Presence Of Swirl Research Articles

Study on the influence of hot streak and swirl on the film cooling performance of the leading edge of the guide vane

In order to study the impacts of the non-uniform conditions of the combustor exit on the flow loss of the turbine guide blade and the cooling performance of the leading edge film, a hot streak and swirl distribution generation program has been developed to implement the parameterization specification of the non-uniform flow state. In addition, the calculation of this paper is based on GE-E3, the numerical simulation analysis is conducted for the swirl/hot streak of the positive blade on the leading edge of the film cooling guide blade. The results showed that the presence of hot streak increased the non-uniformity of vane heat load and had no effect on vane wall pressure distribution. The presence of swirl changes the pressure distribution on the vane wall, affects the migration form of hot streak in the passage, and reduces the cooling effect of the film cooling on the vane. The temperature at the outlet section of the guide vane is uniform.

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.

An investigation into the performance and diagnostics from different chordal integration schemes in asymmetric flow

The purpose of the work is firstly to explore the proposal from a previous North Sea Flow Measurement Workshop paper that increasing the number of chordal locations above 4 yields little improvement in the performance of ultrasonic flow meters. Secondly the work examines the relationship between profile factor and symmetry on theoretical velocity profiles and how that changes with an increased number of chordal locations. Finally, the benefits of more paths for the purposes of swirl cancellation are reviewed, particularly when axial asymmetry and swirl are present concurrently.It is found that in the presence of axial asymmetry there is a significant performance improvement to be had with an increased number of chordal locations.A relationship between profile factor and error is also apparent. The interpolation polynomial and weight function are used to visualise the quadrature and explain the correlation. The theory that more chordal locations will improve the correlation between error and profile factor is investigated, however initial results suggest this is not true.The theory behind swirl cancellation is explained and the velocity profile diagnostics of common designs in the presence of swirl and axial asymmetry are shown. Examples of how the user can be fooled into thinking all is well in the presence of both axial asymmetry and swirl are also shown. The sensitivity of some designs to swirl is also examined.The modelling suggests that in cases where swirl and axial asymmetry are present together and non-axial velocity components are not removed by swirl cancellation or flow conditioners, a change in traditional velocity profile diagnostics cannot be used to indicate the magnitude of the error.

Numerical stability analysis of a vortex ring with swirl

The linear instability of a vortex ring with swirl with Gaussian distributions of azimuthal vorticity and velocity in its core is studied by direct numerical simulation. The numerical study is carried out in two steps: first, an axisymmetric simulation of the Navier–Stokes equations is performed to obtain the quasi-steady state that forms a base flow; then, the equations are linearized around this base flow and integrated for a sufficiently long time to obtain the characteristics of the most unstable mode. It is shown that the vortex rings are subjected to curvature instability as predicted analytically by Blanco-Rodríguez & Le Dizès (J. Fluid Mech., vol. 814, 2017, pp. 397–415). Both the structure and the growth rate of the unstable modes obtained numerically are in good agreement with the analytical results. However, a small overestimation (e.g. 22 % for a curvature instability mode) by the theory of the numerical growth rate is found for some instability modes. This is most likely due to evaluation of the critical layer damping which is performed for the waves on axisymmetric line vortices in the analysis. The actual position of the critical layer is affected by deformation of the core due to the curvature effect; as a result, the damping rate changes since it is sensitive to the position of the critical layer. Competition between the curvature and elliptic instabilities is also investigated. Without swirl, only the elliptic instability is observed in agreement with previous numerical and experimental results. In the presence of swirl, sharp bands of both curvature and elliptic instabilities are obtained for $\unicode[STIX]{x1D700}=a/R=0.1$, where $a$ is the vortex core radius and $R$ the ring radius, while the elliptic instability dominates for $\unicode[STIX]{x1D700}=0.18$. New types of instability mode are also obtained: a special curvature mode composed of three waves is observed and spiral modes that do not seem to be related to any wave resonance. The curvature instability is also confirmed by direct numerical simulation of the full Navier–Stokes equations. Weakly nonlinear saturation and subsequent decay of the curvature instability are also observed.

Rayleigh–Taylor Instability of Swirling Annular Layer With Mass Transfer

The interfacial instability of Rayleigh–Taylor type at the cylindrical boundary involving the liquid phase and vapor phase of a fluid has been considered when the vapor is warmer than the liquid. We use viscous potential flow theory to include the viscosity at the interface. To examine the stability of the arrangement, the normal-mode analysis is performed together with the effect of heat as well as mass transfer and free swirl. The physical system consists of an annular fluid layer restricted in a cylinder with vapor phase in the core. This work investigates the effect of a variety of variables on the instability of the interface. It is found that when the heat transfer constant increases, the range of stability increases. Also, the range of stability increases faster in the presence of swirling.

