Swirl Vortex Research Articles

Improved assessment of aortic 3D blood flow with combined k-t accelerated 3D CINE bSSFP & 4D flow MRI

Background To determine hemodynamic parameters from 4D flow MRI, vessel boundaries are typically depicted by calculating a 3D phase contrast MR angiogram (PC-MRA) from 4D flow magnitude and flow images. However, this approach is limited by 1) low blood-tissue contrast of the magnitude images and 2) velocity weighting of PC-MRA may not fully depict areas of slow or swirling (vortex) flow. As a result, 3D flow analysis at the aortic root has been challenging due to the presence of vortex flow distal to the aortic valve. Fast 3D balanced steady state free precession (bSSFP) time-resolved MRI sequences offer a promising alternative, providing anatomical images with improved blood-tissue contrast. The goal of this feasibility study was to integrate results from 3D CINE bSSFP with 4D flow MRI to improve the segmentation of vessel anatomy and thus 3D blood flow assessment compared to standard segmentation using PC-MRA data alone.

Improving flow performance of irrigation pump station intake

The Irrigation Improvement Project is being implemented at a national scale in Egypt with a target of improving the old irrigation system in the Nile Delta for increasing water-use efficiency and agricultural production. The objective of this research is to study the influence of existing circular sump shape on the flow conditions of tertiary canals (mesqa) pump station. Field measurements were conducted on the Efrank (1) mesqa pumping station. Three-dimensional Computational Fluid Dynamics model solved the Unsteady Reynolds-Averaged Navier–Stokes equations for predicting the occurrence of vortices and swirl in pump intakes. In this study, three different modifications were done. The research shows that existing circular sump shape generates swirl flow. The submerged cone under suction pipes does not reduce the swirl flow and vortex. The installation of vertical splitter wall between the two vertical suction pipes reduces the pre-swirling surface flow and improves the pump performance.

The evolution of swirling axisymmetric vortex rings

Swirling vortex rings form in any turbulent flow where a swirling component is present, such as in combustion chambers or the downwash of helicopter blades. Instabilities on initially non-swirling vortex rings result in a localized swirl velocity being generated within the core. The presence of a swirl component of velocity in a vortex ring modifies the relaxation and evolution of numerical Gaussian cores in a manner that is currently unknown. The evolution of Gaussian axisymmetric vortex rings of size 0.2 < Λ < 0.5, with Gaussian swirls of magnitude 0.0 < W < 0.5, is analyzed with reference to the governing equations. A relaxation time, at which the initial Gaussian approximation has minimal influence on the subsequent evolution, has been estimated for each case. An axial vortex forms along the axis of the ring and is responsible for the growth of a shear layer that is found to form at the leading edge. The circulation based Reynolds number is set at 10 000 to encourage the growth of shear layer instabilities from within this region. Secondary vortex rings are subsequently shown to evolve from the Kelvin-Helmholtz instability for shear layers of sufficient strength and are convected around the original ring and shed from the system. It is shown that complete settling of the strain rate within the core does not occur until all sheddings have ceased. Increasing the swirl magnitude past that considered in this paper is expected to result in the original ring losing its structure before the instability can occur. The evolution is found to be qualitatively similar to that of a piston generated axisymmetric vortex ring with swirl, with both cases eventually reaching a similar quasi-steady state.

Hydro-mechanical foundation for blood swirling vortex flows formation in the cardio-vascular system and the problem of artificial heart creation

Abstract Leonardo da Vinci perhaps was the first who paid attention to the energetic efficiency of existence of vortices emerging near sines of Valsalva and defining normal functioning (opening) of aortal valve. However up to now a fundamental problem of defining of mechanisms of mysterious energetic efficiency of functioning of cardio-vascular system (CVS) of blood feeding of the organism is still remaining significantly not solved and this is, for example, one of the main restriction for the creation of artificial heart and corresponding valve systems. In the present paper, results witnessing possible important role of the very hydro-mechanical mechanism in the realization of the noted energetic efficiency of CVS due to formation in the CVS of spiral structural organization of the arterial blood flow observed by methods of MRT and color Doppler-measuring in the left ventricular of the heart and in aorta (A.Yu.Gorodkov,et.al.).

