Initial Swirl Research Articles

Do emptying bottles show self-induced liquid rotation?

An inverted liquid bottle with a small neck diameter empties through periodic admission of air bubbles at the neck, followed by liquid discharge, a process termed ‘glugging’. In contrast, a large Taylor bubble rises to the air–water interface in the bottle for large neck diameters, followed by an instant interface collapse and a chaotic liquid discharge. We numerically find that a spiral large-scale rotating structure due to churning motion develops in the liquid during time evolution in an emptying bottle, though an initial swirl is not imposed. The induced structure is strong for a large neck bottle, and the circulation strength is maximum near the neck region. The spiral structure’s strength decreases for small neck diameters, and a pure oscillatory ‘glugging’ mode is preserved. The high circulation strength near the neck region for the large neck bottle causes liquid to accelerate and is the reason for the existing empirical models on liquid discharge to deviate from experimental observations.

Influence of critical parameters on combustion and emission characteristics of methanol/diesel dual fuel compression combustion engine

Replacing fossil fuels with clean fuels as power sources is an effective method to reduce greenhouse gas and pollutant emissions, and methanol is a potential solution due to its excellent physical and chemical properties. The study comprehensively investigated the influences of the methanol substitution ratio (Rm), three initial cylinder parameters, and three diesel injection parameters on the combustion and emission characteristics of a methanol/diesel dual fuel compression combustion engine. A CFD model coupling with the reaction mechanism for a dual-fuel engine was established and fully verified. The results indicate that methanol substitution for diesel benefits emissions reduction at low load and improves fuel economy at high load. Delaying the diesel injection time and increasing the diesel injection duration time deteriorate fuel economy but reduce NOx emissions. Soot and NOx emissions exhibit a sudden change at a diesel injection angle of 70°. Increasing the initial temperature of the combustion chamber promotes combustion while increasing the initial pressure improves fuel economy. The effect of the initial swirl ratio is mainly observed at low load, where an increase in the initial swirl ratio improves fuel economy, reduces ringing intensity (RI), and lowers soot emissions. The conclusion of this article will guide the development of clean power sources.

The Effect of a Three-Blade Tube on the Pneumatic Transport of Pebble Particles

In this paper, the Computational Fluid Dynamics–Discrete Element Method (CFD-DEM) coupling method was used to simulate the pneumatic transport of pebble particles in a three-blade spiral tube. The results showed that the flow field distribution rotated along the circumference after loading. The maximum velocity of the flow field after loading was manifested as rotation along the circumference. In addition, the swirl intensity decreased exponentially with the increase in conveying distance, and the maximum swirl intensity had a saturation value. After reaching the saturation value, it is not evident that increasing the initial air velocity significantly affected swirl variation. The smaller the pitch, the greater the initial swirl intensity. The swirling flow was conducive to the fluidization of particles, but it would bring a significant energy loss. Increasing the swirl can increase the degree of particle dispersion. There is an optimal tangential airflow velocity, which allows the particles to fully spin and stay in the suspension zone without being thrown onto the pipe wall by excessive centrifugal force. At this time, the energy efficiency reaches the highest level. A 5.87 m/s velocity was deemed the optimal tangential airflow velocity for conveying 3 mm particles.

Quantitative analysis of heat transfer characteristics and advantages in opposed-piston 2-stroke diesel engines

Opposed-piston 2-stroke diesel engines (OP2S) have lower combustion chamber surface-area-to-volume ratio, resulting in lower transfer loss but also excessive surface temperature. Investigation of combustion parameters on heat transfer, which provide a chance in improving combustion efficiency and solving surface overheating issue in OP2S at the same time, is yet to be undertaken. In this paper CFD simulation by CONVERGE software has been carried out to study heat transfer advantages in OP2S. Effect of initial swirl ratio and injection phase on combustion efficiency and heat transfer of combustion chamber surface area is investigated. Results show that OP2S has obtained peak combustion efficiency of 0.97, which is 0.02 higher than that of conventional diesel engine (4S). Also, combustion efficiency loss due to undesirable swirl ratio is only 20 % of 4S. Lowest heat transfer ratio achieved by OP2S is 0.045 of fuel energy, which is 34 % lower than that of 4s. However, heat transfer ratio of cylinder wall in OP2S is at least twice of that in 4S, and increase significantly with swirl. Unable to utilize squish, OP2S would suffer from at most 0.1 lower combustion efficiency compared to 4S when injection is retarded to TDC. Heat transfer ratio in OP2S is less sensitive to variation of injection phase, and stays at least 0.01 lower than 4S for all injection phase studied. In conclusion, OP2S achieved higher combustion efficiency while significantly cutting heat transfer loss compared to 4S at optimized swirl ratio and injection phase, proving its potential as a high-efficiency power source. Thermal load issue on cylinder wall in OP2S can be fixed by lowering swirl ratio. Reducing heat transfer loss in OP2S with delayed injection is undesirable, however, since combustion efficiency would suffer.

