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Dry powder inhalers (DPIs) are widely employed to treat respiratory diseases, offering numerous advantages such as high dose capacity and stable formulations. However, they usually face challenges in achieving sufficient pulmonary drug delivery and minimizing excessive oropharyngeal deposition. This review provides a new viewpoint to address these challenges by focusing on the role of swirling flow, a crucial yet under-researched aspect that induces strong turbulence. In the review, we comprehensively discuss both key classic designs (tangential inlet, swirling chamber, grid mesh, and mouthpiece) and innovative designs in inhalers, exploring how the induced swirling flow initiates powder dispersion and promotes delivery efficiency. Valuable design considerations to effectively coordinate inhalers with formulations and patients are also provided. It is highlighted that the delicate manipulation of swirling flow is essential to maximize benefits. By emphasizing the role of swirling flow and its potential application, this review offers promising insights for advancing DPI technology and optimizing therapeutic outcomes in inhaled therapy. [Display omitted] [ABSTRACT FROM AUTHOR]

A numerical investigation of the Nusselt number, heat transfer augmentation efficiency, and friction factor in a laminar flow tube with triangular perforated nail head twisted tape (TPNHTT) is reported using ANSYS 19.2 Fluent. The effects of triangular cut (each side 3 mm) in the middle pitch of the tape along the height, diameter, and top diameter of the nail head (10, 2, and 2.5 mm, respectively) have been explored for (300 ≤ Re ≤ 1800) in a tube of 22 mm diameter. In this paper, implementation has been done with a TPNHTT varying width (14 ≤ b ≤ 20) twist ratio (TR) ranging from (3 ≤ TR ≤ 6), inserts in a tube for laminar flow. Twisted tape (TT) produces a swirl flow associated with fluid resulting in heat transfer enhancement and pressure drop characteristics other than that for the plain tube (PT). The performance of the Nusselt number and friction factor increased up to 123.62% and 495.30%, respectively, on the application of TPNHTT as compared with PT. A maximum thermal performance efficiency of 2.98 has been achieved using the twisted‐tape ratio of the current tube in laminar flow at a Reynolds number of 1700. In addition, correlation equations (11) and (12) have been developed for the friction factor and Nusselt number valid for 300 ≤ Re ≤ 1800, 14 ≤ b ≤ 20, and 3 ≤ TR ≤ 6. The study has proved that applying TT is an upgraded approach for laminar convection heat transfer. This novel work finding will be supportive for researchers to design the latest heat exchangers. [ABSTRACT FROM AUTHOR]

A three-lobed helical pipe was installed downstream of the bend of a vertical-horizontal pneumatic pipeline. The swirl characteristics under different helical pipe structures were investigated. Results show that: (a) the maximum velocity region rotates quasiperiodically, and the smaller the pitch, the faster the rotation; (b) the 3D morphological changes of the axial velocity distribution in downstream sections are similar: from an arch to a pit and finally to a uniform flat top. The tangential velocity appears as a Rankine vortex near the wall; (c) the swirl decays rapidly along the downstream. The initial swirl intensity, proportional to the helical pipe length, increases first and then decreases with decreasing pitch, whereas the structural parameters have minimal effect on the swirl decay rate; (d) the helical tube remarkably increases the system energy consumption, and the total pressure drop is inversely proportional to the pitch and proportional to the length. [ABSTRACT FROM AUTHOR]

In open flow simulations, the dispersion characteristics of disturbances near synthetic boundaries can lead to unphysical boundary scattering interactions that contaminate the resolved flow upstream by propagating numerical artifacts back into the domain interior. This issue is exacerbated in flows influenced by real or apparent body forces, which can significantly disrupt the normal stress balance along outflow boundaries and generate spurious pressure disturbances. To address this problem, this paper develops a zero-parameter, physics-based outflow boundary condition (BC) designed to minimize pressure scattering from body forces and pseudo-forces and enhance transparency of the artificial boundary. This "balanced outflow BC" is then compared against other common BCs from the literature using example axisymmetric and three-dimensional open swirling flow computations. Due to centrifugal and Coriolis forces, swirling flows are known to be particularly challenging to simulate in open geometries, as these apparent forces induce non-trivial hydrostatic stress distributions along artificial boundaries that cause scattering issues. In this context, the balanced outflow BC is shown to correspond to a geostrophic hydrostatic stress correction that balances the induced pressure gradients. Unlike the alternatives, the balanced outflow BC yields accurate results in truncated domains for both linear and nonlinear computations without requiring assumptions about wave characteristics along the boundary. [ABSTRACT FROM AUTHOR]

This is a numerical study of gyrotactic microorganism, heat and mass transfer futures of hybrid Williamson nanofluid made up of $ \textrm{water} - \textrm{Ag}/\textrm{MWCNT} $ water − Ag / MWCNT nanoparticles over swirling cylinder with Cattaneo–Christov heat flux. Suitable similarity transformations are presented to convert the governing partial differential equations into ordinary differential equations. The set of ordinary differential equations along with boundary conditions are solved by using the finite element technique. The sketches of swirling velocity, axial velocity, temperature, concentration and density of microorganism with individual pertinent quantities, such as volume fraction parameter of $ \textrm{Ag} $ Ag nanoparticle $ (0.01 \lt \phi 1 \lt 0.04), $ (0.01 < ϕ 1 < 0.04) , volume fraction parameter of $ \textrm{MWCNT} $ MWCNT nanoparticle $ (0.01 \lt \phi 2 \lt 0.04) $ (0.01 < ϕ 2 < 0.04) , Magnetic field parameter $ (0.1 \lt M \lt 0.7), $ (0.1 < M < 0.7) , Weissenberg number $ ({0.5 \lt \textrm{We} \lt 0.8}) $ (0.5 < We < 0.8) , Prandtl number $ ({2.2 \lt \textrm{Pr} \lt 8.2}), $ (2.2 < Pr < 8.2) , Reynolds number $ ({0.5 \lt \textrm{Re} \lt 2.0}), $ (0.5 < Re < 2.0) , Chemical reaction parameter $ (0.1 \lt \textrm{Cr} \lt 0.7) $ (0.1 < Cr < 0.7) , Peclet number $ ({0.1 \lt \textrm{Pe} \lt 0.7}), $ (0.1 < Pe < 0.7) , Bio-convection Lewis number $ (1.0 \lt \textrm{Sb} \lt 1.6) $ (1.0 < Sb < 1.6) , Biot number $ (0.2 \lt \textrm{Bi} \lt 0.8) $ (0.2 < Bi < 0.8) , thermal relaxation parameter $ (0.5 \lt \gamma \lt 2.0) $ (0.5 < γ < 2.0) and Suction parameter $ ({0.1 \lt {V_0} \lt 0.7}) $ (0.1 < V 0 < 0.7) , are depicted through graphs. Moreover, the numerical estimates of local density number of microorganisms, heat and mass transfer rates for different parameters are specified in a tabular form. The calculations show that local skin friction coefficient, Sherwood number and local density of microorganism intensify with increasing values of both volume fraction parameters $ ({\phi 1})\textrm{ } $ (ϕ 1) and $ ({\phi 2}) $ (ϕ 2). Also, the density of microorganisms and profiles of concentration are elevated in the fluid region with rising values of Weissenberg number. Temperature of hybrid nanofluid deteriorates with increasing values of thermal relaxation parameter. [ABSTRACT FROM AUTHOR]

