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Upstream vortex has a significant effect on the secondary flow structure of the downstream turbine in the stage environment. This study investigates the secondary flow structure with non-axisymmetric endwall profiling (NAEW) under the interaction of co-rotating incoming vortex (Vic). A half-delta wing vortex generator is utilized to model Vic. The turbine cascade case which exhibited maximum reduction of the cascade loss with NAEW under no incoming vortex is studied. The mechanism of loss reduction with NAEW under the interaction of Vic is analysed. Vic could decrease the secondary flow near the endwall region by affecting the horseshoe vortex transport in the cascade. However, its loss reduction was lower than the loss increments of Vic itself. The arrival of Vic at the leading edge of the cascade increased the strength of the horseshoe vortex, resulting in a significant increase in loss. Under the interaction of Vic, NAEW decreased the blade loading near endwall region, which resulted in the reduction of cascade loss. [ABSTRACT FROM AUTHOR]

The article presents the results of a study of the characteristics of the wake vortex of aircraft with turboprop engines. Using the example of the An-12 aircraft, it is shown that rotating propellers make a noticeable contribution to the propagation of the vortex trail behind the aircraft. This is proved by some studies, as well as numerous observations. It also describes a technique for studying the wake vortex of aircraft with propellers. The method is based on the method of discrete vortices. The relevance of such studies is due to the growing interest of carrier companies in aircraft with turboprop engines. It has been proven that when transporting passengers and cargo on such vessels over distances of 700–800 km, maintenance and fuel costs are reduced by about 30–40%. Therefore, the fleet of turboprop aircraft, such as An-22, An-70, An-12, as well as Tu-95, Il-38, C-130, etc., has been preserved so far. New turboprop aircraft are being developed and put into operation: A-400M, Il-114, Il-112M. The vortex trail behind such aircraft also poses a danger to other aircraft flying behind. A feature of the propagation of the wake vortex behind aircraft with propellers is the interaction of vortices coming off the airframe and vortices from the propellers. As a result, due to the rotation of all the screws in one direction, symmetry is broken in the propagation of vortices descending from the right and left halves of the wing. Therefore, it is important to understand how differently the vortices that descend from the airframe of an aircraft with turboprop engines behave. For the convenience of the study, the method of accounting for the effect of vortices from screws is integrated into a special calculation and software package, also based on the method of discrete vortices. In it, when calculating the characteristics of the wake vortex, the flight weight, speed and altitude of the aircraft, its flight configuration, atmospheric conditions, proximity of the earth, axial velocity in the core of the vortex and some other factors are taken into account. This complex has passed the necessary testing and state registration. A number of measures were carried out to validate and verify the developed complex, confirming the operability of the programs included in it and the reliability of the results obtained from it. The results of the study of the characteristics of the wake vortex behind the Antonov-12 aircraft in the form of vertical velocity spectra and fields of perturbed velocities at various distances from it are presented. It is shown that propellers noticeably affect the propagation of the wake vortex behind turboprop aircraft. This circumstance must be taken into account by the crews of aircraft flying behind such aircraft.

During swimming, many fishes use pectoral fins for propulsion and, in the process, move substantial amounts of water rearward. However, the effect that this upstream wake has on the caudal fin remains largely unexplored. By coordinating motions of the caudal fin with the pectoral fins, fishes have the potential to create constructive flow interactions which may act to partially recapture the upstream energy lost in the pectoral fin wake. Using experimentally derived velocity and pressure fields for the silver mojarra (Eucinostomus argenteus), we show that pectoral–caudal fin (PCF) coordination enables the circulation and interception of pectoral fin wake vortices by the caudal fin. This acts to transfer energy to the caudal fin and enhance its hydrodynamic efficiency at swimming speeds where this behaviour occurs. We also find that mojarras commonly use PCF coordination in nature. The results offer new insights into the evolutionary drivers and behavioural plasticity of fish swimming as well as for developing more capable bioinspired underwater vehicles.

Wheels contribute significantly to the aerodynamic performance of ground vehicles. Many studies have focused on investigating a single wheel either in isolation or in a wheelhouse. However, there has been less focus on the flow field around a rear wheel, especially when considering varying proximity to the front wheel, despite its importance on aerodynamic forces. In this study, a generic reference body is modified and fitted with a rear wheel within a wheelhouse and analysed while the wheel spacing varies. Reynolds-Averaged Navier–Stokes (RANS) modelling was employed to allow for multiple variations to be considered and the model produced results in good agreement with experimental results. The results confirm that two upper rear wheelhouse outflow vortices are only present when the wheel spacing is short. It was found that the drag values were minimal for the wheel spacing at a critical distance of 1.5 wheel diameters. At this wheel spacing, the formation of the outboard jetting vortex is prevented at the rear wheel, and hence, the rear wheel drag is reduced by more than 10%. Any further reduction in the spacing does not provide any drag benefits. Also, the outflow from the front wheelhouse is projected further away from the body, drawing flow from the rear wheelhouse into the outboard jetting vortex. [ABSTRACT FROM AUTHOR]

