Effect Of Swirl Research Articles

Effect of swirl on fluctuation of pressure drop in a gas–liquid slug flow

Slug flow as one of the typical two-phase flow patterns occurs widely in industry. The fluctuating phenomenon in slug flow is harmful to the pipeline system and should be suppressed. Flow-pattern modulation by swirl has been widely used to satisfy practical application. In this work, influences of swirl on pressure gradient and interface morphology in a gas–liquid slug flow were studied by visualization experiments. The results showed that slug flow will transform to swirling intermittent flow when the gas and liquid velocity is relatively high. In this case, pressure drop in the slug flow is higher and its fluctuation within a relatively narrow range compared with those in a non-swirl slug flow; the probability density function distribution is more concentrated in the swirling intermittent flow; the slug flow transforms to the flow pattern altering between gas column and gas slug. The slug flow was kept downstream of the swirler when the gas and liquid velocity is relatively low. In this case, effects of swirl on both pressure drop and interface morphology are not obvious. Along the streamwise direction, the morphology interface, fluctuation of pressure drop and pressure signals showed that the swirling intermittent flow gradually transforms to non-swirl slug flow. Finally, the transition boundaries between these flow patterns were proposed and compared with other published transition boundaries in swirling and non-swirling flows.

On the use of PIV, LII, PAH-PLIF and OH-PLIF for the study of soot formation and flame structure in a swirl stratified premixed ethylene/air flame

Soot formation and oxidation are investigated in swirl stratified premixed ethylene/air flames at atmospheric pressure. The effects of both swirl and stratification are studied to understand the relationship between the flame structure, soot precursors and soot. The topology of the flame is obtained with particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) on hydroxyl radical (OH). The production of polycyclic aromatic hydrocarbons (PAHs) is investigated using PLIF by mainly probing the aromatic compounds with two benzene rings (i.e. naphthalene) that are known to actively participate in soot nucleation and growth. Soot production is investigated using laser-induced incandescence (LII), giving quantitative data on the soot volume fraction. Extensive information on the flame structure and the mechanisms of formation/consumption of soot is gathered based on the coupling of these laser diagnostics. An image analysis of velocity, OH, PAHs and soot distributions enables us to propose a scenario that describes the link between the inception, growth, aggregation and oxidation processes. In particular, the data reveal the presence of distinct zones for these processes: a thermal decomposition region in which PAHs contributes to nascent soot formation, organised as filaments along the interface between the PAH region and the inner recirculation zone (IRZ); a mixing region controlled by large moving structures that favour the growth and aggregation of nascent soot into mature soot; and an oxidation region leading to the fast consumption of soot particles. These processes are impacted to varying extents by the intensities of swirl and stratification.

Experimental study of swirl-stabilized turbulent premixed and stratified LPG/air flames using optical diagnostics

Experiments are carried out to investigate the effects of mixture stratification, velocity ratio, and swirl on the LPG/air flame structures using a swirl-stabilized axisymmetric burner. Stereo Particle Image Velocimetry (SPIV) technique is used to measure the velocity field of non-reacting and reacting flows. Chemiluminescence imaging technique is used to measure the OH*/CH* signals of premixed and stratified flames. The mixture stratification ratio at the burner exit is varied from 1 to 5 by changing the equivalence ratios of the inner and outer streams between 0.32 and 1.60. The swirl intensity of the inner and outer streams is varied independently by using two different sets of axial swirlers. The ratio of velocities between the inner and outer streams ranged from two to three. Examination of the non-reacting flow field showed that the combination of axial swirlers plays a crucial role in the formation of the streamlines which would help to sustain the flames. Analysis of reacting flow fields of different cases revealed the robustness of the flame structure to the stratification of the mixture. Further investigation on the Abel-inverted chemiluminescence images showed that the transition from premixed to stratified condition makes the flame more compact and closer to the exit of the burner. The flame structure is similar among stratified conditions with the increasing stratification ratios confirming the robustness of the flame structure to the stratification of the mixture. Under the operating conditions studied, the flame structure is more sensitive to changes in the velocity ratio or swirler combination relative to the stratification ratio.

