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A numerical solution of the Prandtl boundary layer equation for a steady plane incompressible flow at a given pressure gradient is derived. The gradient is determined by the well-known Rankine solution describing flow past a half-body. The contour of that body is obtained by means of superimposing a uniform flow on the point source flow. It is established that the solution of the problem for the boundary layer equation does not involve a zero surface friction point, that is, the flow under consideration is separationless. [ABSTRACT FROM AUTHOR]

The design of organic Rankine cycle (ORC) turbines often requires dealing with transonic flows due to the cycle efficiency requirements and the matching of the temperature profiles with heat sources and sinks, as well as the nature of organic fluids, often featuring high molecular weight. Consequently, the use of convergent-divergent turbine stators has been widely established as a solution in the published literature for use in both axial- and radial-inflow machines. With respect to the latter layout in particular, the available design guidelines are still limited. The present work shows the results of an investigation into a series of ORC radial-inflow convergent-divergent nozzles that differ with respect to the vane count and the designed metal angle of the outlet. These stators were designed by fitting the divergent portion of a sharp-edged minimum-length nozzle, designed by means of the method of characteristics (MoC) adapted to dense gases, into a radial-inflow turbine stator. The geometries were analysed by means of steady-state RANS CFD calculations, and the results were used to assess the influence of the design parameters on the nozzle losses and downstream flow field uniformity, showing that conflicting trends exist between optimum stator efficiency and optimum downstream flow field uniformity. [ABSTRACT FROM AUTHOR]

The dynamic behavior of an elastic capsule with an initially oblate spheroidal shape during crosstype optical separation was numerically investigated. The penalty immersed boundary method was adopted for the fluid-membrane interaction, and the optical force calculation was conducted by using the ray optics method including the ray-surface intersection algorithm. The oblate elastic capsule of b/a=0.5 with different surface Young's moduli and different initial inclination angles was considered. The oblate capsule with higher surface Young's moduli was less deformed, and was more migrated for each initial inclination angle. Unlike the oblate rigid particle, the initially inclined capsules with moderate inclination angles were similarly migrated since the oblate elastic capsule was deformed during rotation near the laser beam axis. The oblate capsules can be separated according to the surface Young's modulus, except for nearly non-inclined capsules. As the fluid velocity decreased, the migration distance increased. The maximum deformation parameter was insensitive to the fluid velocity. Furthermore, a new dimensionless number (Sec) was introduced to predict the migration distance of the oblate elastic capsule. [ABSTRACT FROM AUTHOR]

This second paper in a series of two reports on the performance of a new instrument for studying chemical reaction dynamics and kinetics at low temperatures. Our approach employs chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy to probe photolysis and bimolecular reaction products that are thermalized in pulsed uniform flows. Here we detail the development and testing of a new Ka-band CP-FTMW spectrometer in combination with the pulsed flow system described in Paper I [J. M. Oldham, C. Abeysekera, B. Joalland, L. N. Zack, K. Prozument, I. R. Sims, G. B. Park, R. W. Field, and A. G. Suits, J. Chem. Phys. 141, 154202 (2014)]. This combination delivers broadband spectra with MHz resolution and allows monitoring, on the /xs timescale, of the appearance of transient reaction products. Two benchmark reactive systems are used to illustrate and characterize the performance of this new apparatus: the photodissociation of SO2 at 193 nm, for which the vibrational populations of the SO product are monitored, and the reaction between CN and C2H2, for which the HCCCN product is detected in its vibrational ground state. The results show that the combination of these two well-matched techniques, which we refer to as chirped-pulse in uniform flow, also provides insight into the vibrational and rotational relaxation kinetics of the nascent reaction products. Future directions are discussed, with an emphasis on exploring the low temperature chemistry of complex polyatomic systems. [ABSTRACT FROM AUTHOR]

In the present study, a flow rig with optical access intended for spray investigations in exhaust system-relevant conditions was analysed in terms of flow and temperature in the spray area using numerical simulations. The operation of the rig was examined for a wide range of exhaust mass flow rates, temperatures and various forms of UWS (urea-water solution) spray plumes. The locations of the injector and thermocouple were verified. Both conventional and flash-boiling injections were considered to assess the effect of the interaction of sprays with a gas flow. The results showed a highly uniform flow in the visualisation area, with only minor fluctuations near the walls. A similar observation was carried out for the temperature distribution. It was found that the extreme operating conditions caused substantial deformations of the spray plumes. However, the selected injector location allowed us to properly observe the spray formation regardless of the flow conditions. The study showed that the examined test rig enabled reliable spray investigations for a wide range of operating points. [ABSTRACT FROM AUTHOR]

The novel coronavirus (SARS-CoV-2) has spread at an unprecedented rate, resulting in a global pandemic (COVID-19) that has strained healthcare systems and claimed many lives. Front-line healthcare workers are among the most at risk of contracting and spreading the virus due to close contact with infected patients and settings of high viral loads. To provide these workers with an extra layer of protection, the authors propose a low-cost, prefabricated, and portable sanitising chamber that sprays individuals with sanitising fluid to disinfect clothing and external surfaces on their person. The study discusses computer-aided design of the chamber to improve uniformity of sanitiser deposition and reduce discomfort due to excessive moisture. Advanced computational fluid dynamics is used to simulate the dispersion and deposition of spray particle, and the resulting wetting pattern on the treated person is used to optimise the chamber design. [ABSTRACT FROM AUTHOR]

The calculation of Chezy's resistance coefficient (CRC) is typically not provided a priori in a design problem, and its value is often selected subjectively from the literature in most open channels and conduits for the uniform flow. The evaluation of this coefficient is crucial to channel design and for computing its normal depth. The primary purpose of this research study is to revisit the mathematical formulation for the resistance coefficient. A general explicit relation of the resistance coefficient in turbulent flow is set with different geometric profiles of conduits and channels, mainly the horseshoeshaped tunnel using the rough model method (RMM). CRC is firmly based on the internal walls' absolute roughness of the channel, the liquid kinematic viscosity, the longitudinal slope, the discharge and the filling rate. Additionally, a simplified method is proposed to determine CRC with a restricted number of variables such as the kinematic viscosity, the absolute roughness, the slope of the conduit, and the discharge. Based on studying the variation of CRC as a function of the filling rate, another explicit expression is provided to compute this coefficient efficiently when its maximum value is reached. To demonstrate how Chezy's resistance coefficient can be calculated in a horseshoe-shaped tunnel, some examples of calculations are proposed. [ABSTRACT FROM AUTHOR]