To provide deep dives about aerodynamic loss mechanisms in Wells turbines for wave energy conversion, a loss audit analysis was performed by numerical experiments in a monoplane Wells turbine with guide vanes. The interactions between the tip-leakage and leading-edge vortices during the stall process were captured by an improved vortex identification method, which revealed the relationship between vortex interactions and stall mechanisms by identifying coherent structures and tracking the vortex core trajectory. Finally, the influence of vortex interactions on exergy transfer was quantified. The results indicate that the lost kinetic energy and mixing losses dominate the loss generation in the Wells turbine stage under stall conditions. Under the beneficial effect of tip leakage flow, leading-edge separation first begins at the equilibrium region between the tip-leakage and leading-edge vortices. As the leading-edge vortices expand toward the blade tip, the intensified leading-edge vortex interacts with the casing suction-side corner vortex and accelerates the dissipation of the tip-leakage vortices. Consequently, the contributions of viscous irreversibilities outweigh those of shaft work, being the dominant factor in the decrease in flow exergy, leading to a decrease in exergy utilization by 38.46% from the pre-stall condition to the stall condition. [ABSTRACT FROM AUTHOR]

The wind resistance of a model of a large container ship was investigated experimentally and numerically under various conditions to investigate the aerodynamic performance and identify approaches for reducing wind resistance. The container ship model with and without six types of forecastle fairing was tested in a wind tunnel under conditions of full load and various uneven loads in different wind directions. The model test found that a specially designed forecastle fairing and certain container configurations are effective in reducing wind resistance. Then, a numerical simulation was performed to investigate the characteristics of the flow field around the test model. The comparisons and analyzes of the pressure distribution, streamlines, and vortex structure illuminate the mechanism of load reduction caused by the forecastle fairing and container configurations that are useful for reducing wind resistance. The optimization of a container ship for wind resistance is dominated by the effect of the container configuration; the contributions of forecastle fairing are secondary. When the overall effects of forecastle fairing and container configuration are considered, the streamlined load is the variant most optimized for wind resistance.

Triple flickering buoyant diffusion flames of methane gas in equilateral triangle arrangement, as a nonlinear dynamical system of coupled oscillators, were computationally investigated. The four distinct dynamical modes (in-phase, death, rotation, and partially in-phase), that were originally observed in candle-flame experiments, were computationally reproduced for the first time. The four modes were interpreted from the perspective of vortex interaction and particularly of vorticity reconnection and vortex-induced flow. Specifically, the in-phase mode is caused by the periodic shedding of the trefoil vortex formed by the reconnection of three toroidal vortices; the death mode is due to the suppression of vortex shedding at small Reynolds numbers; the rotation mode appears as three toroidal vortices alternatively shed off with a constant phase difference; the partially in-phase model is caused by the vorticity reconnection of two toroidal vortices leaving another one shedding off in anti-phase. This work well establishes a bridge between the vortex dynamics and the nonlinear dynamics of the triple-flame system, which is believed to play a key role in understanding larger dynamical systems of multiple flickering flames. [ABSTRACT FROM AUTHOR]

Vortex-induced motion (VIM) is a critical issue for floating structures made of one or more columns, due to its significant impacts on their operational stability. Supported by column-type floating platforms, floating offshore wind turbines (FOWTs) may also experience large-amplitude VIM responses in current flow. Existing research on FOWTs has mostly focused on their wind/wave induced responses, yet less attention has been paid to their responses in current flow. In this paper, the VIM of the OC4 semi-submersible FOWT platform is studied numerically over a wide range of flow velocity. Three incidence angles, i.e., 0°, 90°, and 180°, are considered and the effect of current incidence on platform VIM is analysed. Results show that the so-called lock-in phenomenon is present and that a large transverse response amplitude of more than 0.3D persists until Vr = 30, with its maximum reaching over 0.8D at Vr = 8. Meanwhile, the transverse response amplitude for cases with the incidence angle of 180° is generally smaller, with a narrower lock-in regime, than those under the other two incidence scenarios. Flow field visualisation reveals that upstream vortices continuously interact with the downstream side column when the incidence angle turns to 180°, impacting the vortex shedding process and consequently fluid forces of the downstream column. [ABSTRACT FROM AUTHOR]

