features and flame stability limits are obtained for the present burner.

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2

Kida, Shigeo, and Hideaki Miura. "Swirl Condition in Low-Pressure Vortices." Journal of the Physical Society of Japan 67, no. 7 (July 15, 1998): 2166–69. http://dx.doi.org/10.1143/jpsj.67.2166.

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3

Verbeek, Anton A., Thijs W. F. M. Bouten, Genie G. M. Stoffels, Bernard J. Geurts, and Theo H. van der Meer. "Fractal turbulence enhancing low-swirl combustion." Combustion and Flame 162, no. 1 (January 2015): 129–43. http://dx.doi.org/10.1016/j.combustflame.2014.07.003.

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4

Jeong, Hwanghui, and Keeman Lee. "Effect of Swirl Angles and Combustion Characteristics of Low Swirl Model Combustor." Journal of the Korean Society of Propulsion Engineers 20, no. 4 (August 1, 2016): 40–49. http://dx.doi.org/10.6108/kspe.2016.20.4.040.

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5

Wang, Y., W. Xu, H. Yin, Y. Zhang, and H. S. Dou. "Numerical study on the influence of pre-swirl angle on internal flow characteristics of centrifugal pumps." AIP Advances 12, no. 4 (April 1, 2022): 045019. http://dx.doi.org/10.1063/5.0085903.

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The effect of inlet pre-swirl on the performance of a centrifugal pump is studied by numerical simulation. The governing equations are Navier–Stokes equations and the shear stress transport k–ω turbulence model. The numerical results show that the optimal operating point moves from the low flow region to the high flow region as the pre-swirl angle shifts from positive to negative. It is found by contours of Omega–Liutex that the positive pre-swirl angle is able to weaken the vortex on the blade suction and reduce the energy dissipation. On both the 0.5Q0 and 1.2Q0 operating conditions, the proportion of entropy production loss in the impeller and volute is about 60% and 30%, respectively. As the pre-swirl angle changes from negative to positive, the entropy production loss in the inlet and outlet pipes increases slowly, and the entropy production loss in the volute and impeller shows a decreasing trend and the peak area of entropy loss moves toward the outlet. Under the four pre-swirl angles, the main frequency is always the passing frequency of the blade. The pre-swirl angle affects the pressure fluctuation at the main frequency but has little effect at the secondary frequency. The change in velocity pulsation amplitude in the impeller in the positive pre-swirl angle is smaller than that in the negative pre-swirl angle. As a result, for the positive pre-swirl angle, the turbulent kinetic energy density in the impeller is low, and the energy loss is low, compared with negative pre-swirl. Under the low flow condition (0.5Q0), the change in velocity pulsation amplitude in the inertial range of the energy spectrum under negative pre-swirl is greater than that under positive pre-swirl.

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6

Wang, Xuegao, Jun Hu, Jin Guo, Baofeng Tu, and Zhiqiang Wang. "An experimental investigation on the interaction between inlet swirl distortion and a low-speed axial compressor." Science Progress 103, no. 3 (July 2020): 003685042094092. http://dx.doi.org/10.1177/0036850420940920.

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The aim of this article mainly lies in two aspects. The first is to investigate the effect of inlet swirl distortion on the performance and stability of a low-speed compressor experimentally. The second is to quantify swirl pattern revolution through the compressor and find out background causes of the change in compressor performance. Swirl distortion makes the leading-edge incidence opposite between tip and hub regions, compared to that of clean flow. And the compressor performance change is ultimately determined by these two aspects. Results indicate that negative bulk swirl improves pressure rise, and the effect is on the contrary to the positive bulk swirl. Under the condition of paired swirl, pressure rise also presents a reduction. All these three types of swirl have little effect on the stall boundary. Although swirl distortion shows clear recovery at rotor exit, downstream components still work at off-design conditions due to the induced nonuniformity in axial velocity and total pressure.

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7

Balakrishnan, P., and K. Srinivasan. "Pipe jet noise reduction using co-axial swirl pipe." Aeronautical Journal 121, no. 1238 (March 6, 2017): 488–514. http://dx.doi.org/10.1017/aer.2017.5.

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ABSTRACTThe present experimental work highlights the acoustic far field and flow field characteristics of confined co-axial swirling pipe jets. Co-axial confinements with six vanes at angles of 0°, 20° and 40° are considered here. Two pipe lengths of L/D=0.5 and 2 are studied. The Mach numbers studied range from 0.85 to 1.83. An increase in the pipe length causes suppression of the transonic tones in non-swirl pipe jets. Swirl reduces the low frequency noise components and increases the high-frequency components compared to non-swirl jet. The broadband shock associated noise is mitigated by the swirl pipe jets. However, the screech tone is completely eliminated by the swirl pipe jets. Further, swirl pipe jets radiate low levels of noise at all the emission angles compared to non-swirl pipe jets, for both the pipe length cases at supersonic Mach numbers. Increase in the pipe length enhances the shock associated noise and OASPL for the non-swirl pipe jet. Centreline pitot survey and schlieren visualisation show a reduction in core length, reduction in the number of shock cells, weakening/destruction of the shock cells by the swirl pipe jets compared to the non-swirl pipe jets.

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8

Hsu, Yun, and Christopher E. Brennen. "Effect of Swirl on Rotordynamic Forces Caused by Front Shroud Pump Leakage." Journal of Fluids Engineering 124, no. 4 (December 1, 2002): 1005–10. http://dx.doi.org/10.1115/1.1511164.

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Unsteady forces generated by fluid flow through the impeller shroud leakage path of a centrifugal pump were investigated. The effect of leakage path inlet swirl (pump discharge swirl) on the rotordynamic forces was re-examined. It was observed that increasing the inlet swirl is destabilizing both for normal and tangential rotordynamic forces. Attempts to reduce the swirl within the leakage path using ribs and grooves as swirl brakes showed benefits only at low leakage flow rate.

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9

Kang, D. M., F. E. C. Culick, and A. Ratner. "Combustion dynamics of a low-swirl combustor." Combustion and Flame 151, no. 3 (November 2007): 412–25. http://dx.doi.org/10.1016/j.combustflame.2007.07.017.

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10

Li, Shuai, Yan Liu, Mohammad Omidi, Chuang Zhang, and Hongkun Li. "Numerical Investigation of Transient Flow Characteristics in a Centrifugal Compressor Stage with Variable Inlet Guide Vanes at Low Mass Flow Rates." Energies 14, no. 23 (November 25, 2021): 7906. http://dx.doi.org/10.3390/en14237906.

