Small Cylinder Research Articles

Metagratings for underwater acoustic wavefront manipulation

Metagratings are flat periodic assemblies of small scatterers, engineered to achieve effects such as steering, beamforming, or absorption. They have recently received attention in both electromagnetism and acoustic fields. In this work, we report the design, modeling, and experimental characterization of metagratings to steer underwater acoustic wavefronts towards anomalous directions (i.e. not classically allowed by Snell-Decartes relationships) with high efficiency (close to 100%). They are build from simple assemblies of small brass cylinders, hold by 3D-printed plastic supports, and can redirect ultrasonic wavefronts either in reflection mode (when placed in front of a reflective surface like e.g. the water / air interface) or in transmission mode. Furthermore, we demonstrate how metagratings build from an asymmetrical pattern of multiple basic elements can achieve near perfect asymmetrical transmission: a wavefront incident from side of the structure is fully transmitted, while a similar wavefront incoming from the other side is fully reflected, achieving an acoustic one-way mirror effect. This work combine theoretical analysis, finite element modeling, and experimentation in water tanks to explore and demonstrate the potential of such metagratings for various applications in underwater acoustics, like communication, noise mitigation, and stealth.

Large eddy simulation of turbulent wake from dual-step cylinders

Numerical computations of the three-dimensional flow past dual-step cylinders using large eddy simulations are performed. The Reynolds number based on the diameter of the large cylinder, ReD, is fixed at 2000. The diameter ratio between the two cylinders is kept constant in all computations, i.e., D/d=2, where d is the diameter of the small cylinder. Investigations are carried out at different aspect ratios (ARs), defined as the ratio between the length of the large cylinder and its diameter L/D=0.2,0.5,1.0,1.5. Vortex dislocation phenomenon is observed in all the cases near the step discontinuity. The higher AR cases, L/D=1.0,1.5, exhibit similar trends with regard to wake dynamics, while they are quite different in the lower AR cases, L/D=0.2,0.5. Kelvin–Helmholtz instability is present in the wake of the dual-step cylinder with higher AR. Stable in-phase shedding and downwash characterize the wake of higher AR configurations, while oblique shedding (and flipping) is the key feature in the lower AR counterparts. Unique features are observed in the L/D=1.0 configuration that marks the transition between shedding modes.

Tunable Elliptical Cylinders for Rotational Mechanical Studies of Single DNA Molecules.

The angular optical trap (AOT) is a powerful technique for measuring the DNA topology and rotational mechanics of fundamental biological processes. Realizing the full potential of the AOT requires rapid torsional control of these processes. However, existing AOT quartz cylinders are limited in their ability to meet the high rotation rate requirement while minimizing laser-induced photodamage. In this work, we present a novel trapping particle design to meet this challenge by creating small metamaterial elliptical cylinders with tunable trapping force and torque properties. The optical torque of these cylinders arises from their shape anisotropy, with their optical properties tuned via multilayered SiO 2 and Si 3 N 4 deposition. We demonstrate that these cylinders can be rotated at about 3 times the rate of quartz cylinders without slippage while enhancing the torque measurement resolution during DNA torsional elasticity studies. This approach opens new opportunities for previously inaccessible rotational studies of DNA processing.

Kármán Street-Boundary Layer Interactions In Turbulent Flow

Understanding the intricate interplay between turbulent boundary layers and wake structures caused by obstacles in the flow is key to assessing the local shear stress fields as well as the drag. These types of flows can be relevant to natural phenomena including sediment and nutrient transport. While existing literature predominantly explores the flow downstream of cylinders mounted perpendicular to bounding surfaces or downstream of cylinders positioned outside the boundary layer region, this work experimentally studies the turbulent boundary layer passing over a cylindrical obstacle positioned near and parallel to the surface of an underlying solid wall. Planar particle image velocimetry (PIV) was performed in an open recirculating water channel for three test cases at a friction Reynolds number Reτ = 1320. Key parameters investigated include the cylinder diameter relative to the boundary layer thickness (D/δ = 0.09 and 0.01) and the gap between the cylinder and the wall (G/δ = 0.09), where the range of D/δ used is smaller than most examples found in the literature. Instantaneous and averaged velocity and vorticity fields are examined based on the PIV measurements. The results in Fig. 1 show how von Kármán vortex streets and turbulent boundary layer structures interact to form unique flow features. The larger cylinder generates a clear separation downstream of its axis as well as a wake that remains coherent over a distance δ downstream. The smaller cylinder with D/δ = 0.01 generates a much narrower and weaker wake, but still shows a clear influence on time-averaged velocity profile. Future experiments will evaluate flow conditions further downstream as well as additional values of G/δ for the same D/δ values.