Interaction Between Swirl Number Fluctuations and Vortex Shedding in a Single-Nozzle Turbulent Swirling Fully-Premixed Combustor

Flame response to imposed velocity fluctuations is experimentally measured in a single-nozzle turbulent swirling fully-premixed combustor. The flame transfer function is used to quantify the flame's response to imposed velocity fluctuations. Both the gain and phase of the flame transfer function are qualitatively similar for all operating conditions tested. The flame transfer function gain exhibits alternating regions of decreasing gain with increasing forcing frequency followed by regions of increasing gain with increasing forcing frequency. This alternating behavior gives rise to gain extrema. The flame transfer function phase magnitude increases quasi-linearly with increasing forcing frequency. Deviations from the linear behavior occur in the form of inflection points. Within the field, the current understanding is that the flame transfer function gain extrema are caused by the constructive/destructive interference of swirl number fluctuations and vortex shedding. Phase-synchronized images of forced flames are acquired to investigate the presence/importance of swirl number fluctuations, which manifest as fluctuations in the mean flame position and vortex shedding in this combustor. An analysis of phase-synchronized flame images reveals that mean flame position fluctuations are present at forcing frequencies corresponding to flame transfer function gain minima but not at forcing frequencies corresponding to flame transfer function gain maxima. This observation contradicts the understanding that flame transfer function gain maxima are caused by the constructive interference of mean flame position fluctuations and vortex shedding, since mean flame position fluctuations are shown not to exist at flame transfer function gain maxima. Further analysis of phase-synchronized flame images shows that the variation of the mean flame position fluctuation magnitude with forcing frequency follows an inverse trend to the variation of flame transfer function gain with forcing frequency, i.e., when the mean flame position fluctuation magnitude increases, the flame transfer function gain decreases and vice versa. Based on these observations it is concluded that mean flame position fluctuations are a subtractive effect. The physical mechanism through which mean flame position fluctuations decrease flame response is through the interaction of the flame with the Kelvin–Helmholtz instability of the mixing layer in the combustor. When mean flame position fluctuations are large the flame moves closer to the mixing layer and damps the Kelvin–Helmholtz instability due to the increased kinematic viscosity, fluid dilatation, and baroclinic production of vorticity with the opposite sign associated with the high temperature reaction zone.

Investigation on Flow Field of Cyclone Separator Used in Circulating Fluidized Bed Boiler

The Reynolds stress model (RSM) provided by FLUENT software was applied to study flow field of a cyclone separator used in some circulating fluidized bed. The pressure distribution and velocity distribution was analyzed. The simulation results reveal the strong swirling flow and vortex structure in cyclone separator.

The effects of injection pressure and swirl on in-cylinder flow pattern and combustion in a compression–ignition engine

In-cylinder swirl flow is well known to influence emissions behaviour in diesel engine combustion. The post-oxidation part of the combustion stands for typically 25 - 45 % of total Heat Release and is of paramount importance for engine out particulate matter (PM) emissions, especially during an engine transient, at low λ. To investigate the link between in-cylinder flow and engine out emissions, single-cylinder and optical engine measurements were performed. Injection pressure, swirl and tumble were varied, and emission data, together with high speed photography of in-cylinder flow field during the injection- and the post-oxidation events, were measured. Particle image velocimetry (PIV) software was used to evaluate the flame luminescence images and to calculate the flow field in the cylinder, crank angle resolved during combustion. The glowing soot structures from the combustion were used as tracers. Single cylinder tests with an active valve train were used, which gave a controlled variation in swirl number, 0.4 to 6.7, and tumble number, 0.5 to 4.0. The main findings is that the injection pressure strongly affects the flow field in the cylinder, both before and during the post-oxidation period. Correlations between measured engine out soot emissions and changes in in-cylinder flow has been found and was coupled to the changes in swirl and injection pressure. The observed swirl vortex in the post-oxidation period deviates strongly from solid body rotation. The unsymmetrical rotation was found to be a function of injection pressure. This deviation is concluded to affect the soot oxidation in form of increased turbulence during the post-oxidation period.

A coupled numerical approach on museum air conditioning: Energy and fluid-dynamic analysis

In the museum environment, the temporal stability and the spatial uniformity of the indoor microclimatic parameters are necessary primarily for the correct artwork conservation and then for the occupant thermal comfort. Therefore, a HVAC system is usually necessary.This paper above all emphasizes the integration of Building Energy Performance Simulation (BEPS) and Computational Fluid Dynamics (CFD) codes. This coupled numerical approach can provide accurate information about both the HVAC system energy request and the indoor microclimatic control (temporal and spatial distribution of the parameters).Then, a case study concerning a typical museum exhibition room is examined.The annual energy request for three types of all-air system, as well as the temporal variation of indoor temperature and relative humidity, is evaluated by means of a BEPS code. Energy savings can be obtained using a system with desiccant wheel (11%) or enthalpy wheel (9%), compared to the base system. As regards indoor relative humidity control, this is more critical for summer conditions, and the best performance is obtained by the system with desiccant wheel.Then, the spatial microclimatic control is analyzed by means of a CFD analysis, for various thermal load conditions and different air diffusion xequipments. The best performances are obtained by using the swirling (vortex) diffusers; also the perimetrical stripes of slot diffusers show satisfactory performances. Finally, in order to evaluate the ability of air diffusion equipments to assure good ventilation effectiveness, an analysis of the mean age of air is carried out too.