Numerical investigation of water droplets trajectories during natural gas dehydration inside supersonic separator

Reliable estimation of the condensed water droplets trajectories inside Supersonic separators (3Ss) during the dehydration process is essential for proper design and safe operation. Most of previous researches ignored the actual sizes of condensed droplets and predicted the particles trajectories for pre-specified diameters. In this article and for the first time, real trajectories are computed by considering the actual particle size distribution (PSD) of the condensed droplets in the presence of swirl, nucleation and growth processes during the dehydration of methane rich natural gas (MRNG) inside Laval nozzle for various diffuser angles. Furthermore, the injection of water droplets to facilitate the condensation process has not been addressed previously.Our simulation results indicate that even for the most optimal geometry and at extremely large centrifugal accelerations of 500,000 g, the condensed particles from MRNG are exceedingly small and can't reach the 3S walls for practical straight tube lengths. Our findings are verified with several previously reported experimental measurements and theoretical investigations results, borrowed from literature. To ensure proper dehumidification, sufficiently large water droplets are assumed to be injected preferably after the throat location. The computed results indicate that by injecting 5 μm diameter particles into MRNG of Khangiran refinery sweet gas stream and increasing its wetness fraction up to 0.12, the dehydration process is successfully achieved in an optimally designed supersonic separator.

Investigations on the influence of swirl intensity on solid-fuel ramjet engine

In this paper, the influence of swirl intensity on solid fuel regression rate and combustion phenomena in a solid fuel ramjet has been investigated numerically and experimentally. First, an in-house code has been developed to solve axisymmetric Reynolds-averaged Navier–Stokes equations of unsteady turbulent swirling compressible flow field with chemical reactions. Second, experiments have been conducted in a solid fuel ramjet without swirl to validate the developed code for solid fuel decomposition; then the predictive capability of the code is validated by using; swirling flow passes through sudden expansion combustor, shock-induced combustion case, and a semi-infinite plate. Third, unsteady simulations are carried out for reacting turbulent flows with and without swirl in a solid fuel ramjet using high-density polyethylene (HDPE) solid fuel. Then, the computational results are analyzed and discussed. The results show that, the presence of swirl is more effective in enhancing the regression rate and the turbulent mixing throughout the ramjet. Increase swirl number increases the heat and mass transport at the fuel surface and hence increases the regression rate.

Analysis of Effect of Inlet Swirl In Four Stroke Single Cylinder Diesel Engine With Different Inlet Valve Geometries Using CFD

Flow patterns are essential to ensure that the engine can produce high performance with the presence of swirl and tumble effect inside the engine cylinder. This paper provides the simulation of air is simulated in the software to predict the flow pattern. The flow pattern is simulated by using the steady state pressure based solver. The domain used for the simulations predicated on the particular engine parameters. Mistreatment the CFD problem solver ANSYS FLUENT, the CFD simulation is earned for four totally different geometries of the valve. The geometries consist of Horizontal, Vertical, curve and arc springs. In this simulation, only the intake strokes are simulated. From this results show that the velocity of the air flow is high during the sweeps the intake stroke takes place. This situation is produced more swirls and tumble effect during the compression, hence enhancing the combustion rate in a whole region of the clearance volume of the engine cylinder. This will initiate to the production of tumble and swirl in the engine cylinder.

Experimental and numerical visualizations of swirling flow in a vertical pipe

This paper presents a comparison between the experimental and numerical simulations of turbulent swirling flow induced by twisted tape in vertical pipe. A novel measurement technique, phased array ultrasonic velocity profiler (UVP), has been developed for 2D velocity field visualization in swirling flow. A phased array with basic frequency 4 MHz has been designed, it has eight piezoelectric elements and each element transmits ultrasound beam. The advantage of this sensor is that the ultrasound beam can be controlled easily by changing the time delay of signal transmission for each element. A vector reconstruction algorithm is presented showing how the velocity vector of particles can be calculated from Doppler-shift frequencies taken from the output signals of two receiver elements. Two-dimensional velocity field has been visualized and it is found, as expected, that the presence of swirl cause a significant increase in the magnitude of the measured tangential velocity. Furthermore, a numerical calculation is performed and qualitatively compared with experimental results. The numerical result is obtained by solving three-dimensional, Reynolds-averaged Navier–Stokes equations by the commercial CFD code FLUENT® v.14.5 with RNG k-e turbulence model. The qualitative comparison between phased array UVP and CFD results shows good agreement with the average velocity field. Experimental and numerical findings and parametric trends based on the effects of swirling flow are summarized and discussed.