Enhancing hydrodynamic forces through miniaturized control of square cylinders using the lattice Boltzmann method

This study investigates the influence of small control cylinders on the fluid dynamics around a square cylinder using the Lattice Boltzmann Method (LBM). Varying the gaps (L) between the main and control cylinders from 0 to 6, four distinct flow regimes are identified: the solo body regime (SBR), shear layer reattachment (SLR), suppressed fully developed flow (SFDF), and intermittent shedding (IS). The presence of control cylinders results in significant reductions in flow-induced forces, with drag coefficient (CD) and root mean square values of drag and lift coefficients (CDrms and CLrms) decreasing by approximately 31%, 90%, and 81%, respectively. The SFDF flow regime exhibits the lowest fluid forces compared to other regimes. The effects of tiny control cylinders on the fluid flow characteristics of a square cylinder are examined using the Lattice Boltzmann Method (LBM) in this research work. The gaps (L) between the main and control cylinders are varied in the range from 0 to 6. The size of each control cylinder is equal to one-fifth of the primary cylinder. According to the findings, there are four distinct flow regimes as the gap spacing varies: solo body regime (SBR), shear layer reattachment (SLR), suppressed fully developed flow (SFDF), and intermittent shedding (IS) for gap spacing ranges 0 ≤ L ≤ 0.2, 0.3 ≤ L ≤ 0.9, 1 ≤ L ≤ 3, and 3.2 ≤ L ≤ 6, respectively. Additionally, it has been noted that the amplitude of variable lift force is reduced when the gap separation between the main and control cylinders is increased. When compared to solo cylinder values, it is found that the presence of small control cylinders in the flow field results in a considerable reduction of flow-induced forces. The SFDF flow regime was determined to have the lowest fluid forces compared to the other flow regimes studied. Our findings highlight the efficacy of small control cylinders in mitigating flow-induced forces and controlling flow characteristics. The LBM proves to be a valuable computational technique for such fluid flow problems.

Cooking-related burn injuries at Muhimbili National hospital and knowledge about safe use of liquefied petroleum gas in Dar Es Salaam, Tanzania: A cross-sectional study

BackgroundCooking-related burn injuries are a public health problem, and may be even more likely to occur in countries that are experiencing a transition to cleaner cooking fuels like liquefied petroleum gas (LPG). The risk of burns from cooking with these newer fuels, and safety measures or training to prevent injuries, is not well documented. This study examines the burden of burn injuries and burn prevention education provided to consumer by LPG stove and cylinder vendors. MethodsA cross-sectional study was conducted among 100 burn patients admitted to Muhumbili National Hospital from February 2022 to January 2023 to assess cooking-related burns. ResultsWe found that among 377 patients with all burn injuries, 100 (26.5%) were cooking-related, with charcoal (51%) and LPG (35%) stoves being the most reported. Females (61%) were more affected than males (39%), and lower education levels were more likely to be associated with burn injuries. Of all burn patients admitted, 57 (15.1%) died. Among those who experienced a cooking-related burn, 7 (7%) died. Children were more affected (59%) by any cooking-related burn injuries, but adults were more likely to experience LPG-related burns (56%). Small cylinders with a burner placed directly over the cylinder as one unit, without a connecting hose, caused less injury than stoves using a larger cylinder with a rubber connecting hose. ConclusionSafety measures for LPG stoves and fuels, including policies to increase awareness and prevent burn injuries, must be prioritized in countries like Tanzania that are transitioning from solid fuels to LPG fuels for cooking.

