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We consider ( - α )-homogeneous solutions to the stationary incompressible Euler equations in R 3 \ { 0 } for α ≧ 0 and in R 3 for α < 0 . Shvydkoy (2018) demonstrated the nonexistence of ( - 1 )-homogeneous solutions (u , p) ∈ C 1 (R 3 \ { 0 }) and ( - α )-homogeneous solutions in the range 0 ≦ α ≦ 2 for the Beltrami and axisymmetric flow; namely, that no ( - α )-homogeneous solutions (u , p) ∈ C 1 (R 3 \ { 0 }) for 1 ≦ α ≦ 2 and (u , p) ∈ C 2 (R 3 \ { 0 }) for 0 ≦ α < 1 exist among these particular classes of flows other than irrotational solutions for integers α . The nonexistence result of the Beltrami ( - α )-homogeneous solutions (u , p) ∈ C 2 (R 3 \ { 0 }) holds for all α < 1 . We show the nonexistence of axisymmetric ( - α )-homogeneous solutions without swirls (u , p) ∈ C 2 (R 3 \ { 0 }) for - 2 ≦ α < 0 . The main result of this study is the existence of axisymmetric ( - α )-homogeneous solutions in the complementary range α ∈ R \ [ 0 , 2 ] . More specifically, we show the existence of axisymmetric Beltrami ( - α )-homogeneous solutions (u , p) ∈ C 1 (R 3 \ { 0 }) for α > 2 and (u , p) ∈ C (R 3) for α < 0 and axisymmetric ( - α )-homogeneous solutions with a nonconstant Bernoulli function (u , p) ∈ C 1 (R 3 \ { 0 }) for α > 2 and (u , p) ∈ C (R 3) for α < - 2 , including axisymmetric ( - α )-homogeneous solutions without swirls (u , p) ∈ C 2 (R 3 \ { 0 }) for α > 2 and (u , p) ∈ C 1 (R 3 \ { 0 }) ∩ C (R 3) for α < - 2 . This is the first existence result on ( - α )-homogeneous solutions with no explicit forms. The level sets of the axisymmetric stream function of the irrotational ( - α )-homogeneous solutions in the cross-section are the Jordan curves for α = 3 . For 2 < α < 3 , we show the existence of axisymmetric ( - α )-homogeneous solutions whose stream function level sets are the Jordan curves. They provide new examples of the Beltrami/Euler flows in R 3 \ { 0 } whose level sets of the proportionality factor/Bernoulli surfaces are nested surfaces created by the rotation of the sign ' ' ∞ ′ ′ . [ABSTRACT FROM AUTHOR]

We consider circular Rayleigh problem which is incompressible, inviscid axial flows to axisymmetric disturbances. For this problem, we derived unbounded parabolic instability region which intersects with Batchelor and Gill semicircle instability region under certain condition. This has been illustrated with examples. Furthermore, we obtained supremum bound for the growth rate of an unstable mode, amplification factor. [ABSTRACT FROM AUTHOR]

The current work evaluates the effectiveness of the pressure-corrected osculating axisymmetric flows method in the design of hypersonic wavecatcher intakes with shape transition. The original osculating axisymmetric flows method, which is essentially used in waverider design, has drawbacks in accurately demonstrating the three-dimensional flowfield due to ignoring the cross-flow effects between the osculating planes. This negatively impacts the intake performance due to the presence of lateral pressure gradients. The pressure-corrected method takes into account these effects by incorporating lateral pressure gradient corrections into the original design methodology using cross-flow velocity information. This results in the generation of three-dimensional streamlines rather than the two-dimensional streamlines of the original method. The semirectangular-to-ellipse wavecatcher intake is selected as the subject of investigation, and the design procedure is reviewed. The characteristics of the wavecatcher intakes with a design point of Mach 6.0 are studied. Computational fluid dynamics analysis of pressure-corrected wavecatcher intakes is presented to assess the design technique. It is found that the initial conical shock impinges at the intake's entrance and the streamtube is completely captured. Furthermore, the comparison with the original wavecatcher intake indicates that the pressure-corrected wavecatcher intake demonstrated better performance in terms of total pressure recovery and flow uniformity. The wavecatcher intake with entrance-to-exit shapes transition showed higher performance than those with the same entrance and exit shapes. [ABSTRACT FROM AUTHOR]

Flow inside the axial test turbine VT-400 is measured by using a standard methodology of Particle Image Velocimetry (PIV). The studied area lies between the stator and rotor wheel in meridional plane. This area covers both: the regular flow near hub and the endwall secondary structures as well. Regular structure of wakes and jets past stator blades is observed in terms of mean velocities and turbulence intensity. The fluctuations are close to isotropy and the energy distribution across length-scales exhibits almost Kolmogorov scaling. Near the hub, we observe secondary vortices. Despite the positive radial ejections in that regions, these secondary vortices drift towards the hub, they dissipate energy and circulation and their core grows in size. [Display omitted] • Particle Image Velocimetry measurement in Stereo configuration inside test axial turbine. • Meridional (i.e. axial × radial) plane past the stator wheel endwall at underloaded, nominal and overloaded regime. • Observation of wakes and jets; wake/jet amplitude do not follow velocity magnitude; periodicity corresponds to geometry of stator wheel. • Fluctuations in region of wakes and jets up to 10%; spatial spectra follows Kolmogorov law with depletion at the wake periodicity. • Secondary flow contain radial ejections and secondary vortices of single orientation; these vortices drift towards the hub. [ABSTRACT FROM AUTHOR]

Background: In selected cases of cardiogenic shock, veno-arterial extracorporeal membrane oxygenation (V-A ECMO) is combined with trans valvular micro axial flow pumps (ECMELLA). Observational studies indicate that ECMELLA may reduce mortality but exposing the patient to two advanced mechanical support devices may affect the early inflammatory response. We aimed to explore inflammatory biomarkers in a porcine cardiogenic shock model managed with V-A ECMO or ECMELLA. Methods: Fourteen landrace pigs had acute myocardial infarction-induced cardiogenic shock with minimal arterial pulsatility by microsphere embolization and were afterwards managed 1:1 with either V-A ECMO or ECMELLA for 4 h. Serial blood samples were drawn hourly and analyzed for serum concentrations of interleukin 6 (IL-6), IL-8, tumor necrosis factor alpha, and serum amyloid A (SAA). Results: An increase in IL-6, IL-8, and SAA levels was observed during the experiment for both groups. At 2–4 h of support, IL-6 levels were higher in ECMELLA compared to V-A ECMO animals (difference: 1416 pg/ml, 1278 pg/ml, and 1030 pg/ml). SAA levels were higher in ECMELLA animals after 3 and 4 h of support (difference: 401 ng/ml and 524 ng/ml) and a significant treatment-by-time effect of ECMELLA on SAA was identified (p = 0.04). No statistical significant between-group differences were observed in carotid artery blood flow, urine output, and lactate levels. Conclusions: Left ventricular unloading with Impella during V-A ECMO resulted in a more extensive inflammatory reaction despite similar end-organ perfusion. [ABSTRACT FROM AUTHOR]