The wind resistance of a model of a large container ship was investigated experimentally and numerically under various conditions to investigate the aerodynamic performance and identify approaches for reducing wind resistance. The container ship model with and without six types of forecastle fairing was tested in a wind tunnel under conditions of full load and various uneven loads in different wind directions. The model test found that a specially designed forecastle fairing and certain container configurations are effective in reducing wind resistance. Then, a numerical simulation was performed to investigate the characteristics of the flow field around the test model. The comparisons and analyzes of the pressure distribution, streamlines, and vortex structure illuminate the mechanism of load reduction caused by the forecastle fairing and container configurations that are useful for reducing wind resistance. The optimization of a container ship for wind resistance is dominated by the effect of the container configuration; the contributions of forecastle fairing are secondary. When the overall effects of forecastle fairing and container configuration are considered, the streamlined load is the variant most optimized for wind resistance. [ABSTRACT FROM AUTHOR]

One of the most common systems in engineering problems is the multi-column system in the form of an equilateral-triangular arrangement. This study used three-dimensional numerical simulations to investigate the flow around three cylinders in this arrangement at the super-critical Reynolds number R e = 3 × 10 6 , concentrating on the influence on the spacing ratio ( L / D ) among cylinders. The instantaneous vortex structures, Strouhal numbers, fluid force coefficients, and pressure distributions are analyzed thoroughly. The present study demonstrated that fluid dynamics is sensitive to L / D , by which five different flow patterns are classified, namely single bluff body flow ( L / D ≤ 1.1 ), deflected gap flow ( 1.2 ≤ L / D ≤ 1.4 ), anti-phase flow ( 1.5 ≤ L / D ≤ 2.3 ), in-phase flow ( 2.5 ≤ L / D < 3.5 ), and co-shedding flow ( L / D ≥ 3.5 ). Critical bounds are identified by significant transitions in the flow structure, discontinuous drop and jump of S t , and force coefficients. [ABSTRACT FROM AUTHOR]

Wheels contribute significantly to the aerodynamic performance of ground vehicles. Many studies have focused on investigating a single wheel either in isolation or in a wheelhouse. However, there has been less focus on the flow field around a rear wheel, especially when considering varying proximity to the front wheel, despite its importance on aerodynamic forces. In this study, a generic reference body is modified and fitted with a rear wheel within a wheelhouse and analysed while the wheel spacing varies. Reynolds-Averaged Navier–Stokes (RANS) modelling was employed to allow for multiple variations to be considered and the model produced results in good agreement with experimental results. The results confirm that two upper rear wheelhouse outflow vortices are only present when the wheel spacing is short. It was found that the drag values were minimal for the wheel spacing at a critical distance of 1.5 wheel diameters. At this wheel spacing, the formation of the outboard jetting vortex is prevented at the rear wheel, and hence, the rear wheel drag is reduced by more than 10%. Any further reduction in the spacing does not provide any drag benefits. Also, the outflow from the front wheelhouse is projected further away from the body, drawing flow from the rear wheelhouse into the outboard jetting vortex.

This paper aims to further the understanding of the mixing process of in-line twin synthetic jets (SJs) and their impact in the near-wall region in a flat-plate laminar boundary layer. A numerical study has been carried out, in which colored fluid particles and the Q criterion are used to track the SJ-induced vortex structures at the early stage of the evolution. Interacting vortex structures at four selected phase differences are presented and analyzed. It is found that the fluid injected at the early stage of the blowing stroke mainly contributes to the formation of the hairpin legs, the fluid injected near the maximum blowing mainly contributes to the formation of the hairpin head, and the fluid injected at the late stage of the blowing stroke contributes very little to the formation of the hairpin vortex. It is also confirmed that, irrespective of the phase difference, the hairpin vortex issued from the upstream actuator is more capable of maintaining its coherence than its counterpart issued from the downstream actuator. The influence of the interacting vortex structures on the boundary layer is also studied through investigating excess wall shear stress. In all cases, a pair of streaks of high wall shear stress can be observed with similar size. Among them, the streaks have the strongest wall shear stress, with the largest gap at phase difference 0 when partially interacting vortex structures are produced. The findings can provide valuable guiding information for the applications of synthetic jets in heat transfer, mixing control, and flow control in a crossflow. [ABSTRACT FROM AUTHOR]

Vortex loops are compact toroidal structures wherein fluid rotation forms a closed loop around a fictitious axis, manifest in many natural occurrences. These phenomena result from brief impulses through vents or apertures in fluid systems, such as in caves, volcanic crusts, downbursts, or the descent of liquid droplets. The majority of naturally occurring and laboratory-generated vortex loops, studied for fundamental research on their formation, growth, instability, and dissolution, are classified as incompressible. This categorisation denotes negligible alterations in thermodynamic properties within the vortex loop. However, a distinct category of vortex loops emerges from processes involving artillery, shock tubes, explosions, chemical interactions, and combustion. This class primarily constitutes compressible vortex loops. Their presence in flow fields spans over a century, and they have been observed since the application of open-ended shock tubes to explore phenomena like diffracting shock waves, blast wave interactions with objects, and noise mitigation. The study and comprehension of compressible vortex loops and their interactions have historically relied heavily on optical techniques, lacking comprehensive insight into the intricate flow dynamics. Nevertheless, the advancements in flow visualisation tools and computational capabilities in the 21st century have significantly aided scientists in scrutinising and characterising these vortex loops and their interactions in intricate detail. Unfortunately, a comprehensive review of the literature addressing compressible vortex loops originating from shock tubes, their evolution, and interactions with shockwaves and various objects, including walls, appears lacking. This review article aims to address this gap. [ABSTRACT FROM AUTHOR]

