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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]

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]

Porous baffles can be used to enhance heat transfer in various engineering applications, including electronic cooling, gas turbine blades, and chemical reactors. Also, the backward-facing step is a widely used configuration in fluid dynamics studies due to its simplicity and relevance to real-world geometries. This study examines heat transfer and flow characteristics in a backward-facing step channel featuring a heated bottom wall and two porous baffles. A computational fluid dynamics model, validated against prior research, is used to investigate flow and temperature fields. The innovation of this work lies in the application of multi-objective optimisation to search for a set of solutions that establish a trade-off between the average Nusselt number and the pressure drop. The optimisation specifically considers various parameters of the porous baffles, including height, width, distance from the step, and Darcy number, to identify optimal design configurations. Results show that porous baffles significantly improve heat transfer compared to a backward-facing step channel without them, despite an increase in pressure drop due to their presence. This work offers valuable insights into the trade-off between heat transfer performance and pressure drop, crucial for designing efficient heat transfer systems. By exploring the Pareto-Frontier, which represents various optimal design solutions, the study provides practical guidance when seeking to optimise heat transfer in backward-facing step channels with porous baffles. The findings contribute to advancing the understanding of heat transfer enhancement, highlighting the potential of porous baffles as a viable solution for improving thermal management in engineering systems. [ABSTRACT FROM AUTHOR]

A computational model is developed to obtain a helicopter rotor blade's vibration characteristics and aerodynamic behavior. A mathematical model of the wake is also developed, consisting of fundamental wake geometry. A Bo 105 helicopter rotor blade is considered for computational aerodynamic analysis. A fluid–structure interaction model of the rotor blade with surrounding air is developed, where the finite element model of the blade is coupled with the computational fluid dynamics model of the surrounding air. The fluid–structure interaction model analyzes aerodynamic coefficients, velocity profiles, and pressure profiles. The resonance frequencies and mode shapes are also obtained by the computational method. A small-scale model of the rotor blade is manufactured, and experimental analysis of similar contemplation is conducted to validate the numerical results. Wind tunnel and vibration testing arrangements are used for the experimental validation of the aerodynamic and vibration characteristics, respectively. The wake and vortex analysis showed that the swirl velocity is minimum, and the axial velocity is maximum at the vortex center. The axial velocity decreases, and swirl velocity increases with increasing the distance from the vortex center to the core radius. Finally, an application of experimentally validated computational methodology for helicopter rotor blade to evaluate aerodynamic characteristics in a fluid–structure interaction environment along with the characterization of resonance properties is outlined where the results follow an expected pattern. [ABSTRACT FROM AUTHOR]

The review paper presents the various passive methods used in the heat exchanger in detail with their advantages and disadvantages over the active methods. The paper studies the experimental and numerical studies of twist tape as an insert due to its retrofit capability and easy handling advantages. The experimental studies are categorized based on the geometrical parameter of the twist tape insert. The twisted tape with similar geometries is compiled in the same section. For example, twist tape with a clockwise twist, anticlockwise twist, alternate twist, or twist tape with a twist and no twist in the same section. It is a concise form that basically illustrates the studies based on similar geometrical parameters. The study covers both experimental and numerical studies and presents the advantages of experimental and numerical studies over one another. There is a section that shows statistical analysis of the Nusselt number and friction factor for various swirl flow inserts with comparison to the plain tube. The selection of twist tape inserts for the heat exchanger depends upon the cost and feasibility at the required point of application of the heat exchanger. This is done by comparing the thermal performance factor of the insert in the heat exchanger. The thermal performance factor of a particular insert in a tubular heat exchanger must be greater than 1, to justify its capability as a good insert. Finally, future recommendations are suggested to further carry out the work in this domain. [ABSTRACT FROM AUTHOR]

Cone-disk systems find frequent use such as conical diffusers, medical devices, various rheometric, and viscosimetry applications. In this study, we investigate the three-dimensional flow of a water-based Ag-MgO hybrid nanofluid in a static cone-disk system while considering temperature-dependent fluid properties. How the variable fluid properties affect the dynamics and heat transfer features is studied by Reynolds's linearized model for variable viscosity and Chiam's model for variable thermal conductivity. The single-phase nanofluid model is utilized to describe convective heat transfer in hybrid nanofluids, incorporating the experimental data. This model is developed as a coupled system of convective-diffusion equations, encompassing the conservation of momentum and the conservation of thermal energy, in conjunction with an incompressibility condition. A self-similar model is developed by the Lie-group scaling transformations, and the subsequent self-similar equations are then solved numerically. The influence of variable fluid parameters on both swirling and non-swirling flow cases is analyzed. Additionally, the Nusselt number for the disk surface is calculated. It is found that an increase in the temperature-dependent viscosity parameter enhances heat transfer characteristics in the static cone-disk system, while the thermal conductivity parameter has the opposite effect. [ABSTRACT FROM AUTHOR]

The arteriovenous fistula (AVF) is commonly faced with stenosis at the juxta-anastomotic (JXA) region of the vein. Implantation of a flexible nitinol stent across the stenosed JXA has led to the retention of functioning AVFs leading to the resulting AVF geometry being distinctly altered, thereby affecting the haemodynamic environment within it. In this study, large eddy simulations of the flow field within a patient-specific AVF geometry before and after stent implantation were conducted to detail the change in flow features. Although the diseased AVF had much lower flow rates, adverse flow features, such as recirculation zones and swirling flow at the anastomosis, and jet flow at the stenosis site were present. Larger velocity fluctuations (leading to higher turbulent kinetic energy) stemming from these flow features were apparent in the diseased AVF compared to the stented AVF. The unsteadiness at the stenosis created large regions of wall shear stress (WSS) fluctuations downstream of the stenosis site that were not as apparent in the stented AVF geometry. The larger pressure drop across the diseased vein, compared to the stented vein, was primarily caused by the constriction at the stenosis, potentially causing the lower flow rate. Furthermore, the WSS fluctuations in the diseased AVF could lead to further disease progression downstream of the stenosis. The change in bulk flow unsteadiness, pressure drop, and WSS behaviour confirms that the haemodynamic environment of the diseased AVF has substantially improved following the flexible stent implantation. [ABSTRACT FROM AUTHOR]