The spread of blast dust throughout the tunnel becomes a common problem in drill and blast tunneling,the key to breaking through the problem is the creation of a dust control area on the working face.In view of this key problem, a wet string grid dust removal crawler vehicle was developed, the power of the vehicle came from the diesel generator, and further, the air cooler of the diesel generator was used to generate airflow, and the suction process formed by the on-board axial flow fan was coupled to create a dust control area of the working face after blasting.The results show that when the frequency of the axial flow fan is adjusted to 30 Hz, the airflow speed of the wet chord grid section reaches 3.34 m/s, and the dust removal efficiency is the highest, with a value of 94.3%.Compared with the non-use of the dust removal vehicle, when the air outlet of the air cooler is front, horizontal front, horizontal rear, the dust concentration is reduced by 74.37, 92.39 and 50.53%.Finally, the optimized wet grid dust removal crawler was installed in the Dading tunnel, and the actual dust reduction efficiency was about 78.49%. The results obtained provide an important technical way to improve the working environment of the drilling and blasting construction tunnel. [ABSTRACT FROM AUTHOR]

In practical aerodynamic scenarios, interactions between curved shock waves and boundary layers with composite shock curvatures in both streamwise and spanwise directions are encountered more frequently than those induced by planar oblique shocks. To gain a more systematic understanding of this phenomenon in physics, internal and external axisymmetric curved shock wave/boundary layer interactions (AC-SBLI) are being studied analytically by establishing the underlying relations within the flow structures. Specifically, based on reconstructing the dominant structures of AC-SBLI as a semi-analytical model, this study focuses on the impacts of shock spanwise curvatures on separation and the mechanism of their action. It reveals that spanwise curvatures affect the separation in both internal and external AC-SBLI, but each exhibits a different influence pattern, emphasizing apparent axisymmetric characteristic. The spanwise curvatures exert influence indirectly by altering the compression ratio and directly by affecting the distribution of streamwise shock intensities. These findings propose a new approach to estimating the flow structures in AC-SBLI, where analyzing the spanwise curvatures will assist with comprehending other more intricate three-dimensional separation phenomena. [ABSTRACT FROM AUTHOR]

For a pre-swirl pump-jet propulsor (PJP), the stator inevitably induces the problem of rotor–stator interaction (RSI). In this paper, the mechanism of RSI in a PJP is analyzed through dynamic mode decomposition (DMD). The coherent flow structures and corresponding frequencies have been decomposed and analyzed. The results show that the dominant frequencies of pressure fluctuation in the stationary domain are BPF (rotor blade passing frequency) and its multiples. In contrast, the dominant frequencies in the rotational domain are SPF (stator passing frequency) and its multiples. The frequencies of k*SF (SF, shafting frequency; k = 4, 5, and 8) have also been found. The mode structure corresponding to the SPF is stable and has the highest mode energy. The reconstruction residual formula is introduced, and the axial velocity flow field is reconstructed well by the DMD modes compared with the raw flow field. This research can provide a reference for studying and suppressing RSI in a PJP. [ABSTRACT FROM AUTHOR]

Tip clearance cavitation (TCC) is a type of vortex cavitation. It widely exists in axial flow hydraulic machinery and has significant negative influence on the mechanical service life and the operating stability. It is necessary to suppress the tip clearance vortices (TCV) to control the TCC in engineering applications. Based on the analysis of the advantages and disadvantages of the present various suppression strategies, a new coupling method is proposed in this study by combining the damping approach and the diversion approach. Porous medium material is used to realize the coupling effect. A 2 mm span length porous tip is installed on the solid tip surface of a hydrofoil under two gap sizes conditions (representing two types of gap flow pattern), and excellent suppression results of the TCV and TCC are obtained. The characteristics and mechanism of the clearance flow are analyzed by numerical simulation. The numerical accuracy is verified by experimental qualitative observations. The simulation results show that the temporal and spatial stability of the clearance flow field is enhanced, and the leakage velocity and the TCV strength are weakened via the combined action of damping and diversion effects. There is a difference in the damping mechanism between the two gap flow patterns. It is a comprehensive result of viscous dissipation and momentum loss in the jet pattern represented by the small gap size, and primarily, the result of momentum loss in the rolling pattern represented by the large gap size. [ABSTRACT FROM AUTHOR]

In numerical linear stability investigations, the rates of change of the kinetic and thermal energy of the perturbation flow are often used to identify the dominant mechanisms by which kinetic or thermal energy is exchanged between the basic and the perturbation flow. Extending the conventional energy analysis for a single-phase Boussinesq fluid, the energy budgets of arbitrary infinitesimal perturbations to the basic two-phase liquid–gas flow are derived for an axisymmetric thermocapillary bridge when the material parameters in both phases depend on the temperature. This allows identifying individual transport terms and assessing their contributions to the instability if the basic flow and the critical mode are evaluated at criticality. The full closed-form energy budgets of linear modes have been derived for thermocapillary two-phase flow taking into account the temperature dependence of all thermophysical parameters. The influence of different approximations to the temperature dependence on the linear stability boundary of the axisymmetric flow in thermocapillary liquid bridges is tested regarding their accuracy. The general mechanism of symmetry breaking turns out to be very robust. [ABSTRACT FROM AUTHOR]

Cyclodextrins (CDs), due to its unique 'outer hydrophilic and inner hydrophobic' structure, can be used as excellent carriers to protect active aroma compounds. The hydrodynamic conditions in the reactor substantially influence the characteristics of the cyclodextrin inclusions. Based on this, this study investigated the effects of the impeller type and the rotational speed on the characteristics of the inclusion complexes, meanwhile the corresponding scale-up process was also investigated. Results showed that the pitched blade turbine was the optimum impeller due to better axial flow performance. The average particle size, polydispersity index (PDI), loading capacity and the major aroma concentration of the inclusion complexes prepared at 5 and 120 L reactors did not have significant difference compared to the inclusion complexes prepared at 0.5 L reactor under conditions of geometry similarity and constant power per unit volume, which verified the feasibility of the scale-up rule of the encapsulation process. [ABSTRACT FROM AUTHOR]

Conceptual design studies performed with reduced-order approaches allow feasibility and sizing considerations of air-breathing engines to be configured at an affordable computational cost. The present study is devoted to exploring the design space of a dual-mode ramjet engine operating in scramjet mode by means of reduced-order analysis to assess the effects of propulsive system design configurations on component level and overall performance characteristics. The approach proposed in this work combines axisymmetric flow configuration used for the design of supersonic/hypersonic intakes and solutions of one-dimensional flow governing equations coupled with finite-rate chemistry and thermophysical properties tables in the numerical domains of the combustor and nozzle components. The scramjet design space is generated by varying parameters which are flight Mach number and altitude, intake truncation angle, intake exit Mach number and equivalence ratio. Performance outputs of total pressure recovery factor, compression ratio, captured air mass flow rate, intake startability index, thrust, specific impulse, fuel consumption and overall efficiency are computed for each design scenario. The generated database is visualized via performance maps and analyzed in terms of propulsive characteristics. A feature importance study is also conducted to quantify the effects of design parameters on the propulsive performance. • Reduced-order modeling of propulsion systems decreases the complexity of analysis. • Scramjet design space consists of thermal choking, non-ignition, and propulsive zones. • Uninstalled thrust strongly depends on combustor inlet and cruise Mach numbers. • Total pressure recovery is the dominant factor dictating the intake efficiency. • Low speed flow at burner inlet yields autoignition but may cause thermal choking. [ABSTRACT FROM AUTHOR]