Effects of intake swirl on the fuel/air mixing and combustion performance in a lateral swirl combustion system for direct injection diesel engines

To study how intake swirl affects the combustion performance of the lateral swirl combustion system (LSCS), experiments under different swirl ratios were carried out in a single-cylinder diesel engine to optimize the circumferential injection angle (CIA) and test the eventual combustion performance. Then, simulation under different swirl ratios was conducted to reveal the influence mechanisms of intake swirl on the fuel/air mixing characteristics of the LSCS.Experimental results show that, as the swirl ratio (SR) was increased from 0 to 1.0, the optimal CIA increased 2.5° in the opposite direction to that of the intake swirl. Besides, the LSCS obtained better combustion performance with SR = 0 than with SR = 1.0, especially at high loads and low excess air coefficients. Simulation results indicate that, generating intake swirl weakens the wall-flow-guided and interferential interactions of the LSCS, thereby deteriorating the in-cylinder air utilization and fuel/air mixing uniformity, especially at high loads and low excess air coefficients, in which the interactions between the LSCS chamber and spray jets is strong due to the enhanced spray penetration ability. Therefore, the LSCS without intake swirl obtains the optimal fuel/air mixing and combustion performance in DI diesel engines.

THE EFFECTS OF SWIRL AND TUMBLE RATIOS ON THE ENGINE PERFORMANCE OF MOTORBIKES

Nowadays, motorbikes are still the main and most popular transport in Asian countries, especially, in Vietnam. However, the manifold intake systems in motorbikes are usually designed in a simple structure, which can reduce engine performance and increases fuel consumption in motorbikes. This paper presents the study of the improvement of the intake system in a 125cc motorbike engine to enhance air-fuel mixing quality that can increase the engine performance. The study employs the ANSYS software to obtain an optimal intake systemthrough the tumble and swirl ratios in different simulation cases. Another model wasalso built by Matlab/Simulink to examine the effects of swirl and tumble ratios on engine performance and fuel consumption at various engine speeds. The simulation results show that the modified intake system withan incline angle of 30o has optimal tumble and swirl ratios. Accordingly in conclusion, power output and torque of the engine with the modified intake system are higher, while the fuel consumption is lower than previouslyfound.

Performance and heat transfer evaluation of convex lens solar water heater with serrated, triangular cut and perforated twist inserts

This paper studies the performance and heat transfer analysis of Solar water heating systems incorporated by Convex lenses also with two types of twists CSPT(combined Serrated Perforated Twists) and CTPT(combined Triangular cut Perforated Twists) with twist ratios 3 and 6. Convex lenses are preferred to utilize the diffusible radiation and it focuses the solar rays in single point on the absorber plate. It helps the riser tube to get higher solar radiation at the instant. Nearly 45 lenses fixed over the glass and focusing radiations to 9 rows of riser tubes. Generally, twists give a swirling effect to the working fluid and it enables the water to catch up high heat from the riser tubes. In this case, CSPT and CTPT are introduced to examine the heat transfer characteristics. The experiments are carried out for plain and CTPT, CSPT collectors. Reynolds number and the Nusselt numbers are lying between 190 - 1266 and 4.104-16.7331. The friction factor is in the range of 0.035 to 0.1155. The implementation of convex lenses with the insertion of CSPT and CTPT helped to earn better heat transfer. CTPT with minimum twist ratio 3 has provided 1.9 times higher efficiency as compared to CSPT twist inserts. It enhances the overall efficiency by up to 9% than the conventional one.

Thermal performance in a modified header solar water heating system using salt hydrate technology with twisted tape insert

In this study, the thermal performance of a solar water heater while using Epsom salt as a phase change material and the temperature maintenance in water are explained in detail. Here the Epsom salt (Magnesium Sulfate hepta hydrate form) acts as an energy-storing medium that is used as mixed with water. Generally, the solar water heating system maintains water temperature at an optimum level at day time and very less in the night time when there is no radiation. When using Epsom salt, mixing with water, the Epsom content absorbs heat and it keeps the heat with itself for a long time. So the heat remains in the water at night time too. Therefore a constant rate of temperature is maintained in water during day and night time. Besides, with the insertion of HT (Helix Twist) is used to excel in the heat transfer rate between water and tube by increasing the swirl effect of water. The circulation of water is carried out by the Thermosyphon effect. The results confirmed that this proposed solar water heater provides higher efficiency up to 92%, which is higher than the conventional SWH efficiency of 82%. The average Nusselt number is 18% greater than the conventional one. Apart from efficiency enhancement, the addition of Epsom salt provides some health benefits like pain relief, reduction of insulin resistance in the body with an increase in magnesium, and Sulfate content and for plants by supplying the used water. It is most important that it is advisable to use the water for bathing purposes only.