The paper considers the fragmentation of fluid films and, in particular, the used similarity numbers that characterize the process of fragmentation. Based on the analysis of a previously proposed mathematical model for a rotating fluid film evaporating in the Leidenfrost regime, the Sf criterion is proposed. It represents the relationship between the pressing inertial mass force acting on the fluid film and the dynamic effect of vapor from the heating wall. [ABSTRACT FROM AUTHOR]

Introducing swirling velocity at the inlet is one of the best ways to enhance the transport properties of flow through the pipes. Flow of fluids in small tubes have important applications involving fluid mixing or heat transfer and the flow in these small devices appears to be laminar in nature. Non-Newtonian fluids have wide variety of applications in small pipes ranging from heat-pipes to micro heat exchangers. Hence, it becomes very important to enhance the transport properties of fluids flowing through small devices. To enhance the transport characteristics, the method of introducing swirling of fluid at the inlet of the pipe is chosen. Further, the effect of important dimensionless parameters such as the power-law index of the fluid (characterizes fluid rheology), Reynolds number, the inlet swirl velocity profile shape (transition radius) and the inlet swirl number on the heat transfer characteristics is investigated. The qualitative and quantitative aspects of the heat transfer problem are discussed with particular focus on temperature contours and determination of Nusselt number. Results from the present study show that the power-law index of the fluid and Reynolds number plays an important role in enhancing the heat transfer. Increase in the flow Reynolds number and decrease in the power-law index tend to increase heat transfer strongly. It is also revealed that the inlet swirl number and the profile shape (transition radius) have a weak effect on the augmentation of heat transfer. A correlation is proposed to determine the heat transfer in the form of Nusselt number based on the flow Reynolds number and power-law index. [ABSTRACT FROM AUTHOR]

The effect of the injection pressure on the dynamic flow characteristics of a lean direct injection gas turbine combustor under nonreactive conditions during liquid fuel atomization was investigated. The location of the internal recirculation core, size of the vortex breakdown bubble, and shape of the precessing vortex core and shear layer were confirmed by increasing the fuel injection pressure. It was found that as the fuel injection pressure increased, the momentum of the droplets increased. The tangential momentum of the constant main air swirl flow transferred to the droplets increased as the pressure increased, causing the swirl strength to decrease. It was confirmed that, as the swirl intensity decreased with increasing injection pressure, the shape of the precessing vortex core generated in front of the combustor became shorter, and the size of the central recirculation area also decreased. [ABSTRACT FROM AUTHOR]

An investigation has been made into a turbulent combustion of an air–propane mixture in a swirl flow. To calculate an averaged velocity of a chemical reaction, use was made of a combination of an eddy dissipation model and a kinetic model with account for turbulent pulsations. The influence of a weak swirl on flame localization is low. If the length of the recirculation zone occurring in a strong flow vortex exceeds the length of the preflame zone, the flame front is entraped by the recirculation zone and moves upstream towards the channel inlet where flame stabilization occurs. At the initial segment of the flow, the chemical reaction is determined by Arrhenius kinetics. In the region directly adjacent to the flame, the combustion mechanism controlled by turbulence becomes significant. [ABSTRACT FROM AUTHOR]

While turbulent flow characteristics in the region upstream of wall-mounted obstacles (often called the junction region) are well described for many engineering systems, uncertainty remains about flow characteristics upstream of the large, immobile boulders that are commonly found in steep gravel-bed streams. This uncertainty is largely due to the unique bed features (e.g., relatively large bed roughness, a permeable bed) and hydraulic characteristics (e.g., variable submergence) present at boulders, which may affect flow characteristics. This study reports results of laboratory volumetric particle image velocimetry (PIV) experiments performed upstream of model boulders for fully submerged (FS) and partially submerged (PS) conditions. Several atypical junction flow characteristics were documented. Mean-flow reversal and spiraling streamlines (commonly associated with horseshoe vortices) were not documented, though limitations in near-bed measurement extents contributed to this result in several cases. Nevertheless, modest increases in local rotation rate (assessed via vorticity magnitude and swirling strength) were observed near where the horseshoe vortex is typically expected. Mean-flow data also suggest that notable mass flux into the permeable bed occurred upstream of boulders. Several effects of submergence on junction flow characteristics were also identified. Compared with the FS condition, the PS condition exhibited more rapid deceleration of the mean streamwise velocity, stronger downward velocities near the bed that extended over a wider transverse area, stronger increases of the near-bed turbulent kinetic energy, and oppositely signed streamwise-vertical Reynolds stresses near the water surface. The improved understanding of flow upstream of boulders provided here will aid future river engineering and restoration efforts. [ABSTRACT FROM AUTHOR]

The use of multiple perspective views is a possible pathway towards the combined measurement of multiple time-resolved flow properties by filtered Rayleigh scattering (FRS). In this study, a six view observation concept is experimentally verified on a aspirated pipe flow. The concept was introduced in our previous work, and it has the ability to simultaneously measure high-accuracy time-averaged and time-resolved three-component velocity, pressure and temperature fields. To simulate time-resolution, multi-view FRS data at a single optimised excitation frequency are selected and processed for multiple flow properties. Time-averaged and quasi-time-resolved FRS results show very good agreement with differential pressure probe measurements and analytical temperature calculations and lie within ± 2 m/s of complementary laser Doppler anemometry (LDA) velocity measurements for all operating points. The introduction of a multistage fitting procedure for the time-resolved analysis leads to a significant improvement of the precision by factors of 4 and 3 for temperature and axial velocity and 18 for pressure. Moreover, both processing methods show their capacity to resolve flow structures in a swirling flow configuration. It is demonstrated that the developed multi-view concept can be used to determine multiple flow variables from a single-frequency measurement, opening the path towards time-resolved multi-parameter measurements by FRS. [ABSTRACT FROM AUTHOR]