One of the most common systems in engineering problems is the multi-column system in the form of an equilateral-triangular arrangement. This study used three-dimensional numerical simulations to investigate the flow around three cylinders in this arrangement at the super-critical Reynolds number Re=3×106, concentrating on the influence on the spacing ratio (L/D) among cylinders. The instantaneous vortex structures, Strouhal numbers, fluid force coefficients, and pressure distributions are analyzed thoroughly. The present study demonstrated that fluid dynamics is sensitive to L/D, by which five different flow patterns are classified, namely single bluff body flow (L/D≤1.1), deflected gap flow (1.2≤L/D≤1.4), anti-phase flow (1.5≤L/D≤2.3), in-phase flow (2.5≤L/D<3.5), and co-shedding flow (L/D≥3.5). Critical bounds are identified by significant transitions in the flow structure, discontinuous drop and jump of St, and force coefficients.

Based on the equations of the f-plane shallow water model, a new set of nonlinear models for the interaction of the vortices in the f-plane shallow water system are established by using perturbation expansion and multi-scale method. These models have different nonlinear characteristics. The asymptotic analytical solution(vortex solution) is obtained by using Newton iteration method and quasi-spectral method. In the simulation process, different from the previous studies, the initial values were constructed by using the asymptotic analytical solution for the first time to simulate the interaction process of the vortices. The result shows that the single vortex maintains a stable state for a long time under fixed parameters. The approximate critical distances of the binary vortices are different under different nonlinear effects. When the distance between binary vortices is less than, equal to, or greater than the critical distance, the binary vortices merge, rotate or separate. In addition, when the vortices interact, the critical distance of mKdV-type vortex is slightly larger than that of KdV-type vortex. This indicates that the nonlinear effect increases the energy loss rate during the interaction of the vortices and weakens the intensity of the interaction until the vortices are separated and do not affect each other. [ABSTRACT FROM AUTHOR]

This paper aims to further the understanding of the mixing process of in-line twin synthetic jets (SJs) and their impact in the near-wall region in a flat-plate laminar boundary layer. A numerical study has been carried out, in which colored fluid particles and the Q criterion are used to track the SJ-induced vortex structures at the early stage of the evolution. Interacting vortex structures at four selected phase differences are presented and analyzed. It is found that the fluid injected at the early stage of the blowing stroke mainly contributes to the formation of the hairpin legs, the fluid injected near the maximum blowing mainly contributes to the formation of the hairpin head, and the fluid injected at the late stage of the blowing stroke contributes very little to the formation of the hairpin vortex. It is also confirmed that, irrespective of the phase difference, the hairpin vortex issued from the upstream actuator is more capable of maintaining its coherence than its counterpart issued from the downstream actuator. The influence of the interacting vortex structures on the boundary layer is also studied through investigating excess wall shear stress. In all cases, a pair of streaks of high wall shear stress can be observed with similar size. Among them, the streaks have the strongest wall shear stress, with the largest gap at phase difference 0 when partially interacting vortex structures are produced. The findings can provide valuable guiding information for the applications of synthetic jets in heat transfer, mixing control, and flow control in a crossflow.

Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total theoretical added mass of a general non-uniform double disk is proposed when it is in the zone which vortex interaction take places. The results show that a non-uniform double disk has better hydrodynamic performance as compared to the uniform double configuration for a given spacing. It is also observed that the mode and direction of the vortex shedding are different for uniform and non-uniform arrangements in a given spacing and KC value. [ABSTRACT FROM AUTHOR]

The investigation of the coupling relationship between mixing enhancement and convective stretching bears practical and scientific significance. In this paper, Lagrangian perspective is adopted for compressible vortex interaction visualization to emphasize the effect of inner flow dynamics other than the vorticity structure on mixing performance. Transport characteristics of the flow are studied through a blob of passive particles. The results demonstrate that Lagrangian coherent structures are faithfully tracked throughout the moving of particles, and the blob initially arranged upon the ridge of Lagrangian coherent structures exhibits efficient stretching. In this sense, the physical meaning of Lagrangian coherent structure as a material barrier and maximum stretching direction is highlighted. On this basis, mixing characteristics are investigated through the introduction of helium concentration blob considering viscous diffusion. Characterized by high growth rate of mixing and low mixing time, mixing enhancement is achieved with the aid of significant stretching directly reflected by high average finite-time Lyapunov exponent in the region of blob deposition, offering an optimal strategy for fluid mixing. [ABSTRACT FROM AUTHOR]