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This study numerically investigates the beneficial effects of positive pre-swirl on the aerodynamic performance and internal flow field in a centrifugal compressor stage with variable inlet guide vanes (VIGVs) at low mass flow rates. Four positions of VIGV are considered, including 0°, 30°, 45°, and 60° angle. The latter three positions of VIGV induce positive pre-swirl. Numerical results show that as positive pre-swirl increases, the aerodynamic performance curve of the stage moves in the low mass flow rate direction. In the three cases of positive pre-swirl, there was an improvement of approximately 9.95% of stall/surge margin greater than in conditions with no pre-swirl. The regulation of IGV can effectively improve the unstable flow of the compressor stage at low mass flow rates. A low frequency that has a great influence on the internal flow of the compressor stage is found, and the unstable flow caused by low frequency is analyzed by the combination of streamline distribution, spectrum analysis, vector, entropy increase, and modal decomposition method. Meanwhile, the modal decomposition method and flow field reconstruction techniques are used to investigate the coherent flow structures caused by low frequency under different guide vane openings.

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11

Trinchenko, Alexey. "Low-temperature swirl method of burning combustible waste." E3S Web of Conferences 91 (2019): 04003. http://dx.doi.org/10.1051/e3sconf/20199104003.

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Burning combustible industrial waste increases the efficiency of using raw materials while at the same time solving the issues of protecting the environment from pollution by eliminating waste dumps. The paper deals with the low-temperature swirl method of waste incineration of microbiological production  hydrolytic lignin. A combustion device has been developed that allows using hydrolytic lignin as a fuel for the production of electrical energy and heat without illumination of the torch and with high efficiency and reduced emissions of gaseous pollutants into the atmosphere. On the basis of the developed model of the boiler TP-35U, a quantitative estimate of the level of nitrogen oxides was made when introducing the low-temperature swirl method. The results of the calculations show the advantages of low-temperature swirl combustion of hydrolytic lignin.

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12

Hu, Bo, Yulong Yao, Minfeng Wang, Chuan Wang, and Yanming Liu. "Flow and Performance of the Disk Cavity of a Marine Gas Turbine at Varying Nozzle Pressure and Low Rotation Speeds: A Numerical Investigation." Machines 11, no. 1 (January 5, 2023): 68. http://dx.doi.org/10.3390/machines11010068.

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In marine gas turbines, variations in rotational speed occur all the time. To ensure adequate cooling effects on the turbine blades, the valves need to be adjusted to change the pressure upstream of the pre-swirl nozzle. Changing such pressure will have significant effects on the local or overall parameters, such as core swirl ratio, temperature, flow rate coefficient, moment coefficient, axial thrust coefficient, etc. In this paper, we studied the flow characteristics within the pre-swirl system of a marine gas turbine at low rotational speed by varying the pressure at the pre-swirl nozzle. The corresponding global Reynolds number ranged from Re = 2.3793 × 105 to 9.5172 × 105. The flow in the rotor-stator cavities was analyzed to find the effects of nozzle pressure on the radial velocity, core swirl ratio, and pressure. According to the simulation results, we introduced a new leakage flow term into the formulary in the references to calculate the values of K between the inner seal and the pre-swirl nozzle. The matching characteristics between the pre-swirl nozzle and the inclined receiving hole was predicted. Performance of the pre-swirl system was also analyzed, such as the pressure drop, through-flow capacity, and cooling effects. After that, the moment coefficient and the axial thrust coefficient were predicted. This study provides some reference for designers to better design the pre-swirl system.

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13

Pazur, W., and L. Fottner. "The Influence of Inlet Swirl Distortions on the Performance of a Jet Propulsion Two-Stage Axial Compressor." Journal of Turbomachinery 113, no. 2 (April 1, 1991): 233–40. http://dx.doi.org/10.1115/1.2929091.

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Aeroengine intakes containing S-shaped diffusers produce different types of inlet swirl distortions and essentially a combination of a twin swirl and a bulk swirl. The main object of this investigation was to assess the influence of inlet swirl distortions on the performance of a transonic two-stage axial compressor installed in a turbo jet bypass engine Larzac 04. A typical inlet swirl distortion was simulated by a delta-wing in front of the engine. An experimental method was investigated to measure the performance map of the installed low-pressure compressor for different engine operating lines. The influence of an inlet swirl distortion with different strengths on the performance map of the compressor was investigated experimentally. It is shown that the performance parameters decrease and a temperature distortion is generated behind the compressor. As the basis of the theoretical investigations of the performance map, including inlet swirl distortions, a computing model considering four compressors working in parallel was established. The model is based on the idea that an inlet swirl distortion can be substituted by two fundamental types of swirl components, i.e., a bulk swirl corotating, and a bulk swirl counterrotating to the revolution of the compressor. Computed performance maps of the compressor will be discussed and compared with the experimental data.

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14

Sogbesan, Oluwasujibomi, Colin P. Garner, and Martin H. Davy. "Effects of intake-port throttling on combustion behaviour in diesel low-temperature combustion." International Journal of Engine Research 19, no. 8 (September 29, 2017): 827–38. http://dx.doi.org/10.1177/1468087417732881.

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This article describes the effects of intake-port throttling on diesel low-temperature combustion at a low and medium load condition. These conditions were known for their characteristically high hydrocarbon emissions predominantly from over-mixed and under-mixed mixture zones, respectively. The investigation was carried out to supplement current findings in the literature with valuable information on the formation of high hydrocarbon emissions with increasing swirl levels generated by intake-port throttling. This was achieved through the use of cycle-resolved high hydrocarbon measurements in addition to cycle averaged emissions and in-cylinder pressure-derived metrics. While there was negligible overall effect at the moderately dilute low-load conditions, increasing swirl has been shown to be beneficial to premixing efficacy under highly dilute conditions with extended ignition delay. This potential advantage was found to be nullified by the swirl-induced confinement of fuel and combustion products to the central region of the cylinder leading to poor late cycle burn rates and increased smoke emissions. High hydrocarbon emissions from the squish and head quench regions were reduced by an increase in swirl ratio.

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15

Elbaz, A. M., H. A. Moneib, K. M. Shebil, and W. L. Roberts. "Low NOX - LPG staged combustion double swirl flames." Renewable Energy 138 (August 2019): 303–15. http://dx.doi.org/10.1016/j.renene.2019.01.070.