A combined positron emission particle tracking (PEPT) and X-ray computed tomography (CT) technique is presented, and its utility is demonstrated through investigation of flow in a pipe with twisted tape swirl insert with varying flow conditions (diameter-based Reynolds numbers 16,300–63,300). A description of this technique is given, as well as data handling practices used to relate geometric information captured by CT to fluid flow data gathered via PEPT. It is found that the CT component is readily capable of capturing the stainless steel insert geometry in this present system, but the use of combined plastic and metal materials leads to artifacts in imaging of the plastic surface. Nonetheless, CT data are related to PEPT flow measurements, and average velocity fields are calculated via a pseudo-framing and interpolation scheme and used to visualize and interrogate key flow phenomena within the system. Radial velocity profiles of the mean flow characteristics are seen to collapse to a nearly common form across all flow conditions considered. Helical vortices are seen propagating through the flow field, generated by bypass flow around the gap between the insert and pipe wall, with additional coherent secondary flow structures seen in the higher Reynolds number cases. These findings enhance the understanding of the mixing mechanisms in these swirl flows and encourage the continued development of PEPT-CT methodologies for 3D flow measurements in optically inaccessible systems. [ABSTRACT FROM AUTHOR]

In this paper, we apply a framework based on decomposition techniques to study the synchronization of flow velocity with acoustic pressure and heat release rate in swirl flames. The framework uses the extended proper orthogonal decomposition to identify regions of the velocity field where velocity and heat release fluctuations are highly correlated. We apply this framework to study coupled interactions associated with period-1 and period-2 type thermoacoustic instability in a technically premixed, swirl-stabilized gas turbine-type model combustor operated with hydrogen-enriched natural gas. We find the structures in the flame surface and the heat release rate correlated with the dominant coherent structures of the flow field using extended POD. We observe that the correlated structures in the flow velocity, flame surface and heat release rate fields share the same spatial regions during thermoacoustic instability with period-1 oscillations. In the case of period-2 oscillations, the structures from flame surface and heat release rate field are strongly correlated. However, these structures contribute less to the coherent structures of the flow field. Using the temporal coefficients of the dominant POD modes of the flow velocity field, we also observed 1:1 and 2:1 frequency locking behaviour among the time series of acoustic pressure, heat release rate and the temporal coefficients of the first two dominating POD modes of velocity field during the state of period-1 and period-2 oscillations, respectively. These frequency-locked states, which indicate the underlying phase-synchronization states, correlate with coherent structures in the flow velocity field. [ABSTRACT FROM AUTHOR]

This work investigates the influences of precessing vortex cores (PVCs) on the coherent interactions in the transient flow and heat release fields of a weak premixed swirling flame, based on a 10-kHz simultaneous measurement of OH* chemiluminescence and stereoscopic particle image velocimetry together with the state-of-the-art vortical and heat release rate (HRR) network analyses. The PVC effect is studied by contrasting the lifted helical and attached symmetric states of a unique transitioning V-shaped flame, corresponding to an alternate quasi-periodic appearance and disappearance of PVC in the inner shear layer (ISL). The results suggest that the emergence of PVC significantly escalates the coherent oscillation in the ISL, leading to the break of the scale-free topology in the vortical network. However, the PVC also promotes coherence in the local HRR variation, resulting in improved connectivity in the positive HRR network and enhanced assortative mixing in the negative HRR network. Furthermore, the flame mode transition is also captured by the differences in the mean degree of the positive HRR network and the power-law fitting goodness of the negative HRR network, showing promises of complex network analysis in distinguishing the flame dynamical modes. [ABSTRACT FROM AUTHOR]

The pre-swirl system is essential for delivering cooling air to turbine blades within aviation engines. To explore the impact of the inner seal on the pre-swirl system, a high pressure ratio and high rotational speed experimental platform was constructed. The impact of inner seal inflow and outflow on the pre-swirl system's performance was evaluated. In response to the adverse effects of inner seal inflow on the system, a bypass structure was proposed to divert the inner seal flow, and the optimization effects and underlying mechanisms of the bypass structure were analyzed through a combination of experimental and numerical simulation approaches. The results indicate that the impact of inner seal outflow on the system is minimal, with the maximum variation in the temperature drop efficiency remaining below 1.9% under experimental conditions. Inner seal inflow, on the other hand, can have a significant negative impact on the system's performance. At a pressure ratio of 1.6, increasing inner seal inflow ratio leads to a decline in temperature drop efficiency from 0.55 to 0.43, representing a reduction of 21.8%. The bypass structure for inner seal can effectively prevent the mixing of inner seal flow with the mainstream within the pre-swirl cavity, reducing the pressure and temperature within the pre-swirl cavity. At a pressure ratio of 1.6 and inner seal inflow ratio of 15%, the specific work done by the airflow increased from 9.23 to 12.72 kW/(kg/s), increased by 37.8%, and the system temperature drop efficiency increased from 0.426 to 0.546, representing a 28.0% increase. [ABSTRACT FROM AUTHOR]

Precessing vortex core (PVC), a typical vortex structure, universally exists in swirling flow fields and originates from the Kelvin–Helmholtz instability of the swirling shear layer. In the combustion chamber, pressure pulsations from PVC might resonantly couple with acoustic modes, leading to thermoacoustic oscillations which is a significant challenge in the development of rocket engines and gas turbines. The present work focuses on the time-averaged and unsteady flow characteristics of different swirling flow fields in the premixed swirling combustor. The PVC observed in the swirlers adopted presents a single helical structure and the PVC frequency is proportional to the incoming flow velocity. Moreover, another low-frequency helical mode located in the downstream region of the flow fields has been identified and categorized as PVC type II to be distinguished with common PVC mode in this study, which originates from the precession of the central recirculation zone. The experimental results further emphasize the effects of the swirling injector geometry on PVC and the low-frequency helical modes. This indicates that as the diameter of the bluff body or the divergence cup angle increases, the energy of the PVC mode decreases while that of the helical mode increases significantly. In addition, the PVC mode would be gradually suppressed as the tail size of the bluff body increases. These results, especially the coexistence of the PVC mode and the low-frequency helical mode, are rarely reported in previous studies, and they may provide an effective guidance for investigating the mechanism and control of thermoacoustic oscillations. [ABSTRACT FROM AUTHOR]