In this paper, we examine the shape effects of different nanoparticles of an incompressible, unsteady flow of a nanofluid Al 2 O 3 with water H 2 O as the base fluid over a rotating disk. Magnetic field results are also added. In this research, four distinct shapes of Al 2 O 3 nanoparticles, i.e., sphere, blade, cylinder and brick, have been employed. Every shape is suspended at the same volume. After using the Von Karman transformation, the Navier–Stokes equation, along with the magnetic field effect and the thermal energy equation, is numerically solved by using the bvp4c MATLAB solver. The effects of various parameters on the velocity field and temperature profile are illustrated graphically. This analysis is validated by comparing it to the previously described research. Furthermore, increasing the volume fraction parameter 0 ≤ ϕ ≤ 0. 1 % causes the radial, tangential, and axial velocities near the disk for the shapes brick, cylinder, and blade to decrease and increase for the shape sphere. The fluid rotating in front of the disk rotates more slowly for small values of the unsteadiness parameter α ̂. The magnetic field M has a significant influence on the axial flow when the suction parameter values are small, but this impact is limited when the suction parameter values are large. [ABSTRACT FROM AUTHOR]

In this paper, we have analyzed the bifurcation of stagnation points in the non-Newtonian flow of the FENE-P fluid through a channel induced by peristalsis. The stream function for the flow under consideration is developed under negligible inertia and streamline curvature effects. A nonlinear autonomous system is developed for scrutiny of the critical points. A dynamical system approach is used to examine the stability of bifurcation points. Streamline patterns, and local and global bifurcation diagrams are plotted for analysis of the backward flow, trapping, and augmented flow regions. The impacts of important embedded parameters, i.e., extensibility parameter and Deborah number on local and global bifurcation diagrams, are also examined. The whole analysis reveals that two critical conditions appear in the flow field that are actually responsible for the conversion of backward flow to trapping and trapping to augmented flow. It is further seen that bifurcations occur at lower flow rates for increasing Deborah's number while an opposite trend prevails for increasing the extensibility parameter. A comparison of bifurcations between planar and axisymmetric flows is also performed. It is observed that a greater area of the trapping region is encountered for axisymmetric flow than that for planar flow. [ABSTRACT FROM AUTHOR]

When rotating noise sources, such as turbomachinery, are investigated using phased microphone array measurements and beamforming, sidelobes appear on the resulting beamforming maps. Sidelobes can be decreased by increasing the number of microphones. However, if the investigated phenomenon is steady, then there is a cost-effective alternative: performing asynchronous measurements using phased arrays having a limited number of microphones. The single beamforming maps can be combined in order to arrive at results that are superior in resolution and sidelobe levels. This technique has been investigated in the literature, but according to the authors' best knowledge, has not yet been applied to turbomachinery. This article introduces a means for applying the asynchronous measurement technique and the combination methods for rotating noise sources. The combination methods are demonstrated on two rotating point sources (both in simulations and measurements), and then on an axial flow fan test case. In the case of the two rotating point sources, the achievable improvement in resolution, average-, and maximum sidelobe levels are shown as compared to the single results. In the case of the axial flow fan, it is demonstrated that the combination methods provide more reliable noise source locations and reveal further noise sources. [ABSTRACT FROM AUTHOR]

The present study provides novel insights in how spatial velocity variations in a heterogeneous porous medium cause the dispersion of a passive tracer. The study consists of two parts. The first part describes a series of numerical computations of the axial dispersion in the flow through heterogeneous porous media, idealized as Darcy flow through two-dimensional and three-dimensional patchwork geometries of zones with randomized permeability fields. Data on the axial dispersion were obtained using the mean age theory, which transforms the transient advection–diffusion equation into the steady-state mean age field equation, thus reducing the required computational effort by multiple orders of magnitude. This allowed to consider a sufficiently large number of randomizations to obtain a statistically representative ensemble average, as well as to consider sufficiently large systems to reduce the influence of boundary conditions. In the second part, it is shown that the relation between the axial dispersion coefficient and the velocity can be represented as a series, summing up the effect of velocity differences on all length scales, assuming the velocity differences are analogous to white noise. The sum can be closely fitted by a logarithmic law containing only two parameters with a well-defined physical meaning. A similar logarithmic dependency was also obtained by Saffman, Koch, and Brady. However, the logarithmic dependency obtained in the present work emerges from the heterogeneity of the porous medium, whereas the logarithmic dependency in the aforementioned works emerged from the no-slip boundary conditions at solid surfaces. [ABSTRACT FROM AUTHOR]

When axial flow pumps-as-turbines (PATs) operate under off-design conditions, unstable and unsteady flow structures appear in the internal flow field, resulting in suboptimal functioning. These operating conditions not only decrease the efficiency of the hydraulic machines but also affect their mechanical reliability. This study establishes relative streamline coordinates, based on the blade's mean camber line, to investigate flow instabilities in axial flow PATs from a new perspective. Numerical simulations on an axial flow PAT were performed and validated using experimental data. The results show that flow separation is more likely to occur due to the more curved profile at the blade's suction surface, leading to considerable fluctuations in velocity along the flow direction and enstrophy amplitude near both the hub and impeller shroud. Moreover, the poor matching of the relative inflow angle of the impeller with the blade inlet angle leads to impingement losses near their leading edge, generating unstable flows and significant pressure pulsations, which induces hydraulic instability within the impeller. In addition to rotor-stator interference effects, the curvature of the blade suction surface profile and the bend structure of inlet conduit are significant factors that influence the pressure pulsation distribution of the PAT. An analysis of the enstrophy transport equation indicates that the relative vortex generation and the Reynolds stress dissipation terms play a key role in both vortex generation and dissipation, whereas the viscous term has a lower influence. These findings can serve as a reference for the optimization and efficient design of axial flow PATs. [ABSTRACT FROM AUTHOR]

This study investigates the steady and unsteady behaviors of near-wake flow for axisymmetric models acquired with conical boattails with different slant angles under low-speed conditions. Delayed detached eddy simulation (DDES) was applied for the numerical processes. The Proper Orthogonal Decomposition (POD) was then used to reconstruct the dominant modes of the pressure at the base and velocity fields on the symmetry plane. Both near-wake and far-wake flows were considered in this study to obtain a full pattern of the wake. It was shown that the DDES allows for obtaining a highly accurate wake flow field. The large-scale structure of the base flow with two dominant modes of vortex shedding at StD = 0.19–0.24 and bubble pumping at StD = 0.06–0.08 occurs for the axisymmetric blunt-based model. At boattail angles up to 16°, those frequencies are clearly distinguished from the time series of POD modes of the velocity fluctuations. However, for higher angles, the motions of the "bubble pumping" and vortex shedding combine to generate frequencies in the range of StD = 0.07–0.15. The fully separated flow disturbs a ratio of one-third for the bubble pumping and vortex shedding frequencies, which was shown widely in previous studies. The reduction of frequency band and large-scale features for boattail angles of 16° explains the low drag generated for that configuration. [ABSTRACT FROM AUTHOR]

In this paper, a new type of helical blade is introduced, which is designed to minimize the damage of hydraulic turbine to fish. The experiments test the damage for fish under different pressure and pressure gradients. Also, the parameters of the helical blade turbine are optimized based on the damage thresholds. The consequent axial flow turbine features double-blades with a pitch of 2600 mm and a blade envelope angle of 540°. To assess the turbine's impact on fish, an overlapping mesh method is used to analyze the degree of damage to the fish during operation. The findings show that, compared to traditional designs, the application of helical blade turbine significantly reduced the exposure and duration of negative pressure, high pressure gradient, and high shear force. [ABSTRACT FROM AUTHOR]