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16

Whitfield, A., and A. H. Abdullah. "The Performance of a Centrifugal Compressor With High Inlet Prewhirl." Journal of Turbomachinery 120, no. 3 (July 1, 1998): 487–93. http://dx.doi.org/10.1115/1.2841744.

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The performance requirements of centrifugal compressors usually include a broad operating range between surge and choke. This becomes increasingly difficult to achieve as increased pressure ratio is demanded. In order to suppress the tendency to surge and extend the operating range at low flow rates, inlet swirl is often considered through the application of inlet guide vanes. To generate high inlet swirl angles efficiently, an inlet volute has been applied as the swirl generator, and a variable geometry design developed in order to provide zero swirl. The variable geometry approach can be applied to increase the swirl progressively or to switch rapidly from zero swirl to maximum swirl. The variable geometry volute and the swirl conditions generated are described. The performance of a small centrifugal compressor is presented for a wide range of inlet swirl angles. In addition to the basic performance characteristics of the compressor, the onsets of flow reversals at impeller inlet are presented, together with the development of pressure pulsations, in the inlet and discharge ducts, through to full surge. The flow rate at which surge occurred was shown, by the shift of the peak pressure condition and by the measurement of the pressure pulsations, to be reduced by over 40 percent.

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17

Rusak, Zvi, Jung J. Choi, Nicholas Bourquard, and Shixiao Wang. "Vortex breakdown in premixed reacting flows with swirl in a finite-length circular open pipe." Journal of Fluid Mechanics 793 (March 22, 2016): 749–76. http://dx.doi.org/10.1017/jfm.2016.140.

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A global analysis of steady states of low Mach number inviscid premixed reacting swirling flows in a straight circular finite-length open pipe is developed. We focus on modelling the basic interaction between the swirl and heat release of the reaction. For analytic simplicity, a one-step first-order Arrhenious reaction kinetics is considered in the limit of high activation energy and infinite Peclet number. Assuming a complete reaction with chemical equilibrium upstream and downstream of the reaction zone, a nonlinear partial differential equation is derived for the solution of the flow stream function downstream of the reaction zone in terms of the specific total enthalpy, specific entropy and circulation functions prescribed at the inlet. Several types of solutions of the nonlinear ordinary differential equation for the columnar flow case describe the outlet states of the flow in a long pipe. These solutions are used to form the bifurcation diagram of steady reacting flows with swirl as the inlet swirl level is increased at a fixed heat release from the reaction. The approach is applied to two profiles of inlet flows, the solid-body rotation and the Lamb–Oseen vortex, both with constant profiles of the axial velocity, temperature and mixture reactant mass fraction. The computed results provide theoretical predictions of the critical inlet swirl levels for the appearance of vortex breakdown states and for the size of the breakdown zone as a function of the inlet flow swirl level, Mach number and heat release of the reaction. For the inlet solid-body rotation, flow is decelerated to breakdown as the inlet swirl is increased above the critical swirl level, and there is a delay in the appearance of breakdown with the increase of the heat release of the reaction. For the inlet Lamb–Oseen vortex at low values of heat release, the critical swirl for breakdown is decreased with the increase of heat release while, at high values of heat release, the appearance of breakdown is delayed to higher incoming flow swirl levels with the increase of heat release. The analysis sheds light on the global dynamics of low Mach number reacting flows with swirl and vortex breakdown and on the interaction between vortex breakdown and heat release that affects the shape of the reaction zone in the domain.

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18

JÃ³zsa, Viktor, and Gergely Novotni. "Wavelet analysis of flame blowout of a liquid-fueled swirl burner with quarls." Noise Control Engineering Journal 67, no. 5 (September 1, 2019): 394–403. http://dx.doi.org/10.3397/1/376734.

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Lean swirl combustion is the leading burner concept today, used in several steadyoperating applications to ensure awide operating range and low pollutant emissions. Approaching lean blowout is highly desired by design to achieve the lowest possible NOX emission. It was shown earlier that quarls could significantly extend the operating regime of liquid-fueled swirl burners. In the present study, the accompanying acoustic noise is evaluated by continuous wavelet transformation to show the effect of various quarl geometries on lean flame blowout. However, the desired flame shape of swirl burners is V, first, and a straight flame, and then a transitory regime can be observed before the developed V-shaped flame through increasing the swirl number. If the axial thrust is excessive, blowout might occur in earlier stages. Presently, the characteristic bands before blowout were analyzed and evaluated at various quarl geometries, swirl numbers, and atomizing pressures. The latter parameter also acts as an axial thrust control to adjust the swirl number. firstly, a straight flame, then a transitory regime can be observed before the developed V-shaped flame through increasing the swirl number. If the axial thrust is excessive, blowout might occur in earlier stages. Presently, the characteristic bands before blowout were analyzed and evaluated at various quarl geometries, swirl numbers, and atomizing pressures. The latter parameter also acts as an axial thrust control to adjust the swirl number.

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19

Jebamani, Rathnaraj, and Narendra Kumar. "Studies on variable swirl intake system for DI diesel engine using computational fluid dynamics." Thermal Science 12, no. 1 (2008): 25–32. http://dx.doi.org/10.2298/tsci0801025j.

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It is known that a helical port is more effective than a tangential port to attain the required swirl ratio with minimum sacrifice in the volumetric efficiency. The swirl port is designed for lesser swirl ratio to reduce emissions at higher speeds. But this condition increases the air fuel mixing time and particulate smoke emissions at lower speeds. Optimum swirl ratio is necessary according to the engine operating condition for optimum combustion and emission reduction. Hence the engine needs variable swirl to enhance the combustion in the cylinder according to its operating conditions, for example at partial load or low speed condition it requires stronger swirl, while the air quantity is more important than the swirl under very high speed or full load and maximum torque conditions. The swirl and charging quantity can easily trade off and can be controlled by the opening of the valve. Hence in this study the steady flow rig experiment is used to evaluate the swirl of a helical intake port design for different operating conditions. The variable swirl plate set up of the W06DTIE2 engine is used to experimentally study the swirl variation for different openings of the valve. The sliding of the swirl plate results in the variation of the area of inlet port entry. Therefore in this study a swirl optimized combustion system varying according to the operating conditions by a variable swirl plate mechanism is studied experimentally and compared with the computational fluid dynamics predictions. In this study the fluent computational fluid dynamics code has been used to evaluate the flow in the port-cylinder system of a DI diesel engine in a steady flow rig. The computational grid is generated directly from 3-D CAD data and in cylinder flow simulations, with inflow boundary conditions from experimental measurements, are made using the fluent computational fluid dynamics code. The results are in very good agreement with experimental results.