The object of research is the efficiency of dust collection of fine dust in an apparatus with an intense turbulent mode of phase interaction. One of the most problematic areas of the existing dust and gas cleaning equipment is the low efficiency of collecting fine dust. Effective cleaning of exhaust gases from dust involves the use of multistage cleaning systems, including wet and dry dust cleaning devices, which entails high capital and operating costs. These disadvantages are eliminated in the developed design of the cyclone-vortex dust collector with two contact zones. The device implements both dry and wet dust collection mechanisms, which allows for high efficiency of dust removal at high productivity. The conducted studies of the total and fractional efficiency of dust collection when changing the operating parameters of the developed device showed that the efficiency of collecting fine dust is 98–99 %. The increase in the efficiency of dust collection in the dry stage of the device is due to an increase in centrifugal force. In the wet stage of contact, the efficiency reaches its maximum values due to the vortex crushing of the liquid in the nozzle zone of the apparatus. Studies of the fractional efficiency of the apparatus show that with an increase in the diameter of the captured particles, the efficiency of the dust collection process for dry and wet stages, as well as the overall efficiency, increases. With an increase in the density of irrigation, the overall efficiency of dust collection in the apparatus increases. It has been established that an increase in the efficiency of capturing highly dispersed particles occurs due to turbulent diffusion, the value of which is determined by the frequency of turbulent pulsations and the degree of entrainment of particles during the pulsating motion of packed bodies. To describe the results obtained, a centrifugal-inertial model for a dry contact stage and a turbulent-diffusion model of solid particle deposition for a wet contact stage are proposed, which make it possible to calculate the dust collection efficiency of the contact stages, as well as the overall efficiency of the cyclone-vortex apparatus. [ABSTRACT FROM AUTHOR]

The Lagrangian-particles simulation in the Lofoten Basin area in the Norwegian Sea, based on the GLORYS12V1 reanalysis for the period from 2016-05-31 to 2016-06-28, was used to track the vortex pair consisting of the large quasi-permanent Lofoten Vortex (LV) and a cyclone generated nearby the LV. We show that the cyclone is a part of a shield around the LV. The core of the cyclone is partly located inside the LV. This structure forms an uneven vortex pair. We provide a complementary analysis of Lagrangian maps with temperature, salinity, and relative vorticity at 75 horizons from the surface to the bottom, consider the evolution of the vortex pair and obtain its characteristics. The cyclone moves around the LV passing along its periphery 348.97 km with a speed of 14 cm/s, which is comparable 23 cm/s, the orbital velocity of the LV during the study period. The orbital velocity of the satellite cyclone is 15 cm/s. The mean amplitude of the LV in the period from 2016-05-31 to 2016-06-28 is 12.50 cm, and the mean amplitude of the satellite cyclone for the same period is − 2.92 cm. The average radius of the LV is 57.48 km and 13.42 km for its satellite cyclone. The orbital velocities of the LV and its satellite cyclone (with their mean values of amplitude and radii) are 0.23 m/s and 0.15 m/s, respectively. The average integral (in a volume) relative vorticity of the eddies in the vortex pair is − 1.41 × 1018 c−1 for the LV and 3.19 × 109 c−1 for the satellite cyclone. [ABSTRACT FROM AUTHOR]

Among the apparatuses with a regular arrangement of packing elements creating an in-phase mode of vortex interaction, which ensures high efficiency of the processes, it is interesting to use a standard tubular packing. Such packing allows additional advantages associated with heat supply or extraction directly in the contact zone of the interacting phases, which is very important for conducting some chemisorption processes. The research covers such hydrodynamic regularities as hydraulic resistance during a heat carrier movement in pipes and during external flow around a tubular beam, retained liquid amount and gas content of layer in the external flow around the tubular beam with liquid and gas flows. The research was carried out using an experimental setup with a heat and mass transfer apparatus with regular tubular packing. The medium used during experiments is water-air. The research methodology included standard methods for determining hydraulic resistance and retained liquid amount and visual observation and photographing of gas-liquid flows. The novelty of the research was equations – one for calculating the hydraulic resistance in pipes, taking into account local resistances and pipe roughness. The other ones for determining the pressure losses during the external flow around the tubular beam, the retained liquid amount, and the gas content of the layer, taking into account the vortex interaction of gas and liquid flows. Graphical and calculated dependences of the investigated hydrodynamic characteristics were obtained as a result of the conducted research of the hydraulic resistance during the heat carrier movement in the pipes, as well as the hydraulic resistance and the retained liquid amount during the external flow around the tubular beam with a change in the gas velocity and irrigation density. When the heat carrier flows in the pipes, the numerical values of the hydraulic resistance in the transient mode do not exceed 1.5 kPa, in the developed turbulence mode in the range of the Reynolds number from 1·104 to 6·104 ΔР varies from 1.5 to 53 kPa. With the external flow around the tubular beam, in the developed turbulence mode wg = 4 m/s and L = 25 m³/m²h, the hydraulic resistance is 85 Pa, the retained liquid amount is 4.5·10-3 m. The change in the irrigation density in this mode (developed turbulence) in the L range from 10 to 100 m³/m²h leads to an increase in the hydraulic resistance from 65 to 160 Pa, the retained liquid amount from 2.16·10-3 to 13.6·10-3 m. The calculated dependencies are the basis of the method for calculating the hydrodynamic characteristics of the apparatus with the regular tubular packing, which can be used to calculate industrial devices. [ABSTRACT FROM AUTHOR]