Process intensification (PI) is playing a key role in alleviating the challenge of reducing carbon footprint of many chemical processes and bringing down their development costs. Over the years, many PI technologies have been investigated with rotating packed bed (RPB) technology receiving much of the attention for its potential of significant intensification in terms of capital expenditure, operating costs, and hardware size. In this study, microscale CFD simulations of a rotating packed bed were conducted, and the results were validated with experimental data. The results show the strong relation between the reverse flow at the packing outer periphery and the gas maldistribution factor. The latter is mainly caused by the accelerating flow in the outer cavity. Inside the wire mesh packing, the gas flow is found to be almost fully uniform for nearly half of the total packing depth. Also, turbulent kinetic energy (TKE) levels at the packing outer edge are strongly linked to the slip tangential velocity component, while at its inner edge, they depend mainly on the radial packing velocity. The so-called gas end effect zone is detected by observing the TKE profiles near the packing outer edge. The latter accounts for less than 10% of the total packing depth. The validity of the widely used porous media model in RPBs' packing for both radial and tangential directions is confirmed by the obtained results, but this excludes the packing inner and outer edges. In the inner cavity region, gas exhibits two distinctive behaviors and transits from free vortex flow to swirling flow as the flow becomes close to the vortex core. As a result of this transition, the increase in shear stress accelerates the decrease in the gas tangential velocity in the vortex core and help speed up the favorable pressure gradient and flow establishment beyond the vortex core. [ABSTRACT FROM AUTHOR]

Nanosized yttrium–aluminum garnet (YAG) powders are synthesized in a microreactor with swirling flows by the coprecipitation of yttrium and aluminum hydroxides followed by heat treatment. The resulting mixture of hydroxides is X-ray amorphous according to X-ray phase analysis. Thermal treatment of hydroxides at 1100°C for 1 h leads to the formation of Y3Al5O12 nanocrystals. The method we developed is technologically advanced, easily scalable, saves energy and time, and does not require labor-intensive operati-ons. [ABSTRACT FROM AUTHOR]

Study of swirling flows in channels corresponding to the static approximation of flow channels of the heart and major vessels with a longitudinal–radial profile zR2 = const and a concave streamlined surface at the beginning of the longitudinal coordinate has been carried out. A comparative analysis of the flow structure in channel configurations zRN = const, where N = –1, 1, 2, 3, in the absence and presence of a concave surface was carried out. The numerical modeling was compared with the results of hydrodynamic experiments on the flow characteristics and the shape of the flow lines. The numerical model was used to determine the velocity structure, viscous friction losses, and shear stresses. Numerical modeling of steady-state flows for channels without a concave surface showed that in the channel zR2 = const there is a stable vortex flow structure with the lowest viscous friction losses. The presence of a concave surface of sufficient size significantly reduces viscous friction losses and shear stresses in both the steady state and pulsed modes. [ABSTRACT FROM AUTHOR]

The problem of determining the characteristics of a laminar swirling wall jet of an incompressible fluid is considered. Numerical solutions of the Navier–Stokes equations are obtained in the stationary and non-statitonary formulations. It is shown that the jet characteristics obey a self-similar law at large distances from the jet source, as in the case of a three-dimensional laminar non-swirling jet, but in our case the jet propagates at a certain angle to the initial direction of jet blowing. With a large swirling of flow in the jet, regions of recirculation flow appear and the jet flow becomes unsteady. [ABSTRACT FROM AUTHOR]

The motion of the fluid due to the swirling of a disk/sheet has many applications in engineering and industry. Investigating these types of problems is very difficult due to the non-linearity of the governing equations, especially when the governing equations are to be solved analytically. Time is also considered a challenge in problems, and times dependent problems are rare. This study aims to investigate the problem related to a transient rotating angled plate through two analytical techniques for the three-dimensional thin film nanomaterials flow. The geometry of research is a swirling sheet with a three-dimensional unsteady nanomaterial thin-film moment. The problem's governing equations of the conservation of mass, momentum, energy, and concentration are partial differential equations (PDEs). Solving PDEs, especially their analytical solution, is considered a serious challenge, but by using similar variables, they can be converted into ordinary differential equations (ODEs). The derived ODEs are still nonlinear, but it is possible to approximate them analytically with semi-analytical methods. This study transformed the governing PDEs into a set of nonlinear ODEs using appropriate similarity variables. The dimensionless parameters such as Prandtl number, Schmidt number, Brownian motion parameter, thermophoretic parameter, Nusselt, and Sherwood numbers are presented in ODEs, and the impact of these dimensionless parameters was considered in four cases. Every case that is considered in this problem was demonstrated with graphs. This study used modified AGM (Akbari–Ganji Method) and HAN (Hybrid analytical and numerical) methods to solve the ODEs, which are the novelty of the current study. The modified AGM is novel and has made the former AGM more complete. The second semi-analytical technique is the HAN method, and because it has been solved numerically in previous articles, this method has also been used. The new results were obtained using the modified AGM and HAN solutions. The validity of these two analytical solutions was proved when compared with the Runge–Kutta fourth-order (RK4) numerical solutions. [ABSTRACT FROM AUTHOR]

The calculations of thermohydrodynamic parameters using a mathematical model of a plane swirling flow are compared with experimental data obtained in a vortex chamber and a Ranque vortex tube. It is shown that the proposed generalized solution is in good agreement with experiment and describes a stable flow core in the plane of the vortex cross section. In terms of application, the proposed solution can serve as the basis for engineering methods for the preliminary calculation of vortex apparatuses. [ABSTRACT FROM AUTHOR]