Wake-induced torsional oscillation of two tethered cylinders for energy harvesting

When two cylinders submerged in a uniform flow are arranged in tandem, the downstream cylinder can oscillate in response to the wake from the upstream cylinder. In this investigation, the downstream cylinder is allowed to oscillate freely around the center of a fixed upstream cylinder, mimicking a pendulum-like motion. Our findings suggest that the wake stiffness concept, initially verified for relatively large cylinder spacing (ℓ≥4) and linear transverse cylinder motion, is also relevant for characterizing the wake-induced vibration (WIV) response observed for two tandem tethered cylinders situated in close proximity (2≤ℓ≤4) for Reynolds numbers in the range 1.0×104≲Re≲1.2×105, with tests conducted up to Re≈1.4×105. For small cylinder spacing (ℓ≤2.5), the downstream cylinder attains a maximum oscillation angle amplitude and exhibits consistent vibration, providing reliable potential for energy harvesting. We also explore hysteresis in the WIV response, which is observed to depend on the history of Reynolds number variation. Our findings reveal hysteresis at both the onset and termination of oscillation.

Arbitrary-order sensitivities of the incompressible base flow and its eigenproblem

First-order sensitivities and adjoint analysis are used widely to control the linear stability of unstable flows. Second-order sensitivities have recently helped to increase accuracy. In this paper, a method is presented to calculate arbitrary high-order sensitivities based on Taylor expansions of the incompressible base flow and its eigenproblem around a scalar parameter. For the incompressible Navier–Stokes equations, general expressions for the sensitivities are derived, into which parameter-specific information can be inserted. The computational costs are low since, for all orders, a linear equation system has to be solved, of which the left-hand-side matrix stays constant and thus its preconditioning can be exploited. Two flow scenarios are examined. First, the cylinder flow equations are expanded around the inverse of the Reynolds number, enabling the prediction of the two-dimensional cylinder base flow and its leading eigenvalue as a function of the Reynolds number. This approach computes accurately the base flow and eigenvalue even in the unstable regime, providing, when executed subsequently, a mean to calculate unstable base flows. This case gives a clear introduction into the method and allows us to discuss its constraints regarding convergence behaviour. Second, a small control cylinder is introduced into the domain of the cylinder flow for stabilization. Higher-order sensitivity maps are calculated by modelling the small cylinder with a steady forcing. These maps help to identify stabilizing areas of the flow field for Reynolds numbers within the laminar vortex shedding regime, with the required number of orders increasing as the Reynolds number rises. The results obtained through the proposed method align well with numerically calculated eigenvalues that incorporate the cylinder directly into the grid.

A strategy of mixed tube bundle to improve anti-deposition performance and heat transfer

Ash deposition is a key issue that limits the energy utilization and safety operation of high-energy-consuming equipment in industrial applications, and the clarification of the heat and mass transfer process under ash deposition is vital. To improve the anti-deposition performance of tube bundles and mitigate heat transfer deterioration, a mixed strategy with attached small cylinders arranged behind the tube has been proposed, which overcomes the difficulties faced by irregular and extended surface tube bundles in manufacturing, cleaning, maintenance, and energy consumption. A CFD model incorporating multiple deposition mechanisms is established to investigate the dynamic deposition behavior, heat transfer characteristics, and comprehensive performance of the tube bundles. In particular, the dynamic growth process of the deposition layer on heat transfer surface in this work is achieved through a dynamic mesh smoothing method based on inverse distance weighting interpolation. Parametric studies are conducted on different arrangements and angles (α = 15° - 65°) of the attached cylinders to obtain the optimal comprehensive performance design. The results show that the attached cylinders suppress the formation and development of the wake vortex caused by the primary tube bundle, significantly enhancing the anti-deposition performance of the tube bundles. The length of vortex evolution increases and the separation point of the boundary layer extends with the angles, leading to a transition of the vortex shedding regime between tube bundles. Compared to the benchmark case, Case 1 exhibits a higher anti-deposition and heat transfer performance, where the deposition mass decreases by 43.98% and the PEC reaches the maximum value of 1.11 at α = 45°, which delivers the best comprehensive performance. The results can provide more realistic predictions for the practical design, operation, and maintenance of thermal equipment.