The general mathematical behavior of the expressions used in analyzing the physical phenomena is of considerable importance in engineering practice. In current research, a nonlinear differential equation of second order to determine the cross sections in which the kinematic wave parameters are constant for a range of uniform flow depths is derived. By applying suitable boundary conditions, this equation is solved by Runge–Kutta method. In special cases, this equation is reduced to an analytical solution for the cross sections with constant hydraulic radius. Using this solution, the cross-section shape of the channel in which average flow velocity is constant for a range of uniform flow depths is derived. Reported herein are (a) cross sections with constant kinematic wave parameters and (b) cross sections with constant hydraulic radius. [ABSTRACT FROM AUTHOR]

Stretching of a protein by a fluid flow is compared to that in a force-clamp apparatus. The comparison is made within a simple topology-based dynamical model of a protein in which the effects of the flow are implemented using Langevin dynamics. We demonstrate that unfolding induced by a uniform flow shows a richer behavior than that in the force clamp. The dynamics of unfolding is found to depend strongly on the selection of the amino acid, usually one of the termini, which is anchored. These features offer potentially wider diagnostic tools to investigate structure of proteins compared to experiments based on the atomic force microscopy. [ABSTRACT FROM AUTHOR]

In this work, the fundamentals of upstream flow over cylinders and forming fabrics are investigated, and measures for characterization of fabrics are proposed. Two-dimensional flow over one cylinder, two cylinders, and one and two rows of cylinders, are analysed numerically. By studying different configurations and various Reynolds numbers, the upstream flow features are characterized. It is concluded that cylinders have a short range of upstream flow impact, shortest for rows of cylinders with small spacings. For Re ò [10, 80], the Reynolds number dependency is weak. It is shown that a downstream row positioned in tandem has negligible impact on the upstream flow, while a displaced second row influences the upstream flow if the spacing in the first row is larger than one diameter. The pressure drop required to drive the flow over the cylinders depends non-linearly on the porosity of the configuration. Flow measures of the upstream flow are proposed, which in addition to the volume flow per area are used to characterize fabric flow properties. The conclusions from the cylinder study also hold for industrial fabrics, and it can be explained how properties of the fabric influence the final paper. The wave-length of flow periodicity is studied in relation to drainage marking. This study demonstrates that simulations can greatly improve pure experimental-based fabric characterization.

In this paper, the Chang 6 ultra-low permeability reservoirs in Huaqjing area of Ordos Basin are studied. The reservoir is divided into four types of flow units by using Q-type multi-parameter clustering analysis and SPSS statistical analysis software. The characteristics of reservoir physical properties, sedimentary characteristics, capillary pressure curve and production dynamics were analyzed. The rationality of the results were verified from the static and dynamic points of view. Results show that I type flow unit has good reservoir properties and development effect is fast. The main development target is to maintain long-term stability. The distribution areas of II and III types are large, and cover the main production layer of oil field development and the remaining oil enrichment area. The reservoir properties of the IV type flow unit are worst, and the development is difficult. Efficient development of such reservoirs through the scientific division of the flow unit is important and of practical significance. [ABSTRACT FROM AUTHOR]

Lately, the drip irrigation systems built with pressure compensating (PC) drippers (emitters) inside welded in the drip laterals, find more and more application in Bulgaria, Turkey, Greece and other countries having well-developed irrigation-based agriculture, especially where the ground is not flat but rather is of hilly nature. The main advantage of these systems is the provision of uniform flow rate along the laterals and batteries (blocks) in the whole drip systems irrespectively of the alteration of the operating pressure, and, besides, this allows long laterals to be designed. The recommended operating pressure starts from 0.5 – 1.0 atm and reaches 4 – 5 atm. Reaching equal drip flow rate in these systems is realized thanks to an elastic membrane with fixed strength parameters, located at the outlet of the nozzles in a specially arranged bed (nest) for this purpose. The advertisement of the applications of those nozzles in the company catalogs is very intensive but is it true for all types of pressure compensating drippers? In laboratory conditions we carried out hydraulic tests of drip laterals with inside welded pressure compensating drippers, cylinder type, in order to find out the head losses along the drip lateral. The laterals were with a nominal outer diameter 16 mm, inner diameter 13.8 mm, thickness of the wall 1.1 mm and flow rate 2.1 l/h, at intervals of 33 cm between the drippers, with lengths 60, 80 and 100 m. The results showed considerable head losses, with great deviations from the ones obtained by analytic way through formulas. For example, in a 100 m long lateral, the losses reach 60 to 75% of the applied operating pressure at the beginning of the lateral. Some specific data from the tests – in case of inlet pressure of 18, 20 and 25 m, the head losses are respectively 12, 14 and 17 m which means that in case of flat ground and such with back slope it is almost impossible to realize a length of 100 m and more of the lateral. All drippers will not operate at the horizontal part of the curve “pressure-flow rate” but at the transitional part of this curve. It follows from this that irrespectively of the pressure compensating action of those nozzles, this type of laterals will hardly find application in real conditions in the design of an engineering project for drip irrigation respecting the admissible coefficients of the distribution uniformity of the irrigation water. The same is valid for the other tested laterals as well. Sometimes, laying conventional type of laterals is more appropriate and brings better results. All this is due to the considerable minor head losses in those nozzles because of the sizable constriction of the cross section of the laterals by the nest (bed) of the membrane. [ABSTRACT FROM AUTHOR]

Uniformity of flow distribution is an application subject in many engineering equipment such as in drug delivery and fuel processing reactors. With a uniform distribution of flow during their operation, better heat transfer, temperature control, and low pressure loss can be achieved. In this work, uniformity of flow distribution was studied in parallel micro-channels which were placed in different levels. Four shapes for distributor were studied with two working fluids, blood (as Newtonian fluid and power-law non-Newtonian fluid). Results show that there is different uniformity in each levels as in last level, the flow is less uniform. This trend found in other Reynolds numbers. However, with increasing Reynolds number, the flow is less uniform. Also, RTG distributor has better uniformity in each level than other shapes of distributor with Newtonian fluid, while, when power-law non-Newtonian fluid was used as working fluid, the better uniformity was achieved with TRG distributor. [ABSTRACT FROM AUTHOR]