In this paper, a new theoretical model for the dynamics and stability of a vertical cantilevered aspirating pipe is developed based on the Newtonian method. The effects of the hydrodynamic forces at the free end on the dynamics and stability of the cantilevered pipe are examined in detail. A new comprehensive governing equation is discretized using the Galerkin method. Numerical results are presented to demonstrate the effects of the axial flow velocity ratio, flow angle ratio, and tangential velocity ratio on the eigenfrequency and critical velocity of the cantilevered pipe system. The theoretical model results are also found to be in good quantitative agreement with experimental results. [ABSTRACT FROM AUTHOR]

Approximate streamsurfaces of a three-dimensional velocity field have recently been constructed as isosurfaces of the closest first integral of the velocity field. Such approximate streamsurfaces enable effective and efficient visualization of vortical regions in three-dimensional flows. Here we propose a variational construction of these approximate streamsurfaces to remove the limitation of Fourier series representation of the first integral in earlier work. Specifically, we use finite-element methods to solve a partial differential equation that describes the best approximate first integral for a given velocity field. We use several examples to demonstrate the power of our approach for three-dimensional flows in domains with arbitrary geometries and boundary conditions. These include generalized axisymmetric flows in the domains of a sphere (spherical vortex), a cylinder (cylindrical vortex) and a hollow cylinder (Taylor–Couette flow) as benchmark studies for various computational domains, non-integrable periodic flows (ABC and Euler flows) and Rayleigh–Bénard convection flows. We also illustrate the use of the variational construction in extracting momentum barriers in Rayleigh–Bénard convection. [ABSTRACT FROM AUTHOR]

The study focuses on the flow characteristics with geometrical considerations utilizing electrical-conduct Non-Newtonian Fluid. The tubular concentric annulus is the geometry selected for the investigation. The electric-conductive Non-Newtonian Fluid is a character-wise two-constant Bingham model used in this study. The study also utilized geometry, the magnetohydrodynamic (MHD) effect, and the hall current. The employed system had the inner tube spinning and the outer tube stationary. Prandtl's assumptions of boundary layer principles are applied to solve the governing equations using the finite difference method for various fluid flow parameters, the Gauss-Elimination method to compute the results, and the MHD field and geometrical factors with hall current. This paper discusses fluid flow properties such as axial, radial, tangential velocities, and pressure distribution. Further, the mentioned above flow properties impact the heat transfer effect. This research details how flow parameters in the concentric tube flow process affect the development of heat transfer effects in the MHD field and hall current. [Display omitted] • The development of MHD flow and heat transport have been studied computationally. • The impact of Hall current and Magnetic effect on the flow field has been considered. • This work refers to the non-Newtonian fluid as a two-constant yield stress fluid model. • The heat transfer impact has been calculated using the fluid flow properties. • This work has been done using a variety of fluid and geometric factors. [ABSTRACT FROM AUTHOR]

The windage loss in rotor‐stator gap has an important effect on rotating machinery, especially with higher rotational speed and fluid density. However, the mechanism of axial flow on windage loss in open shaft‐type gap is hardly studied in most literature. To clarify it, the influences of axial Reynolds number Reu and rotational Reynolds number Reω on skin friction coefficient Cf are investigated, and flow characteristics are analyzed with different gap geometry, radius ratio η. First, the results reveal that the Cf remains constant when Reu is less than 2.8 × 104 and increases rapidly as Reu when Reu ≥ 2.8 × 104, which indicates that the effect of axial velocity u on Cf is negligible for low Reu. The positive relative deviation Δ suggests that the axial flow makes windage loss and Cf rise. Besides, a larger number of Taylor vortexes fill with gap when the effect of the centrifugal force is larger than that of the inertial force, but they gradually disappear as Reu. Subsequently, the Cf and Δ increase as η, highlighting that the effect of u on windage loss and Cf is more prominent for larger η. The fact that vorticity near walls is larger than that at the center of gap reveals that windage loss arises from the interaction between walls and fluid rather than the dissipation with fluid itself. Finally, the model of Cf in shaft‐type gap is proposed in different Reω ranges based on numerical results, and the maximum sum of squares error of 1.02 × 10−5 and minimal R2 of 0.969 satisfy the requirement of fitting accuracy and indicate that the fitting model can accurately predict Cf. The conclusions significantly help predict windage loss in open shaft‐type gap with axial flow, and further improve the design for generators of supercritical CO2 turbine‐alternator‐compressor unit. [ABSTRACT FROM AUTHOR]

Entropy generation with activation energy has garnered worldwide attention from researchers due to its extensive applications in thermodynamic design, chemical engineering, and optimization processes. One of the primary reasons for focusing on entropy is the global energy crisis, driven by massive consumption against limited resources. This study elucidates the double diffusion process in the dynamics of a viscous fluid over a stretching cylinder, incorporating considerations of entropy generation and activation energy. The non‐Fourier heat flux model is employed to describe the thermodynamics of the thermal system, while non‐Fick's law is used to elucidate the mass diffusion process. The unsteady phases of axisymmetric flow of the viscous fluid are thoroughly discussed. Transport equations in cylindrical configuration are transformed into ordinary differential equations, and an efficient mathematical method (i.e., homotopy analysis method) is applied to solve the transformed system. The graphical examination reveals the impact of flow parameters on velocity configuration, entropy configuration, temperature configurations, and concentration configurations. Additionally, a comparative benchmark is established with the results from previously published work for authentication and validation purposes. It is noted that concentration and temperature configurations are directly related to the unsteady stretching parameter. Entropy generation exhibits an inverse relationship with the unsteady stretching parameter when close to the stretching cylinder, whereas it shows a direct relationship when the fluid is flowing away from the surface. [ABSTRACT FROM AUTHOR]

In this paper, we mainly focus on the development of the Taylor-Galerkin/Pressure-Correction method (TG/PC) method to solve the flow of a compressible Newtonian fluid under nonisothermal conditions. The process of development needs applying the two-step Lax–Wendroff method on the energy equation, after which two new steps for energy equations will be obtained within the TG/PC algorithm. In addition, for the density component, the Tait equation of state is adopted to relate density to pressure, which also yields a new step within the novel method to give the correction formula of compressible pressure. To perform the analysis of the new algorithm, Poiseuille flow through axisymmetric rectangular channel for the Newtonian thermal flow is utilized as a simple problem test. The effect of nondimensional factors such as Reynolds number (Re) and Prandtl number (Pr) is discussed in this study. The influence of thermal conductivity (k) and viscosity (μ) on the solution components is presented as well. Also, comparison for both compressible and incompressible flows is provided in addition to a comparison between both cases' convergence, as it turns out that the convergence of the incompressible case is better than the compressible case. All the results of the effects presented in this study agree well with the approved physical trend. [ABSTRACT FROM AUTHOR]

We study the accretion flows towards a central Kerr super-spinning attractor, discussing the formation of the flow inversion points, defined by condition u ϕ = 0 on the particles flow axial velocity. We locate two closed surfaces, defining inversion coronas (spherical shells), surrounding the central attractor. The coronas analysis highlights observational aspects distinguishing the central attractors and providing indications on their spin and the orbiting fluids. The inversion corona is a closed region, generally of small extension and thickness, which is for the counter-rotating flows of the order of ≲ 1.4 M (central attractor mass) on the vertical rotational axis. There are no co-rotating inversion points (from co-rotating flows). The results point to strong signatures of the Kerr super-spinars, provided in both accretion and jet flows. With very narrow thickness, and varying little with the fluid initial conditions and the emission process details, inversion coronas can have remarkable observational significance for primordial Kerr super-spinars predicted by string theory. The corona region closest to the central attractor is the most observably recognizable and active part, distinguishing black holes solutions from super-spinars. Our analysis expounds the Lense–Thirring effects and repulsive gravity effects in the super-spinning ergoregions. [ABSTRACT FROM AUTHOR]