Global Regular Axially-Symmetric Solutions to the Navier–Stokes Equations with Small Swirl

Axially symmetric solutions to the Navier–Stokes equations in a bounded cylinder are considered. On the boundary the normal component of the velocity and the angular components of the velocity and vorticity are assumed to vanish. If the norm of the initial swirl is sufficiently small, then the regularity of axially symmetric, weak solutions is shown. The key tool is a new estimate for the stream function in certain weighted Sobolev spaces.

Investigation of rapid flame front controlled knock combustion and its suppression in natural gas dual-fuel marine engine

In this study, a new-type knock mechanism for large-bore marine engines, which differs from the existing end-gas auto-ignition knock theory and detonation wave theory, is fully revealed, using a high time resolution dynamic pressure difference method. The results indicate that the disparate enhancement effects of the flame front on the high-pressure region and the low-pressure region result in an increasing pressure difference, eventually forming the knock. The distinctions between this knock and the conventional end-gas auto-ignition knock were examined. Subsequently, the different functions of swirl in the two knock mechanisms were investigated. The results illustrate that, increasing swirl in end-gas auto-ignition knock can accelerate the termination of flame surface propagation and reduce the end-gas temperature by shortening the end-gas heat accumulation, thereby decreasing the knock intensity. However, reducing swirl in the new-type knock can diminish the combustion intensity of the flame front, thereby reducing its enhancement of the pressure wave. Consequently, a reduction to one-fourth of the initial swirl level can reduce knock intensity by 91%. Particularly, a novel knock suppression method of positioning the jet flame in the opposite direction of the swirl is proposed, which can avoid the local rapid combustion to effectively eliminate knock while maintaining power.

The comprehensive comparison of imaging sign from CT angiography and noncontrast CT for predicting intracranial hemorrhage expansion: A comparative study.

Expansion of intracranial hemorrhage (ICH) is an important predictor of poor clinical outcomes. Various imaging markers on non-contrast computed tomography (NCCT) or computed tomographic angiography (CTA) have been reported as predictors of ICH expansion. We aimed to compare the associations between various CT imaging markers and ICH expansion. Patients with spontaneous ICH who underwent initial NCCT, CTA, and subsequent NCCT between January 2016 and December 2019 were retrospectively identified. ICH expansion was defined as a volume increase of > 33% or > 6 mL. We analyzed the presence of imaging markers such as the black hole sign, blend sign, island sign, or swirl sign on initial NCCT or spot sign on CTA. An alternative free-response receiver operating characteristic curve analysis was performed using a 4-point scoring system based on the consensus of the reviewers. The predictive value of each marker was assessed using univariate and multivariate logistic regression analyses. A total of 250 patients, including 60 (24.0%) with ICH expansion, qualified for the analysis. Among the patients with spontaneous ICH, 118 (47.2%) presented with a black hole sign, 52 (20.8%) with a blend sign, 93 (37.2%) with an island sign, 79 (31.6%) with a swirl sign, and 56 (22.4%) with a spot sign. In univariate logistic regression, the initial ICH volume (P = .038), initial intraventricular hemorrhage (IVH) presence (P < .001), swirl sign (P < .001), and spot sign (P < .001) were associated with ICH expansion. Multivariate analysis confirmed that the presence of initial IVH (odds ratio, 4.111; P = .002) and spot sign (odds ratio, 109.5; P < .001) were independent predictors of ICH expansion. Initial ICH volume, IVH, swirl sign, and spot sign are associated with ICH expansion. The presence of spot signs and IVH were independent predictors of ICH expansion.