Flow field and heat transfer of an impinging swirling jet at low nozzle-to-plate distances have been investigated numerically for three different cases with six different turbulence models. The effects of Reynolds number (2100, 4100, 6100, 8100) and dimensionless nozzle-to-plate distance (H/D = 0.25, 0.5, 0.75, 1) on flow field and heat transfer of the swirling jet are studied parametrically. It is noted that the results of the cases employed exhibit sensitivity to the height of the computational domain defined on the impingement plate, particularly at low nozzle-to-plate distances. It is also seen that one of the cases used is in good agreement with the experimental results by employing Realizable k–ε turbulence model. Parametric analysis results show that the theoretical swirl number decreases with increasing Reynolds number at constant H/D and raises for H/D < 0.75. With the decrease in the Reynolds number from 8100 to 2100, although the H/D loses gradually effect on the heat transfer, H/D = 0.25 continues its effect. It is observed that the pressure peaks and the subatmospheric pressure on the impingement plate change with the nozzle-to-plate distance and Reynolds number. [ABSTRACT FROM AUTHOR]

As part of the drive towards achieving net-zero flight by 2050, the development of ultra-high bypass ratio engines will place greater importance on the efficiency of the low-pressure turbine. Stator-well cavities can be a significant source of loss within this system, primarily due to the ingestion of annulus air, which can rotate at a speed less than that of the disc. This paper presents the results of a joint experimental/numerical campaign to relate windage torque to the flow physics in a scaled, engine-realistic stator-well geometry with superposed flows. The primary variables were the pressure ratio across the stator row and the swirl ratio at inlet to the cavity. This is the first paper to relate simultaneous torque and swirl measurements in a stator-well cavity. The numerical simulations have also provided insight into the fluid dynamic behaviour. A reduction in cavity windage torque with superposed flow rate was shown, consistent with the increase in swirl measured by experiments and predicted by computations. The pre-swirled superposed flows reduce the ingestion of negatively swirling fluid from the annulus, effectively increasing the swirl ratio of the flow in the cavity towards that of the rotor. This reduces windage losses; at the design condition with superposed flow, the cavity windage torque reduced by 60% of that of the reference case. Sealing effectiveness increased with superposed flow rate. This was demonstrated through gas concentration measurement/simulations, a reduced radial flow velocity into the cavity and a reduced mass flow rate across the interstage seal. The application of a turbulent transport model showed that ingestion could be explained by shear-driven diffusion. Ingestion increased as inlet swirl ratio reduced, while the pressure ratio was found to have a negligible influence on windage moment coefficient, swirl ratio and sealing effectiveness. In addition to providing fluid dynamic insight, the gas concentration results can be used for validating thermomechanical models. The results in this paper will be of practical interest to the engine designer who wishes to scale information to engine-operating conditions. [ABSTRACT FROM AUTHOR]

Serious rub-impact fault is easy to induce backward whirling of the rotor, which is not conducive to smooth operation. In this paper, the whirl characteristics of a counter-rotating dual-rotor system without rubbing fault, single disk with rub-impact, and multi-disk with rub-impact are analyzed based on the full-spectrum theory. The characteristics and differences of backward whirls caused by unbalanced excitation and rubbing are studied. Besides, a dual-rotor test rig with rub-impact was built, and the rub-impact experiments of the high-pressure rotor (HPR) and low-pressure rotor (LPR) were carried out, respectively. The results show that the frequency component in the full spectrum of backward whirl induced by unbalanced excitation appears as the rotary speed of HPR and LPR. In the backward whirling caused by rubbing, in addition to the frequency component of the unbalanced excitation, there is also a negative backward whirl frequency with a larger amplitude. The main reason for the occurrence of the backward whirl frequency is the alternating positive and negative work of friction. The backward whirl frequency increases gradually with the increase of rotational speed and rubbing stiffness. When there are multiple disks involved in rubbing, the number of backward whirl frequencies will also increase. The above research is helpful to understand the whirling characteristics of rub-impact dual-rotor systems deeply. [ABSTRACT FROM AUTHOR]

New tests of software packages and turbulence models for validating the problems of highly intense vortex flows past structured energy-effective surfaces are presented. The idea of the testing is based on the discovery of anomalous intensification of separation flows and heat transfer in inclined grooves in plates and channel walls. At the expense of extraordinary pressure differences in the grooves, which are confirmed in experiments, swirl flows with high velocities of return and secondary currents are formed. These velocities are comparable with that of the freestream. Moreover, high-gradient zones with friction and heat removal many times higher (by a factor of from 1.5–2 to 7–9) than the friction and heat removal on a flat wall are formed. By way of illustration, we present the results of testing the VP2/3 software package developed on the basis of original muliblock computational technologies and using intersecting different-in-scale grids. The comparison of the numerical predictions with M.A. Zubin's experiments confirmed the high static-pressure differences between the deceleration zone on the windward slope of an inclined groove and the negative pressure region at the place of tornado-like flow generation on the spherical entry segment and asserted the applicability of the RANS approach in predicting the characteristics of highly-intense swirled flows. [ABSTRACT FROM AUTHOR]

Experimental and numerical studies have been made of the hydrodynamics of isothermal flows in a small-scale cyclone chamber (D = 0.21 m) with two-stage differently directed injection of tangentially blown air (with a cocurrent and countercurrent swirl). It has been established that the character of vortex flow with a countercurrent swire differs significantly from the structure of flow with a cocurrent swirl. The character of velocity and pressure distribution in the chamber′s volume has been revealed for the flows in question. Dimensionless dependences have been obtained for calculating the tangential velocity and pressure in the chamber. It has been shown that results of numerical modeling of vortex flows with the k–ω (SST) turbulence models for the concurrent and countercurrent air swirl are in satisfactory agreement with experimental data. [ABSTRACT FROM AUTHOR]

The flow and heat transfer characteristics of magnetic nanofluids in a circular channel under the action of magnetic fields were studied through numerical simulation based on the finite element method. The results show that there are obvious secondary vortices on the cross-section, and a swirling flow is formed in the duct under the coupling effects of the magnetic field, velocity distribution, and thermal variations which destroys the boundary layer, accelerates the mixing of fluids, and enhances heat transfer. In the studied range, the maximum heat transfer coefficient can be increased by 102.65 %, and the maximum comprehensive heat transfer factor J is 1.69 compared to the ferrofluid not affected by the external magnetic field. In addition, the effect of enhancing heat transfer gradually decreases with the increase of θ, until heat transfer is slightly inhibited when the magnetic field is parallel to the flow direction. [ABSTRACT FROM AUTHOR]