This study presents a numerical investigation of the swirling flow inside a vertical conical container. The container is filled with liquid metal (Prandtl number, Pr=0.015), with the upper disc rotating at a fixed angular velocity while the bottom disc remains stationary. The sidewall of the container is rigid and inclined. In such a configuration, a phenomenon called vortex breakdown can occur, acting like a stagnation point against the axial flow pattern; the purpose of this study is to illustrate how the inclination of the cylinder's sidewall can affect the vortex breakdown and their emergence and suppression, The study encompasses a range of Reynolds numbers (1000≤Re≤2500) and various aspect ratios (1≤H/R≤2.4) where three different angles of inclination (α =5°, 10°, and 15°) are considered. The results are obtained by resolving numerically the governing equations using the finite volume technique. Our findings indicate that, for a given Reynolds number (Re=2000) and aspect ratios in the range of 1.2≤H/R≤1.6, the inclination of the sidewall leads to an earlier occurrence of vortex breakdown. On the other hand, for aspect ratios in the range of 1.8≤H/R≤2.2, the inclination of the sidewall results in the suppression of vortex breakdown. Furthermore, we have observed that the critical Reynolds number (Re_c) at which vortex at which vortex breakdown occurs for aspect ratios of A=H/R=1.4, 1.8, and 2.2 increases with the increasing angle of inclination α. [ABSTRACT FROM AUTHOR]

This paper presents numerical simulations of propeller–hull interaction of a ship model for the dynamic condition, demonstrating the ability of the developed self-propulsion module in OpenFOAM. A dynamic motion class has been developed based on the sliding mesh method to simulate a rotating propeller with ship motions. A body-force method is also implemented to simulate propeller–hull interaction to reduce the computational cost of propeller modeling. Validation studies were carried out for the Japan Bulk Carrier (JBC) ship model. The bare-hull resistance, sinkage, and trim are verified against the experimental data. The propeller open-water hydrodynamic characteristics are then computed and validated using sliding mesh and body-force methods. Finally, the self-propulsion simulations are carried out for the JBC model in calm water with sinkage and trim at the design speed. Numerical predictions of the self-propulsion parameters and axial flow velocity distributions at different transverse locations are presented. [ABSTRACT FROM AUTHOR]

The present article investigates the axisymmetric flow of a steady incompressible Reiner–Rivlin liquid sphere enveloped by a spherical porous layer using the cell model technique. The Brinkman-extended Darcy model is deployed for the porous medium hydrodynamics, and isotropic permeability is considered. The stream function solutions of the governing equations are obtained, which involves the Gegenbauer functions and the modified Bessel functions. An asymptotic series expansion in terms of the Reiner–Rivlin liquid parameter S has been employed to determine the expression of the flow field for the Reiner–Rivlin liquid. Boundary conditions on the cell surface corresponding to the Happel, Kuwabara, Kvashnin, and Cunningham models are considered. Analytical expressions are derived for dimensionless pressure, tangential stress, and the couple stress components using the method of separation of variables and Gegenbauer functions/polynomial. The integration constants are evaluated with appropriate boundary conditions on the inner and outer boundary of the porous zone with the aid of Mathematica symbolic software. Solutions for the drag force exerted by the Reiner–Rivlin fluid on the porous sphere are derived with corresponding expressions for the drag coefficient. Mathematical expression of the drag coefficient, pressure distribution, velocity profile, and separation parameter is established. On the basis of viscosity ratio, permeability parameter, dimensionless parameter, and the volume fraction, variations of the drag coefficient, velocity profiles, fluid pressure, and separation parameter (SEP) are investigated with their plots. The effects of the streamline pattern make the flow more significant for the Mehta–Morse when compared to the other models. Additionally, the mathematical expression of the separation parameter (SEP) is also calculated, which shows that no flow separation occurs for the considered flow configuration and is also validated by its pictorial depiction. This problem is motivated by emulsion hydrodynamics in chemical engineering where rheological behavior often arises in addition to porous media effects. [ABSTRACT FROM AUTHOR]

We examine the flow in and around a falling fluid droplet in a vertically oscillating flow. We assume axisymmetric Stokes flow, and for small deformations to the droplet, the governing equations can be linearized leading to an infinite system of linear ordinary differential equations. In this study, we have analytically solved the problem in the small-capillary limit. We note that the solution locally breaks down at the poles of the droplet. The drag and center of the mass were also obtained. In the case when only odd modes are present, the droplet shows three-dimensional axisymmetric heart-shaped solutions oscillating vertically in time. When only even modes are present, the droplet exhibits axisymmetric stretching and squeezing. [ABSTRACT FROM AUTHOR]

The present study offers a thorough evaluation of the influence of partial slip conditions and viscoelastic behavior on axial fluid flow driven by a cylinder or plate experiencing axial deformation with linear velocity. The momentum transport features a partial velocity slip which generates a nonlinear Robin-type boundary condition, while the energy transport employs a linear thermal slip boundary condition, as opposed to the previous studies that were limited to the no-slip conditions. The adoption of a quadratic surface temperature led to a novel and precise similarity solution. Furthermore, the study investigates the impact of an electrically conducting fluid assumption on momentum transport and viscous heating mechanism on thermal transport. The study utilizes a powerful routine that produces numerical results for a full range of parameters. Numerically evaluated coefficient of skin friction for the viscoelastic fluid flow is analyzed over a range of second-grade fluid parameters. In addition, heat transfer rates are determined for a variety of controlling parameters. A comparison of the present numerical approach with the homotopy scheme used by a previous study is presented and deliberated. [ABSTRACT FROM AUTHOR]

The complex flow of a supersonic jet (Mach number 2.4–2.5) around the blunt aerodynamic body (consisting of a cylinder with a diameter of 16 mm and a truncated cone) was studied using the high-speed shadowgraph technique and computer vision-based visual data processing. The problem considered is directly related to the rocket and space systems stages safe separation problem in a sufficiently dense atmosphere. For systems with a sequential arrangement of stages, their separation often occurs under the rocket engine jet action. The occurrence of lateral forces in violation of axial symmetry can lead to overturning of the discarded stage and undesirable interaction with the outgoing stage. The goals of the paper were to study the pulsation characteristics of the incoming supersonic jet streamlining the body, as well as the pulsations of the bow shock wave in both axisymmetric and asymmetric flows. The recording frame rate in the experiments was up to 775 000 fps. Computer vision and various machine learning approaches were used to process a large number of shadowgraph images. Canny edge detection and Hough transform, as well as a convolutional neural network (CNN) based on YOLOv2 architecture, were used to automatically track the position of the bow shock relative to the body. Jet sound generation was studied - the amplitude dependence on the distance from the nozzle and the evolution in time. The position of the bow shock relative to the streamlined body and flow pulsations over time were analyzed. Bow shock pulsation spectra at zero angle of attack were compared to those at a small angle of attack (α = 2.5°–3°). The power spectral density was also estimated. The slope of the spectra for the zero angle of attack case was found to be horizontal and the spectra for the small angle of attack case had a slope close to −5/3. The strongest of the measured bow shock frequencies were found to be close to those of the jet mixing layer pulsations. The hardware signal spectrum was also measured and this signal can be considered as noise. The described approach makes it possible to obtain the physical characteristics of the flow at any point of interest. It was also shown that the automation of flow visualization experiments using computer vision techniques allows to increase the speed of data processing and obtaining new physical information, which may be important for engineers developing aircraft and spacecraft technologies. • Supersonic jet flow around a blunt body was studied experimentally and also numerically. • Computer vision tools were applied to supersonic flow investigation. • Spectra of jet generated acoustic waves were determined. • Time dependent bow shock positions were automatically measured by the neural network. • Amplitudes of bow shock pulsations and flow fluctuations depend on the angle of the body relative to the jet direction. [ABSTRACT FROM AUTHOR]

