Effect Of Swirl Intensity Research Articles

The influence of swirl intensity on the prediction model of wheat picking speed

AbstractTo study the effect of swirl intensity on the picking speed of wheat particles, a test bench for the transportation status of bulk grain particles was developed, and a theoretical model for the picking speed of wheat particles transported by swirl was established. Firstly, the critical conveying speed is determined through theoretical analysis and budgeted using the C&K model. Then, experiments are conducted to pick up loose grain particles in different flow fields. The particles in the swirling field are gradually rolled up from the windward end and sequentially pushed backwards to be picked up and transported. The picking speed of loose grain particles shows a trend of first increasing and then decreasing with the increase of swirling intensity. Using dimensionless swirl intensity as a variable, a predictive model for the effect of swirl intensity on particle picking speed during swirl conveying of wheat particles is derived.Practical applicationsWhen conveying bulk grain particles through a swirling flow, the intensity of swirling flow is closely related to the picking speed of bulk grain particles. This is extremely important for setting the wind speed of the conveying system, as it directly affects the energy consumption, particle crushing, and conveying efficiency of the entire system. Therefore, it is extremely important to predict the picking speed of bulk grain particles under different swirling strengths to control the corresponding wind speed. Therefore, this study conducts in‐depth research on this issue.

Exploring the Effects of Swirl Intensity on NO Emission in Ammonia-Methane-Air Premixed Swirling Flames

The high emission of nitrogen oxides (NOx) is one of the major obstacles to the practical application of ammonia as a carbon-free fuel. Improving the flow distribution and structure has been demonstrated to achieve low NOx emissions. However, in comparison to hydrocarbon flames, the influence of swirl intensities on ammonia NOx emissions is still not well understood. This study builds upon previous research by further exploring the effects of swirl intensity on NO production in ammonia-methane-air premixed swirling flames. A new adjustable axial swirler was designed to achieve a wide range of swirl numbers. We measured flame morphology, NO emissions, and NO and OH planar laser-induced fluorescence (PLIF) images over extensive ranges of equivalence ratio and ammonia fraction. The study found that increasing the swirl number from 0.6 to 1.0 resulted in a more compact flame, with enhanced reactions in the corner recirculation zone. Varying the swirl number significantly alters the NO concentration in the exhaust gas. The concentration of NO was significantly reduced at an equivalence ratio of 0.90 and an ammonia fraction greater than 80%. NO/OH-PLIF indicated that NO was primarily formed in the main reaction zone, with NO-PLIF intensity in the post-flame zone almost remaining constant at different heights. The integrated intensities of NO and OH-PLIF were obtained at different heights above the nozzle. A positive linear correlation was observed between NO-PLIF plateau intensity and NO mole fraction. The increased heat loss to the wall at larger swirl intensities reduces the flame temperature in the main reaction zone, which inhibit the formation of OH radicals, ultimately resulting in low NO emissions.

Effects of swirl intensity on flame stability and NO emission in swirl-stabilized ammonia/methane combustion

Ammonia is an attractive clean fuel for its potential to reduce CO2 emission and fossil fuel consumption. However, ammonia combustion has been mainly discouraged by the low flammability and the high fuel NOx emissions. This study numerically investigates the effects of swirl intensity on combustion characteristics in swirl-stabilized ammonia/methane combustion. Large eddy simulation was performed by using OpenFOAM, and the accuracy of numerical results was validated by the experiment. The results show that swirl intensity will significantly affects the flow field and flame structure, and flame stability decreases with the swirl number increasing. The high swirl intensity leads to extinguishing at the flame root, while the low swirl intensity cannot generate the central recirculation zone to stabilize the flame. Selective non-catalytic reduction of NO (SNCR) is the key to controlling NO emission, the decrease of temperature will promote the reduction of NO, while the decrease of residence time will inhibit the reduction of NO. Meanwhile, SNCR will weaken the correlation between NO and OH in ammonia/methane combustion. NO emission will decrease with the swirl intensity increasing. In a word, medium swirl number (S ≈ 0.76) is proper to control NO emission and ensure flame stability.

