Swirl Center Research Articles

In-cylinder flow evolution in the horizontal plane of a motoring compression ignition engine

This study used the two-dimensional particle image velocimetry technique to quantify the in-cylinder horizontal plane velocity field evolution in a swirl-supported light-duty single-cylinder diesel engine. The data were acquired at a constant engine speed of 1600 revolutions per minute. For each case, the distance of the laser sheet from the fire deck was varied (z = 5, 10, and 20 mm) to investigate the axial variations in the flow field during the flow evolution in the compression stroke. A vortex identification algorithm was used to detect the swirl center and its deviation from the rigid body rotation. A Bessel fit was obtained using the experimental data. The result revealed that the in-cylinder flow was not axisymmetric. The swirl center approached the geometrical center as the piston approached the top dead center. The flow evolved at the farthest plane from the fire deck. The axial diffusion of angular momentum resulted in the formation of the swirl flow structure in the plane closer to the fire deck. Angular momentum analysis of a simplified geometry has been presented to explain the swirl amplification. The estimated results were compared with the experimental results to show the momentum stratification in the engine cylinder later in the compression stroke.

Experimental Investigation of the In-Cylinder Flow of a Compression Ignition Optical Engine for Different Tangential Port Opening Areas

The push for decarbonization of internal combustion engines (ICEs) has spurred interest in alternative fuels, such as hydrogen and ammonia. To optimize combustion efficiency and reduce emissions, a closer look at the intake system and in-cylinder flows is crucial, especially when a hard-to-burn fuel, such as ammonia is utilized. In port fuel injection ICEs, airflow within cylinders profoundly affects combustion and emissions by influencing the air–fuel mixing phenomenon. Adjusting intake port openings is an important factor in controlling the in-cylinder airflow. In previous experiments with a transparent cylinder, tangential and helical ports demonstrated that varying the helical port’s opening significantly impacts flow velocities, swirl ratios, and swirl center positions (SCPs). In this study, we used a particle image velocimetry technique to investigate how the tangential port’s opening affects intake and in-cylinder flows. Flow velocities were assessed at different planes near the cylinder head, evaluating streamline maps, turbulent kinetic energy (TKE), and SCPs. Under the given experimental conditions, swirl flows were successfully generated early in the compression stroke when the tangential port opening exceeded 25%. Our findings emphasize the importance of minimizing TKE and SCP variation for successful swirl flow generation in engine cylinders equipped with both tangential and helical ports.

Airflow Characteristics Investigation of a Diesel Engine for Different Helical Port Openings and Engine Speeds

Intake airflow characteristics are essential for the performance of diesel engines. However, previous investigations of these airflow characteristics were mostly performed on two-valve engines despite the difference between the airflow of two-valve and four-valve engines. Therefore, in this study, particle image velocimetry (PIV) investigations were performed on a four-valve diesel engine. The investigations were conducted under different engine speeds and helical port openings using a swirl control valve (SCV). The results suggest that the position of the swirl center does not significantly shift with different engine speeds and helical port openings, as the dynamics of the flow remained closely similar. The trends of the airflow characteristics can be best observed during the compression stroke. A higher engine speed increases the angular velocity of the engine more compared to the increase of the airflow velocity and results in a lower swirl ratio of the flow. On the other hand, a higher engine speed leads to a higher mean velocity and the variation of velocity results in a larger turbulence intensity of the flow. Increasing the helical port opening brings a reduction in the swirl ratio and turbulence intensity as more airflow from the helical port disturbs the airflow from the tangential port.

Measurements of turbulence sources in a swirl-supported diesel engine

The combustion efficiency and pollutant formation in swirl-supported diesel engines strongly depend on the in-cylinder turbulent flows. But the physical mechanism of turbulence generation remains inadequately understood. To identify the sources of turbulence at various spatial locations and to understand the relationship between the flow structures and turbulence production, planar particle image velocimetry experiments are performed in this study to characterize the evolution of turbulent flow in a motored optical diesel engine with a compression ratio of 13:1 and a swirl ratio of 1.5. The temporal and spatial distributions of turbulent kinetic energy ( k) and the turbulence sources are correlated. An extremely high k generated by the intake jet during the intake process was observed, and it remains only 1.6%–3.3% during the later compression stroke. Near the cylinder center, k changes significantly with the crank angle and the higher k was always observed near the swirl center. The production via shear stresses correlates with k well. In other regions, k almost keeps unchanged with the crank angle because of the rigid-body-like swirl flow, which results in a negligible net production by flow deformation. In addition, in the middle region, the evolution of radial angular momentum gradient matches with the k evolution reasonably well, which indicates that k may depend on the transport by the squish flow although the underlying physics deserves further exploration.

