Swirling Flow Pattern Research Articles

Blend Tool Design using CFD

A method to utilize computational fluid dynamics (CFD) as a modeling tool to predict the mixing blend tool dynamics is presented. Blender and various tool geometries have been analyzed and computational grids have been created using commercially available CFD software. Simulations have been performed at various rotational tool speeds, treating the toner particle in air as a pseudo-homogenous single phase fluid while utilizing the K-ω turbulence model for the strongly swirling flow pattern. In addition to flow observations, the total moment of the tool surfaces and tool wall shear stress have also been measured as critical blending parameters. The tool area weighted average shear stress and integral tool shear stress have been found to respond to the various tool configuration simulated, suggesting that certain tool configurations have an increased blending functional efficiency for additive distribution and attachment.

CFD study of a simple orifice pulse tube cooler

Pulse tube cooler (PTC) has the advantages of long-life and low vibration over the conventional cryocoolers, such as G-M and Stirling coolers because of the absence of moving parts in low temperature. This paper performs a two-dimensional axis-symmetric computational fluid dynamic (CFD) simulation of a GM-type simple orifice PTC (OPTC). The detailed modeling process and the general results such as the phase difference between velocity and pressure at cold end, the temperature profiles along the wall as well as the temperature oscillations at cold end with different heat loads are presented. Emphases are put on analyzing the complicated phenomena of multi-dimensional flow and heat transfer in the pulse tube under conditions of oscillating pressure. Swirling flow pattern in the pulse tube is observed and the mechanism of formation is analyzed in details, which is further validated by modeling a basic PTC. The swirl causes undesirable mixing in the thermally stratified fluid and is partially responsible for the poor overall performance of the cooler, such as unsteady cold-end temperature.

AMRVAC and relativistic hydrodynamic simulations for gamma-ray burst afterglow phases

We apply a novel adaptive mesh refinement (AMR) code, AMRVAC (Adaptive Mesh Refinement version of the Versatile Advection Code), to numerically investigate the various evolutionary phases in the interaction of a relativistic shell with its surrounding cold interstellar medium (ISM). We do this for both ID isotropic and full 2D jet-like fireball models. This is relevant for gamma-ray bursts (GRBs), and we demonstrate that, thanks to the AMR strategy, we resolve the internal structure of the shocked shell-ISM matter, which will leave its imprint on the GRB afterglow. We determine the deceleration from an initial Lorentz factor y = 100 up to the almost Newtonian y ∼ 0(2) phase of the flow. We present axisymmetric 2D shell evolutions, with the 2D extent characterized by their initial opening angle. In such jet-like GRB models, we discuss the differences with the ID isotropic GRB equivalents. These are mainly due to thermally induced sideways expansions of both the shocked shell and shocked ISM regions. We found that the propagating 2D ultrarelativistic shell does not accrete all the surrounding medium located within its initial opening angle. Part of this ISM matter gets pushed away laterally and forms a wide bow-shock configuration with swirling flow patterns trailing the thin shell. The resulting shell deceleration is quite different from that found in isotropic GRB models. As long as the lateral shell expansion is merely due to ballistic spreading of the shell, isotropic and 2D models agree perfectly. As thermally induced expansions eventually lead to significantly higher lateral speeds, the 2D shell interacts with comparably more ISM matter and decelerates earlier than its isotropic counterpart.

Swirling flow pattern in a non-planar model of an interposition vein cuff anastomosis

One of the main causes of long-term failure of ePTFE grafts is the development of anastomotic intimal hyperplasia which leads to graft thrombosis. Experimental studies with bypass grafts have shown an inverse relationship between mean wall shear stress and intimal hyperplasia. The geometry of the anastomosis has a strong influence on the flow pattern and wall shear stress distribution. The aim of this in vitro study was to investigate the influence of non-planarity in a model of a distal anastomosis with interposition vein cuff, an anastomosis configuration that is increasingly being used because of improved clinical results. Laser Doppler anemometer measurements were carried out in silicone rubber models of interposition vein cuff anastomoses with planar and non-planar inflow. The pulsatile flow waveforms were typical of those found in femoro-infrapopliteal bypass. Axial and radial velocities were measured in the proximal and distal outflow segments. As expected a symmetrical helical flow pattern (Dean flow) was evident in the planar model. The model with non-planar inflow, however, gave rise to swirling flow in both the distal and proximal artery outflow segments for during the systolic phase. In patients, the anastomosis is usually non-planar. Since the configuration depends in part upon the tunnelling of the graft, this may be altered to some extent. Non-planar anastomotic configurations induce a swirling flow pattern, which may normalise wall shear stress, thereby potentially reducing intimal hyperplasia.