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20

Trinchenko, Alexey. "Research of nitrogen oxides generation during low-temperature swirl fuel combustion." MATEC Web of Conferences 193 (2018): 03054. http://dx.doi.org/10.1051/matecconf/201819303054.

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The work is devoted to the solution of the issue of environmental protection from harmful emissions of thermal power plants. Mechanisms of nitrogen oxides generation in a low-temperature swirl furnace process are considered. The analysis of the combustion process characteristics influence on the final level of nitrogen oxide concentration in the flue gases of the boilers is presented. Calculations and experimental studies have shown that the method of low-temperature swirl combustion provides a significant reduction in emissions of nitrogen oxides to the atmosphere.

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21

Yan, Youyou, Mahmood Farzaneh Gord, Gary D. Lock, Michael Wilson, and J. Michael Owen. "Fluid Dynamics of a Pre-Swirl Rotor-Stator System." Journal of Turbomachinery 125, no. 4 (October 1, 2003): 641–47. http://dx.doi.org/10.1115/1.1578502.

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In a “direct-transfer” pre-swirl supply system, cooling air flows axially across the wheel-space from stationary pre-swirl nozzles to receiver holes located at a similar radius in the rotating turbine disc. This paper describes a combined computational and experimental study of the fluid dynamics of such a system. Measurements of total and static pressures have been made using a purpose-built rotor-stator rig, with 24 pre-swirl nozzles on the stator and 60 receiver holes in the rotor. The number of pre-swirl nozzles could be reduced, and it was possible to calculate CD, the discharge coefficient of the receiver holes. Information on the flowfield was also obtained from three-dimensional, incompressible steady turbulent flow computations. The measurements showed that there was a significant loss of total pressure between the outlet from the pre-swirl nozzles and the rotating core of fluid in the wheel-space. This loss increased as the pre-swirl flow-rate and inlet swirl ratio increased, and as the number of nozzles decreased. CD increased as the swirl ratio at the receiver hole radius approached unity; also CD decreased as the number of nozzles decreased. Computed pressures and tangential velocities were in mainly good agreement with the measurements. The computations help to explain the reasons for the significant losses in total pressure and for the relatively low values of CD in this pre-swirl system.

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22

Tsai, Feng Chin, and Rong Fung Huang. "Topological Flow Structures of Annular Swirling Jets." Journal of Mechanics 17, no. 3 (September 2001): 131–38. http://dx.doi.org/10.1017/s1727719100004494.

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AbstractThe effects of blockage and swirl on the macro flow structures of the annular jet past a circular disc are experimentally studied through the time-averaged streamline patterns. In the blockage-effect regime, the flows present multiple modes, single bubble, dual rings, vortex breakdown, and triple rings, in different regimes of blockage ratio and swirl number. The topological models of the flow structures are proposed and discussed according to the measured flow fields to manifest the complex flow structures. The single bubble is a closed recirculation bubble with a stagnation point on the central axis. The dual-ring flow is an open-top recirculsation zone, in which a pair of counter-rotating vortex rings exists in the near wake. The fluids in the dual rings are expelled downstream through a central jet-like swirling flow. A vortex breakdown may occur in the central jet-like swirling flow if the exit swirl number exceeds critical values. When the vortex breakdown interacts with the dual rings, a complex triple-ring flow structure forms. Axial distributions of the local swirl number are presented and discussed. The local swirl number increases with the increase of the exit swirl number and attains the maximum in the dual-ring mode. At large exit swirl numbers where the vortex breakdown occurs, the local swirl number decreases drastically to a low value.

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23

YEGIAN, D. T., and R. K. CHENG. "Development of a Lean Premixed Low-Swirl Burner for Low NOxPractical Applications." Combustion Science and Technology 139, no. 1 (October 1998): 207–27. http://dx.doi.org/10.1080/00102209808952088.

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24

Sun, Yicheng, Yufan Fu, Baohui Chen, Jiaxing Lu, and Wanquan Deng. "Numerical Simulation and Experimental Study on Flow Field in a Swirl Nozzle." Shock and Vibration 2021 (January 25, 2021): 1–9. http://dx.doi.org/10.1155/2021/6626715.

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In order to study the internal flow characteristics and external droplet velocity distribution characteristics of the swirl nozzle, the following methods were used: numerical simulations were used to study the internal flow characteristics of a swirl nozzle and phase Doppler particle velocimetry was used to determine the corresponding external droplet velocity distribution under medium and low pressure conditions. The distributions of pressure and water velocity inside the nozzle were obtained. Meanwhile, the velocities of droplets outside the nozzle in different sections were discussed. The results show that the flow rate in the swirl nozzle increases with the increase in inlet pressure, and the local pressure in the region decreases because of the excessive velocity at the internal outlet section of the swirl nozzle, resulting in cavitation. The experimental results show that under an external flow field, the minimum droplet velocity occurs in the axial direction; starting from the axis, the velocity first increases and then decreases along the radial direction. Swirling motion inside the nozzle and velocity variations in the external flow field occur under medium and low pressure conditions. The relationship between the inlet pressure and the distributions of water droplets’ velocities was established, which provides a reference for the research and development of the swirl nozzle.

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25

Parra, Teresa, David Pastor, Ruben Pérez, and José Molina. "Numerical Modelling of Swirl-Stabilized Turbulent Lean Non-Premixed Flames." Advanced Engineering Forum 29 (August 2018): 62–66. http://dx.doi.org/10.4028/www.scientific.net/aef.29.62.

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Numerical simulations have been performed to analyze the interaction of confined coaxial high-swirl jets in both cases: isothermal and reactive flows. Besides different setups of swirl injectors have been tested to study the influence of swirl in the flames for both stoichiometric and lean mixtures. The aim was to quantify the nitrogen oxide emissions as well as the flow pattern for different swirling annular air jet and non-swirling inner fuel jet. This simple setup is widely used in burners to promote stabilized flames of lean mixtures producing ultra low NOx emissions.