Multiwavelength High-resolution Observations of Chromospheric Swirls in the Quiet Sun

Abstract We report observations of small-scale swirls seen in the solar chromosphere. They are typically 2 Mm in diameter and last around 10 minutes. Using spectropolarimetric observations obtained by the CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope, we identify and study a set of swirls in chromospheric Ca ii 8542 Å and Hα lines as well as in the photospheric Fe i line. We have three main areas of focus. First, we compare the appearance, morphology, dynamics, and associated plasma parameters between the Ca ii and Hα channels. Rotation and expansion of the chromospheric swirl pattern are explored using polar plots. Second, we explore the connection to underlying photospheric magnetic concentration (MC) dynamics. MCs are tracked using the SWAMIS tracking code. The swirl center and MC remain cospatial and share similar periods of rotation. Third, we elucidate the role swirls play in modifying chromospheric acoustic oscillations and found a temporary reduction in wave period during swirls. We use cross-correlation wavelets to examine the change in period and phase relations between different wavelengths. The physical picture that emerges is that a swirl is a flux tube that extends above an MC in a downdraft region in an intergranular lane. The rotational motion of the MC matches the chromospheric signatures. We could not determine whether a swirl is a gradual response to the photospheric motion or an actual propagating Alfvénic wave.

Effects of Squish Flow on Tangential Flow and Turbulence in a Diesel Engine

Emission and fuel consumption in swirl-supported diesel engines strongly depend on the in-cylinder turbulent flows. But the physical effects of squish flow on the tangential flow and turbulence production are still far from well understood. To identify the effects of squish flow, Particle image velocimetry (PIV) experiments are performed in a motored optical diesel engine equipped with different bowls. By comparing and associating the large-scale flow and turbulent kinetic energy (k), the main effects of the squish flow are clarified. The effect of squish flow on the turbulence production in the r−θ plane lies in the axial-asymmetry of the annular distribution of radial flow and the deviation between the ensemble-averaged swirl field and rigid body swirl field. Larger squish flow could promote the swirl center to move to the cylinder axis and reduce the deformation of swirl center, which could decrease the axial-asymmetry of annular distribution of radial flow, further, that results in a lower turbulence production of the shear stress. Moreover, larger squish flow increases the radial fluctuation velocity which makes a similar contribution to k with the tangential component. The understanding of the squish flow and its correlations with tangential flow and turbulence obtained in this study is beneficial to design and optimize the in-cylinder turbulent flow.

Evaluation of Ramp-Type Micro Vortex Generators Using Swirl Center Tracking

The evolution of the primary vortex pair downstream of micro vortex generators placed in a supersonic stream is compared using a swirl center tracking technique, for standard, slotted, and split-ramp-type vortex generators. Evolution of vortex strength, determined using circulation, and distribution of vortices, determined using contours of helicity, are also compared. Results show that secondary vortices emerge stronger, and liftoff heights drop, with the introduction of slot (slotted micro vortex generator) or gaps (split-ramp micro vortex generator). Near-surface contours of axial velocity and integral properties of the boundary layer are then compared to evaluate the effects of the evolution of the vortical structures on the flowfield. Results shows that the split-ramp device results in the most energetic near-surface flow but the worst outgoing boundary-layer integral properties, whereas the slotted-ramp devices with taper fare well on both counts. The computations performed in this work involve supersonic flow past single micro vortex generators at Mach 2.5 and use an immersed-boundary method to render the control devices. The flow solver is suitable for high-speed turbulent flows and has been extensively validated in earlier works. The turbulence model used is Menter’s shear-stress transport version.

정상유동 장치에서 유동 특성 평가 방법에 대한 연구(4) - 유속분포(2)