Investigation on Circular Array of Turbulent Impinging Round Jets at Confined Case: A CFD Study

Jet impingement has immense applications in industrial cooling, such as glass tempering, turbine blades, electrical equipment, etc. The interplay in-between several jet arrangements and the effect of swirl intensity require enormous study to achieve steady heat transfer. This paper numerically investigates an inline array of 25 circular confined swirling air jets impinging vertically on a flat surface. In this regard, three-dimensional simulations are executed using the finite volume method for a number of control parameters, such as Reynolds number (Re = 11600, 24600, and 35000), impinging distance (H/D = 0.25, 0.5, 1), swirl number (S = 0.3 and 0.75) and jet-to-jet separation distance (Z/D = 2.5), where, D is the nozzle diameter. Impinging pressure distribution, flow velocity, surface Nusselt number, and Reynolds stresses are investigated for different operating conditions. The results reveal that both the wall pressure and surface Nusselt number are comparatively uniform in the case of high swirl flow. Moreover, distinct heat transfer behavior is observed from the unconfined condition for high swirl flow in which the heat transfer is constant after a certain radial distance. The Reynolds normal stress adjacent to the nozzle exit is more rigorous than the downstream regions while Reynolds shear stress varies unpredictably along the radial direction. In addition, an estimated 102 % enhancement in average Nusselt number is observed for high swirl flow, at a Reynolds number increment from 11600 to 35000. This enhancement is evident by 23 % in terms of thermal performance factor. Besides, the average Nusselt number and thermal performance factor augmented by 19 % and 8 %, respectively, for an increased swirl intensity at low a Reynolds number (Re =11600).

Effects of swirl intensity on interfacial and wall friction factors of annular flows in a vertical pipe

Interfacial and wall friction factors, fi and fw, of air-water swirling annular flows in a vertical pipe of diameter D = 30 mm were measured in three sections of L* (=L/D) = 7.3, 13 and 31, where L is the distance from a swirler. The gas and liquid volumetric fluxes, JG and JL, were 12.5 ≤ JG ≤ 20.0 m/s and 0.071 ≤ JL ≤ 0.213 m/s, respectively. The interfacial swirl number, si, defined by Viθ/Viz, where Viθ and Viz are the azimuthal and axial components of interfacial velocity, was introduced as an indicator of swirl intensity. For z* (=z/D) ≤ 7, where z is the axial coordinate in the test section, the si increased with z* at low JG and JL, and slightly decreased with z* at high JG and JL. The si decreased for z* > 7 and reached zero at z* ≈ 30. The fw estimated using the three-fluid model was larger than that estimated using the two-fluid model since the droplet flow rate was not negligible even in swirling annular flows. The three-fluid model was therefore more appropriate for evaluation of fi and fw than the two-fluid model. The ratio fw∗ increased with s¯i for s¯i > 0.25, where fw∗ is the ratio of fw to that of non-swirling flows and s¯i is the averaged value of si in the section. The ratio fi∗ increased with s¯i for s¯i > 0.18, wherefi∗ is the ratio of fi to that of non-swirling flows. Correlations in terms of s¯i have prospect to evaluate the fi and fw in swirling annular flows.

The Effect of Swirl Intensity on the Flow Behavior and Combustion Characteristics of a Lean Propane-Air Flame

The effect of swirl number (Sn) on the flow behavior and combustion characteristics of a lean premixed propane Flame Ф = 0.5 in a swirl burner configuration was numerically verified in this study. Two-dimensional numerical simulations were performed using ANSYS-Fluent software. For turbulence closure, a standard K-ε turbulence model was applied. The turbulence-chemistry interaction scheme was modeled using the Finite Rate-Eddy Dissipation hybrid model (FR/EDM) with a reduced three-step reaction mechanism. The P1 radiation model was used for the flame radiation inside the combustion chamber. Four different swirl numbers were selected (0, 0.72, 1.05, and 1.4) corresponding to different angles (0°, 39°, 50°, and 57.8°). The results show that the predicted model agrees very well with the experimental data, especially with respect to the axial and radial velocity and temperature profiles. An outer recirculation zone (ORZ) is present in the combustor corner at Sn = 0 and an inner recirculation zone (IRZ) appears at the combustor centerline inlet at a critical Sn = 0.72. When the Sn reaches an excessive value, the IRZ moves toward the premixing tube, leading to a flame flashback. The flame structure and its length are strongly affected by changes in the Sn as well as the formation of NOx and CO at the combustor exit.