Abstract Channels with parabola-shaped cross-section are widely used in water conservancy and hydropower engineering, agricultural irrigation and drainage engineering, so it is necessary to determine the accurate normal depth values for design of open channels, operation management and analysis of gradually varied flow. However, the governing equations are nonintegrable for cubic and semi-quintic parabola-shaped channels in terms of the wetted perimeters. In this study, the Simpson's numerical integral method is introduced to approximate the two nonintegrable wetted perimeters for cubic and semi-quintic parabola-shaped channels which can meet the requirements of engineering design well in the commonly using range of engineering. Subsequently, the approximate wetted perimeters are substituted into the uniform flow equation and the uniform flow equation deforms optimal model identically. The optimal model parameters are determined by the 1stOpt software based on Marquardt algorithm and two explicit calculation formulas for the normal depths of cubic and semi-quintic channels are proposed. At the same time, two direct calculation formulas for normal depths of semi-cubic and quadratic parabola-shaped channels are presented as well. Four sets of formulas for normal depths of parabola-shaped channels are presented and their maximum relative errors are 0.52%, − 0.37%, − 0.22% and 0.57%, respectively, which have wide range of application, high precision, concise form and can provide some better guidance for engineering design and operation management. Highlights • The Simpson's numerical integral method is firstly introduced to approximate the two nonintegrable wetted perimeters for cubic and semi-quintic parabola-shaped channels accurately. • Two explicit formulae for normal depths of cubic and semi-quintic parabola-shaped channels are obtained with high precision, wide range of application firstly. • Two explicit formulae for normal depths of semi-cubic and quadratic parabola-shaped channels are obtained with higher precision, wider range of application than those of former studies. [ABSTRACT FROM AUTHOR]

Rotating cylinders with different diameters placed in uniform flow were investigated experimentally. The aspect ratios, AS (ratio of the length and the diameter) of cylinders, with the same length L=0.59m were 1.85, 2.21, 2.73 and 5.78 with respective diameters of 0.319, 0.267, 0.216 and 0.102 m. The non-dimensional rotation rate, α, was the ratio of the rotating surface speed and the flow speed, which varied from 0 to 8 for the 0.319 m diameter cylinder. Hydrodynamics of the cylinders were analyzed based on two different conditions: cylinders in flow condition and rotating cylinders in flow condition. For the cylinders in flow, the influence of the aspect ratio and Reynolds number on the hydrodynamics coefficient and Strouhal number was discussed, the critical transition area was found at 1.0×105⩽Re⩽1.59×105. For the cylinders rotating in flow, initial area, increasing area and equivalent area were defined to describe the variation of mean of hydrodynamics as the increase of rotation rates. The range of these areas was decided by the rotation rate and aspect ratio of the cylinders. Different from the mean hydrodynamics, for the Strouhal number (vortex shedding) and Root mean square of lift for the rotating cylinders, vortex shedding area, weak vortex shedding area and wake fluctuation area were defined to explain them and the range of these areas was only determined by rotation rate. [ABSTRACT FROM AUTHOR]

Highlights • The interaction of drops in various arrangements is studied using the VOF method. • Regime maps on the observed interaction scenarios are presented. • Breakup times of secondary drops are compared to data available for single drops. • Flow and material properties significantly influence interaction phenomena. • A method for the modelling of dense spray regions is suggested. Abstract A Volume of Fluid (VOF) method is applied to study the interaction between two liquid drops with the same initial diameter in uniform flow. Various arrangements of the drops are studied, based on two parameters, namely the initial separation distance and the angle between the line connecting the centres of the drops and the free-stream direction. Initial separation distances of 1.5–5 drop diameters, and angles between β = 0 ∘ and 90° are considered. Simulations for a Weber number of W e = 20 , two Reynolds numbers R e = 20 and 50, and density and viscosity ratios in the range ρ * = 20 –80 and μ * = 0.5 –50 are performed. The movement of the secondary drop with respect to the primary drop, and estimates on the time required for the breakup of the secondary drop as compared to those observed for single drops are evaluated. It is found that the drops collide only in cases corresponding to the shortest initial displacements, while in others they deform and break up independently, similarly or identically to single drops. The same behaviour is reflected in the time required for breakup. Cases where the drops behave independently show breakup times close to those observed for single drops. [ABSTRACT FROM AUTHOR]

In this paper, is the hydrodynamics of three in-line square cylinders in a uniform flow, where the gap between two neighboring square cylinders is equivalent is under investigation. The fluid dynamics around those multiple bluff bodies, including time-mean drag coefficients, time-mean lift coefficients and Strouhal numbers, are considered at the Reynolds number R e ≈ 1 0 0. Through numerically solving the nonlinear hydrodynamic problem, we show that the drag force acting on the first square cylinder is always larger than that acting on the remaining two square cylinders. From the perspective of wake structures, with keeping the increase of the gap between two neighboring square cylinders, the wake structures become much more complicated, including attachment of shear layer, interaction between shear layer and vortex, interaction between vortex and vortex, etc. Moreover, the Strouhal number of three square cylinders are approximately equaled when the dimensionless gap between two neighboring square cylinders is less than 2. [ABSTRACT FROM AUTHOR]

Highlights • The principle of uniform flow may explain the morphology of microvascular networks. • A gradient descent algorithm is devised to find networks that optimize general combinations of functions and constraints. • On model capillary beds, uniform flow networks provably have the same flows as uniform conductance networks. • A theoretical zebrafish trunk network that optimizes uniform flow quantitatively matches real zebrafish microvascular data. • Networks constrained by material and transport costs undergo a phase transition if the relative burden of the two is varied. Abstract Within animals, oxygen exchange occurs within vascular transport networks containing potentially billions of microvessels that are distributed throughout the body. By comparison, large blood vessels are theorized to minimize transport costs, leading to tree-like networks that satisfy Murray's law. We know very little about the principles underlying the organization of healthy micro-vascular networks. Indeed capillary networks must also perfuse tissues with oxygen, and efficient perfusion may be incompatible with minimization of transport costs. While networks that minimize transport costs have been well-studied, other optimization principles have received much less scrutiny. In this work we derive the morphology of networks that uniformize blood flow distribution, inspired by the zebrafish trunk micro-vascular network. To find uniform flow networks, we devise a gradient descent algorithm able to optimize arbitrary differentiable objective functions on transport networks, while exactly respecting arbitrary differentiable constraint functions. We prove that in a class of networks that we call stackable, which includes a model capillary bed, the uniform flow network will have the same flow as a uniform conductance network, i.e., in which all edges have the same conductance. This result agrees with uniform flow capillary bed network found by the algorithm. We also show that the uniform flow completely explains the observed radii within the zebrafish trunk vasculature. In addition to deriving new results on optimization of uniform flow in micro-vascular networks, our algorithm provides a general method for testing hypotheses about possible optimization principles underlying real microvascular networks, including exposing tradeoffs between flow uniformity and transport cost. [ABSTRACT FROM AUTHOR]