Effect of Prediffuser Angle on the Static Pressure Recovery in Flow Through Casing-Liner Annulus of a Gas Turbine Combustor at Various Swirl Levels

A numerical study has been performed in an axisymmetric diffuser followed by a casing-liner annulus of a typical gas turbine combustor to analyze the flow structure and pressure recovery in the geometry. Static pressure recovery in a gas turbine combustor is important to ensure high pressure of air around the liner. However, the irreversible pressure losses reduce the static pressure recovery from the ideal value. The presence of swirl in the flow from compressor and prediffuser geometry before the dump diffuser influences the flow pattern significantly. In this study, flow structures are numerically predicted with different prediffuser angles and inlet swirl levels for different dump gaps. Streamline distributions and pressure plots on the casing and liner walls are analyzed. Static pressure recovery coefficients are obtained from the pressure distributions across the combustor. The effect of dump gap on the static pressure recovery has also been evaluated. It is observed that the best static pressure recovery can be obtained at optimum values of inlet swirl level and prediffuser angle. Dump gap is found to have significant influence on the static pressure recovery only at small prediffuser angle.

Numerical investigation of pulverized coal aero mixture combustion at the presence of flow swirling

Numerical investigation results of burning pulverized coal aero mixture in the presence of swirl flow have been presented. The mathematical model has been chosen allowing describing correctly the pulverized coal combustion processes in the furnace with a swirl burner.

The acoustic analogy in an annular duct with swirling mean flow

AbstractThis paper is concerned with modelling the effects of swirling flow on turbomachinery noise. We develop an acoustic analogy to predict sound generation in a swirling and sheared base flow in an annular duct, including the presence of moving solid surfaces to account for blade rows. In so doing we have extended a number of classical earlier results, including Ffowcs Williams & Hawkings’ equation in a medium at rest with moving surfaces, and Lilley’s equation for a sheared but non-swirling jet. By rearranging the Navier–Stokes equations we find a single equation, in the form of a sixth-order differential operator acting on the fluctuating pressure field on the left-hand side and a series of volume and surface source terms on the right-hand side; the form of these source terms depends strongly on the presence of swirl and radial shear. The integral form of this equation is then derived, using the Green’s function tailored to the base flow in the (rigid) duct. As is often the case in duct acoustics, it is then convenient to move into temporal, axial and azimuthal Fourier space, where the Green’s function is computed numerically. This formulation can then be applied to a number of turbomachinery noise sources. For definiteness here we consider the noise produced downstream when a steady distortion flow is incident on the fan from upstream, and compare our results with those obtained using a simplistic but commonly used Doppler correction method. We show that in all but the simplest case the full inclusion of swirl within an acoustic analogy, as described in this paper, is required.

Lift-off and stabilization of n-heptane combustion in a diesel engine with a multiple-nozzle injection

This paper presents a joint numerical and experimental investigation of flame lift-off and stabilization mechanisms in heavy-duty diesel engines. The injection strategy, employing different nozzle configurations, allows for quantification of the impact of varying inter-jet angle spacing in the presence of swirl. For this purpose, three different inter-jet angles are chosen in this study; 45°, 90° and 135°. Large-eddy simulations are performed utilizing a detailed chemical kinetic mechanism for n-heptane to resolve the turbulent fuel and air mixing and to capture the important species surrounding the ignition and flame-fronts to describe the flame stabilization process. Measurements are carried out for OH chemiluminescence to identify the flame lift-off position in an optical accessible engine. In general, the swirl flow in the ambient air shows a great impact on the lift-off, with a 15% difference in the lift-off lengths on the upwind and downwind side of the jet. The LES results show that important ignition reactions undergo in a broad region in front of the lift-off position. With decreasing inter-jet angle, it is shown that the impact of transportation of hot products from adjacent jets becomes more prominent. Hot reservoirs surrounding the lift-off length increase the local ambient temperature and augment the auto-ignition process by mixing of the cold injected fuel and hot air.

Axisymmetric magnetic vortices with swirl

New solutions for compact vortex rings and vortices in the presence of swirl and toroidal magnetic field are presented. Steady solutions are found for thin-core vortex rings, generalizing the classical results of Kelvin and Hicks. An exact family of steady spherical solutions is found in the case when the underlying governing equation, originally due to Hicks, is linear. Proper matching of the pressure is critical in obtaining these solutions, for which another 19th century equation proves key. Contour dynamics simulations show the existence of counter-propagating dipolar structures when both swirl and magnetic fields are present.