Fano cavity test and investigation of the response of the Roos chamber irradiated by proton beams in perpendicular magnetic fields up to 1 T

Objective. The aim of this work is to investigate the response of the Roos chamber (type 34001) irradiated by clinical proton beams in magnetic fields. Approach. At first, a Fano test was implemented in Monte Carlo software package GATE version 9.2 (based on Geant4 version 11.0.2) using a cylindrical slab geometry in a magnetic field up to 1 T. In accordance to an experimental setup (Fuchs et al ), the magnetic field correction factors kQB⃗ of the Roos chamber were determined at different energies up to 252 MeV and magnetic field strengths up to 1 T, by separately simulating the ratios of chamber signals MQ/MQB⃗, without and with magnetic field, and the dose-conversion factors Dw,QB⃗/Dw,Q in a small cylinder of water, with and without magnetic field. Additionally, detailed simulations were carried out to understand the observed magnetic field dependence. Main results. The Fano test was passed with deviations smaller than 0.25% between 0 and 1 T. The ratios of the chamber signals show both energy and magnetic field dependence. The maximum deviation of the dose-conversion factors from unity of 0.22% was observed at the lowest investigated proton energy of 97.4 MeV and B⃗ = 1 T. The resulting kQB⃗ factors increase initially with the applied magnetic field and decrease again after reaching a maximum at around 0.5 T; except for the lowest 97.4 MeV beam that show no observable magnetic field dependence. The deviation from unity of the factors is also larger for higher proton energies, where the maximum lies at 1.0035(5), 1.0054(7) and 1.0069(7) for initial energies of E0 = 152, 223.4 and 252 MeV, respectively. Significance. Detailed Monte Carlo studies showed that the observed effect can be mainly attributed to the differences in the transport of electrons produced both outside and inside of the air cavity in the presence of a magnetic field.

A data–driven sensibility tool for flow control based on resolvent analysis

This study presents a novel application of data-driven resolvent analysis algorithm for flow control. The objective is to identify key coherent structures connected to regions of the flow that are highly sensitive to structural changes. Modifying such regions, i.e., including momentum source terms, flow stabilizers, or changing the shape of the body under study, we can control the appearance of flow instabilities. The method is tested in two different applications: the laminar flow behind a two-dimensional circular cylinder and a turbulent channel flow including heat transfer to the endwall. In the first test case, the flow unsteadiness is controlled by including two stabilizers (formed by two small cylinders) in the areas suggested by resolvent analysis. This is a benchmark problem in fluid dynamics that serves to validate the idea of using this tool for flow control. In the second test case, data-driven resolvent analysis is applied as a mean to control, enhance or reduce, convective heat transfer. Modifications in the geometry, in the form of cavities and ribs included in the areas pointed by resolvent analysis, show the possibility of enhancing heat transfer while reducing drag. The findings highlight the importance of resolvent analysis in understanding flow dynamics and designing effective flow control strategies.

Tilt Angle Effect on Natural Convection Heat Transfer from an Inclined Array of Square Cylinders

Natural convection heat transfer from an inclined array of square cross-section cylinders is experimentally studied. Three cylinders of side length D = 0.02 m and 1 m length are used to form the inclined array. Three-cylinder axis inclination angles to the horizontal of 30°, 45°, and 60° are considered. The cylinders are heated using an internal heating element of constant heat flux. Surface temperatures are measured along the three surfaces of each cylinder; upper, lower, and the front side at nine points spaced evenly by 10 cm. The local circumference average temperature is obtained at each point. Four center-to-center distances to side length S/D = 1.25, 1.75, 2.25, and 2.75 are used. Local Nusselt numbers and the modified Rayleigh numbers are obtained for each cylinder at each circumference averaged temperature point. Results show that the lower cylinder heat transfer is least affected by the array compared to that of its single one followed by the middle and the upper cylinder for all S/D and the inclination angles used. The Nusselt number is degraded from that of the single cylinder at a small S/D and that degradation decreases as the S/D increases for all angles. It is observed that the Nusselt number enhances at the small cylinder axis tilt angle of 30°, followed by 45°, and 60°, especially at high modified Rayleigh numbers. New novel general empirical correlations for Nusselt numbers are obtained for each S/D using the cylinder axis tilt angle, the modified Rayleigh numbers, and the cylinder number in the array as parameters. A new general correlation is obtained for the array using the modified Rayleigh number, S/D, the cylinder axis tilt angle, and the cylinder sequential order number as parameters. These new correlations will help any engineering applications using such a configuration of the array.