Thermoacoustic instability drivers and mode transitions in a lean premixed methane-air combustor at various swirl intensities

In this study, an in-house developed fully compressible solver utilizing high-order numerical discretization schemes is used to study the effects of swirl intensity on thermoacoustic instabilities in a lean premixed swirl stabilized combustor. Turbulent combustion modeling is achieved using large eddy simulations along with dynamically thickened flame combustion model. Obtained results reveal that there are two critical burner swirl numbers in which the combustor dynamics change drastically. Results show that the combustor is stable at low swirl numbers (S ≤ 0.5). However, as the swirl intensity increases, the combustor experiences thermoacoustic instabilities. The first critical swirl number lies within the range of 0.5–0.6, in which a transition occurs in the combustor dynamics from a state of stable operation to thermoacoustic instabilities. The second critical swirl number (S = 0.9) corresponds to the transition of different thermoacoustic instability modes. The combustor experiences limit cycle instabilities coupled with the first tangential acoustic mode of the combustor for 0.6 ≤ S < 0.9, while for S > 0.9 the instabilities are burst like and coupled with the second tangential acoustic mode of the combustor. The combustor experiences instabilities coupled with both the first and the second tangential modes, when the burner swirl number is 0.9. In order to evaluate key parameters inducing the thermoacoustic instabilities, heat release fluctuations are calculated through hydrodynamic flow features (central and side recirculation zones, coherent structures, and precessing vortex core). Investigations show that all the above features contribute almost equally in inducing heat release fluctuations in-phase with the acoustic perturbations at low swirl numbers. However, as the swirl number increases, side recirculation zone and coherent structures play the key role in producing heat release fluctuations in-phase with the acoustic perturbations, while central recirculation zone has the least effects on driving the instabilities.

The Effect of Swirl Intensity on Heat Transfer of Swirling Coaxial Impinging Jet

The results of numerical simulation of convective heat transfer under coaxial jet impinging on a surface are presented. The effect of jet’s peripheral component swirling on the heat transfer enhancement by changing the number of tangential nozzles for creating jet is analyzed.

Effect of Swirl Strength on the Flow and Combustion Characteristics of Pulverized Biomass Flames

ABSTRACTThis article reports on the effect of swirl intensity on the flow and combustion characteristics of pulverized olive waste (OW) burning. Numerical simulations are carried out using the computational fluid dynamics (CFD) Commercial Software “Fluent ANSYS14” by choosing appropriate model parameters. The biomass furnace consists of a vertical cylinder equipped with a swirling co-flow injection burner. The particles of pulverized biomass (OW) are injected transversally into the furnace just near the co-flow exit, via four square-shaped injection nozzles. The non-premixed combustion model with mixture fraction/PDF model for turbulence-chemistry interactions is used. Standard k-ε turbulence model closure, discrete phase model (DPM) for tracking the motion of individual particle and P-1 radiation model for flame radiation inside the combustor are used in the numerical simulation. Four different swirl numbers Sn = 0.38, 0.95, 1.2 and 1.42 are used in this study in order to investigate the swirl intensity effect on the flow and combustion behavior. The results showed that the flow and the flame characteristics such as axial velocity, streamlines, gas temperature, flame length and CO2, CO and O2 concentrations are affected by the swirl intensity.

希薄予混合燃焼器における火炎伝播挙動に及ぼす旋回強さの影響

希薄予混合燃焼器における火炎伝播挙動に及ぼす旋回強さの影響

Experimental Research on High Temperature Corrosion Prevention Technology for Water Wall of Opposed Wall Fired Ultra Supercritical Boiler

In order to solve the problem of high temperature corrosion to water wall of opposed wall fired ultra supercritical boiler, comprehensive study is carried out by combining theoretical analysis and experimental research, obtaining the variation of flue gas composition before and after introduction of near wall wind and effect of primary air velocity, central air opening, swirl intensity of outer secondary air and inner secondary air opening on composition of flue gas in near wall region. The results show that 1) the introduction of near wall wind significantly improves reducing atmosphere in near wall region; 2) among the four parameters listed above, swirl intensity of outer secondary air and inner secondary air opening have greater influence on composition of near wall flue gas; 3) under the comprehensive effect of swirl intensity of outer secondary air and inner secondary air opening, the volume fraction of CO in near wall flue gas can be controlled below 1500ppm, which effectively disturbs the condition for high temperature corrosion.

The Basic Research of Internal Combustion Engine Performance in Different Swirl Ratio

In order to investigate the effect of swirl intensity on the performance of the diesel engine, the 4JB1 diesel engine was taken as the research subject and KIVA-3V program was used to calculate the temperature, pressure, NOx and SOOT in cylinder and the performance of dynamic and economy of the diesel engine by changing the value of swirl ratio. The results show that increasing the swirl ratio in the cylinder can make the hybrid combustion of fuel and air sufficiently, improving the combustion temperature and pressure in the cylinder, enhanced the power of the diesel engine and reduced fuel consumption. The generation of NOx increased with the increases of swirl ratio and the production of SOOT decreased with the increases of swirl ratio.