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26

Han, J. O., and S. S. Kim. "Effects of Swirl on High-Speed Combustion in a Single-Shot Optical SI Engine." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 206, no. 4 (October 1992): 237–47. http://dx.doi.org/10.1243/pime_proc_1992_206_184_02.

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Single-shot tests in a single-cylinder, optical SI engine operated by a rapid compression and expansion machine were performed in order to investigate the combined effects of engine speed, ignition position and swirl on early combustion and overall performance. For central ignition, swirl showed consistently favourable effects on combustion-related performance. However, at half-radius ignition the desirable swirl effect persisted at low engine speeds but faded away as the speed increased. This reversing of trends can be partially explained by differences in the maximum cylinder pressure, flame growth rate and flame front wrinkling.

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27

Rodriguez-Martinez, Victor M., James R. Dawson, Tim O'Doherty, and Nickolas Syred. "Low-Frequency Combustion Oscillations in a Swirl Burner/Furnace." Journal of Propulsion and Power 22, no. 1 (January 2006): 217–21. http://dx.doi.org/10.2514/1.12010.

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28

Massaguer, Josep M., and Isabel Mercader. "Instability of swirl in low-Prandtl-number thermal convection." Journal of Fluid Mechanics 189 (April 1988): 367–95. http://dx.doi.org/10.1017/s0022112088001065.

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In the present paper we examine low-Prandtl-number thermal convection using a highly truncated modal approach. For the horizontal structure we assume a hexagonal planform as in Toomre Gough & Spiegel (1977) but including a vertical vorticity mode. The system develops a non-zero vertical vorticity component through a finite-amplitude instability. Following this, the system displays a Hopf bifurcation giving rise to periodic oscillations. The mechanism for this instability is associated with the growth of swirl in the azimuthal direction. We have found three different types of periodic solutions, possibly associated with subharmonic bifurcations, and their structure has been examined.A large part of the present work is devoted to exploring the cases of mercury and liquid helium - or air - as the best-known examples of low and intermediate-Prandtl-number fluids. Results for mercury are quite satisfactory as far as frequencies and fluxes are concerned and they show reasonable agreement with experimental measurements at mildly supercritical Rayleigh values. On the other hand, for liquid helium or air agreement is poor.

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29

Mansour, Mohy, and Yung-Cheng Chen. "Stability characteristics and flame structure of low swirl burner." Experimental Thermal and Fluid Science 32, no. 7 (July 2008): 1390–95. http://dx.doi.org/10.1016/j.expthermflusci.2007.11.012.

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30

Legrand, Mathieu, José Nogueira, Antonio Lecuona, Sara Nauri, and Pedro A. Rodríguez. "Atmospheric low swirl burner flow characterization with stereo PIV." Experiments in Fluids 48, no. 5 (November 18, 2009): 901–13. http://dx.doi.org/10.1007/s00348-009-0775-6.

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31

Deng, Yangbo, Hongwei Wu, and Fengmin Su. "Combustion and exhaust emission characteristics of low swirl injector." Applied Thermal Engineering 110 (January 2017): 171–80. http://dx.doi.org/10.1016/j.applthermaleng.2016.08.169.

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32

ten Thij, G. D., A. A. Verbeek, and T. H. van der Meer. "Application of Fractal Grids in Industrial Low-Swirl Combustion." Flow, Turbulence and Combustion 96, no. 3 (October 27, 2015): 801–18. http://dx.doi.org/10.1007/s10494-015-9670-9.

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33

Hwang, Donghyun, Cheolwoong Kang, and Kyubok Ahn. "Effect of Mixing Section Acoustics on Combustion Instability in a Swirl-Stabilized Combustor." Energies 15, no. 22 (November 14, 2022): 8492. http://dx.doi.org/10.3390/en15228492.

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An experimental study was performed to investigate the characteristics of two different combustion instability modes in a swirl-stabilized combustor. The first is the eigenfrequency corresponding to the half-wave of the combustion chamber section, and the second is the quarter-wave eigenmode of the inlet mixing section. The purpose of this study is to understand the effects of the swirl number on each combustion instability mode and analyze their generalized characteristics. Premixed gases composed of hydrocarbon fuels (C2H4 and CH4) and air were burned by independently varying the experimental conditions. Three dynamic pressure transducers and a photomultiplier tube were installed to detect pressure oscillations and heat release fluctuations in the inlet and combustion chamber sections, respectively. A high-speed camera was used to capture the instantaneous flame structures. In the swirl-stabilized combustor, the bands of the dominant frequencies were strongly dependent on the swirl number of the swirler vane. When the swirl number was low, the entire combustion system was often coupled with the quarter-wave eigenmode of the inlet mixing section. However, as the swirl number increased, the combustion instability mode was almost independent of the mixing section acoustics. Analysis of the phase difference and flame structure clearly demonstrated the differences between each eigenmode. The results provide new insights into the effect of the resonance mode in the inlet mixing section on combustion instability, depending on the swirl number in the swirl-stabilized combustor.

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34

Yazdani, Kaveh, Ehsan Amani, and Hamid Naderan. "Multi-objective optimizations of the boot injection strategy for reactivity controlled compression ignition engines." International Journal of Engine Research 20, no. 8-9 (August 31, 2018): 889–910. http://dx.doi.org/10.1177/1468087418795599.

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In this study, multi-objective optimizations of a reactivity controlled compression ignition engine are performed. The main focus is the investigation of effects of seven design variables, including swirl ratio, the first and second start of injections (SOI1 and SOI2), and four injection rate-shape parameters, on the objective parameters, namely, gross indicated efficiency, the second-law efficiency, ringing intensity, and emissions. The results show that in the low swirl ratio range (swirl ratio < 1), the emissions decrease by either increasing boot length or decreasing boot velocity. The physical analysis reveals that this is due to the penetration of the high-reactivity fuel vapor in whole squish area and a large portion of the crevice. This is because the more uniform mixture in the squish region slightly mitigates the formation of hot spots and NOx, and the propagation of reaction deeper into the crevice considerably reduces carbon monoxide and unburned hydrocarbons there. The sensitivity analysis manifests that swirl ratio has the strongest effect on all objectives, and besides swirl ratio, SOI2 has the greatest impact on gross indicated efficiency and emission, while SOI1 has the strongest influence on second-law efficiency and ringing intensity. The optimal case with an advance of SOI1 and a slight retard of SOI2, that is, a longer duration between the two injections, a lower swirl ratio (of 0.5) with respect to the base case, and appropriate injection rate-shape parameters (a high boot length and low boot velocity), achieves the gross indicated efficiency of 54% and merit function of 615.