Numerical Study on Wave Dissipation and Mooring Force of a Horizontal Multi-Cylinder Floating Breakwater

A three-dimensional numerical model was established based on ANSYS-AQWA (R19.0) software for the purpose of analyzing the hydrodynamic characteristics of a floating breakwater. This study examines three distinct floating breakwaters with different cross-sectional designs in order to evaluate their respective wave dissipation capabilities. It is suggested that the horizontal multi-cylinder floating breakwater exhibits a superior ability to dissipate waves when compared to both the single-cylinder and square pontoon configurations and can be deemed the most advantageous shielding strategy for potential engineering applications. Subsequently, this study examines the effects of influential parameters, including a large cylinder diameter, a small cylinder diameter, the angular position of the small cylinder, and the height and period of the incident wave, on the wave transmission coefficient. An empirical formula for the wave transmission coefficient was derived based on the numerical results. Additionally, the effects of influential parameters, including wind speed, current velocity, incident wave height and period, and water depth, on the maximum total mooring force were investigated. Furthermore, an empirical formula for the maximum total mooring force is proposed for practical implementation in engineering.

Enhancing Solar Thermal Efficiency: PCM Integration for Compact Energy Storage Systems

The optimal utilization of solar energy presents a challenge in meeting round-the-clock hot water demands while accommodating limited space in modern architectural designs. Solar collectors, operating solely during daylight hours and weather-dependent, necessitate efficient energy storage to meet evening and morning peak hot water consumption in households. Current architectural trends, marked by smaller boiler rooms, further compound the challenge of integrating conventional solar tanks, emphasizing the critical need for compact energy storage solutions. Addressing this challenge, this paper proposes a ground-breaking solution: a solar tank infused with phase change material (PCM). This innovative tank design not only boasts smaller dimensions but also significantly higher heat capacity compared to conventional counterparts. Crucially, the PCM solar tank enables solar collectors to operate at lower temperatures, potentially elevating the overall efficiency of the solar collector system. The proposed storage system comprises two synergistic heat-absorbing units: a solar water heater and a PCM-based heat storage unit. While the solar water heater fulfills the daytime hot water supply, the PCM storage unit accumulates and retains heat throughout the day, ensuring continuous hot water availability during night hours and overcast periods. Leveraging small cylinders filled with paraffin, serving as the PCM, integrated with solar collectors maximizes solar energy absorption and storage. This paper meticulously compares the performance of the PCM-based thermal energy storage system with conventional sensible heat storage systems, presenting insightful conclusions derived from the comparative analysis. The findings underscore the remarkable efficiency and efficacy of the PCM-based solution in meeting the challenges posed by solar energy intermittency and limited space constraints, offering a promising avenue for sustainable and efficient solar energy utilization in residential settings.