The behavior of the velocity and shear stresses in two-phase laminar stratified flow near a triple point (TP), formed in the flow cross-section by the intersection of the interface with the conduit wall, is reconsidered. Differently from the no-slip boundary condition that showed a possibility of diverging shear stresses upon approaching the TP, we allow a slip of the fluids at the wall that can be prominent in the TP region. The Navier's boundary condition is used, which considers a linear relationship between the slip velocity and the strain rate component perpendicular to the surface. The solution for the velocity field in the TP region is obtained in terms of a power series of the distance from the TP having a discrete set of powers. Similarly to the solution obtained with no-slip B.C., a so-called 'characteristic equation' is obtained. Its solution yields a discrete set of non-integer powers that are dependent on the dynamic viscosity ratio and the contact angle. However, contrary to the no-slip solution, with Navier's B.C, each of these powers introduces a tower of terms resulting from the relation between the slip velocity and the velocity derivative at the wall. In addition, the solution also includes a tower of integer powers. The solution yields the velocity and the shear stress fields, as well as the flux of the force per length that acts on an arbitrary surface in the flow field. The latter is obtained by considering an equivalent 2D representation of the stress tensor. These are examined in comparison to the corresponding results obtained when no-slip at the wall is imposed. The relaxation of the wall shear stresses in cases where the no-slip condition predicts diverging wall shear stresses at the TP is demonstrated. It is shown that if the local velocity in the TP region is a limit of a global no-slip solution, the scaled velocity field in the TP region is independent of the details of the global flow field. • Two-phase stratified axial flow near the wall-interface junction (Triple Point, TP). • Removal of wall shear singularity in the TP region by allowing axial wall slip. • Navier's boundary condition is imposed on the wall in the TP region. • An analytical solution for the local flow field is obtained. • The local solution is independent of the global two-phase flow field details. [ABSTRACT FROM AUTHOR]

Hybrid nanofluids have gained much attention due to their better stability, enhanced thermal conductivity, and physical strength. This manuscript investigates nanofluid flow, induced due to an infinite plate, which is moving (at a constant velocity) toward/receding from normal stagnation point flow. The surface of the plate is suspended and immersed with water as a base fluid and nanoparticles, namely Copper and Alumina. The flow is governed by Reynolds number (Re), which is proportional to the constant velocity of the moving plate and is an exact reduction of the Navier–Stokes equations. Moreover, Hiemenz's planar and Homann's axisymmetric flows normal to the stagnation point are considered. Heat transport analysis is carried out by using Cattaneo–Christov theory with Ohmic heating and heat source/sink effects. The governing equations are solved by bvp4c in MATLAB. The behavior of skin friction, flow, and energy distribution is perceived by variation of pertinent parameters. The numerical and asymptotic solutions are computed for the wall shear stress parameter. It is seen that the numerical solution matches its asymptotic behaviors over an intermediate range of small and large valued Reynolds number. The asymptotic values (small-Re) of wall stress reduces for plate advancing toward the stagnation-point flow and receding from the stagnation-point flow for Hiemenz and Homann flow. The increment in magnetic parameter reduced the fluid flow by generating a resistive force against it; however, the energy of the system is enhanced because of it. The augmentation of nanofluid volume fraction initiates the random motion among the nanoparticles which raises the temperature field. Thermal relaxation time parameter causes the particles to require supplementary time for the conduction of heat toward the adjacent particles, which declines the thermal transport. In general, the thermal transport is enhanced for the hybrid nanofluids rather than mono nanofluids. [ABSTRACT FROM AUTHOR]

Steady axisymmetric two-dimensional flows driven by radiation and gas pressures in the conical funnel formed by the supercritical accretion disc are examined using the fully self-similar treatment. The effect of alpha-viscosity is also considered. The self-similar solutions are found to be classified into three types: successful outflows of hollow-conical or funnel-filled solutions, failed inflows, which are gravitationally bound, and unphysical cases, where the flow meets the singularity or the radiation energy density becomes negative. [ABSTRACT FROM AUTHOR]

Hydrogen released from complex multi-pipeline leakage sources can increase the difficulty of predicting the risk region of hydrogen and the probability of explosion accident. To investigate the collision and mixing features of subsonic hydrogen jets released from multi-pipeline leakage sources, an experimental platform for gas visualization and quantitative measurement is constructed. The differences in flow field structure and concentration distribution of vertical axisymmetric hydrogen jet, vertical asymmetric hydrogen jet and mixed hydrogen jets are compared and analyzed. Furthermore, the effects of multiple factors on the jet centerline, concentration decay, hazardous volume and diffusion height of the mixed region are predicted. The numerical simulation results are verified by the experimental data. Results indicate that the asymmetric hydrogen jet causes the mixed region centerline of hydrogen to deviate from the vertical axis under the combined effect of momentum-dominant and buoyancy. With the increase of the volumetric flow rate, the slope of the mixed region centerline initially decreases and then increases, with the smallest slope occurring at a volumetric flow rate of 159 NL/min. Either the increase of the leakage orifice diameter or the decrease of the distance between two leakage orifices can cause the slope of the mixed region centerline to decrease. Among three factors, the leakage orifice diameter has the most obvious effect on the concentration decay. The hydrogen diffusion height gets the highest when the ratio of leakage orifice diameter to pipeline inner diameter is 0.4 among five leakage orifice diameters. The distance between two leakage orifice has no significant influence on the hazardous volume. The investigation provides valuable data to support the prediction of the dangerous range of hydrogen leakage in complex multi-pipeline leakage sources. • Hydrogen released on the subsonic mixed jets was investigated. • The features of the axisymmetric, asymmetric, and mixed jets were compared. • The gas collision, merging, and diffusion from the mixed jets were studied. • The concentration distribution and decay on the mixed region was investigated. • The hydrogen volume and diffusion height of the mixed jets was obtained. [ABSTRACT FROM AUTHOR]

The velocity fields and impinging pressure characteristics of confined jet impinges on a flat surface subject to the influence of various axial stages of a flat plate were experimentally examined. The instantaneous flow patterns, time-averaged flow patterns and velocity characteristics, velocity histories, and impingement pressure distributions were obtained using flow visualisation, particle image velocimeter (PIV), hot-wire anemometer measurement, and pressure detection techniques, respectively. From the analysis of the flow patterns, three characteristics of flow regimes are identified – laminar vortical wake, transition, and turbulent vortical wake – in the domain of Reynolds number and jet-to-wall distance. In laminar vortical wake mode, a 'fat' pair of counter-rotating vortices appears between the confining surface of the nozzle and the flat plate. This results in a large region of turbulent intensities due to the entrainment of the jet flow. In transition mode, shear-layer vortices appear on the shear layer of the bifurcated jet. In turbulent vortical wake mode, the large momentum of jet fluids impinges the flat plate and deflects radially. The counter-rotating vortices and shear-layer vortices no longer exist in the wake of the bifurcated jet. The large eddies quickly break up into small eddies as the momentum of the jet-dominated flow. No obvious peak value of oscillating frequency was detected in this flow mode along the shear layers of the bifurcated impinging jet. The momentum of the fluid structures is converted into stagnation pressure on the flat plate when a strong jet impinges on it; therefore, the impingement pressure is large, consequently. The impingement pressure in the mode of the turbulent vortical wake was significantly greater than that in the modes of laminar vortical wake and transition. [ABSTRACT FROM AUTHOR]