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Abstract In this paper, we discuss a type of bicompressible surfaces and unstabilized amalgamated Heegaard splittings using curve complex. [ABSTRACT FROM AUTHOR]

Abstract Model experiments were carried out to investigate the performance of different types of 1:8.3-scale model square fish cages in a uniform flow. The model cages were designed using different netting materials, mesh types, and cage depths. Shape deformation, volume reduction, and drag force were used as key parameters to characterize the cage performance. The results indicate that cages using polyethylene netting for the four sides and wire-netting for the bottom generally show better performance than those composed entirely of polyethylene netting; specifically, the former undergoes less shape deformation and volume reduction than the latter. The mesh type (square or diamond mesh) had a noticeable effect on shape deformation and drag force but a limited effect on cage volume reduction. Moreover, for the cages with wire-netting bottom and polyethylene sides, the bottom net tended to drift parallel to its undisturbed orientation when the sides were composed of square mesh netting. In contrast, the bottom net drifted obliquely upward on the downstream side when diamond mesh netting was used for the side nets. It was also confirmed that drag force per unit volume of the cages with wire-netting bottom was larger than that for the cages composed entirely of polyethylene netting. Highlights • Model cages with different netting materials, mesh types and cage depths were tested. • Effects of cage design parameters on hydrodynamic characteristics were investigated. • Volume reduction of cages was accurately estimated using tiny LED markers. [ABSTRACT FROM AUTHOR]

Highlights • A discrete model for UZ- type mini-hydrocyclone arrangement was set up. • Parameters affect flow uniformity were analyzed and optimized. • Flow uniformity among ZZ- type, UU- type and UZ- type in the condition of identical geometrical and operational parameters was compared. Abstract Mini-hydrocyclones have commonly been used for high precision separation due to structural simplicity and having no moving parts. When they are placed in parallel, their throughput capacity can increase significantly for large industrial applications. Flow uniformity is closely correlated with separation performance. In this study, we developed a discrete model of a UZ-type mini-hydrocyclone group. What's more, Separation experiments were performed for mini-hydrocyclone groups in ZZ-, UU-, and UZ-type arrangements. The results of the discrete model were compared to the experimental data. It was found that higher flow uniformity could be obtained with a lower split ratio or shorter inlet header length. Meanwhile, a larger head loss or flow distribution coefficient usually resulted in better uniformity in the outlet velocity of the manifold and less uniformity in the pressure drop. The UZ-type mini-hydrocyclone group was less maldistributed than the other arrangements under identical geometrical conditions and operational parameters. This study provides a guideline for designing arrangement of parallel mini-hydrocyclone groups in compact parallel manifolds. [ABSTRACT FROM AUTHOR]

Abstract A novel computational framework which combines the lattice Boltzmann method (LBM) and an improved immersed boundary method (IBM) based on a dynamic geometry-adaptive Cartesian grid system is introduced for the fluid–structure interaction (FSI) problems at moderate and high Reynolds numbers. In this framework, the fluid dynamics is obtained by solving the discrete lattice Boltzmann equation. The boundary conditions at the fluid–structure interfaces are handled by an improved IBM based on a feedback scheme, which drives the predicted flow velocity (calculated after the LBM stream process without the IBM body force) near the immersed boundaries to match the solid velocity. In the present IBM, the feedback coefficient is mathematically derived and explicitly approximated. The Lagrangian force density is divided into two parts: one is the traction caused by the predicted flow velocity, and the other is caused by the acceleration of the immersed boundary. Such treatment significantly enhances the numerical stability for modelling FSI problems involving small structure-to-fluid mass ratios. A novel dynamic geometry-adaptive refinement is applied to provide fine resolution around the immersed geometries and coarse resolution in the far field. The overlapping grids between two adjacent refinements consist of two layers. In order to enhance the numerical stability, two-layer "ghost nodes" are generated within the immersed body domain which is a non-fluid area. The movement of fluid–structure interfaces only causes adding or removing grids at the boundaries of refinements and consequently a high mesh-update efficiency is guaranteed. Finally, large eddy simulation models are incorporated into the framework to model turbulent flows at relatively high Reynolds numbers. Several validation cases, including an impulsively started flow over a vertical plate, flow over stationary and oscillating cylinders, flow over flapping foils, flexible filaments in a uniform flow, turbulent flow over a wavy boundary, flow over a stationary sphere and a dragonfly in hovering flight, are conducted to verify the accuracy and fidelity of the present solver over a range of Reynolds numbers. Highlights • An adaptive IB–LBM–LES method is developed. • The IBM feedback coefficient is derived and approximated. • The Lagrangian force is divided into predicted flow and IB acceleration tractions. • The method can perform weakly coupled FSI simulations for small mass ratios. • Several validation cases are conducted. [ABSTRACT FROM AUTHOR]

Abstract Multiple flexible cylinder structures, such as marine risers and cables, are key equipment for the production and transportation of oil and gas in offshore engineering. Till now, little information is available on flow-induced vibration (FIV) of more than two side-by-side flexible cylinders. Though some FIV characteristics of multiple flexible cylinders can be predicted based on the knowledge of two flexible cylinders undergoing vortex shedding, there are still some other characteristics that remain unrevealed, which require further experimental investigations on more than two flexible cylinders. In this paper, the FIV of three- and four-cylinder system in a side-by-side arrangement with a distance of 6.0 D between cylinder centerlines was experimentally studied in a towing tank. The flexible cylinder models with mass ratio of 1.90 and aspect ratio of 350 were mounted horizontally and towed along the tank to simulate the uniform flow. The towing velocity ranged from 0.05 to 1.0 m/s and the corresponding Reynolds number varied from 800 to 16000. The experimental results were discussed in detail, including the maximum RMS displacement amplitudes, dominant frequencies, dominant modes, time-varying displacements at the measurement points, displacement response spectra, spanwise evolutions of the RMS displacement and space-time varying displacement contour. It can be found that the multi-mode response characteristics of the three-cylinder system in a side-by-side arrangement are obviously distinct from those of the four-cylinder system due to the effect of complex wake flow behind the cylinders. These findings are very meaningful for the design of a group of flexible cylinders in engineering applications. Highlights • A towing tank experiment was conducted to investigate the FIV of three- and four-cylinder systems in a side-by-side arrangement. • The IL dominant frequencies were roughly two times of those of the counterpart in the CF direction for the three-and four-cylinder systems when the lock-in phenomenon occurred. • The multi-mode FIV characteristics of the three side-by-side cylinders were obviously distinct from those of the four-cylinder system. [ABSTRACT FROM AUTHOR]