Effects of swirl intensity on heat transfer and entropy generation in turbulent decaying swirl flow

In the present work, numerical simulations of turbulent incompressible nonisothermal pipe flows were conducted to investigate the effect of inlet swirl intensity and streamwise swirl decay on heat transfer and local entropy generation in the flow. The RANS, energy and entropy equations along with Shih's realizable k–ε turbulence model were numerically solved using second order finite volume upwind discretization scheme. The CFD model results showed very good agreement with established LDV measurements. The streamwise trends of Nusselt and Stanton numbers were studied at different inlet swirl intensities. A new CFD-based empirical correlation for predicting the entropy augmentation number as a function of swirl number was proposed. It is shown that the swirl number radically affects the local entropy generation due to viscous dissipation in the inner core of the Rankine vortex structure.

Effect of swirl on hydrodynamics and separation performance of a spray granulation tower with array nozzles

In order to understand the asphalt granulation and separation processes in a new technique of solvent deasphalting, this work performs a detailed numerical and experimental study on the hydrodynamics and separation characteristics of low-density particles in a spray granulation tower, the swirl intensity of which can be adjusted by changing the jet direction of four nozzles. The effect of swirl intensity on the fluid behavior and separation performance is investigated. The results show that a jet-driven swirling flow is formed, which depends heavily on the swirl intensity. As swirl increases, the tangential velocity increases and the jet entrainment decreases, which are both beneficial to the tower performance. A multistage variation of separation efficiency is observed in both experiment and simulation.

Numerical simulation of strongly swirling turbulent flows through an abrupt expansion

Turbulent swirling flow through an abrupt axisymmetric expansion is investigated numerically using detached-eddy simulation at Reynolds numbers = 3.0 × 10 4 and 1.0 × 10 5. The effects of swirl intensity on the coherent dynamics of the flow are systematically studied by carrying out numerical simulations over a range of swirl numbers from 0.17 to 1.23. Comparison of the computed solutions with the experimental measurements of Dellenback et al. (1988) shows that the numerical simulations resolve both the axial and swirl mean velocity and turbulence intensity profiles with very good accuracy. Our simulations show that, along with moderate mesh refinement, critical prerequisite for accurate predictions of the flow downstream of the expansion is the specification of inlet conditions at a plane sufficiently far upstream of the expansion in order to avoid the spurious suppression of the low-frequency, large-scale precessing of the vortex core. Coherent structure visualizations with the q-criterion, friction lines and Lagrangian particle tracking are used to elucidate the rich dynamics of the flow as a function of the swirl number with emphasis on the onset of the spiral vortex breakdown, the onset and extent of the on-axis recirculation region and the large-scale instabilities along the shear layers and the pipe wall.

Effect of Swirl Intensity on Total Pressure Losses in Draft Tube of Bulb Turbine

Effect of Swirl Intensity on Total Pressure Losses in Draft Tube of Bulb Turbine

Flame characteristics of hydrogen-enriched methane–air premixed swirling flames

The effect of hydrogen addition in methane–air premixed flames has been examined from a swirl-stabilized combustor under unconfined flame conditions. Different swirlers have been examined to investigate the effect of swirl intensity on enriching methane–air flame with hydrogen in a laboratory-scale premixed combustor operated at 5.81 kW. The hydrogen-enriched methane fuel and air were mixed in a pre-mixer and introduced into the burner having swirlers of different swirl vane angles that provided different swirl strengths. The combustion characteristics of hydrogen-enriched methane–air flames at fixed thermal load but different swirl strengths were examined using particle image velocimetry (PIV), OH chemiluminescence, gas analyzers, and micro-thermocouple diagnostics to provide information on flow field, combustion generated OH radical and gas species concentration, and temperature distribution, respectively. The results show that higher combustibility of hydrogen assists to promote faster chemical reaction, raises temperature in the reaction zone and reduces the recirculation flow in the reaction zone. The upstream of flame region is more dependent on the swirl strength than the effect of hydrogen addition to methane fuel. At lower swirl strength condition the NO concentration in the reaction zone reduces with increase in hydrogen content in the fuel mixture. Higher combustibility of hydrogen accelerates the flow to reduce the residence time of hot product gases in the high temperature reaction zone. At higher swirl strength the NO concentration increases with increase in hydrogen content in the fuel mixture. The effect of dynamic expansion of the gases with hydrogen addition appears to be more dominant to reduce the recirculation of relatively cooler gases into the reaction zone. NO concentration also increases with decrease in the swirl strength.