Combined evaluation of second order turbulence model and polydispersion model for two-phase boiling flow and application to fuel assembly analysis

High-thermal performance PWR (pressurized water reactor) spacer grids require both low pressure loss, high wall heat transfer coefficient and high critical heat flux (CHF) properties. A further detailed understanding of the main physical phenomena (wall boiling, entrainment of bubbles in the wakes, recondensation) is needed and can be reached by numerical simulation. In the field of fuel assembly analysis or design by means of CFD codes, the overwhelming majority of the studies are carried out using two-equation eddy viscosity models (EVM) as turbulence model, especially the standard K − ɛ model, while the use of Reynolds Stress Transport Models (RSTMs) remains exceptional. In contrast, extensive testing and application over the past three decades have revealed a number of shortcomings and deficiencies in eddy viscosity models. Indeed, the K − ɛ model is totally blind to flow rotation, e.g., in the presence of swirls. This aspect is crucial for the simulation of a hot channel in a fuel assembly. In fact, the mixing vanes of the spacer grids generate swirls in the coolant water, which enhances the heat transfer from the rods to the coolant in the hot channels and thus limits boiling. In this work, all the models are implemented in NEPTUNE_CFD, a three dimensional multi-fluid code developed especially for nuclear reactor applications, in the framework of the NEPTUNE project (EDF, CEA, AREVA-NP, IRSN). In a previous work, we have evaluated computational fluid dynamics results obtained with RSTM against single-phase liquid water tests equipped with a mixing vane and against two-phase boiling cases (DEBORA-tube and ASU-annular channel tests). In the present work, a geometry closer to actual fuel assemblies is considered. It consists of a rectangular test section in which a 2 × 2 rod bundle, equipped with a simple spacer grid with mixing vanes, is inserted. The influence of the turbulence model on target variables supposed to be related to CHF limitation is discussed. Numerical investigations on the optimised angle of mixing vanes are addressed. In addition, the impact of a detailed description of the bubble size distribution on the boiling flow with realistic geometry is addressed. The relative importance of the correct description of this modelling of polydisperse bubble size is due to the dependency of (i) main hydrodynamic forces, like drag, as well as of (ii) inter-phase transfer area with respect to the individual bubble size. The effects of the phenomena of coalescence or break-up and the main influences of mean bubble diameter on the void fraction and fluid velocity in the vicinity of the grids are underlined. The study of this 2 × 2 rod bundle case is a further step towards a physically reliable local CFD modelling of the two-phase boiling flow in real fuel assemblies, including spacers grid structures.

Local bubble size distribution, gas–liquid interfacial areas and gas holdups in an up-flow ejector

Particle image velocimetry (PIV) was used to measure local bubble size distributions (BSD), gas–liquid interfacial areas and gas holdups in an up-flow ejector, based on the water–air system with different liquid and gas flow rates under the presence/absence of the swirl body. The results show that the bubble flow patterns are different whether to add the swirl body into the nozzle, especially at low gas flow rate because the bubbles formed “bubble chain” in the ejector with swirl. The mean bubble sizes D 32 of the two are both related to the pressure drop between import and export, gas ratio and liquid flow. The interfacial area and D 32 are both mainly dependent on the local gas holdups. The mean bubble sizes in the absence of swirl body are smaller than that in the presence of swirl under different operating conditions. The gas holdups and interfacial area are larger with swirl than those without swirl. With the increase of the gas fraction, the differences of D 32, a t and e G become smaller.

Flow structure, wall pressure and heat transfer characteristics of impinging annular jet with/without steady swirling

The detailed impinging annular jet characteristics with/without induced swirling motion are experimentally studied. Obtained flow and wall pressure data confirm the classical observation for conventional annular impinging jet, with the flow exhibiting simple round impinging jet-like features at sufficiently large separation distances. In contrast, no such transition occurs in the presence of swirling. At short and intermediate separation distances, the swirling annular jet causes more non-uniform distributions of wall pressure and heat transfer on the impingement plate compared to the conventional annular jet. However, the reverse holds at large separation distances.