Featured Application: A gas torch can be used for preheating in welding applications. New gas torches were designed by modifying the inner and outer structures, which led to uniform flow at the outlet and enhanced the temperature uniformity of a steel plate during preheating. The torches were examined through a numerical and experimental study. The objective of this study is to improve the exit flow uniformity of a gas torch with multiple exit holes for effective heating of a steel plate. The torch was simulated, and combustion experiments were performed for validation. Based on a basic model, three different revised models were designed and analyzed with the software ANSYS FLUENT 18.2. The flow uniformity (γ) of the velocity distribution at the multiple exit holes was investigated with the pressure drop ranging from 100 to 500 Pa. The basic model had flow uniformity ranging from 0.849 to 0.852, but the three new models had γ1 = 0.901–0.912, γ2 = 0.902–0.911, and γ3 = 0.901–0.914, respectively. The maximum percentage difference of the flow uniformity index between the three new models and the basic model was 7.3%. The basic model with nonuniform flow distribution made a temperature difference of the back side of the steel plate from the center to the edge of around 229 °C, while the modified model with uniform flow distribution had a smaller temperature difference of 90 °C. The simulation results showed good agreement with our experimental results for both the basic model and the modified model. The modified gas torch made a wider and more uniform temperature distribution on a preheated steel plate than the basic one. The results revealed that a trade-off between cost and flow uniformity, as well as the new gas torch, could be applied to a steel-plate preheating process before welding. [ABSTRACT FROM AUTHOR]

In overbank flow due to the interaction mechanism between the main channel and floodplain, the flow property of the compound sections gets affected. The complexity is more when the compound channels have non-prismatic floodplains. Additional complexity occurs during the interaction between the subsections as well as due to non-uniformity of flow through converging parts of the compound channel. For prediction of flow, calculation of energy loss parameters from section to section is an important task for river engineers. In this paper, an experimental investigation for the energy losses of converging compound channels for different flow depths along the converging path is performed. The loss of energy due to contraction and compound geometry for a compound channel is evaluated, and the dependency of energy loss for such channels is analyzed. A generalized multivariable regression model has been developed to predict the energy slope with high accuracy. Using the expression of the energy loss concept, the discharge capacity in the converging compound is found to provide good results as compared to other standard model exists in the literature. [ABSTRACT FROM AUTHOR]

The pressure gradient in the dual volute radial turbocharger turbines is the primary source of the vortices' formation in rotor passages. The effects of the upstream non-uniform flow conditions on the development of secondary flows are not well known. In this study, the effect of highly skewed and non-uniform mass flow on the secondary vortices in different admission cases in a dual entry turbine was investigated using CFD modeling. The results agree well with the experiment, and show that increasing the inequality of the pressure between the entries leads to a reduction in the turbine's performance. Some useful energy dissipates due to mixing the flows of the entries. Isolating the rotor sectors in the tongues region was applied with the purpose of limiting the mixing. Also, the vortices' behavior in the rotor passages with different surface pressure ratios for the passage sides were investigated for both equal and partial admission. The surface pressure of the airfoil pressure side was more effective on the tip and trailing edge vortex than the suction side, while the leading-edge root vortex did not change by any variation in the surface pressure ratio. The vortices' center location shifted with the pressure variation, and consequently, by decreasing the pressure level, the center of the tip vorticity turned to the upstream sections, and the leading-edge root vortex center moved closer to the pressure side. [ABSTRACT FROM AUTHOR]

In this paper, a convected frequency-domain approach for acoustic scattering prediction is suggested, for sources and scattering surfaces in a uniform constant flow. Frequency-domain moving-medium formulations are used for prediction of the incident acoustic pressure and acoustic pressure gradient. The latter is required for evaluation of the hardwall boundary condition in a moving medium and allows a convected definition of the equivalent sources. The scattering approach is validated by the analytical case of scattering of a pulsating monopole source by a rigid sphere. The applicability of the methodology to moving-medium problems is demonstrated for rotating and pulsating monopole point sources in a uniform flow, located near an infinite flat scattering surface. The suggested approach allows frequency-domain scattering predictions for sources in a uniform constant flow of any subsonic velocity, enabling direct inclusion of convection effects on incident and scattered acoustics. The hardwall boundary condition is thus evaluated directly in a moving medium. The need for a Lorentz transform is obviated, overcoming the complexity it introduces and the limitations it imposes. [ABSTRACT FROM AUTHOR]

A Fluid-Structure Interaction (FSI) conventional case study is proposed to be used as a benchmark for numerical analyses. Experimental tests were carried out to provide targets for comparisons; in particular, the study regarded the estimate of the deformed configuration ("flying shape" in the sailing field) of a square sail under a uniform flow regime in a wind tunnel facility. Several tests have been carried out at different wind velocities. The sailcloth has been characterized by means of mono-axial tensile tests obtaining Young's and shear moduli as well as Poisson's coefficients, which have then been used as input parameters for numerical analyses. Test results are considered a benchmark target deserving challenging aspects for numerical simulations in spite of the selected simple test geometry and conditions. Numerical tests have been carried out by means of a commercial software (ADINA™). Analyses used a strongly coupled partitioned approach between a Finite Volume Method (FVM) based on Reynolds Averaged Navier Stokes (RANS) equations, whereas a Finite Element Method (FEM) has been adopted for the structural field. A comparison has been eventually carried out assessing different numerical models. A good overall agreement between experimental and numerical results has been obtained by suitably setting FSI simulation algorithms. [ABSTRACT FROM AUTHOR]