Heat transfer and fluid flow in nano-encapsulated PCM-filled undulated cavity

This article discusses the heat transfer characteristics of the mixed convection of NEPCM-fluid (Polyurethane/ Nonadecane dispersed in water) contained within a wavy-sided walls cavity. Mixed convection is caused by an adiabatic rotating cylinder located in the cavity center, while natural convection results from deferential heating of side walls. The upper and lower walls of the cavity are insulated. The Galerkin finite element method (GFEM) implemented in COMSOL CFD package is employed to solve the governing equations. The influence of the nanoparticles volume fraction (Ø = 0.02, and 0.05), cylinder radius (R = 0.05, 0.15, and 0.25), cylinder rotating speed (Ω = 100, −500, 500, and 1000), the dimensionless fusion temperature (θfu = 0.1, 0.25, and 0.5), wavy side walls undulation peaks number (N = 1 to 4) on the flow pattern and temperature field are presented. The results revealed that the heat transfer enhances by increasing the angular speed of the cylinder and its radius, also an enhancement in heat transfer is obtained by upgrading the volume fraction of NEPCM, however, it was noticed that for small cylinders, the counterclockwise rotation of the cylinder reduced the heat transfer rate as the rotation opposed the direction of natural heat convection. In addition, the waviness pattern has a specific impact on each case, for example, N = 4 denotes the best result for only the cases Ω = -500 or 500 when R = 0.25 and Ø = 0.05, while the heat transfer is negatively affected by increasing N for the other cases. On another hand, the impact of θfu on the heat transfer rate was found to be insignificant. Globally, at the biggest cylinder radius, higher Ø and highest angular speed an enhancement by more than 900 % can be achieved.

The investigation of V-shaped arrays with non-uniform diameter cylinders for high performance hydrokinetic energy conversion

Harnessing hydrokinetic energy through vortex-induced vibration (VIV) is of great significance. The energy capture efficiency of VIV cylindrical arrays still has great potentials for making further progress. This paper investigates the energy conversion performance of cylinder cluster arrays with non-uniform diameter positioned at the upstream, midstream, and downstream locations, utilizing the downstream VIV enhancement effect. The cylinder arrays consist of five cylinders with non-uniform diameters of 2, 3, and 4 cm, resulting in a total of eight different V-shaped configuration scenarios. Through numerical simulation, it is found that the optimal flow velocity for maximizing the cylinder vibration amplitude is 0.8 m/s. In the condition of 0.8 m/s flow velocity, this study investigates the impact of cylinder diameter and the array arrangement on lift force, amplitude response, vortex shedding frequency, converted power, and efficiency. If the diameter of a cylinder is smaller than that of its upstream cylinder, cylinder experiences an enhanced amplitude, and the magnitude of this enhancement increases with the difference in diameters between the two cylinders. The blocking effect in the cylinder array occurs at a distance of two times the diameter. It has been observed that the small diameter cylinder demonstrates exceptional performance, achieving the highest converted power of 6.58 W (88% higher than the single cylinder) and the highest conversion efficiency of 68 % (75% higher than the single cylinder) in the convergent V-shaped array. The divergent V-shaped array achieves a maximum total converted power of 17.12 W (14% higher than the average conversion efficiency of single 2 cm, 3 cm, 4 cm cylinders), while the convergent V-shaped array achieves a maximum total conversion efficiency of 44% (24% higher than the average conversion efficiency of single 2 cm, 3 cm, 4 cm cylinders). This study presents an innovative perspective on the VIV enhancement effect in energy conversion, specifically focusing on multi-cylinder arrays with non-uniform diameters.

Elasto-compliance of harmonically stimulated soft micro-gaps during electro-magneto-kinetic flows.

In this article, we develop and solve an analytical model to understand the elasto-hydrodynamic force response of a deformable, soft substrate, under dynamic loading; wherein the microfluidic gap between the substrate and load is subjected to electro-magneto-hydrodynamic interactions. As a simple physical system, we model the coupled fluid-structure-interaction characteristics when a rigid, small cylinder is permitted to impinge harmonically on an infinitely large elastic, soft substrate, and an oscillatory, squeeze flow establishes in the micro-gap formed between the two. We discuss the different observations and mechanics in terms of the governing Dukhin, Hartmann, and electroviscous numbers. The influence of electromagnetic stimuli on the flow, and its implications vis-à-vis the substrate compliance is the focus of the article. We reveal that for pure magnetohydrodynamics of the gap electrolyte, the transverse magnetic field and the induced streaming potential resist outward squeeze flow, thereby generating substantial amplifications in the force response. On the contrary, the effect of electro-magneto-hydrodynamics on the force response was strongly affected by the orientation and intensity of the transverse electric field. Notably, such variations depended significantly on the electrokinetic parameters, oscillation frequency, and substrate stiffness, whose effects were intertwined with the transverse and streaming potential electric fields. Further, possibilities of squeeze flow reversal due to opposing electromagnetic forces is observed, which may again modulate the compliance of the substrate in different mannerisms.