This study provides a sedimentological, stratigraphic and palaeocurrent investigation of Upper Eocene to Lower Oligocene deep-sea fan deposits found in the central part of the Pindos foreland basin in western Greece. According to facies analysis, the examined succession at Amfilochia area has 13 sedimentary facies and 10 facies and sub-facies associations. Depositional elements include abyssal plain pelagics, outer fan, inner fan, and slope deposits. Outer fan sediments are classified as lobe-axis, lobe-off-axis, lobe-fringe, and distant lobe-fringe deposits, while inner fan sediments are classified as channel-fill, crevasse-splay, internal and external levee deposits. The stratigraphic study shows an upward shift from abyssal plain pelagics to outer, inner fan, and finally slope deposits, implying submarine fan system progradation and progressive infilling of a deep-water sediment depocentre. The sediments were deposited in the foredeep of the Pindos foreland system and correspond to the system's underfilled stage, when sedimentation was unable to exceed the accommodation provided by lithospheric flexure. They point to deposition near the onset of the Pindos orogen, after the closure of the Pindos basin because of the collision of the Apulian with the Pelagonian microplate during the Cretaceous-Palaeogene period. Palaeocurrent data from sole marks show bipolar directions associated with two distinct spreading sub-marine fan deposits. As a result, the study region was split into Upper (major SE-direction flow) and Lower (major NW-direction flow) parts, indicating that axial flows were predominant during sediment deposition. However, as the deposition of the elements continued, the progradation of both systems constrained the space accommodation because of the increased basin sediment supply and forced an increase in the degree of basin confinement that changed the compensational to aggradational stacking pattern. The goals of this research are to develop an updated facies model for these deep-sea fans as well as a robust correlation framework for the various stratigraphic units in the central Pindos foreland basin. This research also connects the stratigraphic development of deep-sea fan deposits to the evolutionary phases of the Pindos foreland system, providing fresh insights into the palaeogeographic circumstances in the Pindos foreland basin. [ABSTRACT FROM AUTHOR]

Addressing the issue of leakage in practical scenarios involving hose pumps, this paper conducts an analysis on hose pumps with existing compression gaps. The model is simplified to represent the two-dimensional Newtonian fluid pulsating flow of a single-sided sine wave passing through the tube. The study derives the axial flow velocity distribution within the tube while establishing correlations between the leakage volume, tube clearance, pressure differential, deformed cross-sectional length of the tube, rotor speed (which exhibits a negative correlation), the deformation length of the tube in the x-direction, and the fluid's dynamic viscosity (demonstrating a positive correlation). Utilizing a bidirectional fluid-structure coupling method, this analysis investigates hose pumps with compression gaps. Specifically, it examines the flow field pressure, velocity, and vortex intensity of two Newtonian fluids with Reynolds numbers of 10–30 and 6000–15 000, respectively, within a 180° bend tube with a curvature-to-inner-diameter ratio of 4.6. This analysis is conducted under inlet velocities of 0.32 and 0.6 m/s, and outlet pressures of 0 and 0.1 MPa. The study identifies the positions of extreme leakage rates, elucidating the flow field characteristics and their impact on leakage. Furthermore, it investigates the causes of secondary flows within the tube, concluding that the fluid inside the tube exhibits symmetric helical motion. This research establishes the periodic variations in flow field vortex intensity and secondary flow intensity, along with the conclusion that leakage rates are positively correlated with axial vortex intensity and negatively correlated with secondary flow intensity. [ABSTRACT FROM AUTHOR]

The natural transition in boundary layers on axisymmetric bodies with superhydrophobic surfaces is studied using numerical methods. By boundary layer, we mean the boundary layer around the forebody and around the parallel body of an underwater vehicle. A method of calculating basic laminar flows on axisymmetric bodies with superhydrophobic curved surfaces is proposed, and a method of linear stability analysis for the boundary layers that considers the slip-velocity boundary condition for small disturbances is established. The eN method is used to predict the transition locations of the boundary layers. On a superhydrophobic surface, the slip velocity on the wall increases and then decreases along the streamwise direction, resulting in a maximum value at the forebody. The boundary layer thickness on a superhydrophobic surface becomes smaller than that on an ordinary surface. The superhydrophobic surface stabilizes the boundary layer and thus delays the natural transition. As the slip length on the superhydrophobic surface increases, the unstable zone shrinks, and the transition location moves further downstream, indicating that the delay effect of the superhydrophobic surfaces becomes stronger. As the oncoming flow velocity increases, the transition location on the superhydrophobic surface moves upstream and then downstream, leading to a "dangerous" velocity, at which the transition location is closest to the leading edge. The underlying mechanism of the dangerous velocity phenomenon is discussed: An increasing velocity has both stabilizing effect and destabilizing effect on the boundary layer. [ABSTRACT FROM AUTHOR]

This paper revisits the linear stability analysis of oscillatory-driven flows between two oscillating cylinders against non-axisymmetric disturbances. This study is motivated by the lack of a sufficiently reliable theoretical analysis giving insight into the experimentally observed spiral-like non-axisymmetric patterns when the cylinders are counter-oscillating. A new generalized time-dependent algebraic eigenvalue problem is constructed from the linearized set of the three-dimensional Navier–Stokes equations around the purely azimuthal basic state. Numerical evaluation of the critical eigenvalues combining both Floquet theory and spectral method reveals the existence of frequency ranges where this basic state becomes unstable against three-dimensional non-axisymmetric disturbances before it does so for two-dimensional axisymmetric ones. Indeed, as the oscillation frequency of the cylinders increases, the azimuthal wave number of the critical eigensolution is found to change from 0 to 2 to 1 and then back to 0. The primary bifurcation exchange between two instability modes with different azimuthal wave numbers occurs via different types of codimension-2 bifurcation points giving rise to discontinuities in the critical axial wave number where reversing and non-reversing non-axisymmetric Taylor vortex flows are identified. In addition, by extending our numerical calculations to the co-oscillating case, we show that the axisymmetric disturbances are the most unstable confirming thus existing experimental findings. Furthermore, a Wentzel–Kramers–Brillouin (WKB) analysis is performed to shed light on the asymptotic behavior of these time-dependent flows in the low-frequency limit when the cylinders are slowly oscillating. [ABSTRACT FROM AUTHOR]