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35

Novotni, Gergely, and Viktor Józsa. "Sound Pressure Level Analysis of a Liquid-Fueled Lean Premixed Swirl Burner with Various Quarls." Acoustics 2, no. 1 (March 1, 2020): 131–46. http://dx.doi.org/10.3390/acoustics2010010.

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Swirl burners are widely used in numerous practical applications since they are characterized by low pollutant emission and a wide operating range. Besides reliable operation, a burner must fulfill noise emission regulations, which is often a sound pressure level in dB(A) when people are affected. Therefore, the present paper evaluates the overall sound pressure level (OASPL) variation of a 15-kW liquid-fueled turbulent atmospheric swirl burner at various setups. Firstly, the combustion air flow rate was adjusted, which induced a swirl number modification due to the fixed swirl vanes. Secondly, the atomizing pressure of the plain-jet airblast atomizer was modified, which also affected the swirl number. High atomizing air jets notably increased combustion noise by intensifying the shear layer. Thirdly, a geometrical modification was performed; 0°–60° half cone angle quarls in 15° steps were installed on the lip of the baseline burner for extended flame stability. By filtering the OASPL to the V-shaped flames, a linearly decreasing trend was observed as a function of swirl number. Their derivative also has a linearly decreasing characteristic as a function of the atomizing pressure.

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36

Nasr, G. G., A. J. Yule, J. A. Stewart, A. Whitehead, and T. Hughes. "A new fine spray, low flowrate, spill-return swirl atomizer." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 225, no. 4 (April 2011): 897–908. http://dx.doi.org/10.1243/09544062jmes2675.

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A novel high liquid pressure fine spray swirl atomizer has been developed, which incorporates a spill-return orifice into the rear face of the swirl chamber with the aim of giving a significant reduction in flowrate while maintaining the droplet size. The initial work modified a commercial atomizer to add spill return. However, drop sizes were considered to be too large and a new design was constructed based on an earlier work on efficient high-pressure (up to 120 bar) swirl atomization. The resulting fine sprays can be used for various applications such as humidification, cleaning, coating, cooling, and decontamination. The atomizer has been characterized for different geometries, supply pressures, and spill-return orifice sizes using a Laser Particle Sizer and Phase Doppler Anemometry. For an exit orifice of 0.3mm diameter and spill orifice 0.5mm diameter, the drop size (Sauter mean diameter) is less than 20m for flowrates as low as 0.1litre/min and with a mean axial drop velocity of approximately 12m/s. An average liquid volume flux of 0.014(cm3/s)/cm2 is obtained in the spray at 150mm downstream.

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37

Han, Han, Pengfei Wang, Ronghua Liu, and Chang Tian. "Experimental study on atomization characteristics and dust-reduction performance of four common types of pressure nozzles in underground coal mines." International Journal of Coal Science & Technology 7, no. 3 (May 27, 2020): 581–96. http://dx.doi.org/10.1007/s40789-020-00329-w.

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Abstract Pressure nozzle is commonly used in the dust-reduction techniques by spraying of underground coal mines. Based on the internal structure, the pressure nozzle can be divided into the following types: spiral channel nozzle, tangential flow-guided nozzle and X-swirl nozzle. In order to provide better guidance on the selection of nozzles for the coal mine dust-reduction systems by spraying, we designed comparing experiments to study the atomization characteristics and dust-reduction performance of four commonly used nozzles in the coal mine underground with different internal structures. From the experimental results on the atomization characteristics, both the tangential flow-guided nozzle and the X-swirl nozzle have high flow coefficients. The atomization angle is the largest in the spiral non-porous nozzle, and smallest in both the X-swirl nozzle and the spiral porous nozzle. The spraying range and the droplet velocity are inversely proportional to the atomization angle. When the water pressure is low, the atomization performance of the spiral non-porous nozzle is the best among the four types of nozzles. The atomization performance of the X-swirl nozzle is superior to other types when the water pressure is high. Under the high water pressure, the particle size of the atomized droplets is smallest in the X-swirl nozzle. Through the experiments on the dust-reduction performance of the four types of nozzles and the comprehensive analysis, the X-swirl nozzle is recommended for the coal mine application site with low water pressure in the dust-reduction system, while at the sites with high water pressure, the spiral non-porous nozzle is recommended, which has the lowest water consumption and obvious economic advantages.

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38

Helgadóttir, Ásdís, Sylvain Lalot, Francois Beaubert, and Halldór Pálsson. "Mesh Twisting Technique for Swirl Induced Laminar Flow Used to Determine a Desired Blade Shape." Applied Sciences 8, no. 10 (October 10, 2018): 1865. http://dx.doi.org/10.3390/app8101865.

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Swirling flow has been shown to increase heat transfer in heat exchangers. However, producing swirl while not presenting a severe pressure drop can be a challenge. In this paper, a desired shape of guidance blades for laminar swirl flow is determined by numerical simulation in OpenFOAM. Emphasis is on the mesh technique, where a predefined blade shape is formed by mesh twisting, or morphing. The validity of numerical simulations on a twisted mesh is shown by comparing it to the theoretical solution of laminar flow in a pipe without swirl and guidance blades. A sensitivity study shows that a cell size ratio of 0.025 of diameter is sufficient and affects the solution minimally. To determine the desired shape of guidance blades previously found optimal swirl decay and velocity profile for laminar swirling flow are utilized. Three blade shapes are explored: (I) with a twist angle that varies with axial location only; (II) having a deviation angle matching the theoretical deviation angle for laminar swirling flow; (III) same as II but with a hollow center. Simulations are performed for Re = 100 and swirl number S = 0.2 . Case II is able to sustain swirl longest while maintaining a low pressure drop and is therefore a desired swirler shape profile as predicted theoretically.

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39

Shi, R. X., and B. Chehroudi. "Velocity Characteristics of a Confined Highly-Turbulent Swirling Flow Near a Swirl Plate (Data Bank Contribution)." Journal of Fluids Engineering 116, no. 4 (December 1, 1994): 685–93. http://dx.doi.org/10.1115/1.2911836.