Effects of pitching motion profile on energy harvesting performance of a semi-active flapping foil are numerically studied using immersed boundary method. Firstly, the numerical method is validated by considering a sinusoidal pitching semi-active flapping foil at Re = 1000 and a uniform flow over a stationary foil at Reynolds number Re = 500. Then, we consider a semi-active flapping foil with Reynolds number Re = 1000 and study the effect of sine-like and cosine-like pitching motion on the energy harvesting performance at reduced frequency f ∗  = 0.16. We study the pitching, with a gradual change from a sinusoid/cosinusoid to a square wave as β is increased from one. We found that increasing the value of β is ineffective to enhance energy harvesting efficiency for sine-like pitching motion, which is in agreement with the results of Deng et al. (2015) and Teng et al. (2016), however, for cosine-like pitching motion, the highest energy harvesting efficiency of 51.81% is recorded for pitching amplitude θ 0  = 60° and β  = 2.0. Meanwhile, we observed that cosinusoidal pitching motion is more efficient for energy harvesting than sinusoidal pitching motion, and non-cosinusoidal pitching motion can enhance the harvesting efficiency compared to cosinusoidal pitching motion. In detail, we report the different performances of the sine-like and cosine-like pitching motion to study the mechanical mechanism of enhancing energy harvesting efficiency. [ABSTRACT FROM AUTHOR]

A pipeline-riser system is a typical complex pipe configuration in which the non-uniformity of gas/liquid flow is observed to be significant under certain flow rates. This article interprets slugging flow, the most common flow regime in a pipeline-riser system, in the context of non-uniformity, which differs from the approaches used to characterise slugging cycles in previous studies. By comparing data collected by several transmitters positioned locally on the riser and comparing flow in a simple vertical pipe, both the temporal and spatial non-uniformity of the gas/liquid distribution in the riser is presented and interpreted; the relationship between them is also illustrated. The non-uniformity of the flow provides an effective means to quantitatively evaluate the severity of slugging in a pipeline-riser system under different operating conditions. In addition to flow uniformity, specific flow characteristics can be affected by operating conditions as well as pipe configuration. Several factors closely related to the design of experimental facilities and procedures are investigated by a case study of three experimental loops with different layouts and dimensions, and several general findings are summarised. The results may contribute to a better and more specific understanding of gas/liquid flow mechanisms in a pipeline-riser system in addition to serving as a means to evaluate the features of laboratory pipeline-riser systems and the applicability of laboratory results in industrial cases. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the vibrational characteristics and the coupled wake dynamics of two elastically mounted side-by-side square cylinders in a uniform flow stream. A series of fluid-structure interaction simulations is performed at low Reynolds number for two vibrating configurations, namely combined and independent. In the combined vibrating configuration, two square cylinders are tied together through a linkage as one single rigid body with a fixed relative position between them. The elastically mounted system is free to vibrate with the two-degrees-of-freedom (2-DOF) in the streamwise and transverse directions. For the independent vibrating condition, each cylinder is free to vibrate independently with 2-DOF motion in the streamwise and transverse directions which result into the coupled 4-DOF system interacting with the vortex wakes. The computational results of the independent vibrating condition are compared with the combined vibrating counterpart for identical fluid-structure parameters. Three representative gap ratios g * = 1.2 , 1.6 and 2 are selected for a detailed comparison, whereby the gap ratio g * is defined as the spacing between the inner cylinder surfaces to the diameter of the cylinder. Two-dimensional simulations are examined for a broad range of reduced velocity U r  ∈ [1, 40] at mass ratio m * = 10 . The effects of reduced velocity on the force responses, the vibration amplitudes, and the vorticity contours are analyzed systematically to understand the underlying vortex-induced vibration (VIV) and the wake physics of the side-by-side system. The effect of three-dimensional flow mechanics is further explored and the independent vibrating condition at the reduced velocity corresponding to the maximum synchronization is considered for two representative gap ratios g * = 1.2 and 2. All the simulations are performed via a nonlinear partitioned iterative scheme for the coupled fluid-structure system based on the Navier–Stokes and the rigid-body equations. [ABSTRACT FROM AUTHOR]

Grate-fired boilers are commonly used to burn biomass/wastes for heat and power production. In spite of the recent breakthrough in integration of advanced secondary air systems in grate boilers, grate-firing technology needs to be advanced for higher efficiency and lower emissions. In this paper, innovative staging of combustion air and recycled flue gas in a 13 MW th waste wood-fired grate boiler is comprehensively studied based on a numerical model that has been previously validated. In particular, the effects of the jet momentum, position and orientation of the combustion air and recycled flue gas streams on in-furnace mixing, combustion and pollutant emissions from the boiler are examined. It is found that the optimized air and recycled flue gas jets remarkably enhance mixing and heat transfer, result in a more uniform temperature and velocity distribution, extend the residence time of the combustibles in the hot zone and improve burnout in the boiler. Optimizing the air and recycled flue gas jet configuration can reduce carbon monoxide emission from the boiler by up to 86%, from the current 41.0 ppm to 5.7 ppm. The findings of this study can serve as useful guidelines for novel design and optimization of the combustion air supply and flue gas recycling for grate boilers of this type. [ABSTRACT FROM AUTHOR]

Bottleneck (especially the moving bottleneck) widely exists in the urban traffic system. However, little effort has been made to study the impacts of the moving bottleneck on traffic flow (especially the evolution and propagation of traffic flow). In this article, we introduce the speed of a moving bottleneck into a traffic flow model, then propose an extended macro traffic flow with a moving bottleneck, and finally use the proposed model to study the effects of a moving bottleneck on the evolution and propagation of traffic flow under uniform flow and a small perturbation. The numerical results indicate that the moving bottleneck has prominent influences on the evolution of traffic flow under the two typical traffic situations and that the impacts are dependent on the initial density. [ABSTRACT FROM AUTHOR]

Two tandem filaments in a uniform flow are simulated by using a penalty immersed boundary method. First, we investigate two identical filaments, duplicating the 'inverted drafting'. We then fix the structural parameters of the leader while vary that of the follower in kb2 and ρs2. It is found as the follower is stiffer or lighter than the leader, the follower flaps in larger amplitude than the leader. While the drag force acting on the follower is lower than that of the leader, which is in conflict with the so-called 'inverted drafting'. However, if we compare the dynamics of the follower to that of an isolated filament with the same structural properties, the 'inverted drafting' holds again. Furthermore, we investigate the characteristic of energy transfer between filaments and their surrounding fluid. The correlation parameter Clv indicates the follower extracts more energy than the leader except for the cases with ρs2 ≤ 0.2. [ABSTRACT FROM AUTHOR]