Experimental Study on the Effects of Shear on Co‐Currently Swirling Steam‐Water Flow Instabilities

AbstractThe shear effect of co‐currently flowing water on the flow instabilities induced by swirling steam was investigated. With shear, a 22–27 % decrease in velocity fluctuation amplitude was observed. The decrease was 29–41 % on an exponential and 12–17 % on a proportional basis. Shear reduced the layer thickness on increasing the inlet water pressure from 1 to 2 bar by 1.9–2.9 and 6.35–12.89 % at steam inlet pressures of 1 and 2 bar, respectively. The ratio of the swirl intensity along the dimensionless axial length scale and the initial swirl intensity was changed from &lt; 1 to &gt; 1 across critical point due to the nearly equal values of buoyancy and rotational frequencies. A critical limit of the initial swirl intensity within the control plane was investigated wherein the swirl‐induced instabilities can be attenuated uniformly and the rotational effects dominate over the gravity waves and buoyancy.

Wake rotation impacts on wake decay

This study considers the behavior of a well-conditioned swirling turbulent wake. A custom swirling wake generator was used to produce a swirling wake absent of a tower that complicates the flow regime. Four swirling wakes were studied with swirl numbers ranging from 0.19 to 0.37 and compared to a non-swirling counterpart. Two-component Laser-Doppler Anemometry was used to measure mean and turbulent quantities in the wake. Measured profiles were analyzed based on similarity theory applied to a swirling wake. The results show that wake behavior was impacted by the initial swirl strength. Generally, wake growth rate and axial deficit decay rate increased with higher levels of swirl, and tangential velocity decay rate increased with lower levels of swirl. However, the wake that diffused fastest was the case with a swirl number of 0.27.

The effect of the initial swirl of the supersonic flow of humid air on the adiabatic wall temperature

The paper presents the results of measuring the adiabatic wall temperature of an axisymmetric channel during acceleration of the moist air flow in it to supersonic speed. The initial swirl was imparted to the flow (swirling parameter S = 0.5, 1.0, 2.5). The relative initial humidity (RH) of the flow varied in the range of 10 ÷ 90%. When the flow was accelerated to supersonic speeds, part of the moisture condensed, which influenced the wall temperature. It is shown experimentally that with an increase in the initial moisture content of the flow to certain values, the distribution of the wall temperature for a flow without initial swirl (S = 0) and with swirl with S = 0.5, 1.0 practically coincide. However, from a certain value of RH, the wall temperature in the case of a swirling flow decreases in comparison with a flow without swirling. The maximum decrease in the wall temperature was achieved at RH = 90%. An increase in the initial swirl to S = 2.5 led to a greater decrease in the wall temperature, while the mass air flow through the channel decreased by 26% at an identical pressure drop.

Numerical Simulation of Swirl Flow Characteristics of CO2 Hydrate Slurry by Short Twisted Band.

The development of oil and gas resources is gradually transferring to the deep sea, and the hydrate plugging of submarine pipelines at high pressures and low temperatures is becoming an important problem to ensure the safety of pipeline operations. The swirl flow is a new method to expand the boundary of hydrate safe flow. Numerical simulation of the hydrate slurry flow characteristics in a horizontal pipeline by twisted band has been carried out, and the flow of CO2 hydrate slurry in low concentration has been simulated by the RSM and DPM models. The results show that the heat transfer efficiency is also related to Re and particle concentration. The velocity distribution has the form of symmetrical double peaks, and the peaks finally merge at the center of the pipeline. Vortexes firstly appear on both sides of the edge of the twisted band, and then move to the middle part of the twisted band. Finally, the vortex center almost coincides with the velocity center. The rotation direction of hydrate particles is the same as the twisted direction of the twisted band, twist rate (Y) is smaller, Re is larger, and the symmetric vortex lines merge farther away. The initial swirl number is mainly related to Y, but not Re. The swirl flow attenuates exponentially, and its attenuation rate is mainly related to Re, but not Y. Compared with ordinary pipelines, the swirl flow can obviously improve the transportation distance of hydrate slurry.

Feasibility of a combined swirl and blending sign on non-contrast computed tomography for predicting early hematoma expansion after spontaneous intracerebral hemorrhage.