Enhanced momentum and heat transport in a three-dimensional rotating disk boundary layer due to the consideration of a wavy disk surface is an already known fact in the literature. Such a transport enhancement is primarily associated with two fundamental attributes of the wavy disk: the increased surface area and the enhanced convection due to the surface undulations. However, there exists no further information about their individual role, mutual interaction, and individual share in enhancing the convective transport in the rotating disk boundary layer. This study aims to investigate these facts in detail by considering radially heterogeneous different wavy configurations on the disk surface. It is revealed that the said attributes contribute non-trivially to enhance the transport phenomena. Their impactful role is identified due to the strengths of circumferential and crossflow velocity components, the magnitude of flow swirl angle, and hence due to the coefficients of skin friction and their inter relationship. In this regard, a fundamental benchmark regarding the relative strength of the two coefficients of skin friction is identified from the flat disk case. Decisive observations regarding the impact of surface undulations and the increased surface area of the wavy disk on the enhanced convective transport are made with the aid of this benchmark. It is observed that the enhanced transport phenomena, especially the heat transfer, mainly depend upon the further dominance of the circumferential velocity component. In the situations of increased dominance of rotational flow K w > K f , the increased convection and surface area collectively contribute to enhance the thermal transport while in a reverse situation K w < K f the convection contributes adversely by even reducing the impact of the increased surface area. In the neutral situation where the dominance of rotational velocity is neither increased nor decreased (i.e., K w ≈ K f ), any increase in the transport phenomena is wholly due to the increased surface area. Therefore, the presence of surface undulations or increase in surface area is not the only criterion for an optimum rise in the transport phenomena, rather the impact of surface undulations on the velocity profiles is important which is manipulated due to their positioning on the disk surface. It is observed that the presence of surface undulations in the central and intermediate regions on the disk surface causes to increase the gradients of the crossflow velocity while their presence in the near rim location causes to enhance the gradients of the circumferential velocity. Thus, the configurations that have higher undulations in the near rim region outperform the other configurations. [ABSTRACT FROM AUTHOR]

The response characteristics of the bi-swirl coaxial injector under oscillating backpressure were investigated numerically based on coupled level-set and volume of fluid model. The backpressure oscillation frequency was set ranging from 1000 to 5000 Hz. The frequency and amplitude response characteristics of liquid films were analyzed under different injection conditions. The amplitude of the pressure response inside the injector was determined by the acoustic damping of the system. Due to the central gas core inside the inner injector, the inner injector manifold was found to be more sensitive to the backpressure oscillation. The frequency characteristic of the liquid film response indicated the presence of the characteristic frequency where the response amplitude was maximum. This characteristic frequency was linearly positively correlated with the mass flow rate of the inner injector, while the flow in the outer injector could suppress the response amplitude of liquid films. Meanwhile, the nonlinearity of the response was dominated by the inner liquid film and was also the strongest at the frequency with the highest response amplitude. The simulated flow fields showed that the oscillation of the ambient airflow periodically hindered the liquid film, leading to Klystron effect. Finally, it was suggested that the characteristic frequency was related to the axial velocity of the inner liquid film at the injector outlet and the acoustic length of the gas core. In addition, the response amplitude of liquid films was found to be controlled by the spray cone angle and the total mass flow rate of propellants. [ABSTRACT FROM AUTHOR]

This paper aims to find an exact solution for the von Kármán swirling viscous fluid flow caused by the infinite radius rotating disk with uniform suction. The swirling flow occurred at infinity or far from the rotating disk, and two conditions were considered. The first condition is when the direction of swirling flow at infinity is the same as the direction of angular velocity that the rotating disk has. The second condition is when the direction of the rotating disk and that of the swirling flow are opposites. When there are no swirling flow at infinity and no suction on the surface of the rotating disk, the pressure distribution is just a function of distance above the disk. The similarity transformation converts the governing equations from partial differential equations into ordinary differential equations and then is solved analytically with the HAN method. In this study, three cases were considered. The first case is a swirling flow at infinity that has the opposite and same direction of the rotating disk when there is no suction on the disk's surface. The second case is no swirling flow at infinity, but the suction occurs on the rotating disk's surface. The third one is both suction on the rotating disk and swirling flow. In the first case, it was observed that when the angular velocity of the fluid at a distance away from the disk is insignificant compared to the angular velocity of the disk, the skin friction coefficient reaches the maximum value and vice versa when the angular velocity of the fluid increases at a distance away from the disk, the value of skin friction coefficient decreases. In the second case, it was observed that the more the surface suction increases, the more the skin friction coefficient increases. Hence, the skin friction coefficient on a porous disk on which suction occurs is higher than on a normal non-porous disk. The results demonstrate that when parameters such as s = a = 0, the pressure will be a distance function above the disk if we put r = 0 . [ABSTRACT FROM AUTHOR]

Swirl cooling can not only increase the area of the heat exchange wall covered by the coolant, but also improve the average heat transfer intensity and uniformity of the target surface. SST k-ω turbulence model is utilized in the conjugate heat transfer numerical simulation. Based on C3X blades, leading edge swirl cooling structure of the corresponding areas are modified. The flow and heat transfer characteristics of swirl cooling are analyzed at different cross-sections and positions. It is found that there exists an optimal aspect ratio and hole spacing to minimize the temperature gradient on the swirl cavity wall. The swirling motion in the swirl cavity can significantly increase the heat transfer coefficient of the wall surface. [ABSTRACT FROM AUTHOR]

The free-surface vortex at the end of tundish casting sequence induces slag carryover into the mold, which can induce reduction in metal yield, deterioration in billet quality, and disruption to production. In this paper, the results of multiphase flow behavior in both tundish and mold during the formation process of free-surface vortex calculated by large eddy simulation (LES) model the RNG k-ɛ model were firstly compared, then the effect of rotating speed of stopper-rod on vortex and mold was numerically investigated based on the LES model. The results showed that the LES model offers a more precise simulation of multiphase flow, providing a better representation of tundish swirl evolution, fluctuations at the steel/slag interface, and slag phase motion. When the rotating speed of stopper-rod is 60 r/min, the fluctuation of mold flux is minimized, with a maximum surface velocity of 0.12 m/s, a slag carryover velocity of 0.122 kg/s at the moment of vortex penetration, and the amount of residual steel is reduced by about 600 kg, the critical height of the 1st and 2nd strands is reduced by 13.5 mm and 15.5 mm, respectively, which performs clear advantage over the schemes of 0, 30, and 90 r/min. The present study can offer theoretical guidance on suppressing free-surface vortex in tundish on the premise of improving the multiphase flow in mold. [ABSTRACT FROM AUTHOR]