In order to accurately and reliably analyze in details the cavitation mechanism and their impact on flow structures, a three-dimensional unsteady .cavitating .turbulent .flow .around .the .three-dimension .Clark-y .hydrofoil .is .investigated .be .using .a Partially-Average Navier Stokes (PANS) model based on Shear Stress Transport (SST). To track the interface of the liquid and the vapor, a Volume of Fluid (VOF) model is employed based on homogeneous mixture approach. To capture the interaction between the cavitation and the flow structure, a bridging method (PANS) between RANS and DNS have been chosen. This technique is able to resolve the unsteady turbulent structures by employing a more consistent methodology. The present numerical .results .are .validated .with .experimental .data. .The .interaction .between .the .cavitation .and .the .fluid .vortex .is .analyzed .and discussed. The numerical results show the capability of the presented model to predict the re-entrant jet and cavitation cloud shedding accurately.

Supercritical carbon dioxide (S-CO2) Brayton cycle system is a promising closed-loop energy conversion system frequently mentioned in the automotive and power generation field in recent years. To develop a suitable design methodology for S-CO2 turbines with better performance, an understanding of the vortex flow patterns and associated aerodynamic loss inside a S-CO2 turbine is essential. In this paper, a hundred-kilowatt level S-CO2 axial turbine is designed and investigated using a three-dimensional transient viscous flow simulation. The NIST Span and Wagner equation of state model that considers the real gas effects is utilized to estimate the thermodynamic properties of the supercritical fluid. The numerical methods are experimentally validated. The results indicates that the aspect ratio and tip-to-hub ratio are different in the S-CO2 turbine from that in the gas turbine, and the vortex flow patterns are influenced notably by these geometrical parameters. Both the vortex structure and moving tracks of passage vortices are changed as a result of large centrifugal force. An interaction between tip leakage vortex and hub passage vortex is observed in the impeller passage and its formation and development mechanism are revealed. To further explore the aerodynamic loss mechanism caused by vortex interaction, the energy loss in the impeller passage is analyzed with the enstrophy dissipation method, which can not only accurately calculate the energy loss but also estimate how the vortical motions occur. It is found that the enstrophy and energy loss can be effectively reduced by vortex interaction between tip leakage vortex and hub passage vortex. The results in this study would increase the knowledge of vortex flow patterns in S-CO2 turbine and the proposed enstrophy production method can be used intuitively to provide a reference for flow vortical motion study in turbines.

The analysis of operation of heat and mass transfer apparatuses and dust collectors with a mobile packing (MP) has allowed creating the designs of apparatuses with a combined regular- suspended packing, which allow using the advantages of vortex interaction of flows in the layer of a regular packing with mechanical cleaning of deposits in the chaotic motion of suspended discrete contact elements. The studies of the hydraulic resistance and the retained liquid amount have been performed in the apparatuses with a tubular- suspended and tubularfountaining packing and their comparative analysis. In order to calculate the hydraulic resistance, the retained liquid amount and the layer gas content, the calculated dependences are presented, taking into account the vortex interaction of gas and liquid flows. [ABSTRACT FROM AUTHOR]

Interaction of a vortex with a blade, wing or fin may involve both rapid distortion of the incident vorticity field and unsteady flow near the surface. A variety of flow visualization methods were applied in the experiment to observe the change of flow characteristics during a streamwise vortex–surface interaction. Particle image velocimetry measurements were carried out on a 2-D flow field in the near-wall area. The topology structure of the flow field during the vortex–surface interaction was obtained. The near-wall vorticity layer caused by the primary vortex formed secondary vortex. The initial strength of the incident vortex and distance between vortex core and the surface are the main parameters that affect the characteristics of flow field. The relevant results will help further study on the mechanism of interaction. [ABSTRACT FROM AUTHOR]