Controlled formation of multi-scale porosity in ionosilica templated by ionic liquid.

Mesoporous systems are ubiquitous in membrane science and applications due to their high internal surface area and tunable pore size. A new synthesis pathway of hydrolytic ionosilica films with mesopores formed by ionic liquid (IL) templating is proposed and compared with the traditional non-hydrolytic strategy. For both pathways, the multi-scale formation of pores has been studied as a function of IL content, combining the results of thermogravimetric analysis (TGA), nitrogen sorption, and small-angle X-ray scattering (SAXS). The combination of TGA and nitrogen sorption provides access to ionosilica and pore volume fractions, with contributions of meso- and macropores. We then elaborate an original and quantitative geometrical model to analyze the SAXS data based on small spheres (Rs = 1-2 nm) and cylinders (Lcyl = 10-20 nm) with radial polydispersity provided by the nitrogen sorption isotherms. As a result, we found that for a given incorporation of a templating IL, both synthesis pathways produce very similar pore geometries, but the better incorporation efficacy of the new hydrolytic films provides higher mesoporosity. Our combined study provides a coherent view of mesopore geometry, and thereby an optimization pathway of porous ionic membranes in terms of accessible mesoporosity contributing to the specific surface. Possible applications include electrolyte membranes with improved ionic properties, e.g., in fuel cells and batteries, as well as molecular storage.

The flow around a stepped cylinder with turbulent wake and stable shear layer

The turbulent external flow around a three-dimensional stepped cylinder is studied by means of direct numerical simulations with the adaptive mesh refinement technique. We give a broad perspective of the flow regimes from laminar to turbulent wake at $Re_D=5000$ , which is the highest ever considered for this flow case. In particular, we focus on the intermediate Reynolds number $Re_D=1000$ that reveals a turbulent wake coupled with a stable cylinder shear layer (subcritical regime). This flow shows a junction dynamics similar to the laminar $Re_D=150$ , where no hairpin vortex appears around the edges, and just two horseshoe vortices are visible. A new stable vortex in the form of a ring, which coils around the rear area, is also identified. In the turbulent wake, the presence of three wake cells is pointed out: the large and small cylinder cells together with the modulation region. However, the modulation dynamics varies between the subcritical and turbulent regimes. A time-averaged, three-dimensional set of statistics is computed, and spatially coherent structures are extracted via proper orthogonal decomposition (POD). The POD identifies the (long-debated) connection between the N-cell and the downwash behind the junction. Furthermore, as the Reynolds number increases, the downwash phenomenon becomes less prominent. Eventually, a reduced-order reconstruction with the most energetically relevant modes is defined to explain the wake vortex interactions. This also serves as a valuable starting point for simulating the stepped cylinder wake behaviour within complex frameworks, e.g. fluid–structure interaction.

Longitudinal wave propagation in an elastic cylinder embedded in a viscoelastic fluid

Abstract A novel analytical investigation of longitudinal wave propagation in an elastic cylinder embedded in a viscoelastic fluid is proposed. The Maxwell model is used to describe the viscoelastic fluid behavior. With appropriate boundary conditions, a complex dispersion equation of longitudinal wave has been established. The aim of this paper is to study the effect of the fluid rheological properties on the longitudinal wave characteristics (attenuation and velocity). It is shown that the attenuation is the sum of a viscous and non viscous component. The viscosity induced attenuation is predominant at low frequencies. On the other hand, the effect of the liquid amount and elastic cylinder radius on the attenuation and velocity are studied. A critical normalized liquid thickness is highlighted. Beyond this critical value, the influence of the outer boundary condition can be neglected. At last, among other interesting phenomena, it is highlighted that if the Deborah number increases, the attenuation decreases. This variation characterize a stiffening of the viscoelastic medium. In addition, the obtained results show that the viscosity measurement should be performed at low frequencies using small elastic cylinder radius. Accordingly, these investigations are novel and can be applied in geophysics, food industry, medicine, non-destructive testing of materials, design and development of fluid sensors.