In the scale-up of chemical production in a microfluidic system, it is challenging to prevent flow maldistribution from a single inlet into stacked multiple microchannel exits. In the present study, a compact flow distributor equipped with a fluidic damper is developed by computational fluid dynamics (CFD) along with experimental validation. A microfluidic flow distributor, which is equipped with an optimized fluidic damper and consists of 25 exit channels, is fabricated as an integrated body using a digital light processing (DLP) type 3D printer. The 3D printed flow distributor with a CFD-optimized fluidic damper is found to achieve a low maldistribution factor (MF) of 2.2% for the average flow rate over 25 exit channels while inducing only a minor increment (＜6%) in the pressure drop. A generalized manual is proposed for the design of optimal flow distributors with different scale-up dimensions. Using the manual, an optimal flow distributor with 625 stacked microchannels with a MF of only 1.2% is successfully designed. It is expected that the design manual and the rapid printing platform will allow the efficient development of multi-channel stacked micro-devices such as those in drug delivery and energy conversion systems where equidistribution of fluid flow is highly demanded. [ABSTRACT FROM AUTHOR]

Methanol steam reforming inside micro-reactors is considered as one of the effective approaches for on-board supplying hydrogen for fuel cells. Porous copper fiber sintered felts (PCFSFs) are a new kind of catalyst support for micro-reactors developed in recent years. However, there is a lack of approach to control their porosity configurations due to their random structure. A two-step optimization method was proposed to optimize the PCFSFs’ porosity configuration. Firstly, the topology structures of PCFSFs were optimized based on the best flow distributions obtained from macroscopic numerical analyses, and two kinds of PCFSFs with twelve porosity distributions were fabricated through the multi-step mold pressing and solid-phase sintering method. Secondly, the porosity distributions of the semi-optimized PCFSFs were optimized by investigating their reaction characteristics under different gas hourly space velocities (GHSVs) and reaction temperatures. The results indicated that PCFSFs with porosity distribution along the Left-Right direction (PCFSF-LRs) exhibited better reaction performance than PCFSFs with porosity distribution along the Upside-Underside direction (PCFSF-UUs). The methanol conversion and H 2 flow rate for the PCFSF-LRs with porosity distribution of 0.7–0.9–0.8 and 0.8–0.9–0.7 kept on a high level (above 92% and 0.59 mol/h, respectively), regardless of the change of GHSVs and reaction temperatures in most cases. The H 2 selectivity of the PCFSF-LR of 0.7–0.9–0.8 was the highest under large GHSVs and all tested reaction temperatures. The demonstrated effect of counteracting, even reversing the conventional influence of the GHSV and temperature on the performance of methanol steam reforming may be attributed to the more uniform flow distribution in the two PCFSF-LRs. [ABSTRACT FROM AUTHOR]

In-line quality control diagnostics for roll-to-roll (R2R) manufacturing techniques will play a key role in the future commercialization of the polymer electrolyte membrane fuel cell (PEMFC) used in automotive applications. These diagnostics monitor the fabrication of the membrane electrode assembly (MEA), which detect and flag any non-uniformity that may potentially harm PEMFC performance and/or lifetime. This will require quantitative thresholds and a clear distinction between harmful defects and harmless coating irregularities. Thus, novel fuel cell hardware with quasi in-situ infrared (IR) thermography capabilities is utilized to understand how bare spots in the cathode electrode impact MEA lifetime. An accelerated stress test (AST) simulates chemical and mechanical degradation modes seen in vehicular operation. The actual open circuit voltage and rate of change of this voltage are used as in-situ indicators for MEA failure, enabling capture of the progression of failure point development. Bare spot coating irregularities located at the center of the electrode were found to have no impact on MEA lifetime when compared to a pristine MEA. However, MEA lifetime was found to be considerably shortened when these same irregularities are located at the cathode inlet and, especially, the anode inlet regions of the fuel cell. [ABSTRACT FROM AUTHOR]

Applying fertilizer through drip irrigation system is a very important method to save fertilizer and labour. Three manifold layouts (water supply in one end for transversal drip tapes (M1), water supply in both ends for transversal drip tapes (M2) and water supply in one end for longitudinal drip tapes (M3)) and four different fertilizer solution concentrations (50.00 g L −1 (C1), 66.67 g L −1 (C2), 100 g L −1 (C3) and 200 g L −1 (C4)) were selected to investigated the effect of the manifold and concentration on water fertigation uniformity. Results showed that the emitter at the extreme end of the manifold needed more time to clean the rudimental fertilizer in the drip tapes. The minimal flushing time increased from 8 to 13, 4 to 7 and 7 to 12 min with increasing the fertilizer concentration from C1 to C4 for M1, M2 and M3, respectively. The drip irrigation system needed more time for flushing to reduce the risk of emitter clogging when a higher fertilizer solution concentration was applied. In order of performance, M2 had the highest water and fertilizer uniformity, followed by M3 and lastly by M1. The fertilizer solution concentration had no significant effect on water distribution. However, it had a significant effect on fertilizer distribution. The mass of the applied fertilizer for the drip tapes close to the inlet increased with increasing fertilizer solution concentration from C1 to C4, which indicated that higher fertilizer solution concentration can result in lower fertilizer distribution uniformity. There was a significant effect of the manifold layout on water uniformity. The fertilizer concentration and the interaction between manifold layout and concentration had no significant effect on the water uniformity. Similarly, both the manifold layout and concentration had a significant effect on fertilizer uniformity. The interaction between manifold layout and concentration had a significant effect on the Christiansen’s uniformity (CU) and distribution uniformity (DU) for fertilizer, whilst, a significant effect on emission uniformity (EU) was not found. The manifold layout and fertilizer solution concentration should therefore be considered in the design and operation of fertigation system. [ABSTRACT FROM AUTHOR]