Abstract An experimental study in a recirculating water channel with a square cross section is carried out to study the transient laminar opposing mixed convection heat transfer from two symmetric open cubic cavities. The walls of the cavities facing the openings are subject to a constant wall heat flux boundary condition, the other bounding walls of the cavities and the channel are insulated and adiabatic. The experiments are done under different values of buoyancy strength or modified Richardson number, R i * = G r * / R e 2 from 32.17 to 300.77, channel inclination of 0 ∘ ≤ γ ≤ 90 ∘ , Reynolds number of 500 ≤ R e ≤ 1500, and a fixed Prandtl number of P r = 7. Mean surface temperature distributions and averaged Nusselt numbers have been obtained. Results indicate that depending on the channel orientation and buoyancy strength, the flow and temperature distributions experience an oscillatory behavior and are not symmetric with respect to the channel centerline. In addition, at high R i * numbers, spanwise and axial variation of the heat transfer rates has been reported elucidating the strong three-dimensional (3D) nature of the flow. Empirical correlations for the overall Nusselt number of each cavity are also developed for relations using the Reynolds and modified Grashof numbers over the range of physical parameters considered in this study. Highlights • Mixed convection in a channel with two symmetric cavities is studied experimentally. • Buoyancy strength, duct orientation and Reynolds number effects are presented. • Steady and oscillatory flow and thermal characteristics are reported. • Spanwise and axial variation of the heat transfer rates are obtained. • Correlations for the overall Nusselt number of each cavity are developed. [ABSTRACT FROM AUTHOR]

The flapping foil hydrokinetics turbine is a new method to generate energy from incoming flow field. The numerical simulations have been performed computationally by using two-dimensional unsteady Reynolds-averaged Navier–Stokes equations. It was found that the maximum energy efficiency reached about 35.2% when the reduced frequency was 0.11; at this time, the foil experienced a light dynamic stall and two opposite-sign vorticities were shed from the foil per half of the cycle. This report also studied the energy extraction performance of flapping foil device and the correlation between the foil kinematic parameters and the flow fields around it at actual operating Reynolds number comprehensively. In addition, the vortex variation and the pressure coefficient distribution along the foil's surface were used to demonstrate the mechanism of flapping foil energy generation turbine. The creation and shedding of the leading edge vortex played the critical role in energy transformation between the flow fluid and energy harvesting systems. Therefore, if the timing of the leading edge vortex generation and shedding is controlled, the energy extraction efficiency can be increased considerably. [ABSTRACT FROM AUTHOR]

To analyze the interaction between the turbulent flow structure with the cavitation shedding dynamics, a three-dimensional unsteady cavitating turbulent flow around the three-dimension NACA009 hydrofoil is investigated in this study. The cavitating flow in has been modeled with a homogeneous mixture of liquid and vapor using LES. The interaction between the cavitation and the fluid vortex is analyzed and discussed. The results demonstrate that the vortex stretching is mainly in the center of the cloud cavity and changes quasi-periodically as the cloud cavity evolves. As a result, the mechanism of the inception of cavitation, re-entrant jet and cavitation cloud shedding are accurately captured and predicted by LES in accordance with the experiment data.

The three-layer version of the contour dynamics/surgery method is used to study the interaction mechanisms of a large-scale surface vortex with a smaller vortex/vortices of the middle layer (prototypes of intrathermocline vortices in the ocean) belonging to the middle layer of a three-layer rotating fluid. The lower layer is assumed to be dynamically passive. The piecewise constant vertical density distribution approximates the average long-term profile for the North Atlantic, where intrathermocline eddies are observed most often at depths of 300–1600 m. Numerical experiments were carried out with different initial configurations of vortices, to evaluate several effects. Firstly, the stability of the vortex compound was evaluated. Most often, it remains compact, but when unstable, it can break as vertically coupled vortex dipoles (called hetons). Secondly, we studied the interaction between a vertically tilted cyclone and lenses. Then, the lenses first undergo anticlockwise rotation determined by the surface cyclone. The lenses can induce alignment or coupling with cyclonic vorticity above them. Only very weak lenses are destroyed by the shear stress exerted by the surface cyclone. Thirdly, under the influence of lens dipoles, the surface cyclone can be torn apart. In particular, the shedding of rapidly moving vortex pairs at the surface reflects the presence of lens dipoles below. More slowly moving small eddies can also be torn away from the main surface cyclone. In this case, they do not appear to be coupled with middle layer vortices. They are the result of large shear-induced deformation. Common and differing features of the vortex interaction, modeled in the framework of the theory of point and finite-core vortices, are noted.

The theory of point vortices is used to explain the interaction of a surface vortex with subsurface vortices in the framework of a three-layer quasigeostrophic model. Theory and numerical experiments are used to calculate the interaction between one surface and one subsurface vortex. Then, the configuration with one surface vortex and two subsurface vortices of equal and opposite vorticities (a subsurface vortex dipole) is considered. Numerical experiments show that the self-propelling dipole can either be captured by the surface vortex, move in its vicinity, or finally be completely ejected on an unbounded trajectory. Asymmetric dipoles make loop-like motions and remain in the vicinity of the surface vortex. This model can help interpret the motions of Lagrangian floats at various depths in the ocean.