The motion of the fluid due to the swirling of a disk/sheet has many applications in engineering and industry. Investigating these types of problems is very difficult due to the non-linearity of the governing equations, especially when the governing equations are to be solved analytically. Time is also considered a challenge in problems, and times dependent problems are rare. This study aims to investigate the problem related to a transient rotating angled plate through two analytical techniques for the three-dimensional thin film nanomaterials flow. The geometry of research is a swirling sheet with a three-dimensional unsteady nanomaterial thin-film moment. The problem's governing equations of the conservation of mass, momentum, energy, and concentration are partial differential equations (PDEs). Solving PDEs, especially their analytical solution, is considered a serious challenge, but by using similar variables, they can be converted into ordinary differential equations (ODEs). The derived ODEs are still nonlinear, but it is possible to approximate them analytically with semi-analytical methods. This study transformed the governing PDEs into a set of nonlinear ODEs using appropriate similarity variables. The dimensionless parameters such as Prandtl number, Schmidt number, Brownian motion parameter, thermophoretic parameter, Nusselt, and Sherwood numbers are presented in ODEs, and the impact of these dimensionless parameters was considered in four cases. Every case that is considered in this problem was demonstrated with graphs. This study used modified AGM (Akbari–Ganji Method) and HAN (Hybrid analytical and numerical) methods to solve the ODEs, which are the novelty of the current study. The modified AGM is novel and has made the former AGM more complete. The second semi-analytical technique is the HAN method, and because it has been solved numerically in previous articles, this method has also been used. The new results were obtained using the modified AGM and HAN solutions. The validity of these two analytical solutions was proved when compared with the Runge–Kutta fourth-order (RK4) numerical solutions. [ABSTRACT FROM AUTHOR]

A model was proposed for determining the efficiency of fractional separation in a uniflow cyclone. The model includes parameters that characterize the motion of a particle in the cyclone and, hence, the degree of separation, namely, the distance that the particle travels when moving in a helical path, and this path itself. The separation efficiency in a uniflow cyclone of a new design was experimentally studied. The experiments were carried out with quartz flour of four particle size fractions: 15, 20, 30, and 50 μm. The efficiency of the cyclone in the separation of small particles was high for apparatuses of this type. The separation efficiency curves were analyzed. [ABSTRACT FROM AUTHOR]

This study looks at the impact of a magnetic dipole on swirling flow and heat transmission over a deformable cylinder. This model considers the impacts of alumina alloys nanoparticles as well as linear radiation in (AA7075 and AA7072) viscous nanofluids-based-H2O. The Navier–Stokes equation was utilized to express the predicted flow quantitatively. The partial differential equations (PDEs) required to investigate the flow assumptions were created using the boundary layer approximation of the Navier–Stokes equation. The ordinary differential equations (ODEs) formalism can be employed by modifying the system with similar conversions. The bvp4c methodology is employed to describe a system with no dimensions. The numerical and graphical representations of the data provide a clear understanding of the roles played by the essential physical constituents. The results showed that the increment in aluminium alloys nanoparticles reduces the surface frictional forces, while the incrementation in the magnetic interaction parameter improves the heat transfer of the nanofluid. [ABSTRACT FROM AUTHOR]

The paper presents the results of calculating the thermal-hydraulic heat exchange efficiency processes for direct and swirl (using an inserted twisted tape) pipe air flows at the same transferred heat fluxes and temperature conditions. The calculated energy efficiency, which characterizes the thermal-hydraulic heat exchange efficiency, demonstrated the ratio of transferred heat and energy consumption for pumping the coolant during the heat exchange for these two cases to be almost the same for coolant-flow Reynolds numbers up to 2.5 ⋅104. At large Reynolds numbers, the thermal-hydraulic efficiency of a direct flow heat exchange is higher. [ABSTRACT FROM AUTHOR]

The problem of the evolution of two oppositely swirling vortices in a viscous incompressible fluid is solved. The theory of plane slowly varying recirculation flows is applied to the construction of the solution at long times. [ABSTRACT FROM AUTHOR]

Accounting for 1.5% of thoracic trauma, blunt thoracic aortic injury (BTAI) is a rare disease with a high mortality rate that nowadays is treated mostly via thoracic endovascular aortic repair (TEVAR). Personalised computational models based on fluid–solid interaction (FSI) principals not only support clinical researchers in studying virtual therapy response, but also are capable of predicting eventual outcomes. The present work studies the variation of key haemodynamic parameters in a clinical case of BTAI after successful TEVAR, using a two-way FSI model. The three-dimensional (3D) patient-specific geometries of the patient were coupled with three-element Windkessel model for both prior and post intervention cases, forcing a correct prediction of blood flow over each section. Results showed significant improvement in velocity and pressure distribution after stenting. High oscillatory, low magnitude shear (HOLMES) regions require careful examination in future follow-ups, since thrombus formation was confirmed in some previously clinically reported cases of BTAI treated with TEVAR. The strength of swirling flows along aorta was also damped after stent deployment. Highlighting the importance of haemodynamic parameters in case-specific therapies. In future studies, compromising motion of aortic wall due to excessive cost of FSI simulations can be considered and should be based on the objectives of studies to achieve a more clinical-friendly patient-specific CFD model [ABSTRACT FROM AUTHOR]

We employ Q learning, a variant of reinforcement learning, so that an active particle learns by itself to navigate on the fastest path toward a target while experiencing external forces and flow fields. As state variables, we use the distance and direction toward the target, and as action variables the active particle can choose a new orientation along which it moves with constant velocity. We explicitly investigate optimal navigation in a potential barrier/well and a uniform/ Poiseuille/swirling flow field. We show that Q learning is able to identify the fastest path and discuss the results. We also demonstrate that Q learning and applying the learned policy works when the particle orientation experiences thermal noise. However, the successful outcome strongly depends on the specific problem and the strength of noise. [ABSTRACT FROM AUTHOR]