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Axial and tangential components of the velocity vector are measured using a Laser Doppler Velocimeter (LDV) system in a confined highly turbulent isothermal swirling flow near a swirl plate. The flow has essential features of swirl-stabilized flame combustors. Throughout this study, a constant “nominal” swirl number of 0.36 is generated by air jets from a set of slots in a swirl plate. A low-speed coflowing air, referred to as dilution air, is uniformly distributed around the swirling flow by use of an annular-shaped honeycomb. Three different swirling air flow rates with a fixed dilution flow rate are studied and results are discussed. Detailed mean axial and tangential velocity profiles at several axial locations show that the size and the strength of the central recirculation zone are strongly dependent on the swirling air flow rate. Increasing the swirl air flow rate increases both the radial extent and the axial length of the central recirculation zone. Mean total and reversed air flow rates are calculated by integrating the mean axial velocity profiles. In the setup used in this study and up to the axial positions investigated, the reversed flow rate as a percent of the total flow rate seems to be linearly proportional to the reversed-flow zone area, being independent of the swirl air flow rate at a fixed nominal swirl number value. As swirl air flow rate is increased, the root mean square (rms) of the axial and tangential velocity fluctuations increase monotonically at almost all radial positions except sufficiently away from the swirl plate and near the chamber axis. Several velocity biasing correction methods are reviewed. A simple velocity biasing correction scheme is applied in this study to investigate its effect on the conclusions reached in the study.

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40

Hao, Jiangang, Yang Ding, Chen Yang, Xuhuai Wang, Xiang Zhang, Yong Liu, and Feng Jin. "Study on Unstable Combustion Characteristics of Model Combustor with Different Swirler Schemes." Energies 15, no. 23 (November 27, 2022): 8972. http://dx.doi.org/10.3390/en15238972.

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In this paper, the effect of the swirler scheme on combustion instability is studied. Through the proper orthogonal decomposition (POD) of flame images, Abel inverse transform and other methods, the influence of swirl intensity on the characteristic frequency of combustion instability was emphatically studied. Based on the low order thermoacoustic network (LOTAN) of the combustor, the flame transfer function (FTF) under different swirl schemes was obtained by the optimization method. The experimental results show that the stable combustion equivalence ratio boundary of the system decreases monotonously with the decrease in swirl intensity, while the characteristic frequency of unstable combustion is not monotonous with the swirl intensity (the oscillating frequency of swirler A with the largest swirl intensity is approximately 319 Hz, swirler B is approximately 280 Hz, swirler C with the smallest swirl intensity is approximately 290 Hz). The optimization results of FTF can easily introduce this non monotonic phenomenon. The swirl intensity mainly affects the hysteresis time of the system (the lag time of swirlers A, B and C are 5.98 ms, 6.82 ms and 6.20 ms, respectively), which is mainly caused by affecting the flame structure and convection velocity. At the same time, the FTF obtained by optimization reflects the same trend with the experimental results, and there is no significant difference in value, which proves the rationality of the optimization method. This work emphasizes the importance of FTF for combustion instability analysis.

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41

Li, Z. Q., Z. C. Chen, R. Sun, and S. H. Wu. "New low NO_x, low grade coal fired swirl stabilised technology." Journal of the Energy Institute 80, no. 3 (September 1, 2007): 123–30. http://dx.doi.org/10.1179/174602207x216200.

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42

Cheng, R. K., D. T. Yegian, M. M. Miyasato, G. S. Samuelsen, C. E. Benson, R. Pellizzari, and P. Loftus. "Scaling and development of low-swirl burners for low-emission furnaces and boilers." Proceedings of the Combustion Institute 28, no. 1 (January 2000): 1305–13. http://dx.doi.org/10.1016/s0082-0784(00)80344-6.

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43

Wilhelm, Manuel, and Heinz-Peter Schiffer. "Experimental Investigation of Rotor Tip Film Cooling at an Axial Turbine with Swirling Inflow Using Pressure Sensitive Paint." International Journal of Turbomachinery, Propulsion and Power 4, no. 3 (August 1, 2019): 23. http://dx.doi.org/10.3390/ijtpp4030023.

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Rotor tip film cooling is investigated at the Large Scale Turbine Rig, which is a 1.5-stage axial turbine rig operating at low speeds. Using pressure sensitive paint, the film cooling effectiveness η at a squealer-type blade tip with cylindrical pressure-side film cooling holes is obtained. The effect of turbine inlet swirl on η is examined in comparison to an axial inflow baseline case. Coolant-to-mainstream injection ratios are varied between 0.45% and 1.74% for an engine-realistic coolant-to-mainstream density ratio of 1.5. It is shown that inlet swirl causes a reduction in η for low injection ratios by up to 26%, with the trailing edge being especially susceptible to swirl. For injection ratios greater than 0.93%, however, η is increased by up to 11% for swirling inflow, while for axial inflow a further increase in coolant injection does not transfer into a gain in η .

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44

Li, Y., H. Zhao, and N. Ladommatos. "Analysis of large-scale flow characteristics in a four-valve spark ignition engine." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 216, no. 9 (September 1, 2002): 923–38. http://dx.doi.org/10.1177/095440620221600906.

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A digital particle image velocimetry (PIV) measurement has been carried out to study the large-scale flow characteristics in a single-cylinder engine with a production-type four-valve cylinder head under one intake port deactivation. The measurement plane was located 12 mm below the cylinder head parallel to the flat piston top. Two-dimensional velocity fields from 100 consecutive cycles were acquired at every 30 crank angle interval in the compression stroke to analyse ensemble-averaged mean velocity, cyclic variation of the swirl motion, low-frequency and total velocity fluctuations and their integral length scales. The analysis shows that as one intake port is deactivated, strong swirl forms at the end of the intake stroke and sustains its flow pattern up to the late stage of the compression stroke with the precessing of the swirl centre. Both swirl ratio and swirl centre show significant cyclic variations in the compression process. A low-frequency component with spatial frequency below 0.05 mm-1 (corresponding to a large-scale structure with a spatial scale over 20 mm) is absolutely predominant in the flow field and therefore the low-frequency large-scale flow behaviour determines the basic characteristics of the total in-cylinder flow. The flow field is considerably anisotopic because the integral length scale of any velocity fluctuation components along any direction is different. However, the velocity fluctuation field in the horizontal plane will gradually become homogeneous as the piston moves up in the compression stroke. The integral length scale is in the range of 4-10 mm at an engine speed of 600 r/min. When the engine speed is doubled, flow velocity in the cylinder nearly doubles and velocity fluctuation kinetic energy more than triples though the flow pattern hardly changes.