This paper is the forth investigation on the evaluation methods of flow characteristics in a steady flow bench. In the previous works, it was concluded that the assumption of the solid rotation might cause serious problems and both of the eccentricity and the velocity profile distort the flow characteristics when using the ISM at 1.75B plane. Also particle image velocimetry (PIV) measurement at this position showed that the real velocity profile was far from the assumption of ISM evaluation. In this paper, the planar velocity profiles were measure from 1.75B to 6.00B position by PIV and the characteristics were examined according to the valve angles and lifts for further investigations about the effect of the position on the velocity profile. The results show that <TEX>$26^{\circ}$</TEX> valve angle is always an unique exceptional case in all aspects. If the valve angle is <TEX>$21^{\circ}$</TEX> and below, the planar velocity profiles according to the lift and the position are similar to each other, however, the tangential velocity curves along with the radial direction have common tendencies up to <TEX>$16^{\circ}$</TEX> angle. Also the well arranged swirl behaviors are generally observed at the position above 3.00B and the velocity contour lines come closer to the concentric circle as the valve lift increases. In addition, the gradient of tangential velocity along with the radial direction from the swirl center becomes stable and constant as the position goes downstream. Concurrently the velocity gradient is larger to the eccentric direction of the center. In the meantime the tangential velocity curves along with the radial direction are irregular and various at 1.75B, however, they become regular and reach higher level as the evaluation position goes downstream. At this time the curves of 4.50B are the best fitted to the ideal one. On the other hand in an exceptional case, <TEX>$26^{\circ}$</TEX>, the velocity contours are very complicated over 6mm valve lift regardless the position and the gradient increases to the opposite direction of the eccentric center. Also, 6.00B is a best fitting position in the geometrical cylinder center base. With respect to the swirl center, the distribution range of centers for 1.75B is different to that for the other positions and the eccentricities of this plane are larger regardless the valve angle. After 1.75B, there is no certain tendency in the center position change according to the valve angle and lift. Additionally, the eccentricities are not sufficiently small to neglecting the effect on ISM measurement.

정상유동 장치에서 유동 특성 평가 방법에 대한 연구(1) - 문제의 제기

Abstract : This paper is the first investigation on the evaluation methods of flow characteristics in the steady bench. For this purpose, several assumptions used in the steady flow evaluation are examined, comparing the measured and/or processed results by the conventional impulse swirl meter with the ones by the real velocity through a particle image velocimetry. The results show that the most questionable assumption is the solid rotation of swirl. With regard to this assumption, the flow characteristics by the conventional methods are distorted seriously by both of the eccentricity of the swirl center and non-uniform velocity profile along the cylinder radial direction. In addition, the cylinder axial velocity distribution also has the great effect on the flow characteristics. Key words : Steady flow bench(정상유동장치), Swirl(스월), Impulse swirl meter(충격식 스월 측정기), PIV(입자영상유속계), Velocity profile(속도분포), Eccentricity(편심) Nomenclature 1)  : area of valve inner seat, m 2  : cylinder bore, m

Variations of swirl center according to evaluation position in steady flow bench of SI engine

In this study, the variations of swirl center according to evaluating position have been investigated in a steady flow bench of SI engine. For the experiments, two engine heads with different intake valve angles (11°and 26°) were tested in the flow bench by varying the evaluating position (1.75~6.0B) and valve lift (2~10 mm). Particle image velocimetry was used to measure the velocity field inside the engine cylinder. The swirl center position is found with a critical point theory and the intensity of turbulence is calculated from PIV velocity data. The results show that the center of swirl is located closer to the center of cylinder and turbulence intensity is lower, when the intake valve angle is the smaller. It is conventional to evaluate the swirl ratio at 1.75B position in the steady flow bench of SI engine. At this position, however, the distance of swirl center from the cylinder center scatters significantly for the variation of valve lift, and the turbulence intensity is much stronger regardless of the valve angle. Thus, to estimate the flow at the end of compression stroke in a real engine from the data in the steady flow experiments, the evaluation position should be moved further downstream more than 4.5B.

Swirl-Based Control Method of Cell Orientation-Impact on Control Performance with Eccentricity

The adjustment of cell position and orientation is important in cell micromanipulation of bioengineering, which directly affects the efficiency and success ratio of the micromanipulation. Cell orientation can be adjusted by swirl, which comes from a pair of parallel opposite micro-fluids from two tiny tubes, and the cell in swirl center will rotate. Quantitative control of rotation angle and velocity of the cell can be achieved by adjusting the velocity and frequency of micro-fluid. This control method of cell orientation has prospective applications for its non-contact characteristics. However, cell will not be right in the swirl center in practical operations. And if the eccentric cell can rotate steadily, swirl method will be more reliable. So numerical simulation was conducted to study the movement trajectory of cells with eccentricity, and the influences of eccentric directions and eccentric distances were discussed. The simulation results indicate the feasibility of orientation control of cells with eccentricity by swirl.