Three-dimensional mathematical model was established to investigate the solidification behavior during the continuous casting of a round bloom with the diameter of 0.7 m, where a novel swirling flow submerged entry nozzle (SEN) combined with mold electromagnetic stirring (M-EMS) method was used. The results show that an impinging flow phenomenon, which was normally formed in conventional single-port SEN casting, was effectively eliminated by adopting the new method. Molten steel from the swirling flow SEN port uniformly moved to the solidification front, which improved the dissipation rate of molten steel super-heat. When the rotational direction of the swirling flow in SEN was in the same direction as M-EMS, the super-heat of molten steel in mold can be decreased by 5 K, compared to the use of a conventional SEN with M-EMS. As the current intensity decreased from 310 to 100 A, the super-heat of molten steel in the mold center region was reduced by 3 K. This is due to that the shielding effect of M-EMS on rotational flow momentum from the swirling flow SEN became weak as the stirring intensity decreased. In addition, molten steel temperature near the meniscus under the current intensity of 310 and 100 A was 1787 K and 1790 K, respectively. The solidified shell thickness obtained by using 100 A current intensity was about 1 × 10−3 m larger than that of 310 A current intensity. [ABSTRACT FROM AUTHOR]

A new measurement device, consisting of swirling blades and capsule-shaped throttling elements, is proposed in this study to eliminate typical measurement errors caused by complex flow patterns in gas-liquid flow. The swirling blades are used to transform the complex flow pattern into a forced annular flow. Drawing on the research of existing blockage flow meters and also exploiting the single-phase flow measurement theory, a formula is introduced to measure the phase-separated flow of gas and liquid. The formula requires the pressure ratio, Lockhart-Martinelli number (L-M number), and the gas phase Froude number. The unknown parameters appearing in the formula are fitted through numerical simulation using computational fluid dynamics (CFD), which involves a comprehensive analysis of the flow field inside the device from multiple perspectives, and takes into account the influence of pressure fluctuations. Finally, the measurement model is validated through an experimental error analysis. The results demonstrate that the measurement error can be maintained within ±8% for various flow patterns, including stratified flow, bubble flow, and wave flow. [ABSTRACT FROM AUTHOR]

AbstractGas–liquid swirling pipe flow plays an essential role in phase separators. Bubble motions and flow patterns transitions in the flow are crucial for further investigation of this flow. However, much attention has been paid to these in non-swirl flow instead of swirl flow. In this work, bubble separation generated by a vane-typed swirler in a vertical pipe with an inner diameter of 62 mm was experimentally studied. Superficial air velocities (0.036 − 1.41 m/s) and superficial water velocities (0.02 − 0.95 m/s). The results show that dispersed bubbles gradually transform to gas column flow with increasing superficial water velocities (0.093 − 0.640 m/s) in the swirl flow; gas column flow gradually transforms to swirling intermittent flow with increasing superficial air velocities (0.05 − 0.40 m/s), and one peak increases to two peaks in the probability density function curve of pressure drop; slug flow can transform to swirling intermittent flow. Finally, transition criteria for bubble separation were proposed: when the turbulent fluctuations are strong enough to overcome centrifugal force, then the bubbles move to the pipe center and coalescence with each other, lead to the transition of gas column flow/swirling intermittent flow. [ABSTRACT FROM AUTHOR]

In this study, a novel gas burner combining air swirl and an inverse diffusion flame (IDF) is designed for industrial applications. Numerical simulations using the Reynolds-averaged Navier–Stokes (RANS) method and simplified reaction mechanisms are conducted to predict the turbulent flow and combustion performance of the burner. Detailed flow structures, flame structures and effects of burner configurations are examined. The simulation results indicate that the swirl action of the burner creates a central recirculation zone and two external recirculation zones at the burner head, which stabilize combustion. The tangential velocity is minimal at the center of the burner and decreases with increasing distance from the outlet. As the distance from the exit increases, the maximum tangential velocity gradually decreases, and the peak value shifts towards the wall. This decrease in tangential velocity with axial distance signifies the gradual dissipation of the swirl effect, which disappears near the chamber outlet. The comparisons reveal that altering the number of burner fuel nozzles is more effective in reducing NO emissions than changing the inclination angle of the fuel nozzles, in the given conditions. Favorable combustion conditions are achieved when there are 16 fuel nozzles and the nozzle inclination angle is 60°, resulting in a 28.5% reduction in NO emissions at the outlet, compared to the reference condition. [ABSTRACT FROM AUTHOR]

This study examines the flow of the ternary nanofluid over a rotating stretchable cylinder with a torsional motion under the influence of a Cattaneo–Christov heat flux. In order to accomplish the goals of this simulation, a ternary hybrid nanofluid (THNF) that is based on water and incorporates nanoparticles with three distinct morphologies is considered. For assessing the colloidal mixture of spherical, cylindrical, and platelet shaped nanoparticles, the necessary models are used. By using appropriate similarity transformations, the modeled equations are reduced to a set of ordinary differential equations (ODEs). These ODEs are then solved using the finite element approach. The numerical integration's validity and reliability, as well as the newly obtained results, were thoroughly analyzed. Results reveal that the larger values of Reynolds number enhance the system's inertial force, which resists the liquid accelerating force and declines both velocities and heat transport. The rise in values of volume fractions and Reynolds number declines the skin friction coefficients along swirling and radial directions. The increase in values of both the thermal relaxation time parameter and Reynolds number improves the rate of heat transport. [ABSTRACT FROM AUTHOR]