DNS analysis of boundary layer flashback in turbulent flow with wall-normal pressure gradient

The presence of swirl in combustion systems produces a marked change in their boundary layer flashback behaviour. Two aspects of swirling flow are investigated in this study: the effect of the swirl-generated wall-normal pressure gradient, and the effect of misalignment between the mean flow direction and the direction of flame propagation. The analysis employs Direct Numerical Simulation (DNS) of fuel-lean premixed hydrogen-air flames in turbulent planar channel flow with friction Reynolds number of 180. The effect of swirl on the flashback process is investigated by imposing a wall-normal pressure gradient profile. Analysis of the DNS data shows how the resulting differences in flow field and flame topology contribute to the differences in the overall flashback speed. Misalignment of the flow and propagation directions leads to asymmetry in the flame shape statistics as streaks of high velocity fluid in the boundary layer cleave into the flame front at an angle, yielding an increase in flame surface density away from the wall. Swirl has a stabilising effect on the turbulent flame front during flashback along the centre-body of a swirling annular flow due to the density stratification across the flame front, and produces a reduction in turbulent consumption speed. However the swirl also sets up a hydrostatic pressure difference that drives the flame forward, and the net effect is that the flashback speed is increased. The dominance of hydrostatic effects motivates development of relatively simple modelling for the effect of swirl on flashback speed. A model accounting for the inviscid momentum balance and for confinement effects is presented which adequately describes the effect of swirl on flashback speed observed in previous experimental studies.

Analysis of thermal performance characteristics in variable header solar water heating system by a swirling effect of twisted tapes

ABSTRACT This present study experimentally investigates the hydrothermal performance of a variable header solar water heating system inserted with helix twists (HT) and helix twist with square-cut perforated (HTSCP). Experiments have been conducted between variable header inserted with simple helix and HTSCP with the Reynolds number range from 190 to 1245. From the experimentation, the Nusselt number, friction factor, and thermal performance factor for the twist ratios Y = 3and Y = 6 have been calculated. In general, the overall thermal performance of a solar water heater has been augmented by increasing the mass flow rate, this is achieved from commencing to end providing a uniform flow in all riser tubes by introducing variable header. The experiments have been performed for the ratio of Y = 3 and Y = 6 with square cut of depth ratio (DR) and width ratio (WR) of 0.27. The performance comparison between the HTSCP with the simple helix twists (HT) and plain tube collector proved that the HTSCP-3 significantly performs superior. The HTSCP-3 attained 2.46% higher Nusselt number than the other twists HT-3, HT-6, and HTSCP-6.

Effects of swirl on the heating process of a central gas stream in a tubular flame

This study experimentally investigated the heating process of an axially induced cold gas stream in a swirl tubular flame established through tangential fuel/air pre-mixture injection, aiming to clarify the effects of swirl motion on the heat and mass transfer enhancement. Tubular flame burners with geometry swirl numbers (S) of 0.35 to 1.4 were employed in addition to a conventional slit-type burner to systematically study the flame structure, stability, temperature distribution and flow field. The results show that in comparison to the slit burner without rotation, the swirl tubular flame burner provides a much wider range of stable flame from lean to rich limits even under large flow rates. The heating rate of the inner cold stream by the outer burned gas stream increases as the swirl number raises. Cold flow visualization illustrates that the interface between the two streams is rolled up and instability appears at the interface for the larger swirl numbers of S = 0.7 and 1.4, resulting in enhancement of mixing rate. At large flow rates the two streams are well mixed under cold flow condition, however, they are separated and ordered under combustion condition in the upstream, probably resulted from the burned gas expansion outside the central gas stream. While their mixing rapidly enhances as S raises to beyond 0.7. A simple theoretical analysis illustrates that the enhancement of the heating rate with a rotational motion can be quantitatively evaluated by replacing the numeric unity in Eq. (1) with the value of S + 1. The enhancement seems to be through an increase of heat transfer area at low rotational velocities, or increases of heat and mass transfer rates at high rotational velocities.