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45

Nolan, David S., Nathan A. Dahl, George H. Bryan, and Richard Rotunno. "Tornado Vortex Structure, Intensity, and Surface Wind Gusts in Large-Eddy Simulations with Fully Developed Turbulence." Journal of the Atmospheric Sciences 74, no. 5 (May 1, 2017): 1573–97. http://dx.doi.org/10.1175/jas-d-16-0258.1.

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Abstract A large-eddy simulation (LES) framework with an “eddy injection” technique has been developed that ensures a majority of turbulent kinetic energy in numerically simulated tornado-like vortices is represented by resolved eddies. This framework is used to explore the relationships between environmental forcing mechanisms, surface boundary conditions, and tornado vortex structure, intensity, and wind gusts. Similar to previous LES studies, results show that the maximum time- and azimuthal-mean tangential winds {V}max can be well in excess of the “thermodynamic speed limit,” which is 66 m s−1 for most of the simulations. Specifically, {V}max exceeds this speed by values ranging from 21% for a large, high-swirl vortex to 59% for a small, low-swirl vortex. Budgets of mean and eddy angular and radial momentum are used to show that resolved eddies in the tornado core act to reduce the wind speed at the location of {V}max, although they do transport angular momentum downward into the lowest levels of the boundary layer, increasing low-level swirl. Three measures of tornado intensity are introduced: maximum time–azimuthal-mean surface (10 m) horizontal wind speed ({S10}max), maximum 3-s gusts of S10 (S10-3s), and maximum vertical 3-s gusts at 10 m (W10-3s). While {S10}max is considerably less than {V}max, transient features in the boundary layer can generate S10-3s in excess of 150 m s−1, and W10-3s in excess of 100 m s−1. For high-swirl vortices, the extreme gusts are confined closer to the center, well inside the radius of maximum azimuthal-mean surface winds. For the low-swirl vortex, both the strongest mean winds and the extreme gusts are restricted to a very narrow core.

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46

Lewellen, D. C., and W. S. Lewellen. "Near-Surface Vortex Intensification through Corner Flow Collapse." Journal of the Atmospheric Sciences 64, no. 7 (July 1, 2007): 2195–209. http://dx.doi.org/10.1175/jas3966.1.

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Abstract Results are presented from a large set of large-eddy simulations of a class of unsteady vortex evolution that may sometimes play a role in tornadogenesis or tornado variability. Beginning with a high-swirl parent vortex with an excess of low-swirl flow through the surface/corner/core region, perturbation of the low-swirl near-surface inflow at a large radius can trigger a subsequent dynamic “corner flow collapse” producing dramatic near-surface intensification relative to conditions aloft of an order of magnitude or more in velocity scale. This paper presents a more detailed treatment of the physics and simulation of corner flow collapse, expanding upon the presentation given in a companion paper treating near-surface vortex intensification more generally for both steady and unsteady conditions. The basic scaling of the onset, intensification, structure, and duration of the phenomenon is explored as a function of some of the dominant physical parameters involved. A dimensionless rate of change of the low-swirl flux through the surface/corner flow during the process is identified as a critical governing parameter. Given the mode of triggering near the surface at large radii, the large intensification that can result, and the sensitivity to some of the parameters involved, corner flow collapse may provide a mechanism by which the rear-flank downdraft can promote tornadogenesis and help explain why seemingly similar conditions sometimes produce intense tornadoes and other times do not.

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47

Hemalatha, Arumugam, and Nainarkuppam Mahalakshmi. "Experimental investigations of flow through wide angle conical diffusers with uniform flow and swirl type velocity distortions at inlet." Thermal Science 22, no. 6 Part A (2018): 2571–81. http://dx.doi.org/10.2298/tsci170817223h.

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Swirl is a tangential velocity component of the fluid flow and is often present in the conical diffuser as a result of rotating machinery in the upstream section. The present experimental work is dedicated to study the effect of moderate swirl on wide angle conical diffuser performance and flow development. The experiments were performed in a low-speed open circuit wind tunnel. There are two different diffusers having a cone angle of 14? (with an area ratio 3.0) and 20? (with an area ratio 4.2) were selected for this investigation. The flow parameters have been measured using DANTEC DYNAMICS make constant temperature hot-wire anemometer (CTA). The results showed that the moderate swirl can significantly improve the stalled diffuser (20? cone angle) performance; however, it has a little effect on the diffuser (14? cone angle) having incipient turbulent boundary layer separation. It was confirmed that the introduction of moderate swirl reduces the chances of flow separation in wide angle conical diffusers.

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48

Fishman, G., M. Wolfinger, and D. Rockwell. "The structure of a trailing vortex from a perturbed wing." Journal of Fluid Mechanics 824 (July 10, 2017): 701–21. http://dx.doi.org/10.1017/jfm.2017.331.

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The structure of a trailing vortex from a wing undergoing small amplitude, low frequency heaving motion is investigated using space–time representations determined from stereo particle image velocimetry. The evolution of the vortex shows large fluctuations of axial velocity deficit and circulation during the oscillation cycle. Correspondingly, large variations of swirl ratio occur and onset of pronounced azimuthal vorticity arises. At a given cross-section of the vortex, the pattern of azimuthal vorticity moves around its axis in an ordered fashion as both it and the pattern of velocity defect increase in magnitude and scale. When the swirl ratio attains its minimum value during the oscillation cycle, and this value lies below the theoretically established critical threshold for amplification of azimuthal modes, the magnitude and scale of the pattern of azimuthal vorticity is maximized. Subsequent increase of the swirl ratio yields attenuation of the azimuthal vorticity. Onset of pronounced azimuthal vorticity when the swirl ratio decreases involves rapid amplification, then disruption, of axial vorticity fluctuation.

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49

Khil, Taeock, Yunjae Chung, Vladimir G. Bazarov, and Youngbin Yoon. "Dynamic Characteristics of Simplex Swirl Injector in Low Frequency Range." Journal of Propulsion and Power 28, no. 2 (March 2012): 323–33. http://dx.doi.org/10.2514/1.b34169.

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50

Spangelo, O., T. Slungaard, T. Engebretsen, and O. K. Sonju. "DEVELOPMENT OF A LOW-NOx SWIRL BURNER FOR GASEOUS FUELS." Clean Air: International Journal on Energy for a Clean Environment 7, no. 3 (2006): 203–20. http://dx.doi.org/10.1615/interjenercleanenv.v7.i3.20.

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