Effect of swirl intensity on the flow and combustion of a turbulent non-premixed flat flame

An experiment in a turbulent non-premixed flat flame was carried out in order to investigate the effect of swirl intensity on the flow and combustion characteristics. First, stream lines and velocity distribution in the flow field were obtained using PIV (Particle Image Velocimetry) method in a model burner. In contrast with the axial flow without swirl, highly swirled air induced streamlines going along the burner tile, and its backward flow was generated by recirculation in the center zone of the flow field. In the combustion, the flame shape with swirled air also became flat and stable along the burner tile with increment of the swirl number. Flame structure was examined by measuring OH and CH radicals intensity and by calculating Damkohler number (Da) and turbulence Reynolds number (Re T ). It appeared that luminescence intensity decreased at higher swirl number due to the recirculated flue gas, and the flat flames were comprised in the wrinkled laminar-flame regime. Backward flow by recirculation of the flue gas widely contacted on the flame front, and decreased the flame temperature and emissions concentration as thermal NO. The homogeneous temperature field due to the widely flat flame was obtained, and the RMS in the high temperature region was rather lower at higher swirl number. Consequently, the stable flat flame with low NO concentration was achieved.

Effects of a swirling and recirculating flow on the combustion characteristics in non-premixed flat flames

The effects of swirl intensity on non-reacting and reacting flow characteristics in a flat flame burner (FFB) with four types of swirlers were investigated. Experiments using the PIV method were conducted for several flow conditions with four swirl numbers of 0, 0.26, 0.6 and 1.24 in non-reacting flow. The results show that the strong swirling flow causes a recirculation, which has the toroidal structures, and spreads above the burner exit plane. Reacting flow characteristics such as temperature and the NO concentrations were also investigated in comparison with non-reacting flow characteristics. The mean flame temperature was measured as the function of radial distance, and the results show that the strong swirl intensity causes the mean temperature distributions to be uniform. However the mean temperature distributions at the swirl number of 0 show the typical distribution of long flames. NO concentration measurements show that the central toroidal recirculation zone caused by the strong swirl intensity results in much greater reduction in NO emissions, compared to the non-swirl condition. For classification into the flame structure interiorly, the turbulence Reynolds number and the Damkohler number have been examined at each condition. The interrelation between reacting and non-reacting flows shows that flame structures with swirl intensity belong to a wrinkled laminar-flame regime.

Experimental Investigation of Swirl and Non-Swirl Gas Injections Into Liquid Baths Using Submerged Vertical Lances

The behaviour of the flow of swirl and non-swirl gas injections into a liquid bath was investigated experimentally, using water as modelling fluid to gain an understanding of the mixing process of the Sirosmelt top submerged gas injection system. The effects of swirl intensity, gas injection rates and lance submergence levels on the gas-liquid interaction were determined by measuring the velocity fields and the generation of turbulence in the bath. The results indicate that the swirl gas injection promoted high liquid velocities and high turbulent kinetic energy and hence better mixing in the tank. When two-thirds of the lance was submerged better mixing and high liquid velocities resulted for both gas injection rates investigated. The applicability of the concept of isotropic turbulence for the liquid bath was examined. It was found that the assumption of isotropic turbulence may hold outside the plume region. However, there are a clear indication that turbulence is non-isotropic in the vicinity of the wall region. These findings have implications in the mathematical modelling of gas injection processes.On a étudié expérimentalement le comportement d'écoulement d'injections de gaz, avec et sans tourbillon, dans un bain liquide. On a utilisé des modèles aqueux afin d'obtenir un aperçu du procédé de mélange du système Sirosmelt submergé d'injection de gaz, par le haut. On a déterminé l'effet de l'intensité du tourbillon, des taux d'injection de gaz et des niveaux d'immersion de la lance sur l'interaction gaz-liquide en mesurant les champs de vitesse et la génération de turbulence dans le bain. Les résultats semblent montrer que l'injection de gaz avec tourbillon stimulait des vitesses élevées dans le liquide et une énergie cinétique turbulente élevée et, ainsi, un meilleur mélange dans le réservoir. Les taux élevés d'injection de gaz, comme on s'y attendait, ont produit des vitesses élevées du liquide dans tout le réservoir. L'immersion aux deux tiers de la lance a résulté en un meilleur mélange et en des vitesses élevées du liquide, aux deux taux d'injection de gaz étudiés. On a examiné l'applicabilité au bain liquide du concept de turbulence isotrope. On a trouvé que l'assomption de turbulence isotrope pouvait être retenue en dehors de la région d'injection. Il y a cependant des indications claires que, dans le voisinage de la paroi, la turbulence est non-isotrope. Ces découvertes ont des implications sur la modélisation mathématique des procédés d'injection de gaz.