Doppler weather radars are powerful tools for investigating the inner-core structure and intensity of tropical cyclones (TCs). The Doppler velocity can provide quantitative information on the vortex structure in the TCs. The generalized velocity track display (GVTD) technique has been used to retrieve the axisymmetric circulations and asymmetric tangential flows in the TCs from ground-based single-Doppler radar observations. GVTD can have limited applicability to asymmetric vortices due to the closure assumption of no asymmetric radial flows. The present study proposes a new closure formulation that includes asymmetric radial flows, based on the Helmholtz decomposition. Here it is assumed that the horizontal flow is predominantly rotational and expressed with a streamfunction, but limited inclusion of wavenumber-1 divergence is available. Unlike the original GVTD, the decomposition introduces consistency along the radius by solving all equations simultaneously. The new approach, named GVTD-X, is applied to analytical vortices and a real TC with asymmetric structures. This approach makes the retrieval of axisymmetric flow relatively insensitive to the contamination from asymmetric flows and to small errors in storm center location. For an analytical vortex with a wavenumber-2 asymmetry, the maximum relative error of the axisymmetric tangential wind retrieved by GVTD-X is less than 2% at the radius of the maximum wind speed. In practical applications, errors can be evaluated by comparing results for different maximum wavenumbers. When applied to a real TC, GVTD-X largely suppressed an artificial periodic fluctuation that occurs in GVTD from the aliasing of the neglected asymmetric radial flows. Significance Statement: In tropical cyclone (TC) wind retrievals from single-Doppler weather radar observations, closure assumptions are required for the retrieval equations. The present study proposes a new closure allowing asymmetric radial winds and improving retrievals for TC winds in the previously developed technique. The relative error of the axisymmetric tangential wind in idealized vortices from the new approach is less than 2% at the radius of the maximum wind speed. In applying to a real TC with an elliptical eyewall, we found that the new approach can largely suppress an artificial evolution of the tangential winds in the previous retrieval technique. [ABSTRACT FROM AUTHOR]

This work evaluates use of a dimensionally adaptive (DA) meshing technique to speed CFD modeling of non-reacting pressurized flow in a cylindrical geometry with a center jet and non-axisymmetric secondary jets. The DA-capable approach incorporates an a priori dimensional boundary location and extension of 3-D RANS flow solvers. Recirculation zone length, not flow asymmetry, was the limiting factor in placement of the dimensional boundary between 3-D and axisymmetric meshes. Boundary placement was based on confined turbulent jet theory, which suggests jet attachment is a linear function of cylinder radius, L, expressed as 5.85L. CFD results for a turbulent axial pipe flow showed that as the dimensional boundary was moved upstream, computational time dropped quadratically with the reduction in mesh cells. Further simulations of a 0.2032-m diameter, 1.5-m long reactor with turbulent center primary jet and outer radius secondary jets placed the dimensional boundary at 0.7 m. Results for pressures of 20, 10, and 5 bar and mass flow rates of 75% and 50% of baseline demonstrated two key results. First, flow similarity was preserved across all cases and the predicted jet attachment location was approximately 0.61 m, compared with the theoretical value of 0.594 m. Second, runtime reductions of 79% (pressure) and 82% (flow rate) were seen for the DA meshes compared with fully 3-D meshes. Differences in average exit axial velocities between DA and fully 3-D meshes were 2-4% for the pressure cases and 0.7-1.5% for the flow rate cases. Lastly, comparison with 3-D quartergeometry calculations showed the DA approach to be -10% faster with exit axial velocities within 3-5% of 3-D velocities. [ABSTRACT FROM AUTHOR]

In this paper, we consider the Cauchy problem of the 3D incompressible Keller–Segel–Navier–Stokes equations with partial diffusion, namely we remove the diffusion $ \Delta \rho $ Δ ρ. Using the damping effect of the growth term $ -\rho ^{3} $ − ρ 3 and the geometry of axisymmetric flow without swirl, we prove the global existence of weak solutions for the system. [ABSTRACT FROM AUTHOR]

Traditional high-speed electrolyte flow for removing bubbles and sludges from the inter-electrode gap during electrochemical machining (ECM) usually results in the non-uniform distribution of temperature, bubbles, and sludges, thus deteriorating machining accuracy. Therefore, ECM performed in stationary electrolyte via an efficient flushing method may solve this problem. For this reason, the previous study proposed the stamp flushing method to squeeze out the bubbles and sludge from the inter-electrode gap by shortening the gap width. However, the effectiveness of the stamp flushing method in achieving high replicability has not been systematically investigated. In the present work, the stamp stroke motion was first optimized to improve the flushing efficiency of the stamp flushing method. To obtain higher stamping velocity and to avoid the damage due to the collision between the tool electrode and workpiece, a cushion mechanism was newly installed on the equipment. Based on the optimized stamp stroke motion, the periodical micropatterns fabricated on the tool electrode surface using wire electrical discharge machining (WEDM) were replicated onto the SK4 workpiece using ECM in stationary electrolyte. The dimensional deviation of the workpiece from the tool electrode after ECM was less than 4 μm in the feed direction and approximately 30 μm in the side direction when the initial width of the frontal gap was 10 μm. Outside the inter-electrode gap, the electrolyte flowing along the axial direction (EFAAD) was supplied to rapidly flush out the bubbles and sludge squeezed out by stamp motion to prevent them from backflowing into the inter-electrode gap during the widening phase of the gap after the stamp motion. Since the EFAAD does not affect the electrolyte in the inter-electrode gap, the ECM remains performed in a stationary electrolyte. High replicability was obtained uniformly over the working surface, which originates from the combined effect of small inter-electrode gap width and uniform distribution of temperature, bubbles, and sludge in stationary electrolyte. This work proves the potential of the proposed stamp-flushing method for manufacturing metal parts with high replicability. • The effectiveness of the stamp flushing method in achieving high replicability was demonstrated. • The flushing mechanism of the stamp flushing method was investigated and revealed. • The stamp stroke motion was optimized to improve the flushing efficiency of the stamp flushing method. • The dimensional deviation of the workpiece from the tool electrode after ECM was less than 4 μm in the feed direction. [ABSTRACT FROM AUTHOR]

Cardiogenic shock is a complex and diverse pathological condition characterized by reduced myocardial contractility. The goal of treatment of cardiogenic shock is to improve abnormal hemodynamics and maintain adequate tissue perfusion in organs. If hypotension and insufficient tissue perfusion persist despite initial therapy, temporary mechanical circulatory support (t-MCS) should be initiated. This decade sees the beginning of a new era of cardiogenic shock management using t-MCS through the accumulated experience with use of intra-aortic balloon pump (IABP) and venoarterial extracorporeal membrane oxygenation (VA-ECMO), as well as new revolutionary devices or systems such as transvalvular axial flow pump (Impella) and a combination of VA-ECMO and Impella (ECPELLA) based on the knowledge of circulatory physiology. In this transitional period, we outline the approach to the management of cardiogenic shock by t-MCS. The management strategy involves carefully selecting one or a combination of the t-MCS devices, taking into account the characteristics of each device and the specific pathological condition. This selection is guided by monitoring of hemodynamics, classification of shock stage, risk stratification, and coordinated management by the multidisciplinary shock team. [ABSTRACT FROM AUTHOR]

The present study evaluates the effect of the slinger ring on the forced convection heat transfer in window air conditioners. Slinger rings are fitted around condenser fans to spread the condensate onto the condenser to achieve additional cooling. The single-phase forced convection is simulated to compare the thermal performance of the multiphase flow by the slinger ring. Experiments are performed to validate the numerical results. The numerical results well reconstruct the experimental ones, showing the regional dependent distribution and the discharge of the sprayed condensates by the slinger ring. The slinger ring causes a considerable heat transfer on the condenser coils by spraying the condensates, compared with the single-phase flow. However, the inner region of the slinger ring and the fan is almost the dead zone for the condensate spray, since the strong axial flow protects the entrainment of the splashed condensate, which is explained by the isotherms and velocity vectors. The regions of the occurrence of the additional heat transfer are almost overlapped to those exposed to the condensates sprayed by the slinger ring. The slinger ring contributes to a substantial increase of approximately 17% in the heat transfer on the condenser coils, compared with the single-phase flow. [ABSTRACT FROM AUTHOR]