Numerical Simulation of the 1.2MW Wind Turbine Flow-Field

Based on SIMPLE algorithm, with the control equation in finite volume method and the SST K- φturbulence model, 3D models of the 1.2MW wind turbine are built to analyze the relationship between the output power and the pressure, velocity and turbulent kinetic energy of its different sections. The results show that: The change of aerodynamic performance which is caused by the interaction of blades and tower , reduces the available torque of the wind turbine that caused the decreases of the output power. The flow field region affected by central swirl and adhesive vortex is very small. The region of velocity field was affected by the wheel and wind turbine, even a few hundred meters away, but the region affected by wind turbine was smaller than by the wheel.

Experimental Study on the Effect of Swirler Geometry and Swirl Number on Flame Describing Functions

This paper deals with the response of swirling flames submitted to acoustic velocity disturbances when the rotation of the flow is produced by an axial or a radial swirler. The objective is to compare responses obtained in these two cases. The response is characterized in terms of the flame describing function (FDF), which generalizes the classical flame transfer function concept by considering not only the frequency but also the amplitude of the velocity disturbances. Results indicate that for both types of swirlers, the dynamics is essentially similar for the gains and the phases of the FDF. It is also found that the swirl number value markedly influences the gain response. The characteristic shape of the FDF, with a local minimum and maximum, are found in both cases and these features correspond to mechanisms already described previously: swirl number fluctuations and vortex rollup of the flame. Swirl number fluctuations are induced by the interaction of the incident acoustic disturbances with the swirler. This generates in the two cases a transmitted acoustic wave and a convective vorticity wave. This last wave is characterized by azimuthal velocity perturbations. The mode conversion process giving rise to the latter type of disturbance was already demonstrated in the case of an axial swirler. It is here examined in the radial swirler geometry. It is shown that the mode conversion processes in the two geometries are quite similar and that they produce similar effects on the flame dynamics and response.

Acoustically perturbed turbulent premixed swirling flames

The dynamics of a turbulent premixed confined swirling flame is investigated using large eddy simulation. The flame response is determined by introducing an external acoustic forcing at two modulation frequencies corresponding to characteristic values of the flame transfer function obtained experimentally. These values were found to give different responses in terms of gain in a previous series of experiments. The underlying physical mechanisms identified experimentally are investigated numerically. Simulations confirm that swirl number fluctuations and vortex roll-up govern the flame response. It is also confirmed that the first mechanism is associated with a mode conversion process taking place when acoustic waves impinge on the swirler unit. The axial acoustic velocity disturbance on the upstream side of the swirler generates an axial acoustic wave and an azimuthal convective disturbance in the downstream flow. These combined disturbances are retrieved in the simulation and their effect on the swirl number is extracted. Calculations also indicate that vortex shedding synchronized by the acoustic forcing takes place at the injector lip outlet. Vortices originating from this region are convected in the jet shear layer, impinge on the flame, and roll-up the flame tip. This process interferes with oscillations in the flame angle induced by swirl number fluctuations. The phasing of the flame angle with respect to the instant of vortex shedding from the injector lips determines the lifetime of the vortex before interaction with the flame and controls the strength of this interaction. When this lifetime is reduced, the vortex cannot fully develop and the flame response remains weak. For larger lifetimes, the vortex can fully develop and produce larger heat release rate perturbations. This process depends on the forcing frequency, which determines the phasing between swirl number fluctuations and vortices generation.

Vortex ring with swirl: A numerical study

In this paper, we use a lattice Boltzmann method to study the effect of swirl on the dynamics of an isolated three-dimensional vortex ring in a viscous incompressible fluid. We focus on a fixed Reynolds number of 800 and vary swirl magnitude and vortex core size. Results show that increasing swirl for a fixed core size or increasing core size for a fixed swirl causes vortex ring to slow down or even travel backward initially. A simplified physical explanation for this dynamic behavior is proposed. Our results further show that while a weak swirl causes vortex filaments to undergo helical winding, a sufficiently strong swirl transforms these windings into convoluted three-dimensional vortex structure with vortex loops trailing behind it. Each of these vortex loops may reconnect with itself, through the process of vortex reconnection, to form a ringlet.