The current paper presents a theoretical analysis of swirl flow stability, both inside a tube (vortex tube) and in a free annular swirl flow. The starting concept is the study of the evolution of velocity and temperature fluctuations. Methods of non-equilibrium thermodynamics are used to describe the magnitude of fluctuations and their properties. The important role of the total enthalpy follows from a variational analysis. Moreover, the thermodynamic criterion of the stability is formulated using the total enthalpy, and compared with experiments, numerical results and classical Rayleigh theory support its applicability. It was shown that the solid body vortex is at the margin of stability, which is experimentally observed. Analogously, the potential vortex is by the thermodynamic criterion stable; however, by the Rayleigh criteria it is on the onset of stability. The classical Taylor experiment of flow between two rotating cylinders is analysed from the point of view of this criterion. These results are underlined by swirl tube experiments at the Institute of Aerospace Thermodynamics at Stuttgart University and the annular nozzle experiments performed in the Institute of Thermomechanics CAS in Prague. Both independent experiments confirm the transformation of the initial annular vortex into a stable potential-type vortex. The results of this theory can also be used to explain the exceptional stability of tropical cyclones. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate the effect of coaxial swirlers on acoustic emission and reduction of potential core length in jet engines. Design/methodology/approach: The swirlers are introduced in the form of curved vanes with angles varied from 0° to 130°, corresponding to swirl numbers of 0–1.5. These swirlers are fixed in the annular chamber and tested at different nozzle pressure ratios of 2, 4 and 6. Findings: The study finds that transonic tones exist for the nonswirl jet, creating an unfavorable effect. However, these screech tones are eliminated by introducing a swirl jet at the nozzle exit. Weak swirl shows a greater reduction in noise than strong swirl at subsonic conditions. In addition, the introduction of swirl jets at all pressure ratios significantly reduces jet noise and core length in supersonic conditions, mitigating the noise created by shockwaves and leading to screech tone-free jet mixing. Originality/value: The paper provides valuable insights into the use of coaxial swirlers for noise reduction and core length reduction in jet engines, particularly in supersonic conditions. [ABSTRACT FROM AUTHOR]

Introduction: Uterine artery pseudoaneurysm (UAP) is a rare cause of late postpartum hemorrhage. Insufficient understanding of this condition among clinicians may result in delayed diagnosis and treatment, potentially leading to incorrect interventions and poor prognosis, including fatal hemorrhage and even necessitating hysterectomy in severe cases. Case Report: The patient, a 41-year-old woman with a history of three pregnancies and two deliveries, underwent cesarean section and subsequently experienced persistent small amounts of vaginal bleeding for a duration of two months. Transvaginal ultrasonography revealed a hypoechoic mass in the cervix that was initially misdiagnosed as a cervical fibroid. Approximately 12 h prior to admission, she experienced an episode of acute vaginal bleeding of significant intensity. Emergency transvaginal ultrasound demonstrated an intrauterine mass located in the posterior wall of the cervix with swirling blood flow, exhibiting a to-and-fro pattern. The mass was connected to the left uterine artery adjacent to the cervix through a tear measuring approximately 0.5 cm in diameter. Emergency bilateral uterine artery embolization was performed. After a follow-up period of ten months, there was no recurrence of abnormal vaginal bleeding, and subsequent ultrasound examination confirmed the complete resolution of the cervical lesions. Conclusion: The findings of this case suggest that the UAP undergoes a dynamic process. In the early stages, the lesion may manifest as a small hypoechoic or anechoic area within the myometrium. Color Doppler imaging might not reveal blood flow signals within the lesion, potentially leading to misdiagnosis as other common uterine lesions such as fibroids or cysts. However, considering the close association between UAP and the uterine artery, meticulous observation of the relationship between the uterine artery and its branches is crucial for identifying myometrial lesions to facilitate early detection of UAP and minimize misdiagnosis. [ABSTRACT FROM AUTHOR]

The swirling flow generated by the swirling chamber of the split swirling flow tundish can effectively promote the collision and growth of inclusions. The split swirling flow tundish can promote the removal of inclusions by improving the flow field. In this work, the CFD-PBM coupling model was applied to simulate the transport, aggregation, and floating removal of inclusions in the split swirling flow tundish, and compared with a same-size T-type tundish. The results indicated that the swirl flow can effectively promote the collision-coalescence of inclusions. Comparing the flow field of the split swirl tundish and the T-type tundish, the dead flow fraction of the two tundishes is similar, but the plug flow fraction of the split swirling flow tundish is 4.5% larger than the T-type tundish. Monitoring the volume concentration of inclusions at the outlet of the two tundishes, the inclusion removal rate of the T-shaped tundish and split swirling flow tundish are 29.28% and 34.33%, respectively. Therefore, the split swirling flow tundish is stronger than the T-shaped tundish in removing inclusion. Especially in the removal of small inclusions, the number density of 1.00–28.64 µm inclusions at the outlet of the split swirling flow tundish is 29.97%–65.91% lower than the T-type tundish, the split swirling flow tundish enhances the removal of small inclusions. [ABSTRACT FROM AUTHOR]

Many UAVs today have an S-bend inlet for the sake of stealth; however, the majority of them have a relatively gentle transition of the flow channel. This study presents an experimental investigation of the aerodynamic performance and swirl flow characteristics of a UAV inlet with double 90° bends, which is also integrated with an aircraft fuselage as well as a volute. The influences of angle of attack, sideslip angle, AIP Mach number and freestream speed are explored in detail. The influences of the deflectors installed ahead of the first 90° bend of the inlet and the baffle installed at the bottom of the volute are revealed. It is found that both the deflectors and the baffle are beneficial in enhancing the aerodynamic performance of the inlet and alleviating the intensity of the swirl flow inside the volute. [ABSTRACT FROM AUTHOR]

Efficient metal recovery from industrial wastewater facilitates addressing of the environmental hazards and resource requirements of heavy metals. The conventional electrodeposition recovery method is hampered by the limitations of interfacial ion transport in charge-transfer reactions, creating challenges for simultaneous rapid and high-quality metal recovery. Therefore, we proposed integrating a transient electric field (TE) and swirling flow (SF) to synchronously enhance bulk mass transfer and promote interfacial ion transport. We investigated the effects of the operation mode, transient frequency, and flow rate on metal recovery, enabling determination of the optimal operating conditions for rapid and efficient sequential recovery of Cu in TE&SF mode. These conditions included low and high electric levels of 0 and 4 V, a 50% duty cycle, 1 kHz frequency, and 400 L·h−1 flow rate. The kinetic coefficients of TE&SF electrodeposition were 3.5–4.3 and 1.37–1.97 times that of single TE and SF electrodeposition, respectively. Simulating the deposition process under TE and SF conditions confirmed the efficient concurrence of interfacial ion transport and charge transfer under TE and SF synergy, which achieved rapid and high-quality metal recovery. Therefore, the combined deposition strategy is considered an effective technique for reducing metal pollution and promoting resource recycling.