Influência da coleta, da produção e da estocagem na qualidade dos concentrados de plaquetas

Como o controle de qualidade dos concentrados de plaquetas (CP), feito na data de seu vencimento, não possibilita distinguir o momento e o procedimento que determina a eventual redução de sua qualidade, decidimos investigar, separadamente, a influência da coleta, da produção e da estocagem sobre a qualidade deste hemocomponente. Foram avaliados, em 33 CP randômicos, diariamente, durante cinco dias, os seguintes parâmetros: a agregação, o número de plaquetas e leucócitos, a pO2 e pCO2, o pH, sódio e potássio, a presença de swirling, grumos, hemácias e lipemia e cultura para bactérias. Observamos maior queda da agregação plaquetária com pares de agonistas durante a produção dos CP (de 99,4% para 59,8%, p<0,01), seguida de queda gradativa durante a estocagem, atingindo 40,4% no quinto dia. Durante o período de estocagem observamos também: 1. queda gradativa da concentração de plaquetas (p<0,05), porém com valores sempre maiores que 5x10(10)/70 mL; 2. diminuição da concentração de leucócitos (p<0,05); 3. aumento da pO2 e queda da pCO2 (p<0,05); 4. aumento do pH (p<0,05 a partir do quarto dia) e da concentração de sódio e de potássio (em geral p<0,05); 5. swirling em todos os CP, grumos plaquetários em apenas um e ausência de hemácias e de lipemia em todos; e 6. negatividade das culturas para bactérias. Os resultados demonstram que as alterações foram mais evidentes no processo de produção e sugerem que o controle de qualidade dos CP deve contemplar da coleta ao final do período de estocagem.

Analytical Equilibrium Swirling Inflow Conditions for Computational Fluid Dynamics

T HE specification of swirling inflow conditions is an integral and important part of computational fluid dynamics (CFD) of swirling flows, which are complex flows with many practical applications [1], for instance, in turbulent combustion [2]. To specify a swirling velocity profile with a desired swirl number in a traditional CFDanalysis based on aReynolds-averagedNavier–Stokes (RANS) modeling approach is not an easy task, which becomes even more difficult in advanced CFD approaches such as direct numerical simulation (DNS) or large-eddy simulation (LES). DNS or LES of spatially inhomogeneous turbulent flows requires turbulent inflow boundary conditions [3], which may be generated either from an auxiliary simulation, from a proper orthogonal decomposition and linear stochastic estimation [4], from a digital filter reproducing specified statistical data [5], or simply taken as the mean velocity profile with superimposed fluctuations [6], which is essentially a perturbed inflow. With the presence of swirling, inflow conditions are difficult to specify. For RANS-based CFD, an appropriate mean velocity profile is needed. For DNS and LES, apart from the mean velocity profile, information on an appropriate “turbulent” component is needed as well. Pierce and Moin [7] developed a method for generating equilibrium swirling inflow conditions, which represents a logical, idealized starting point for generating swirling velocity profiles. In their method, the swirling inflow is obtained numerically by solving for the flow driven by fictitious axial and azimuthal body forces, where the axial body force represents themean pressure gradient that drives the physical flow. The azimuthal body force is not physically producible and may be thought of as existing only to overcome drag from the walls. This technique was used in LES of a coaxial jet combustor and good agreement with the experimental data was observed [7]. The method can be regarded as an effective and simple means of generating realistic swirling inflow conditions. In this study, efforts have beenmade to derive an analytical formof the equilibrium swirling inflow conditions. The analytical swirling inflow is easy to implement, as it does not require solving for the flow numerically [7]. The particular forms of the analytical equilibrium swirling velocity profiles have been obtained for swirling annular and round jets, which can be directly applied in the specification of swirling inflow conditions for RANS approaches and further explored for the specification of swirling inflow conditions for DNS and LES, regardless of the turbulent component needed in the timedependent simulations. A desired swirl number at the inflow can also be conveniently achieved by adjusting a constant.

Including Swirl in the Actuator Disk Analysis of Wind Turbines

It is shown that the presence of swirl in the wake of a wind turbine complicates the simple actuator disk analysis that provides such basic results as the Lanchester-Betz limit on the power coefficient. The simple analysis remains valid at high tip speed ratio for a sufficiently small core radius of the hub vortex. As the tip speed ratio decreases, the present analysis eventually becomes invalid. It is, however, reasonable to conclude that including the effects of the hub vortex causes the maximum power coefficient to increase above the Lanchester-Betz limit with decreasing tip speed ratio. The extent to which this conclusion depends on the assumed vortex model was investigated briefly by considering a more general model for the hub vortex. The results strongly imply that some account of the vortex structure of the wake will be required to resolve fully the effects of swirl. Unfortunately there are no measurements currently available for the hub vortex.