In order to solve the problem of fluid accumulation in horizontal gas wells and improve the fluid-carrying capacity and recovery efficiency of gas wells, this paper simulates three internal vortex tools using the commercial software ANSYS FLUENT, and analyzes the drainage recovery efficiency of the three vortex structures and the vortex characteristics of the downstream section vortex field. The results show that the axial velocity of the three-bladed spiral tube in the cyclonic field rotates quasi-periodically with the flow field compared with the internal vortex tube and the rifled tube, and the axial velocity, tangential velocity and vortex intensity of the three-bladed vortex tube guided flow field are the highest; meanwhile, the axial velocity, tangential velocity and vortex intensity of the three-bladed spiral tube guided flow field decay the fastest, and the line rifled tube decays the slowest. The liquid phase in the cyclonic field exhibits obvious spiral motion and maintains a long-distance cyclonic flow state under the action of cyclonic flow. The enhancement of the vortex intensity easily leads to the increase of liquid volume fraction and liquid film thickness at the tube wall. Through the analysis of the energy efficiency of the three structures, it is found that the three-leaf spiral tube is more suitable for the initial phase of drainage transport, while the internal vortex tube is more favorable for the stable phase of transport. The study of the gas-liquid swirl flow of the three swirl tools demonstrated the feasibility of the internal swirl tool for application in horizontal wells. It can provide theoretical guidance and practical basis for effective liquid filling with internal vortex tools in the future. [ABSTRACT FROM AUTHOR]

Accounting for 1.5% of thoracic trauma, blunt thoracic aortic injury (BTAI) is a rare disease with a high mortality rate that nowadays is treated mostly via thoracic endovascular aortic repair (TEVAR). Personalised computational models based on fluid–solid interaction (FSI) principals not only support clinical researchers in studying virtual therapy response, but also are capable of predicting eventual outcomes. The present work studies the variation of key haemodynamic parameters in a clinical case of BTAI after successful TEVAR, using a two-way FSI model. The three-dimensional (3D) patient-specific geometries of the patient were coupled with three-element Windkessel model for both prior and post intervention cases, forcing a correct prediction of blood flow over each section. Results showed significant improvement in velocity and pressure distribution after stenting. High oscillatory, low magnitude shear (HOLMES) regions require careful examination in future follow-ups, since thrombus formation was confirmed in some previously clinically reported cases of BTAI treated with TEVAR. The strength of swirling flows along aorta was also damped after stent deployment. Highlighting the importance of haemodynamic parameters in case-specific therapies. In future studies, compromising motion of aortic wall due to excessive cost of FSI simulations can be considered and should be based on the objectives of studies to achieve a more clinical-friendly patient-specific CFD model [ABSTRACT FROM AUTHOR]

Results of mathematical simulation of the influence of the swirling of a flow of an equilibrially dissociating heattransfer agent (nitrogen tetroxide) in a tube on the heat transfer and the chemical reaction in it are presented. It is shown that an increase in the intensity of swirling of such a flow in a tube increases the rate of heat exchange in it, with the result that the Nusselt number of the flow increases. In this case, the heat transfer in the flow depends not only on the integral intensity of its swirling but also on the method of organization of the flow swirling. It was established that, in the case of active action of the centrifugal forces on this flow, the turbulent disturbances arising in it cause its heat-transfer coefficient to increase, and, in the case of conservative action of the centrifugal forces on the flow, its heat transfer coefficient decreases. It is shown that the rate of heat exchange in the indicated flow can be controlled by changing the tangential component of the velocity of the flow along the radius of the tube. [ABSTRACT FROM AUTHOR]

This study presents Stereoscopic particle image velocimetry measurements of a precessing motion resulting from a sudden expansion of an axisymmetric jet into a coaxial chamber. The sudden expansion has an expansion ratio of 4.9 and an aspect ratio of 2.03. The velocity profile in the inlet tube is measured upstream of the expansion using Laser doppler anemometry. The Reynolds number (Re) is varied from 3160 to 63,870. The time-averaged flow field exhibits an axisymmetric behavior, and the velocity profile near the expansion resembles that of a jet. The half-width and the opening angle of the jet are similar for all Reynolds numbers measured, with values of 3.73 ± 0. 04 ∘ and 8.73 ± 0. 19 ∘ , respectively. Despite its axisymmetry, the flow field contains unsteady coherent structures in nature, which are analyzed using both spectral proper orthogonal decomposition and phase averaging. These structures make the instantaneous flow field asymmetric and create a precession around the central axis of the geometry. The structure of this precession is similar for 8300 ≤ Re ≤ 63,870. For 3160 ≤ Re ≤ 8300 , the precession is very weak and hard to extract from the turbulent flow fields. The Strouhal number (St) increases linearly for 8300 ≤ Re ≤ 23,600, after which it reaches a value of around 0.003. Precessing structures of this kind were previously only reported for swirling sudden expansion flows, fluidic precessing jet nozzles or annular free jets. However, this study shows that they also exist in confined, non-swirling sudden expansion flows, without exiting to an ambient fluid. [ABSTRACT FROM AUTHOR]

This paper presents the results of liquid-fuel model combustor calculations based on different numerical approaches to the development of a verified simulation method of combustor operation. Both steady and transient studies were carried using various RANS turbulent models and the detached eddy simulation (DES) method. The results of these studies were compared with experimental data obtained by optical methods. The largest differences between experiment and calculations are observed for the near-axial flow field where recirculation backflow is formed. This vortex structure can be properly resolved in a DES simulation and in transient calculations based on the SAS SST model. The use of the above-mentioned approaches in combination with the flamelet combustion model provides maximum accuracy in predicting the parameters of reacting swirling flow, in particular the velocity and temperature distributions in the combustor. [ABSTRACT FROM AUTHOR]

A system of the Euler equations that describe two-dimensional steady flows of an ideal fluid is considered. This system is reduced to a nonlinear Laplace equation for the stream function. With the use of the Hirota -function, solutions of three elliptical equations (sin-Gordon, sinh-Gordon, and Tzitzeica equations) are found. A simple method of deriving solutions in the form of rational expressions in elliptical functions is proposed. The resultant solutions describe sources in a swirled fluid, jet flows, chains of sources and sinks, and vortex structures. It is shown that the fluid flux through a closed curve is quantized in the case of the elliptical sin-Gordon equation. [ABSTRACT FROM AUTHOR]