Evaluation of vortex of left ventricular by noninvasive vector flow mapping with Doppler echocardiography

Objective To evaluate the human left ventricular flow field structure by vector flow mapping (VFM),and to seek the formation rules and description parameters of swirl vortex in the human left ventricular.Methods Sixty heathy adults were involved.The velocity distribution images on the section plane of the flow in the left ventricular were obtained bv VFM,and series parameters of vortex including vortex diameter(transverse and vertical diameter),vortex position(transverse and longitudinal position),vortex maximum flow velocity (Vmax)and density number of vortex ring(N)were measured with the software named DSA-RS1.Results A pair of similar vortex showed by VFM in the left ventricle of the heart during the early and late diastole period which were formed by a strong jet flow through the mitral valve were small vortex,and Vmax and N in former were bigger than that in latter(P＜0.05),while a bigger vortex ring continued during the middle diastolic and isovolumic contraction period with a trailing jet in the left ventricle were large whirlpool,and Vmax and N in former were bigger than that in latter(P＜0.05).Conclusions Changes of the intraventricular blood flow field structure can be showed by VFM,and description parameters of vortex concluded from the study can reflect the changes,which can be used as a preliminary quantitative study of the complex flow field structure in heart chamber. Key words: Echocardiography; Ventricular function,left; Hemodynamic phenomena; Vector flow mapping

On the failure of the quasicylindrical approximation and the connection to vortex breakdown in turbulent swirling flow

This paper analyzes the properties of viscous swirling flow in a pipe. The analysis is based on the time-averaged quasicylindrical Navier-Stokes equations and is applicable to steady, unsteady, and turbulent swirling flow. A method is developed to determine the critical level of swirl (vortex breakdown) for an arbitrary vortex. The method can also be used for an estimation of the radial velocity profile if the other components are given or measured along a single radial line. The quasicylindrical equations are rearranged to yield a single ordinary differential equation for the radial distribution of the radial velocity component. The equation is singular for certain levels of swirl. It is shown that the lowest swirl level at which the equation is singular corresponds exactly to the sufficient condition for axisymmetric vortex breakdown as derived by Wang and Rusak [J. Fluid Mech. 340, 177 (1997)] and Rusak et al. [AIAA J. 36, 1848 (1998)]. In narrow regions around the critical levels of swirl, the solution violates the quasicylindrical assumptions and the flow must undergo a drastic change of structure. The critical swirl level is determined by the sign change of the smallest eigenvalue of the discrete linear operator which relates the radial velocities to effects of viscosity and turbulence. It is shown that neither viscosity nor turbulence directly alters the critical level of swirl.

The turbulent characteristics of the gas–solid suspension in a square cyclone separator

Three-dimensional particle dynamics analyzer was employed to study the gas–solid flow in a square-shaped cyclone separator which was designed for large CFB application. Distribution of flow vector, fluctuating velocity, turbulent kinetic energy, turbulent intensity and particle concentration were discussed. The swirling flow inside the cyclone showed the Rankine vortex characteristics, i.e., strong swirling vortex at the central region of the cross-section and weak swirling quasi-free vortex near the wall. The quasi-laminar motion of particles enhanced the turbulent movement at the corners due to particle–particle/wall collision, which led to the local peak value of the turbulent kinetic energy and turbulent intensity. The corner is one of the major region to cause pressure drop because the suspension at the corners consumed more energy of the flow. The corners were found to be beneficial to particle separation mainly because the strong fluctuating flow consumed much of the kinetic energy of both the particle and the gas.

Laminar swirling flow and vortex breakdown in a pipe

Abstract A problem of asymmetric swirling flow in a pipe has been analyzed by the finite volume numerical simulation of the three-dimensional incompressible Navier-Stokes equations expressed in cylindrical polar coordinates. The swirl is generated by one tangential inlet near the closed base of the duct. Because of the high value of the swirl number, S, a vortex breakdown forms near the base of the cylinder; it is of bubble-like shape. Downstream of the bubble the axial flow is at first wavy and finally tends toward the Poiseuille profile, while the swirl decays exponentially. At high enough axial Reynolds number, Re, the flow becomes time dependent.