Characterization of a cyclone spray chamber for ICP spectrometry by computer simulation

The aerosol transport and modification in a typical cyclone spray chamber for ICP spectrometry is simulated for the first time by computational fluid dynamics (CFD). Information that is not accessible experimentally can be gained, for example, about the droplet deposition at different places on the walls inside the chamber. The numerical prediction of the argon flow inside the spray chamber shows a typical swirling flow pattern, as expected in a cyclone chamber. The cyclone spray chamber works primarily like an impact chamber with regard to the deposition behaviour of the aerosol droplets, and not as a typical cyclone used in technical areas. The largest share of the nebulized sample (∼36%) is impacted directly onto the surface in front of the nebulizer. Approximately 17% is deposited on the rest of the curved surface in the plane of the nebulizer. About 29% is collected on the conical bottom, and ∼15% on the conical top of the spray-chamber, respectively. The simulation predicted a value of 2.0% for the aerosol yield at the outlet of the chamber; the experimentally determined value amounted to 2.4%. As can be seen from a comparison of the results obtained from experiment and CFD, computer simulation can be considered as a modern tool for helping to shed light on the processes occurring in spray chambers and for the prediction of their analytical performance.

Visualization of flow fields in a Bubble Eliminator

Bubbles and dissolved gases in liquids greatly influence the performance of fluid power systems, coating solutions, plants in the food industry and so on. To eliminate bubbles from working fluids and to prevent degradation of liquids as well as to avoid possible damage of fluid components is an important engineering issue. Recently one of the authors, Ryushi Suzuki, has developed a new device using swirling flow with the capability of eliminating bubbles and of decreasing dissolved gases in fluids. This device is called "Bubble Eliminator." The swirling flow pattern and pressure distributions in the bubble eliminator greatly influence the effective performance of the bubble removal. In this paper the swirl flow pattern in a transparent bubble eliminator is experimentally visualized and processed as digital images by a high-speed video camera system. Velocity profiles and pressure distributions in the bubble eliminator are calculated and graphically visualized by a three-dimensional numerical simulation. The results of the flow visualization are compared with the numerical simulation. The performance evaluation of the bubble removal effectiveness is numerically and experimentally verified. It is also proposed to augment understanding of 3D flow fields for the swirling flow in the bubble eliminator with scientific flow visualization methods, which combine graphics or real images with haptic displays.

Power Doppler-derived speckle tracking image of intraventricular flow in patients with anterior myocardial infarction: correlation with left ventricular thrombosis

The abnormal spatial distribution of intraventricular flow is superior to clinical and two-dimensional (2-D) echocardiographic variables in predicting left ventricular thrombosis after myocardial infarction. Echocardiography was prospectively performed in 79 patients within 72 h after anterior wall myocardial infarction onset and repeated before discharge. The apical rotating flow pattern in color flow map was recognized as abnormal. By power Doppler echocardiography, the moving blood could generate speckle tracking images to delineate the intraventricular flow. A swirling flow pattern indicating the compartmentalization of left ventricular blood flow with some blood stagnant in the apical dyssynergic area was identified. The flow pattern shown by the speckle tracking image was superior to the color-flow map in correlating with left ventricular thrombosis. It implicated that the more the detail in which we can describe the blood flow pathway, the more information we can realize.

Swirling flows in circular-to-rectangular transition ducts

Swirling flows in three circular-to-rectangular transition ducts, each of them with an aspect ratio of 2.0 at the rectangular exit, have been studied experimentally. The swirling flows were produced by swirlers whose vane angles were at 5°, 10° and 20° inclinded to the incoming flow, respectively. Flow visualization experiments were made at selected cross-sectional planes in the transition ducts. Pressure and velocity measurements were obtained on the contoured duct walls and at the rectangular exit planes, respectively. The results show that the swirling flow pattern evolves into a skewed structure at the exit plane which, in connection with the wall pressure distributions, is asymmetric with respect to the centerline of either the top and bottom walls or the side walls. Moreover, an analysis based on the mean streamwise vorticity equation with the velocity data obtained immediately downstream of the rectangular exit plane indicates that the cross-stream Reynolds stress plays an important role in transporting the streamwise vorticity of the swirling flow into the surrounding fluid.

Study of Flame Stability in a Step Swirl Combustor

A prime requirement in the design of a modern gas turbine combustor is good combustion stability, especially near lean blowout (LBO), to ensure an adequate stability margin. For an aeroengine, combustor blow-off limits are encountered during low engine speeds at high altitudes over a range of flight Mach numbers. For an industrial combustor, requirements of ultralow NOx emissions coupled with high combustion efficiency demand operation at or close to LBO. In this investigation, a step swirl combustor (SSC) was designed to reproduce the swirling flow pattern present in the vicinity of the fuel injector located in the primary zone of a gas turbine combustor. Different flame shapes, structure, and location were observed and detailed experimental measurements and numerical computations were performed. It was found that certain combinations of outer and inner swirling air flows produce multiple attached flames, aflame with a single attached structure just above the fuel injection tube, and finally for higher inner swirl velocity, the flame lifts from the fuel tube and is stabilized by the inner recirculation zone. The observed difference in LBO between co- and counterswirl configurations is primarily a function of how the flame stabilizes, i.e., attached versus lifted. A turbulent combustion model correctly predicts the attached flame location(s), development of inner recirculation zone, a dimple-shaped flame structure, the flame lift-off height, and radial profiles of mean temperature, axial velocity, and tangential velocity at different axial locations. Finally, the significance and applications of anchored and lifted flames to combustor stability and LBO in practical gas turbine combustors are discussed.