For predicting the hematoma expansion of spontaneous intracerebral hemorrhage, spot and swirl signs have been investigated. However, the clinical effectiveness of these signs remains debatable. These signs do not consider the peripheral hypodense lesions, which may imply a greater chance of ongoing bleedings. We proposed a new combined swirl and blending sign and evaluated its clinical usefulness in predicting hematoma expansion in non-contrast computed tomography settings. A total of 201 patients who were diagnosed with spontaneous intracerebral hemorrhage were enrolled. Their clinical and radiologic data were retrospectively reviewed. Patients were classified into hematoma expansion (N.=51) and nonexpansion groups (N.=150), and multivariable logistic regression analyses were performed to identify the factors associated with hematoma expansion. In the hematoma expansion group, an average of 20 mL of volume increase was noted. In multivariate analyses, several factors, including higher systolic blood pressure (P=0.026), larger initial hematoma volume (0.002), spot sign (0.019) and combined swirl and blending sign (<0.001), were identified as reliable predictors of hematoma expansion. A swirl (P=0.396) or blending sign (P=0.124) alone was not identified as a significant predictor of hematoma growth. The sensitivity, specificity, and positive and negative predictive values of the combined swirl and blending sign were 31%, 97%, 80%, and 81%, respectively. A newly defined "combined swirl and blending sign" on non-contrast computed tomography was positively associated with an increased risk of hematoma expansion of spontaneous intracerebral hemorrhage and could be regarded as a reliable predictor in non-contrast computed tomography settings.

INTRINSIC PARAMETERS OF DRY CHOPPED MISCANTHUS FOR COLD PARTICLE DYNAMIC MODELING

Miscanthus is a bioenergy crop that is very easy to cultivate. It has high volatile content with an average energy value of about 18.8 MJ/kg on a dry basis. With the benefits mentioned above, Miscanthus is potential as a fuel for the suspended furnace. Therefore, the furnace design for the Miscanthus particle needs to be developed immediately. A relatively fast and low-cost technique to develop a burner furnace design is the modeling. This study aims to determine the intrinsic parameter values of dry Miscanthus particles needed in cold particle dynamic modeling. The various reasonable experimental techniques were used to obtain these parameter’s values. Then, a series of simulations and experiments of dry chopped Miscanthus dynamic in a special burner was conducted to assess the conformity of these values. The intrinsic parameters values of dry chopped Miscanthus obtained are as follows; shape factor (fs) 0.52, true particle density (ρp) 245 kg m-3, minimum, maximum, and mean particle diameters (dp) 106, 9520, and 1384 µm respectively, and spread parameter (n) 1.22. Qualitatively, the particle dynamic simulation results, using RSM and k-e models, showed similar particle pathlines to the experiment results, in terms of the frequency and intersection of the helical structure formed in the burner cylinder. It indicates that the intrinsic parameter values obtained in this study are reliable results and can be used for further simulation works. In addition, particle dynamics experiments and simulations also revealed that the particle pathline in the burner cylinder tend to move near the cylinder wall in a helical pattern; a single helix pattern in a single tangential inlet burner and a double helix pattern in a double tangential inlets burner. Regardless of the effect of the tangential inlet number, the helical pattern in the burner cylinder was also influenced by the initial swirl number (ISN) of the flow. The lower the ISN, the lower the helical frequency formed and vice versa. This study also proved that at low to moderate swirl intensities, the k-e turbulent model can be relied upon to model particle dynamics in a cyclone burner.