The Effect of Inlet Swirl on Brush Seal Bristle Deflections and Stability

Abstract This paper considers three-dimensional (3D) computational fluid dynamics (CFD) and structural modeling of brush seals, and investigates the effects of inlet swirl on the bristle pack. The model couples aerodynamic forces generated by CFD to a structural model that includes interaction between bristles. At a critical value of inlet swirl, aerodynamic forces cause circumferential slip of the upstream bristle row. In practice, this may lead to instability of the bristle pack and is consistent with anecdotal reports of seal behavior. The critical swirl velocity was reduced when the downstream pressure level was raised, keeping the same upstream total to downstream static pressure difference. This is caused by the increased dynamic head associated with the inlet swirl. Inclusion of a front plate in the seal design does not offer the intended protection to the bristle pack in highly swirling environments. This is associated with highly swirling flow impinging on the bristle tips. Fitting of roughness elements on the upstream face of the front plate could improve stability by reducing swirl of the flow impacting on the bristles. Increasing the bristle diameter and bristle stiffness does not necessarily prevent slip at higher inlet swirl velocities, but reduces the magnitude of slip of the upstream bristles.

Turbulent swirling impinging jet arrays: A numerical study on fluid flow and heat transfer

Impinging jets are generally utilized as an effective medium of heat and mass transfer. Various stream orientations and swirl effect may be a potential candidate to further improve the heat transfer characteristics. This paper numerically examines two different types of arrays of circular multiple jets and the effect of swirl on jets that impinges vertically onto a flat surface situated at a fixed vertical separation distance H = 2D, D the nozzle diameter and at Reynolds number equal to 11,600. In this regard, three-dimensional simulation was performed using finite volume method whereas turbulence was described by SST k-ω model. The results demonstrate that staggered arrangement ensures better mixing and higher velocity as well as heat transfer. The strength of recirculation for swirl jet is larger than that of non-swirl jet. Maximum pressure coefficient occurs at individual stagnation point of each jet, with a secondary peak between two neighboring jets. Strong heat transfer is predicted to occur at around the stagnation region for each non-swirling jet and between the neighboring jets for swirling jets. Turbulences are intense around the periphery of each jet and they coalesce as it moves downward.

Experimental Investigation on the Effects of Swirl on the Exit Turbulent Flow Field of an Unconfined Annular Burner at Isothermal and Reacting Conditions

The objective was to study the effect of change in swirl intensities, S=0.4, 0.7 & 1 of the annular swirling flow on the exit flow field of an unconfined annular swirl burner operated at isothermal (only dry air) and reacting flow (premixed methane air mixture) conditions. Reynolds number at the burner’s annular exit based on its hydraulic diameter (D) was kept constant at 4000. Exit flow field at isothermal conditions was measured using planar particle image Velocimetry rig and processed using commercial software. The percentage decay in the magnitude of peak value of axial velocity obtained from its radial profile at a height of 4D from the burner exit with the change in swirl intensity of 1, 0.7, 0.4 and 0 was 65%, 55%, 47.2% and 13.5%. The jet spreading angle was 6.5o for S=0, 8.4o for S=0.4, 9.8 for S= 0.7 and 14.2o for S=1. Recirculation zone was observed only for S=0.7 and 1.0. The width of the recirculation zone was 3D (S=0.7) and 3.4D (S=1) respectively. The normalized reverse mass flow rates estimated were 0.027 for S = 0.7 and 0.058 for S = 1.0. The magnitude of turbulence intensities at wake shear layer was much higher than the jet shear layer due to the presence of recirculation zones for S= 0.7 and 1.0. The integral length scales calculated were varied in the range of 0.06D0.18D for all swirl intensities. Reaction front was identified by deconvoluting the time mean OH* chemiluminescence using Abel inversion method. The flame became shorter and wider with increase in swirl number which was in consonance with the observation of increase in size of recirculation flow in the isothermal flow. The equivalence ratios at which the lean blow out observed were 0.58, 0.6 and 0.62 for S=0.4, 0.7 and 1.