Turbulent swirling flow in a model of a uniflow-scavenged two-stroke engine

The turbulent and swirling flow of a uniflow-scavenged two-stroke engine cylinder is investigated using a scale model with a static geometry and a transparent cylinder. The swirl is generated by 30 equally spaced ports with angles of 0°, 10°, 20°, and 30°. A detailed characterization of the flow field is performed using stereoscopic particle image velocimetry. Mean fields are calculated using both a fixed coordinate system and a coordinate system based on the instantaneous flow topology. Time-resolved measurements of axial velocity are performed with laser Doppler anemometry, and power spectra are calculated in order to determine vortex core precession frequencies. The results show a very different flow dynamics for cases with weak and strong swirl. In the strongly swirling cases, a vortex breakdown is observed. Downstream of the breakdown, the vortex becomes highly concentrated and the vortex core precesses around the exhaust valve, resulting in an axial suction effect at the vortex center. Mean fields based on the instantaneous flow topology are shown to be more representative than mean fields based on a fixed coordinate system in cases with significant variations in the swirl center location.

Size-scaling effect on the velocity field of an internal combustion engine, part I: Bulk motion

In-cylinder velocity measurements were acquired to study the bulk fluid motion in two geometrically scaled, two-valve, optically accessible, and single-cylinder research engines. Different port geometries (two), different port orientations (two), and both shrouded and nonshrouded intake valves were tested to vary the intake-generated flow. The engines were motored at speeds ranging from 300 to 1200 r/min for the larger engine and from 600 to 1800 r/min for the smaller engine. Prior to testing on the engines, the different head configurations were tested on a steady flow bench. Particle image velocimetry data were taken on a single plane, parallel to the piston surface, in the engines to characterize the large-scale flow phenomena. The mean location of the swirl center and the mean angular velocity were determined by fitting a solid-body profile to the flow. The results showed that the swirl center location was relatively insensitive to engine speed for both engines, but did change position throughout the cycle. The swirl center locations, scaled by the cylinder radii, were found to be in nearly the same location for the two-scaled engines in the same nominal configuration, indicating that the swirl center motion was deterministic in nature. Normalizing the best-fit solid-body angular velocity by the engine rotation rate was found to collapse the data from the multiple engine speeds nearly onto a single curve for a given engine configuration. The angular velocity was found to decrease with crank angle due to wall friction, which was higher for the small engine because of the higher surface-to-volume ratio.

Three-Dimensional Computational Fluid Simulation of Diesel and Dual Fuel Engine Combustion

A 3D computational fluid dynamics model with a reduced detailed chemical kinetics of the combustion of diesel and methane fuels is developed while considering turbulence during combustion to simulate the mixture flow, formation, and combustion processes within diesel and diesel/methane dual fuel engines having swirl chambers. The combustion characteristics of the pilot injection into a small prechamber are also investigated. Modeled results were validated by a group of corresponding experimental data. The spatial and temporal distributions of the mixture temperature, pressure, and velocity under conditions with and without liquid fuel injection and combustion are compared. The effects of engine speed, injection timing, and the addition of carbon dioxide on the combustion process of dual fuel engines are investigated. It is found that in the absence of any fuel injection and combustion, the swirl center is initially formed at the bottom-left of the swirl chamber, and then moved up with continued compression in the top-right direction toward the highest point. The swirling motion within the swirl and main combustion chambers promotes the evaporation of the liquid pilot and the combustion processes of diesel and dual fuel engines. It was observed that an earlier autoignition can be obtained through injecting the pilot fuel into the small prechamber compared with the corresponding swirl chamber operation. It is to be shown that reduced engine emissions and improved thermal efficiency can be achieved by a two-stage homogenous charge compression ignition combustion.

B‐flow sonographic demonstration for assessing carotid atherosclerosis in young patients with heterozygous familial hypercholesterolemia

To determine whether bloodstream swirls detected with B-mode flow (B-flow) sonography at the region of the carotid bifurcation can predict the early progression of atherosclerosis, we prospectively examined the relationships between the size of bloodstream swirls as identified with B-flow sonography, the local mechanical behavior of the common carotid artery (CCA), and some cardiovascular risk factors in young patients with heterozygous familial hypercholesterolemia (FH). Thirty-eight young patients (mean age 25.8 +/- 14.1 years) with FH were evaluated for the following parameters: age, sex, body mass index, degree of dyslipidemia, presence of a plaque, intima-media thickness (IMT), elastic modulus (Ep) and internal diameter of the CCA via duplex scan, wall shear stress, maximal diameter of the bloodstream swirl (Sm) at bifurcation, maximal diameter of the CCA (Cm) at the level of the swirl's center, and diameter ratio (Sm/Cm) via B-flow sonography. Bloodstream swirls of varying size at the site of bifurcation were observed in all patients. Six (15.7%) out of 38 patients exhibited plaques at bifurcation. All plaques were located at the far wall and were in contact with the distal portion of the bloodstream swirl as observed with B-flow sonography. Univariate analysis revealed that Sm/Cm and Sm were positively correlated with age, presence of a plaque, IMT, and Ep and were negatively correlated with shear stress. Multivariate analysis revealed that Sm was significantly correlated with age (P < 0.01) and Ep (P < 0.05). Our results suggest that a bloodstream swirl visualized at the carotid bifurcation with B-flow sonography may be an indicator of a local mechanism for the age-related progression of atherosclerosis in young patients with FH.