The interaction of opposite-signed twist waves on vortex tubes can lead to vortex bursting, a process where the core expands into a double ring-like structure with strong swirling flows. Previous works have studied vortex bursting on rectilinear vortices by axially perturbing the initial core size to generate the twist waves, and observed largely axisymmetric bursting dynamics. In this work, we numerically study bursting on vortical structures with curved centrelines, analysing the interaction between the centreline dynamics, twist wave generation and propagation, and vortex bursting. We focus on axially perturbed helical vortex tubes with small radius-to-pitch ratios up to $0.0625$ , as well as vortex rings with a large radius-to-core size ratio $10$ , both at a circulation-based Reynolds number $5000$. The results show that though the initial twist wave propagation speeds are relatively unaffected by the curvature and torsion of the centreline, the bursting process is altered significantly compared with rectilinear vortices. The self-induced rotation of the centreline of the helical tube induces a non-axisymmetric distortion of the bursting structure, which rapidly breaks up the vortex core into small-scale helical structures. A similar destabilization of the bursting structure also occurs on vortex rings. The enstrophy increase and accelerated energy decay associated with bursting are predominantly determined by the twist wave strength, rather than the curvature and torsion of the centreline. Combined, our findings imply that bursting could play an important role in transferring and dissipating energy of vortical structures in wakes, and turbulent flows in general. [ABSTRACT FROM AUTHOR]

AbstractThis study concerns the numerical simulation of a system of swirling turbulent jets impacting a flat plate, by two numerical models of the closure of the Navier Stokes equations (k-ω sst). The jet impact technique is widely applied in the field of heating, drying and cooling of industrial objects. The experimental test bench comprising a diffuser of diameter D, impacting the perpendicular plate, such that the impact distance H = 4D. The swirl is obtained by a swirl generator, made up of 12 fins arranged at 60° from the vertical, placed just at the outlet of the diffuser. The temperature of the swirling jets blowing on the plate is measured with a VELOCICALC PLUS portable thermo-anemometer device, in different stations. It is noted that this diffuser configuration having balanced inlet temperatures (T, T, T), gives a uniform distribution of temperature and velocity on the surface of the plate. This temperature distribution results from a 95% spread of homogenization of plate heat transfer. The (k-ω sst) model gave temperature and velocity profiles that coincide with those of the experimental results. By way of comparison, the (k-ω sst) model better predicts impacting jets, particularly in fluctuating zones. The latter remains a relatively better numerical simulation tool in terms of quality. [ABSTRACT FROM AUTHOR]

This study focused on using swirling flow as a method to stabilize the detonation behavior and shorten the deflagration-to-detonation transition (DDT) distance of pulse detonation engines; additionaly, the study investigates the effect of swirling flow on flame propagation behavior and DDT distance. A swirling flow in which the circumferential velocity in the radial direction gradually increased from the center toward the wall and decreased near the wall was confirmed. Laser doppler velocimetry (LDV) confirmed that the swirl number is smaller in the axial velocity distribution when the number of swirling injector couplings is small. The DDT shortening ratio obtained using ten swirling injector couplings is larger than that obtained using five couplings. These results indicate that injector-induced swirling flow can increase the burning velocity and is an effective method to shorten the DDT distance. • Swirling flow used to stabilize detonation behavior and shorten DDT distance. • Circumferential velocity distribution across pipe section measured using a particle image velocimetry. • Swirl number of pipe swirling flow measured using a laser Doppler velocimeter. • The swirling flow increased the flame propagation velocity and reduced the DDT distance. [ABSTRACT FROM AUTHOR]

Using the SST k-ω turbulence model, a comprehensive numerical investigation was conducted to analyze the flow and heat transfer characteristics of steam within an isosceles trapezoidal cooling channel with pin-fin arrays modeled from the trailing edge of a F-class gas turbine high-temperature blade. The influence laws of various parameters, including the Reynolds number (Re, from 10,000 to 50,000), dimensionless pin-fin diameter (d/H, from 0.4 to 0.8), and dimensionless pin-fin spacing (S/H, from 1.6 to 2.4), on the flow and heat transfer performance of the isosceles trapezoidal cooling channel with pin-fin arrays were examined. Sensitivity analysis was employed to determine the relative significance of these influence parameters on the cooling performance of the isosceles trapezoidal channel with pin-fin arrays. Finally, the corresponding heat transfer and friction correlations within the investigated parameter range were developed. The research findings reveal that under different Reynolds numbers, as the dimensionless pin-fin diameter increases from 0.4 to 0.8, the friction factor within the isosceles trapezoidal cooling channel with pin-fin arrays increases by a factor of 3.25 to 3.41, while the overall average Nusselt number improves by 31.05% to 37.41%. Conversely, when the dimensionless pin-fin spacing increases from 1.6 to 2.4, the friction factor within the isosceles trapezoidal cooling channel with pin-fin arrays decreases by 67.38% to 69.18%, accompanied by a reduction in the overall average Nusselt number by 24.95% to 31.14%. When both the flow performance and heat transfer performance are taken into account, the importance of the influence parameters ranks as follows: Reynolds number, pin-fin diameter, and pin-fin spacing. It also suggests that smaller pin-fin diameters and larger pin-fin spacing should be selected in the design stage based on the variation laws of integrated thermal-hydraulic performance. The results may provide valuable references and insights for the design of steam cooling structures within high-temperature turbine blade trailing edge channels in advanced gas turbines. [ABSTRACT FROM AUTHOR]

This work primarily focuses on a three-dimensional model of flame propagation and stable combustion in a scramjet chamber. The one-equation LES turbulence model is adopted to close the sub-grid-scale turbulent viscosity terms. The finite-rate combustion model, along with the Jachimowski detailed hydrogen reaction mechanism with eight components and nineteen steps, is used to analyze the flame propagation characteristics of hydrogen combustion in the scramjet combustion chamber. Initially, based on the combustion chamber model, the effect of different injection locations and equivalence ratios on flame kernel formation and the flame propagation process is analyzed. The relationship between different fuel injection conditions and the oxygen consumption rate of the combustion chamber, as well as the total pressure recovery coefficient changes, is investigated. The research focuses on changes in equivalence ratios and injection hole distributions, with injection holes arranged upstream, downstream, and inside of the cavity. The result indicated that when the injection holes were arranged downstream of the cavity, there was a phenomenon of flame backflow into the cavity, which was related to the size of the injection pressure. For this work, the pressure causing flame backflow was approximately 2 MPa. When the injection hole was arranged inside the cavity, the relative distance difference between the injection hole and the upper wall of the cavity led to the formation of two reaction zones in the combustion chamber. When the injection hole was arranged upstream of the cavity, different injection equivalence ratios affected the final stable position and structure of the flame. Therefore, the injection position, injection pressure, and injection equivalence ratio all had a certain impact on the flame kernel formation and flame propagation process. [ABSTRACT FROM AUTHOR]