Inlet Swirl and Dump Gap Effect on Static Pressure Recov ery in Dump Diffuser Combustor u sing Two Equation Turbulence Model

Cold flow through an axi-symmetric dump diffuser, provided with a swirl effect at inlet is studied by using various two equation k-ε turbulent models such as; standard k-ε, RNG k- ε and Realizable k-ε model. There is a liner with a liner dome head of hemispherical in shape is used as a bluff body. From the comparison in between the three k-e turbulent models, it has been observed that the overall prediction of flow variables with Realizable k-e model are much better than others. The effects of dump gap and inlet swirl on velocity distribution and pressure variation on liner and casing walls have been investigated. The static pressure recovery within the diffuser is evaluated from area weighted average pressure at inlet and exit plane. It is noticed that an optimum inlet swirl results in the most effective pressure recovery due to the minimum irrecoverable energy dissipation in the vortices formed in the domain. The optimum swirl number is found to be 0.38 and it occurs when DG (non-dimensional dump gap) is kept as 1.0. The variation in dump gap changes the flow pattern and the possible pressure recovery. As the dump gap is increased, the static pressure is recovered more effectively with moderate swirl level in the inlet flow.

Effect of Swirl on Thermal and Hydraulic Properties of Ice Slurry Flow

Accumulation of ice particles inside the pipes of an ice slurry refrigeration system is a problem that should be avoided to ensure the efficient performance of the system. In the present research, the swirling flow of ice slurry is numerically investigated using the Eulerian-Eulerian model coupled with the kinetic theory of granular flow. The swirling flow is generated by twisted tapes inserted into a smooth pipe. The results show that by swirling the flow, the ice particle diameter may be increased up to about three times larger than the typical particle diameter used in the ice slurry, without particle accumulation. Moreover, for the swirling flow of ice slurry with the ice particle diameter of 0.3 mm, the rate of mass transfer increases 25% while the ice volume fraction at the pipe outlet decreases 30%, compared to the non-swirling flow. Based on the obtained results of swirling flow, correlations for friction factor, mean Nusselt number, and performance parameter are proposed.

CFD Analysis of Swirl Effect in a Diesel Engine Using OpenFOAM

The combustion process is a basic activity performed by internal combustion engines in charge of release chemical energy from a fuel-air mixture and transforms them into mechanical energy to produce work. Principles of fluid mechanics and thermal sciences are applied in the analysis of the complex flows developed during internal combustion processes with the aim of maximizing work, improving energy efficiency, minimizing fuel consumption, and reducing pollutants caused by the heat released in combustion chambers. Computational Fluid Dynamics help analyzing the turbulent flow phenomena presents in inlet flow, compression, combustion, and exhaust flow processes and defining optimization models that describe and improve swirl and tumble flows in combustion chambers of internal combustion engines. The purpose of developing a numerical simulation is to characterize turbulent flows developed in the admission and cylinders of a diesel engine to study the complex and sudden changes in flow parameters in order to describe a combustion process. Therefore, this paper presents a description of the flow behavior in an engine combustion chamber through a virtual environment. RANS k - e turbulence model is computed with OpenFOAM CFD code in order to solve the system of partial differential equations that define the turbulent mixture flow and swirl effects of the flow over the engine combustion chamber. The results of this research have shown a good agreement between numerical and experimental methods; an error rate of 5 % has been reached by using the KEpsilon turbulence model.

Effect of Swirl on Gasification Characteristics in an Entrained-flow Coal Gasifier

AbstractThe three-dimensional (3-D) comprehensive mathematical model was developed to simulate the coal gasification process in an entrained flow gasifier with a swirl burner. The models employed or developed includes the coal devolatilization model, the char combustion and gasification model, the gas homogeneous reaction model, the random-trajectory model, gas turbulence model, and the P-1 radiation model. The solution of models was executed based on the computational fluid dynamics (CFD). By qualitatively comparing the results at different swirl number, the significant influences of swirl on characteristics of coal gasification such as flow distributions, gas temperature and product composition including hydrogen (H2), carbon monoxide (CO), etc., and on the performance of coal gasification such as averaged exit product composition, carbon conversion rate and cold gas efficiency, were in detail discussed. Especially, a proper swirl number (S ≤ 0.65) in favor of gasification was found for the investigated gasifier in this paper.