The three dimensional modal linear stability of the radially stratified q-vortex is investigated. The presence of a radial density gradient in the vortex core biases the vortex stability features over the whole parameter space, i.e. varying the swirl number q, the axial k and azimuthal m wavenumbers and the density-to-vorticity radius ratio ϵ . The high swirl vortex, known to be stable in the constant-density situation becomes unstable to the Rayleigh–Taylor instability (RTI) with high amplification rates for vortex cores denser than the ambient. Hence we carry out a comprehensive stability analysis to measure the consequences of the onset of the RTI on the q-vortex linear stability. The damping effect of viscosity saturates beyond a threshold Reynolds number and we mean to address high Reynolds number situations such as those found in aircraft trailing vortices. Hence we place ourselves in the high Reynolds numbers regime for which vortices with a dense core exhibit a significant increase of the global maximum of the amplification rate. The effect of the radius ratio ϵ is twofold. In the high swirl number regime where the homogeneous modes are stable or weakly amplified, the concentration of denser fluid at the vortex core promotes instabilities. In regions of the (k, q)-plane favouring both the homogeneous instability and the RTI mechanism, the amplification rate peaks for a radius ratio around ϵ ≈ 2 . [ABSTRACT FROM AUTHOR]

Pre-swirl nozzle is an important cooling component that is located inside of aero-engine and exposed to complex vibration excitation, and exploring its vibration characteristics and durability is of significant importance, especially for 3D printing pre-swirl nozzle. The present study provides a novel vibration test method based on equivalent installation stiffness. Firstly, the vibration characteristics of pre-swirl nozzle in real engine assembly state is calculated by the finite element method, and the equivalent constraint fixture is designed and checked based on this. The check results indicate that the designed fixture can well restore the installation stiffness of engine and the strength of the test fixture elements is enough in the vibration test process. Then, the modal characteristics of pre-swirl nozzle are measured by modal test, based on which the accuracy of the finite element model is verified. Finally, a test program of vibration durability is established to evaluate the vibration durability of pre-swirl nozzle, in which the excitation frequency is determined by combining logarithmic frequency sweep and linear frequency sweep and the location of maximum stress is determined based on a novel method (density increasing method). Besides, the calibration of relation between vibration stress and excitation amplitude is completed. Based on the proposed test program, vibration durability test is performed. The results show that the natural frequency of pre-swirl nozzle only decreases by 0.62 % after 5×107 cycles, which indicates that the specimen is always in the stage of fatigue crack initiation over the test duration. [ABSTRACT FROM AUTHOR]

Purpose: Intracranial aneurysms (IAs) are pathological dilations of cerebrovascular vessels due to degeneration of the mechanical strength of the arterial wall, precluded by altered cellular functionality. The presence of swirling hemodynamic flow (vortices) is known to alter vascular endothelial cell (EC) morphology and protein expression indicative of IAs. Unfortunately, less is known if vortices with varied spatial and temporal stability lead to differing levels of EC change. The aim of this work is to investigate vortices of varying spatial and temporal stability impact on ECs. Methods: Vortex and EC interplay was investigated by a novel combination of parallel plate flow chamber (PPFC) design and computational analysis. ECs were exposed to laminar (7.5 dynes/ cm 2 wall shear stress) or low (<1 dynes/ cm 2 ) stress vortical flow using PPFCs. Immunofluorescent imaging analyzed EC morphology, while ELISA tests quantified VE-cadherin (cell-cell adhesion), VCAM-1 (macrophage-EC adhesion), and cleaved caspase-3 (apoptotic signal) expression. PPFC flow was simulated, and vortex stability was calculated via the temporally averaged degree of (volume) overlap (TA-DVO) of vortices within a given area. Results: EC morphological changes were independent of vortex stability. Increased stability promoted VE-cadherin degradation (correlation coefficient r = - 0.84) and 5-fold increased cleaved caspase-3 post 24 h in stable (TA-DVO 0.736 ± 0.05) vs unstable (TA-DVO 0.606 ± 0.2) vortices. ECs in stable vortices displayed a 4.5-fold VCAM-1 increase than unstable counterparts after 12 h. Conclusion: This work demonstrates highly stable disturbed flow imparts increased inflammatory signaling, degraded cell-cell adhesion, and increased cellular apoptosis than unstable vortices. Such knowledge offers novel insight toward understanding IA development and rupture. [ABSTRACT FROM AUTHOR]

Investigation of hydro-turbine runner flow on a full-scale test rig consisting of a spiral casing, a stator, guide vanes, and a runner is difficult due to high cost and labor intensity. Therefore, an approach to modeling the inlet velocity profile of a hydro turbine draft tube is proposed that significantly reduces the cost of testing. In this approach, the draft tube inlet flow is modeled using a special swirl apparatus which is a combination of two swirlers: fixed and rotating. The paper presents the results of analytical calculation of the vane shape that provides a given velocity distribution corresponding to the optimal operation of the hydro turbine. [ABSTRACT FROM AUTHOR]

A mathematical model is presented that describes the movement of gas in a direct-flow cyclone. The equations of motion of the gas phase were solved and profiles for the tangential and axial components of gas velocity were derived based on them. The results obtained are compared with the results of numerical simulation. The latter was carried out in the FlowVision software using the SST turbulence model. Via numerical calculations the change in the tangential and axial components of the gas velocity was determined at distances of 110, 150, 200, and 250 mm from the plate turbulator, or cyclone swirler. [ABSTRACT FROM AUTHOR]