Detailed numerical analyses of pulverised solid fuel flames are computationally expensive due to the intricate interplay between chemical reactions, turbulent multiphase flow, and heat transfer. The near-burner region, characterised by a high particle number density, is particularly influenced by these interactions. The accurate modelling of these phenomena is crucial for describing flame characteristics. This study examined the reciprocal impact between the discrete phase and the continuous phase using Reynolds-averaged Navier–Stokes (RANS) simulations. The numerical model was developed in Ansys Fluent and equipped with user-defined functions that adapt the modelling of combustion sub-processes, in particular, devolatilisation, char conversion, and radiative heat transfer under oxyfuel conditions. The aim was to identify the appropriate degree of detail necessary for modelling the interaction between discrete and continuous phases, specifically concerning mass, momentum, energy, and turbulence, to effectively apply it in high-fidelity numerical simulations. The results of the numerical model show good agreement in comparison with experimental data and large-eddy simulations. In terms of the coupling schemes, the results indicate significant reciprocal effects between the discrete and the continuous phases for mass and energy coupling; however, the effect of particles on the gas phase for momentum and turbulence coupling was observed to be negligible. For the investigated chamber, these results are shown to be slightly affected by the local gas phase velocity and temperature fields as long as the global oxygen ratio between the provided and needed amount of oxygen as well as the thermal output of the flame are kept constant. [ABSTRACT FROM AUTHOR]

Swirl has been employed as a mechanism for enhancing the spreading rate of jets, especially in the multiphase context of liquid droplets suspended in a gaseous jet. This work examines the effect of the swirl phenomenon on the downstream development of turbulent round jet sprays using Euler–Lagrange simulations. Two simulation sets are performed: The first set consists of single-phase simulations, and the second set consists of two-phase large eddy simulations where the droplets are stochastically added to the computational domain using an injection model. The simulations consider five different non-dimensional swirl strengths from 0.0 to 2.0 at a Reynolds number of 50,000. As simulation results, we obtain the total normalized number flux of droplets and for each droplet size bin along with the mean and standard deviation of the droplet velocity distributions. We quantify the influence of swirl on the higher-order statistics of the spray behavior. [ABSTRACT FROM AUTHOR]

This article presents a study of aerothermal performance of tubes with regularly-spaced multi-channel twisted tape elements (RS-MTT) installed. This research aimed to find the proper design RS-MTTs that induce swirl flow which potentially improves fluid mixing between the core fluid and the fluid near the tube wall, thereby accelerating the heat transfer rate. Additionally, the effects of Reynolds numbers and free-spacing ratios (s/y) on heat transfer, friction loss, and thermal performance behaviors were examined. The RS-MTTs having different free-spacing ratios (s/y) of 0.0, 0.25, 0.5, 0.75, and 1.0 were tested. Air was utilized as the testing fluid in experiments with Reynolds numbers (Re) spanning from 6000 to 20,000. The utilization of RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 augmented heat transfer rates up to 1.74, 1.80, 1.85, 1.90, and 2.15 times given by the plain tube alone while the friction factors increased by 4.22, 4.61, 3.87, and 4.05 times, respectively. At the lowest Reynolds number of 6000, the thermal enhancement factors of the tube containing the RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 reached the maximum values of 1.42, 1.35, 1.31, 1.27, and 1.23, respectively. Among the RS-MTTs tested, the RS-MTT with s/y = 0.0 showed the best thermal enhancement factor of 4.56%, corresponding to the heat transfer augmented of 11.52% with a friction penalty of 8.71%. [ABSTRACT FROM AUTHOR]

A mathematical model is developed for a non-Newtonian tangent hyperbolic fluid over a rotating disk by extending the concept of standard von Karman swirling flow. The impact of magnetic field, melting heat transfer, viscous dissipation, and Joule heating are incorporated. The existing leading nonlinear partial differential equations are modified into ordinary differential equations by using similarity transformation. Then, the bvp4c solver is adopted to investigate the solution of modified nonlinear ordinary differential equations with boundary constraints. The probable error (PE) is computed to examine the reliability of the correlation coefficient ( r ∗ ) of the physical parameters. The presence and absence of power-law index parameter are depicted and compared by graphical and tabular form. The rotation parameter is positively correlated and the Weissenberg number is negatively correlated in the presence of the power-law index. Moreover, the Eckert number shows a dual nature in temperature and entropy generation profiles. Finally, velocities, i.e., radial and azimuthal are diminished by enhancing magnetic parameter. [ABSTRACT FROM AUTHOR]

Experimental research was conducted on an annular air jet. The active flow control was introduced by means of tangentially arranged synthetic jets. Flow visualization and measurements of the flow velocity and stagnation pressure on an impingement wall were performed. Tests were carried out with Reynolds numbers ranging from 4000 to 10,000 (evaluated from the outer exit diameter of the annular nozzle). Bistability and hysteretic effects were revealed, because two alternative flow field patterns (A and B) were identified under the same boundary conditions. In the A pattern, a small recirculation area (bubble) of separated flow was attached to the nozzle centerbody. In the B pattern, a large recirculation area of separated flow bridged the entire nozzle-to-wall distance. The effect of the Reynolds number was evaluated: the hysteresis and bistability were not observed for Re ≥ 9000. Concerning the effect of flow control, it was concluded that a moderate swirling effect can effectively suppress the hysteresis and bistability. [ABSTRACT FROM AUTHOR]

The impact of the swirl number on the flow field of a single-stage swirl combustor is investigated using the particle image velocimetry technology. The variations in recirculation zone size, pulsating region, turbulent distribution, vorticity, and Reynolds stress within the combustor are summarized through quantitative analysis of the flow field. Experimental results indicate the following: (1) Under the same air mass flow rate, the length of the recirculation zone in the combustion state is shorter than that in the cold state. (2) The length of the recirculation zone and the axial vortex spacing display a decreasing trend as the swirl number increases, while the width of the recirculation zone demonstrates an increasing trend. (3) For the single-stage swirl combustor, the primary pulsating region is at the swirling jet area at the exit of the swirl. As the swirl number increases, the standard deviation of radial velocity fluctuations and turbulent kinetic energy also increase. (4) The strong shear region of the single-stage swirl combustor can be divided into inner and outer shear layers based on the vorticity distribution and the Q criterion. The vortices in the inner and outer shear layers exhibit opposite orientations according to the vorticity distribution. Overall, the research results can provide basic experimental data for numerical simulation of swirl combustion. [ABSTRACT FROM AUTHOR]