Investigation of Thermohydraulic Characteristics of Vortex Chambers

Local flow swirling is used in power facilities and other technical devices. It is an effective means for acting on the air flow structure and can enhance heat transfer. A swirled flow in axisymmetric channels belongs to the group of 3D flows in the field of centrifugal mass forces. It is characterized by the ratio of two (axial and rotational) or, in some cases, three components of the velocity, the presence of transverse and longitudinal pressure gradients, and high turbulent fluctuations that bring about certain difficulties in the investigation of processes occurring in a swirled flow and it complicates detection of their regularities. Therefore, it is proposed to install a vortex chamber (VC) at the leading edge of a blade or vane of a high-temperature gas turbine. Temperature conditions and flow capacity of VC models were studied by a calorimetric method in a liquid-metal thermostat. The regularities of heat transfer rate on the surface of the cooling channels were determined depending on the number and diameter of inlet (supply) and outlet holes for various pressure drops. The VK designs were optimized considering the effect of their geometry on the formation of various swirl flow structures with different levels of heat transfer enhancement. An analysis was performed with account taken of the throughput capacity of the models. The criterial dependences of the Nusselt number vs. Reynolds number Re were obtained for three VC designs for direct- or reverse-flow direction. The highest heat fluxes were observed on the section of coolant supply via holes, which is explained by a high velocity of the initial flow swirling. Flow swirl breakage and cooling air heating are the cause of a decrease in the relative heat transfer coefficient $${\bar {\alpha }}{\text{.}}$$ The self-similarity mode is observed at a pressure ratio across the vortex chamber above 1.4. The thermal problem was solved using data of the hydraulic tests of the models with air blowing under isothermal conditions. The results of experimental studies can be included in the data bank of heat and mass transfer software products to reduce the labor intensity and time in the development of a cooling system for blades/vanes of high-temperature gas turbines.

Influence of orifice geometry on atomization characteristics of pressure swirl atomizer.

The spray characteristics of the pressure swirl nozzle are experimentally studied using particle dynamics analysis (PDA) and high-speed photography system in this paper, specifically focusing on the dependence of geometrical dimensions of orifice on the spray SMD, velocity magnitude and droplet distribution, and the spray cone angle. It is indicated that the increase of orifice diameter makes the initial swirling velocity lower and the spray liquid film thicker. When the spray cone is fully expanded, the flow rate of 900 μm orifice diameter nozzle increases by 30-40% and the SMD of 900 μm orifice diameter nozzle increases by 8.5% compared with that of 700 μm orifice diameter nozzle. According to the experimental conditions, the relationship between Re and spray angle was calculated as θ = 29.97*Re0.087, ignoring the factors that had little influence on spray angle. The decrease of the orifice length makes the distance of gas-medium shearing action shorten so that thinner oil film near wall cannot be formed by the extrusion of air core, leading to the swirling intensity reducing and the suction effect weakened. The spray cone angle of the 450 μm orifice length atomizer is about 5° smaller than the nozzle of 500 μm orifice length, and more small SMD droplets are not sucked, resulting in the distribution range of spray SMD declining.

An orthogonal numerical simulation experiment study towards the decay characteristics and effective swirl length of the swirling flow in a vortex tool inserted tube

Studying the decay characteristics and effective swirl length of the gas-liquid two-phase swirling flow generated by vortex tools is of great significance for improving its drainage effect. The effective swirl length is a key parameter related to the working performance, installation spacing and downstream pressure dynamics of vortex tools. However, works addressing the effective swirl length are rare in the literature. In this research, the decay characteristics and effective swirl length of a swirling flow and the factors that affect the swirling flow are systematically investigated using the orthogonal numerical simulation experiment method. Good agreements are achieved between existing experimental data and the numerical results of this study. The range analysis results reveal that the helix angle, mandrel diameter and vane axial length play dominant roles in the initial swirl intensity. An increase in the helix angle results in a decrease in the initial swirl intensity, while the mandrel diameter has the opposite effect. The swirl intensity decay rate is mainly affected by the Reynolds number, helix angle and vane axial length; the decay rate has a negative correlation with the first two factors and a positive correlation with the third factor. On this basis, a comprehensive decay model of the swirl intensity is proposed after obtaining the correlations for the geometrical swirl intensity and swirl intensity decay rate. Furthermore, an effective swirl length evaluation method is established, and the optimal vortex tool structure of a typical gas well is obtained with a helix angle of 55°, a mandrel diameter of 38 mm, a vane axial length of 120 mm and a vane width of 15 mm.