Swirling flow structures in electrostatic precipitator

Stereoscopic digital Particle Image Velocimetry (PIV) has been used to make a three-dimensional flow mapping of a volume of approximately 0.1 × 0.1 × 0.15 m in a laboratory model electrostatic precipitator (ESP). The mapped volume covers about two unit cells determined by the 100 mm electrode spacing in the 0.2 × 0.2 × 1.0 m ESP test section of the negative corona, barbed wire, smooth-plate kind. The barbs act as corona fix points, yielding a three-dimensional electrostatic field. The induced large-scale secondary gas velocity structures in the form of unsteadily undulating axial rolls have been analyzed for swirlnumber and location of instantaneous swirl center in 11 axial planes. The flow possesses high levels of turbulence and axial vorticity. Measured particle velocities are corrected for electrical drift to produce gas velocities. Subsequently experimental results are compared to Large Eddy Simulation (LES) results.

Swirling Flows in a Circular-Sectioned 90.DEG. Bend.

Three components of mean velocities and wall static pressure have been measured in swirling flows through a circular-sectioned 90°bend with a curvature radius ratio of 4.0 under the Reynolds number of 60000. The complicated correlation between internal flow behavior and wall pressure distribution has been clarified from a region of upstream straight pipe through a bend to a down-stream one. Also, the shift of axial flow, the movement of the swirl center and the streamwise decay of swirl intensity have been investigated.

Experimental Study of the Swirling Flow in the Volute of a Centrifugal Pump

Detailed three-dimensional velocity distributions, corresponding to design and off-design operation, were measured in two different circumferential cross sections of a volute by means of LDV. It is shown that the swirl has a forced vortex type velocity distribution and that the location of the swirl center changes with mass flow. The throughflow velocity distribution is primarily defined by the conservation of angular momentum. A strong interaction between the throughflow and swirl velocity is observed. Flow visualization in the tongue region reveals a reversal of the velocity at the volute inlet with increasing mass flow. The pressure drop between volute outlet and inlet at low mass flow pushes extra fluid through the tongue gap and increases the mass flow in the volute. The abrupt pressure rise at high mass flow results in local return flow perturbing the flow in the outlet pipe.

Flow visualization measurement of in-cylinder flow by high-speed photographs using an electro-optical shutter

The flow visualization technique was used to measure the in-cylinder flow of an internal combustion engine. Many papers have been published about flow velocity in a cylinder determined with a laser-Doppler velocimeter or hot-wire anemometer to analyze the flow characteristics, but the data are generally for only one point of the cylinder. In this study, metaldehyde was used as a tracer particle for the gas flow and was supplied to an engine specially designed for flow visualization. To photograph the particle path, an electrooptical shutter (PLZT) was adopted because of its electrical controllability. The flow velocity obtained by this measuring system and with laser-Doppler anemometry were compared to examine the measuring system. The trends were almost in agreement, which demonstrates the validity of the measuring system. Two examples of the measured velocity were shown. One is that in-cylinder flow varies cyclically and differences in velocity exist on the same radius at the same moment. The other is that the axis of the swirl center changes considerably during each stroke. The swirl center of the flow was calculated from each particle path, and it was found that the swirl center nearly coincides with the cylinder center near top dead center though it does not at the compression or expansion stroke. Further examinations are required to adapt this technique to three-dimensional flow fields as the system is applicable to the two-dimensional plane.

B111 遠心力場における消炎と火炎構造

By making use of the rotary cylinder combustion device which rotates with the combustible mixture in it, the real effects of the centrifugal force environment in the solid vortex on the flame behaviors are examined. The observed results show the enhanc-ed combustion by the swirl is not always expected, because of the rapid motion of a flame kernel to the swirl center, and the laminarization of turbulent flame. The propaga-tion speed of the flame initiated near the swirl center is considerably reduced, and in some cases, depending on the flame structure, vanishes to extinguish the flame.