In response to the prevalent issue of sand presence in liquid, particularly prominent in petroleum engineering, a novel cyclone separator has been meticulously engineered for fine-particle separation. Experiments and numerical simulation methods have provided a profound understanding of the flow-field characteristics and separation efficacy of this device. The internal architecture of the swirling flow inside the separator features a distinctive central vortex core, complemented by a turbulent secondary vortex formation in the lower section of the underflow. As the axial height increases, the secondary vortex gradually dissipates. An analysis of pressure and velocity distribution within the cyclone separator confirms the establishment of a stable cyclone field in the built-in cyclone and a tendency for the flow field within the tank to exhibit uniformity with increasing height. These flow-field characteristics show that the cyclone separator has a good separation effect on fine-rust particle impurities. Furthermore, the separation efficiency of the novel cyclone separator demonstrates a positive correlation with increasing particle size. Of the parameters studied, variation of the inlet velocity is the best method for obtaining optimum separation efficiency for a cyclone desander with a fixed particle size. Specifically, when the inlet velocity reaches 3 m/s, the desander attains an impressive separation efficiency of up to 70%. [ABSTRACT FROM AUTHOR]

Numerical simulation is applied to investigate the outflow of an incompressible three-dimensional turbulent swirled wall jet. The purpose of the study is to determine the jet flow structure and to compare the characteristics of swirled and nonswirled jets. The numerical solution of the equations of motion is obtained using large eddy simulation with wall resolution (WRLES). The results of the modeling are compared with the data of a unique published study devoted to experimental investigation of swirled wall jets. [ABSTRACT FROM AUTHOR]

The energy required for technological advancement is primarily derived from hydrocarbon combustion, which is a key topic in thermodynamics. The stability of the flame in hydrocarbon combustion is a critical parameter that impacts both burner design and combustion efficiency. Various methods have been employed in the literature to achieve a stable flame, with swirl flow being one technique that enhances combustion performance in engineering applications. This study focuses on the numerical analysis of the SM1 flame from Sydney swirl flames. Initially, the flow incorporating the two-equation Re-Normalization Group (RNG) k-e and Shear Stress Transport (SST) k-ω turbulence models, along with the chemical reactions of CH4 combustion using the GRI 3.0 reaction mechanism, was modeled and compared with experimental data. Subsequently, the numerical results obtained from the Shear Stress Transport k-ω turbulence model, which demonstrated the best agreement with experimental data, were compared with results from a numerical analysis in the literature using the Large Eddy Simulation (LES) turbulence model. The predictive capabilities of these two turbulence models, along with their behavior in the flow region, were evaluated. The comparison revealed that for stable flames within the Sydney swirl flame family, the Shear Stress Transport k-ω turbulence model, which provides results in a more efficient manner, is sufficient compared to the computationally expensive Large Eddy Simulation turbulence model. This choice is made possible by utilizing a solution algorithm tailored to the flow characteristics and appropriate boundary conditions. [ABSTRACT FROM AUTHOR]

Unstable flows in the runner of water turbines, such as reverse flow, vorticity and flow direction transition, are the main factors causing increased losses and decreased efficiency, and changing the geometry structure in the downstream of the runner is an important means of mitigating these instabilities. The different flow fields downstream of runners induced by different locking nut structures are numerically calculated and verified by experimental results. The flow states are evaluated in terms of characteristic quantities such as pressure gradient, swirling flow, reverse flow, and vorticity. The results show a non-negligible effect of the locking nut, which leads to a more uniform pressure distribution, increases the descending speed of the reverse flow rate, and reduces the volume and strength of the vortex. The small locking nut significantly weakens the pressure gradient, reduces the top reverse flow zone, and decreases the vortex volume at the blade flow passage outlet and the size of the downstream disturbance vortex. The extended lock nut reduces the growth rate of the vortex generation rate and the size of the partial vortex, but increases the range of the high-pressure zone, causing the bottom reverse flow and increasing the vortex. [ABSTRACT FROM AUTHOR]

Microbubbles, which are tiny bubbles with a diameter of less than 100 µm, have been attracting attention in recent years. Conventional methods of microbubble generation using porous material and swirling flows have problems such as large equipment size and non-uniform bubble generation. Therefore, we have been developing a hollow ultrasonic horn with an internal flow path as a microbubble-generating device. By supplying gas and ultrasonic waves simultaneously, the gas–liquid interface is violently disturbed to generate microbubbles. Although this device can generate microbubbles even in highly viscous fluids and high-temperature fluids such as molten metals, it has the problem of generating many relatively large bubbles of 1 mm or more. Since the generation of a large amount of microbubbles in a short period of time is required to realize actual applications in agriculture, aquaculture, and medicine, conventional research has tried to solve this problem by increasing the amplitude of the ultrasonic oscillation. However, it is difficult to further increase the amplitude due to the structural reasons of the horn and the behavior of bubbles at the horn tip; therefore, the oscillating area of the tip of the horn, which had not received attention before, was enlarged by a factor of 2.94 times to facilitate the ultrasonic wave transmission to the bubbles, and the effect of this was investigated. As a result, a large number of gases were miniaturized, especially at high gas flow rates, leading to an increase in the amount of microbubbles generated. [ABSTRACT FROM AUTHOR]

An experimental study of combustion in diffusion and coaxial mesoscale burner arrays was conducted. To that end, different linear and planar arrangements were tested, and blow-off limits, flame geometry, and oscillations parameters were determined. The new results of the experiments showed that the coaxial burner arrays, in general, are characterized by leaner values of the blow-off limit compared to premixed flames. Moreover, the large planar arrangement (square 5 × 5) provides the global blow-off equivalence ratio value of about 0.1 at low thermal power operating modes (less than 2 kW). All arrays of coaxial jets feature flame separation into small coaxial flamelets. However, linear coaxial arrangements provide complete flame separation, whereas jets of a planar array are not fully separated and merged in pairs. At the equivalence ratio value less than 0.45, separated flames start oscillating strongly until the blow-off occurs, that is unacceptable in terms of combustion efficiency, pollutant emission, and related parameters. Therefore, the most favorable operating modes correspond to the equivalence ratio ranging from 0.45 to 0.6. [ABSTRACT FROM AUTHOR]

The flow in the draft tube of the water turbine is affected by the upstream flow and the inherent structure accompanied by various undesirable characteristics, affecting the efficient and stable operation of the water turbine. Changing the flow structure downstream of the runner is an important measure to reduce hydraulic loss in the draft tube and improve stability. In this study, three downstream structures of the runner, namely, the non-locking nut, small locking nut, and extended locking nut are numerically calculated and verified using experimental results. The unstable flow characteristics of the draft tube are analyzed using variations in swirling flow, backflow, pressure gradient, and vortex strip. The results show the non-negligible effect of the locking nut, which significantly reduces the rotational momentum flux at the draft tube inlet, accelerates the decay rate of the swirling flow, and suppresses the generation of axial low pressure. The small locking nut significantly reduces the pressure gradient, shortens the backflow zone, and decreases the backflow velocity. The extended locking nut reduces the backflow zone in some sections and reduces the vortex zone of the straight section but prolongs the backflow zone and increases the backflow velocity. [ABSTRACT FROM AUTHOR]