The effect of transverse pitch between a pair of delta-winglet vortex generators arranged in a common flow down configuration on the symmetrical flow structure and heat-transfer performance was numerically investigated. The results showed that symmetrical longitudinal vortices form a common flow down region between the vortices. The fluid is induced to flow from the top towards the bottom of the channel in the common flow region, which is advantageous to the heat transfer of the bottom fin. The vortex interaction increases and the vortex intensity decreases along with the decrease in transverse pitch of vortex generators. Vortex interaction has a slight influence on pressure penalty. The Nusselt number decreases with increasing vortex interaction. The vortices gradually attenuate and depart from each other during the process of flowing downward. A reasonable transverse pitch of delta-winglet vortex generators in a common-flow-down configuration is recommended for high thermal performance.

The generation of longitudinal vortices is an effective method for promoting thermal performance with a relative low-pressure penalty in heat exchangers. The winglet pair can generate symmetrical longitudinal vortices on the cross-section of the channel. The heat transfer and pressure-loss characteristics of a pair of winglet vortex generators with different transverse pitches are numerically studied in this paper. The winglet pair arranged in a common flow up configuration generates a pair of symmetrical longitudinal main vortices with counter-rotating directions. The symmetrical flow structure induces fluid to flow from the bottom towards the top of the channel in the common flow region between the longitudinal vortices. The flow symmetry of the longitudinal vortices and the heat transfer performance are strongly affected by the transverse pitch of the winglet pair owing to the interaction between the longitudinal vortices. The optimal transverse pitch of the studied winglet pair with the best thermal performance is reported. The increments in the vortex intensity and the Nusselt number for the optimal pitch are increased by up to 21.4% and 29.2%, respectively.

A discrete vortex model coupled with a vortex dissipation and vortex core criteria is used to study the unsteady flow past two airfoils in configuration. The unsteady wakes of the airfoils are modeled by discrete vortices and time-stepping is used to predict the individual wake shapes. The coupled flow is solved using a combined zero-normal flow boundary condition and Kelvin condition which result in (2N + 2)X(2N + 2) equations. Results are presented showing the effect of airfoil-airfoil and airfoil-wake interaction on the aerodynamic characteristics of the configuration. The effect of relative velocity, rate of pitching and phase-lag are studied on airfoil performance and wake shape is predicted.

This paper aims to investigate the aerodynamics including the global performance and flow characteristics of a longshrouded contra-rotating rotor by developing a full 3D RANS computation. Through validations by current experiments on the same shrouded contra-rotating rotor, the computation using sliding mesh method and the computational zone with an extended nozzle downstream flow field effectively works; the time-averaged solution of the unsteady computation reveals that more uniform flow presents after the downstream rotor, which implies that the rear rotor rotating at opposite direction greatly compensates and reduces the wake; the unsteady computations further explore the flow field throughout the whole system, along the span and around blade tips. Complex flow patterns including the vortices and their interactions are indicated around the blade roots and tips. For further identifying rotor configurations, the rotor- rotor distance and switching two rotor speeds were studied. The computation reveals that setting the second rotor backwards decreases the wake scale but increases its intensity in the downstream nozzle zone. However, for the effect of switching speeds, computations cannot precisely solve the flow when the rear rotor under the windmill because of the upstream rotor rotating much faster than the other one. All the phenomena from computations well implement the experimental observations. [ABSTRACT FROM AUTHOR]

The interaction of a short cylindrical vortex elongated along the transverse coordinate with a shear flow near a solid surface is considered. A cylindrical vortex with its ends lowered to the bottom of the channel is shown to turn into a vortex ring. The obtained qualitative model is verified by experiment. [ABSTRACT FROM AUTHOR]

In order to accurately and reliably analyze in details the cavitation mechanism and their impact on flow structures, a three-dimensional unsteady .cavitating .turbulent .flow .around .the .three-dimension .Clark-y .hydrofoil .is .investigated .be .using .a Partially-Average Navier Stokes (PANS) model based on Shear Stress Transport (SST). To track the interface of the liquid and the vapor, a Volume of Fluid (VOF) model is employed based on homogeneous mixture approach. To capture the interaction between the cavitation and the flow structure, a bridging method (PANS) between RANS and DNS have been chosen. This technique is able to resolve the unsteady turbulent structures by employing a more consistent methodology. The present numerical .results .are .validated .with .experimental .data. .The .interaction .between .the .cavitation .and .the .fluid .vortex .is .analyzed .and discussed. The numerical results show the capability of the presented model to predict the re-entrant jet and cavitation cloud shedding accurately. [ABSTRACT FROM AUTHOR]