Multi-rotor unmanned aerial vehicles (UAVs) are used in various applications because they can hover and take off and land vertically. Although they are useful for civilian applications, their cruise flight speeds are limited owing to the generation of a pitching moment in a uniform flow. However, aerodynamic forces acting on multi-rotor UAVs have not been precisely examined. The effects of the body-yaw angle, body-pitch angle, and distance between rotors on the pitching moment and thrust in a uniform flow are important considerations when designing UAVs. Furthermore, rotor flow interaction can affect the rotor performance in horizontal flight. The objective of the present study is to examine the thrust and pitching moment of a quad-rotor UAV in a uniform flow using different configurations. First, the rotor thrust and pitching moment on two rotors were measured while changing the relative rotor positions in a wind tunnel. Second, the thrust and moment of a quad-rotor UAV were measured at different yaw directions, pitch angles, and rotors distances. Experiment results clarify that maintaining the yaw direction in a plus configuration, rather than an X configuration, with regard to the flow direction can reduce the pitching moment. [ABSTRACT FROM AUTHOR]

The interaction of tandem inverted flexible flags in a uniform flow is investigated. For the inverted flags, their ends are fixed with their heads freely flapping. A direct numerical simulation is performed for which the Reynolds number is of order 200. Large flapping amplitude as well as large drag force is preferred because more energy may be harvested if more bending energy is generated. For the simple case of two tandem inverted flags, the drag force and flapping amplitude of the rear flag are found to be smaller than those of an isolated inverted flag due to the destructive merging mode of vortices. However, it is still unknown whether more bending energy can be generated when coupled inverted flags are arranged properly. To explore the possibility, inverted flags are proposed to be arranged as two rows, which indicate two lines of inverted flags perpendicular to the direction of the incoming flow, and flags in the front and rear rows are in-line or staggered. First the results for infinite flags with periodic boundary condition are presented. In both the in-line and the staggered arrangements, due to the interactions between the front-rear flags, the flapping amplitude or the maximum bending deformation and bending energy of a flag in the rear row can be enhanced, which may be significantly higher than those of an isolated case. Meanwhile, the bending energy of a flag in the front row is close to that of an isolated case. Second, results for finite inverted flag groups show that antiphase synchronization is preferred. When the group number is large enough, the bending energies of the front and rear flags in the inner groups are close to those in the infinite case. This finding may be helpful for the designing of an efficient energy harvesting device using inverted flags. [ABSTRACT FROM AUTHOR]

In this paper, the magnetic and mechanical design of Lambertson are studied, and then magnetic field measurements are introduced. The results show that the integral field uniformity and effective length meet the physical requirements. The shielding measures shield the stray field effectively and the stray field along the circulating beam orbit is at a very low level. [ABSTRACT FROM AUTHOR]

The synergy between glass melting and glass flow character was investigated by mathematical modelling of a Joule heated glass melting channel with a central longitudinal row of vertical heating electrodes. The glass melt containing sand particles and bubbles entered the channel where different types of the melt flow were set up. The sand particle dissolution and the bubble removal were monitored up to the achievement of phenomena completion. The increasing fraction of energy supplied to the input region of the channel proved to be crucial for setting up the beneficial character of the melt flow and consequent increase of the melting performance. When the temperature of the inputting melt decreased, the melting performance also decreased. The relations of the “energetic model” were derived and applied to predict the beneficial type and conditions of the melt flow. The best results have been obtained for the flow character near the uniform flow. The beneficial state was achieved when each region of the channel was supplied by the energy needed there for glass heating and heat losses. The impact of the temperature of the inputting melt on the detailed character of the melt flow was discussed with the help of the energetic model. [ABSTRACT FROM AUTHOR]

The three-dimensional nonlinear dynamic model of a long marine riser with Kelvin-Voigt viscoelasticity properties under vortex-induced vibration is proposed and investigated. The objective is to find the appropriate viscoelastic coefficients to suppress the nonlinear dynamic response of a marine riser. The pipe is placed in a uniform cross flow and geometric nonlinearities are considered. Two distributed and coupled Van der Pol wake oscillators are applied to characterize the fluctuating lift and drag coefficients, respectively. The highly nonlinear fluid-structure interaction equations are directly coupled and solved by the finite element method. Firstly, the model is validated by comparing with published experimental data and numerical simulation results. Then, modal analysis is performed to determine the impact of viscoelastic coefficients on the natural frequency for different damping values. A nonlinear dynamic analysis is carried out to determine the impacts of the viscoelastic coefficients on displacements, stresses, modal variation and phase portraits. The results show that the viscoelastic coefficients have a significant effect on the natural frequency of the studied marine riser. It is also demonstrated that appropriate viscoelastic coefficients are very important to effectively suppress the maximum displacements and stresses. [ABSTRACT FROM AUTHOR]

In this paper the facility for the simulation of satellite motion based on planar air-bearing deweighting is considered. The air bearing provides almost frictionless horizontal motion of the small satellite mock-ups. Due to the presence of gravitational and air flow disturbances the motion is far from rectilinear and uniform. This paper is devoted to the determination of these disturbances. [ABSTRACT FROM AUTHOR]

Flow-induced vibration (FIV) of multiple marine risers frequently occurs in deepwater applications and might result in serious structural failure due to fatigue damage accumulation. It is known that long marine risers may experience high modes of vibration and behave multi-mode vibration features. Moreover, the interactions of multiple risers subject to FIV are very complex and still unclear. In this paper, a series of experimental tests were carried out to investigate FIV of two side-by-side flexible cylinders with high aspect ratio (length to diameter, L / D = 350) in a towing tank. Four cases of different spacing ratios (center-to-center separation distances to cylinder diameter, S/D = 3.0, 4.0, 6.0 and 8.0) were adopted to examine the effect of spacing on the multi-mode FIV of the two flexible cylinders. The maximum dominant modes are 4th and 6th in cross-flow (CF) and in-line (IL) directions for both side-by-side cylinders, as well as the single one. In the switching region of the adjacent modes of vibration, higher-order mode vibrations are less difficult to excite for side-by-side cylinders. The IL displacement amplitudes of the two cylinders could be enhanced by the remarkably strong interaction between cylinders, even with a center-to-center distance of up to 8.0 cylinder diameter. In addition, the IL FIV behaviors are much more complicated than those in CF direction, for instance the response spectra in IL direction exhibit several large peaks and lots of small spikes around. The IL and CF interactions of the two side-by-side flexible cylinders were also investigated by using the response trajectories collected from seven measurement points at different reduced velocities. [ABSTRACT FROM AUTHOR]