Suction Vortices in a Pump Sump—Their Origin, Formation, and Dynamics

Abstract The origin, formation mechanism, and dynamics of suction vortices in a pump sump have been clarified by large eddy simulation (LES) applied to two different computational models. The first one is a pump-sump model with uniform flow entering a water channel of rectangular cross section and a vertical suction (outlet) pipe installed at its downstream end. LES with different wall boundary conditions have revealed that the origin of a submerged vortex is the mean shear of the approaching boundary layers that develop on the bottom and side walls of the sump. Detailed investigations have revealed that deviation of the mean flow triggers conversion of the vorticity axis to the vertical direction. The local acceleration of the vertical flow stretches the aforementioned vertical vortex, which results in the formation of a submerged vortex. The second one is a simplified computational model composed of a paraboloid of revolution and aims to accurately simulate the stretch of the viscous core of a submerged vortex that has appeared under the suction pipe of the pump-sump model. The differences between the models, especially predictions of the minimum pressure, imply that cavitation could have been initiated in the viscous core, if it had been taken into account, as is observed in the pump-sump experiment at the same condition. Parametric studies with different initial swirl numbers from 0.12 to 16.3 have clarified the behavior of the submerged vortex. It was found that a strong submerged vortex appears only at a relatively small range of the swirl numbers from 1.25 to 3.

Numerical evaluation on the decaying swirling flow in a multi-lobed swirl generator

Accurate predictions of decaying swirling flow behavior in the multi-lobed swirl generator (MLSG) are essential for certain engineering applications. In this study, decaying swirling flow characteristics in an MLSG are examined using the Computational Fluid Dynamics (CFD) technique with a Reynolds stress turbulence model (RSM). The effects of different lobe numbers (n) and pitch length ratios (P/D) on swirl intensity, pressure drop, friction factor coefficient, and decay rate are observed with Reynolds number from 50,000 to 125,000. Combined with the pressure loss, the efficiency of swirl induction is evaluated by introducing a swirl effectiveness (SE) evaluation criterion. The initial swirl intensity is shown to first increases and then decreases as lobe number increases. The maximum value is obtained at lobe number n = 4. The pitch length ratios P/D corresponding to the optimal SE value obtained from different lobe also differ. The optimal SE value is achieved at n = 4 and P/D = 8. The friction factor ratio f s/f p decreases as pitch length ratio increases, but the decreasing trend decelerates over time. Correlations based on the numerical predictions of friction factor ratio f s/f p and decay rate β are presented accordingly.

Investigation on horizontal and deviated wellbore cleanout by hole cleaning device using CFD approach

AbstractThe application of the hole cleaning device in downhole is a new technology for removing cuttings bed, and it can increase the efficiency of cuttings transport. This paper mainly studies the effects of the helical angle and the rotational speed of the blade of the hole cleaning device on the swirl strength of decaying swirl flow and drilled cuttings deposition behavior. A three‐dimensional computational fluid dynamics (CFD) model is established using the Eulerian‐Eulerian two‐fluid model, Realizable k‐ε turbulence model, and Sliding Mesh technique for simulating the two‐phase fluid flow. The results have been compared with available data in the literature, and a good agreement is found. In order to understand the decay behavior of the swirl flow along the flow direction, the initial swirl strength, the swirl number, and the decay rate of swirl are analyzed in detail in single phase. The effects of the swirl flow induced by the blade on the deposition behavior of drilled cuttings under different rotational speed and helical angle are studied. A new deposition index is used to evaluate the effective distance and hole cleaning efficiency of the swirl flow under various parameters. It has been observed that using the hole cleaning device can improve the hole cleaning performance. The research results of this paper is instructive to the design of the hole cleaning device using in the drilling engineering.

Numerical Simulation of the Effects of the Helical Angle on the Decaying Swirl Flow of the Hole Cleaning Device

The application of the hole cleaning device in downhole is a new technology that can improve the problem of cuttings accumulation in the annulus and improve the hole cleaning effect of the wellbore during drilling. In this paper, the Reynolds Averaged Navier–Stokes model, together with the Realizable k-ε turbulence model, are used to perform transient simulations. The effects of rotational speed, blade shape, and helical angle on the initial swirl intensity and its decay behavior along the flow direction are studied. The swirl number, the initial swirl intensity, the decay rate, the tangential velocity distribution, and the variation of pressure are analyzed. The results indicate that the swirl number of the swirl flow exponentially decays along the flow direction. The straight blade and V-shaped blade have different swirl flow induction mechanisms. Under specific drilling parameters, the critical helical angle is determined for both types of blades. When the selection of the helical angle is close to the critical value, the swirl flow will be close to the axial flow, which is of little help in hole cleaning. Moreover, the rotation direction of swirl flow will change when the helical angle exceeds the critical value.