Numerical simulations were carried out to explore the flow characters and swirl distortion features of RAE M2129 S-Duct inlet using detached eddy simulation. Three freestream conditions at Mach 0.21, at angle of attack between 0 and 12 deg and at angle of sideslip between 0 and 12 deg are simulated. Results suggest that the time-averaged flow features and the aerodynamic performance of the S-Duct inlet for three freestream conditions are similar to each other; meanwhile, the time-averaged swirl distortion descriptors are also close to each other. Nevertheless, the instantaneous small-scale turbulent structures primarily induced by the freestream angle of attack lead to the generation of more strong vortices at the inlet exit plane between inlet center cone and the stbd wall, which results in larger fluctuating swirl distortions. Furthermore, the fluctuating velocity in transverse direction is more positively correlated with circumferential velocity, while the fluctuating velocity in longitude direction is more negatively correlated with circumferential velocity. [ABSTRACT FROM AUTHOR]

This paper gives a brief review of studies by Russian and foreign scientists in the field of heat and mass transfer in swirling flows; the vortex effect; swirling and vortex flows in the elements of gas turbine, aerospace, and power engineering; combustion with a swirling flow; and modern methods for the numerical and experimental study of swirling flows, surface vortex generators, heat transfer, and hydrodynamics on macro-, micro-, and nanoscales. The results of these studies were discussed during the seventh conference Heat and Mass Transfer and Hydrodynamics in Swirling Flows. [ABSTRACT FROM AUTHOR]

When a liquid in a tank is extracted or drained through a small port at the bottom of the tank, a dip is observed on top of the liquid column. In the presence of swirling flow due to external disturbances, the dip extends rapidly and penetrates to the bottom of the tank which is termed as an air core vortex phenomenon. When this air core is fully developed and penetrates into the drain port, there will be reduction in the discharge area of liquid at the drain port. The draining time of the liquid will be affected due to change in flow rate caused by this penetration of vortex and hence it is not desirable in applications such as spacecrafts and rockets. This article deals with numerical studies performed to analyze the air core vortex formation of water in cylindrical tanks subjected to axial and radial bulk forces after the commencement of draining, using a commercial CFD software. Moreover, the experimental measurements were taken for a cylindrical tank without inclination and the validation of the 2D and 3D numerical predictions were carried out. The tank rotated at different initial rotational speeds along the axis for the generation of vortex and then drained through a centrally located drain port situated at the base of the tank. The results show that the vortex generation is augmented with increase in the radial bulk force along with a decrease in the axial bulk force which correlates to the increase in inclination of the cylinder. The entire set of simulations was also performed at two times gravity conditions. This study is of practical relevance in spacecrafts and rocket engines as the similar condition prevails in propellant tanks owing to the inclined flight path trajectory that are subjected to increased gravity forces. [ABSTRACT FROM AUTHOR]

The receiver calorimeter (RC) is one of the main elements of the beam path of an atomic beam injector with ballistic focusing. A water-cooled RC developed for an injector of a focused beam of fast deuterium atoms with a beam power of more than 1 MW and pulse duration of 2 s [1] installed at the variable configuration tokamak (TCV) in Lausanne (Switzerland) is considered. The design of the RC includes receiving plates with liquid flow swirlers installed in them to enhance heat transfer and pipe-in-pipe collectors of water inlet and water outlet that provide the movement into a vacuum. These technical solutions made it possible to achieve good energy efficiency of the device with very small overall dimensions and mass flow of the coolant. The design of the main elements of the calorimeter is described. The results of simulation of the coolant flow and heat transfer and some experimental data are presented. [ABSTRACT FROM AUTHOR]

This study numerically investigates the flow and combustion characteristics of a swirl-premixed burner with a curved vane swirler (i.e., curved type) to reduce the pressure loss of the burner nozzle with a conventional vane swirler (i.e., flat type). For the curved type swirler, the pressure loss is decreased by 35 % due to the inhibition of flow separation at the vane, and NOX emission is reduced by 69 % because fuel-air mixing is enhanced at the flame front, leading to more uniform fuel distribution toward downstream. In addition, the characteristics of the jet penetration are analyzed because the jet behavior is crucial to fuel-air mixing. The jet trajectory in non-swirling flow can be reasonably predicted by a conventional formula, but it is difficult to predict the jet trajectory in swirling flow by this formula because of the effect of a radial pressure gradient formed by the swirling flow. [ABSTRACT FROM AUTHOR]

This paper describes the measurement methodology for quantifying the instantaneous full 3D scalar dissipation rate (SDR or χ ) in order to characterize the rate of mixing. Measurements are performed in a near field of a jet-in-swirling-coflow configuration. All three components of χ are measured using a dual-plane acetone planar laser-induced fluorescence technique. To minimize noise, a Wiener filtering approach is used. The out-of-plane SDR component ( χ 3 ) is validated by assuming isotropy between axial and azimuthal components of SDR. An optimum laser-sheet separation distance ( Δ s ) is identified by comparing the SDR components on the basis of instantaneous, mean, and probability density function data. The in-plane resolution needs to match the Batchelor scale ( λ B ) for the central difference scheme-based SDR deduction. However, the out-of-plane resolution, Δ s , requirement is different owing to the use of two-point difference based SDR and systematic biases. The optimum Δ s is found to be 2.5 λ B . Finally, measurement guidelines are provided to assess the accuracy of 3D SDR measurements. [ABSTRACT FROM AUTHOR]

To capture pollutants in various buildings and structures, it is necessary to use local exhaust systems. It is proposed to increase one of the criteria for the local exhaust efficiency, i.e. the rate of pollutants capture, due to the impact of a swirling annular jet and the occurrence of a reverse air flow. In order to do that, a circular exhaust was placed coaxially in an outer cylindrical casing, in which the air flow was swirled due to the tangential supply of two supply jets into the casing, resulting in a vortex dome, which contributed to an increase in the efficiency of such a vortex exhaust. The change in the axial air velocity at a distance from the vortex exhaust was experimentally and numerically studied for 11 structures, in each of which 4 different ratios of exhaust and supply air flow rates were set. In the studied applications of the proposed exhaust systems, the velocity increases significantly at a certain range of distances from them. A combination of design and mode parameters that contribute to the highest capture rate by vortex exhaust has been determined. The results obtained can be used to design efficient exhaust systems to capture pollutants. [ABSTRACT FROM AUTHOR]