Control of Immersion Nozzle Outlet Flow Pattern through the Use of Swirling Flow in Continuous Casting.

A water model is used to investigate the effect of imparting a swirl flow in the entrance region of a nozzle. The study is aimed at the injection region of continuous casting process. The purpose is to make the injection velocity more uniform and so reduce the disturbance of the free surface. It was shown using the water model that a uniform outlet flow could be obtained by imposing a swirling flow pattern in the entrance region of a divergent nozzle. This suggests that the outlet flow pattern in a continuous caster may be controlled by introducing swirl flow in the molten metal using an externally imposed magnetic field.

Numerical Analysis of the Unsteady Gap Flow between Corotating Disks through the Finite-Element Method.

The unsteady flow fields in a narrow-gap flow between two corotating circular disks are investigated numerically by solving the time-dependent Navier-Stokes equations through the SMAC-FEM (simplified marker and cell finite-element method). In each triangular torus element, quadratic velocity elements and a linear pressure element are used. The conclusions are as follows. (1) When disks suddenly start rotating, they induce a secondary flow in the gap flow. As the primary swirling flow pattern develops into a nearly solid rotation, the secondary flow grows and then becomes very weak. (2) Since the viscous force is weaker in the gap flow with larger Reynolds number, the secondary flow is stronger in the early period. (3) The torque coefficients on both sides of a rotating disk decrease rapidly and then become constant. These constants are much smaller than that for a rotating disk in a stationary housing.

Airflow in the Cylinder of a 2-Stroke Cycle Uniflow Scavenging Diesel Engine During Compression Stroke

The scavenging process of a 2-stroke cycle engine dominates not only fresh-air charging but also the airflow in a cylinder at the compression end. So, the combustion performance of a 2-stroke cycle diesel engine depends on scavenging efficiency ηs, and the scavenging-air swirl intensity in the cylinder. In this report, first, the scavenging airflow is investigated by operating a 2-stroke cycle engine rig. From the LDV measurement of the air velocity in a cylinder during the compression stroke, it is shown that the scavenging port made by the combination of a large-angle port and a small-angle port has high scavenging ability and sufficient swirl intensity for air-fuel mixing. Secondly, the numerical analysis method of the gas flow in a cylinder during the compression stroke is developed. This method employs an approximation of a 2-D axisymmetrical flow to save computation time, but uses, for the initial condition, the calculated results of a 3-D scavenging flow simulation to ensure the accuracy of the starting swirl-flow pattern which is deeply affected by the port arrangement. Some calculated results are compared with the experimental data, and it is concluded that this method can simulate the flow pattern in a cylinder during the compression stroke with good accuracy.

On airflow in the cylinder of a two-stroke-cycle uniflow scavenging diesel engine at the compression stroke. (2nd Report, Numerical analysis).

The swirl flow at a compression stroke in a cylinder of the two-stroke-cycle uniflow scavenging diesel engine plays a very important role in the combustion performance. In this report, the numerical analysis method of the gas flow in a cylinder at the compression stroke is developed. This method is proceeded by and approximation of a 2-D axisymmetrical flow to save computation time, but uses, for the initial condition, the calculated results of a 3-D scavenging flow simulation to ensure the accuracy of the starting swirl flow pattern which is deeply affected by the port arrangement. Some calculated results are compared with the experimental data of a model engine, and it is concluded that this method can simulate the flow pattern in s cylinder at the compression stroke with good accuracy.

Computational Fluid Dynamics Applied to Three-Dimensional Nonreacting Inviscid Flows in an Internal Combustion Engine

The three-dimensional inviscid flowfield between the face of the piston and the top of the cylinder in a reciprocating internal combustion engine is calculated for a complete four-stroke cycle (intake, compression, power, exhaust). The fluid dynamic aspects are emphasized; combustion is simply modeled by constant-volume heat addition. The computational method is an explicit time-dependent finite-difference solution of the governing fluid dynamic equations. The results show that a well-defined three-dimensional swirling flow pattern is established during the intake stroke, and that this swirl persists throughout the complete four-stroke cycle. Such a flowfield will have direct influence on I.C. engine combustion phenomena. Moreover, the radial distributions of pressure and temperature show a nearly-axisymmetric behavior, while the three-dimensional results in the valve plane show a striking similarity to previous two-dimensional results. The present investigation is the first three-dimensional calculation of the flowfield for all four strokes, and has important implications for future work in the application of computational fluid dynamics to I. C. engine analysis.