Experimental and Numerical Study on the Use of Guide Vanes in the Dilution Zone

Abstract The importance of gas turbine blades is to convert the thermal energy into shaft work output, which makes the turbine blades as one of the critical components of the gas turbines. Besides the mechanical stresses caused by the centrifugal force and the fluid forces, the thermal stresses arise because of the temperature gradient within the blade materials. This paper aims to have a uniform circumferential temperature field at the combustor exit, consequently reducing the thermal stresses caused by the non-uniform temperature distribution along the turbine blade. The validation of the simulation results with the experiments showed an acceptable agreement with the available experimental data. The agreement includes the uniformity factor and the normalized mixture fraction at two different flowrates. Furthermore, another location of the guide vanes, external guide vanes, was experimentally and numerically tested. The results show that the external guide vanes with a 30 deg orientation gave the most uniform temperature flow for the two different flowrates. Compared with the internal guide vanes with the same orientation, the external guide vanes gave a 7.5% higher uniformity factor and a 2% lower pressure drop. The main reason for this result is that the external guide vanes direct the cold stream to penetrate the dilution zone with an angle enhance the swirling effect which are the main factors for excellent mixing, while the pressure drop is lower as the external guide vanes are facing the lower flowrate which is the secondary stream. Another advantage of the external guide vanes over the internal ones is that they are subjected to less thermal stresses as they are facing the cold flow. Furthermore, the external guide vanes are reachable and easy to maintain compared with the internal guide vanes.

Numerical Study on the Effects of Tumble and Swirl on Combustion and Emission Characteristics of an LPG Direct Injection Engine

Recently, global warming caused by greenhouse gases has been highlighted, so many studies have been carried out for developing eco-friendly products. In the vehicle industry, various techniques have been developed for eco-friendly engines. A previous fuel injection system, injecting fuel at the intake port, had difficulty precisely controlling the air/fuel ratio in the cylinder. Therefore, the fuel injection system has been changed to a direct injection system injecting fuel directly inside the cylinder. Due to concerns about fossil fuel depletion and the instability of oil prices, various alternative fuels are currently becoming popular. Liquefied petroleum gas (LPG) is an alternative fuel that has similar characteristics to gasoline. LPG can be used in gasoline engines without sophisticated modification of the engine. For these reasons, the present work focuses on a numerical investigation of the combustion and emission characteristics of LPG direct injection (LPDI) engines by using tumble and swirl. For conducting the simulation, commercial software STAR-CD ver. 4.26 was used. The study was performed at the minimum spark advance for best torque (MBT) of the stoichiometric excess air ratio (λ = 1.0) and the lean-burn excess air ratio (λ = 1.5) with changes in the intake port geometry to induce in-cylinder flow changes.

Effects of air swirl on the combustion and emissions characteristics of a cylindrical furnace fueled with diesel-biodiesel-n-butanol and diesel-biodiesel-methanol blends

In this research, the effects of air swirling on the emission and combustion characteristics of a cylindrical furnace fueled with various diesel-biodiesel-n-butanol and diesel-biodiesel-methanol blends were studied. The tests conducted on a burner with a radial air swirler and different vane angles (15°, 25°, 35°, 45°, 60°, and 90°) that was mounted to the combustion chamber. The results showed that the air swirler with vane angles of 35° and 60° can improve the CO and HC emission. Also, the CO2 and NOx emissions improved at the angles of 45° and 60°. The results indicated that the use of n-butanol and methanol as the mixture with diesel-biodiesel blends can improve the CO and HC emissions compared to neat diesel combustion. However, a five percent increase in methanol and butanol amount resulted in an increase (around 18%) in these pollutants. On the other hand, an increase in the percentage of alcohol in fuel mixture can reduce CO2 and NOx emissions up to 12%. According to the results, the mean temperature of combustion gas decreased about 2% in some points with the addition of n-butanol and methanol in the fuel mixture due to the small cetane number and lower heating value of these alcohols compared to diesel and biodiesel. The results indicated that air swirler with the vane angle of 60° had a better condition for the reduction of pollutants among other angles.