Experimental Velocity Data Research Articles

On the accuracy of Eulerian-Lagrangian CFD simulations for spray evaporation in turbulent flow

CFD simulation of droplet evaporation in turbulent flows is challenging as the accuracy and reliability of the results strongly depend on the available sub-models and their modeling parameters. This study presents a systematic sensitivity analysis focused on the impact of the most widely used discrete random walk (DRW) model, the constant time scale coefficient (CL), the turbulence model, and the drag coefficient model. CFD simulations with the Eulerian-Lagrangian approach are employed. The analysis is based on grid-sensitivity analysis and validation with measurements of spray evaporation in a heated turbulent airflow. The results show that using the DRW model leads to a good agreement between the CFD results and the experimental data of droplet size and droplet mean velocity, attributed to the turbulent fluctuations inducing droplet dispersion. The best performance is observed for the standard k-ε turbulence model with CL = 0.30 and 0.45. This is mainly attributed to the reasonable interaction time between droplets and turbulent eddies at these CL values. The three drag coefficient models (i.e., Spherical, Ischii-Zuber, and Grace) lead to similar results due to the low droplet Reynolds number.

Analysis of natural convection in a representative cavity of a room considering oscillatory boundary conditions: An experimental and numerical approach

Natural convection heat transfer in cavities commonly occurs in various engineering problems. Specifically, the problem of a differentially heated cavity with oscillatory boundary conditions arises in the design of energy-saving strategies or energy evaluations within the building sector. This work addressed numerically and experimentally the natural convection in a full-scale room subjected to diurnal heating and nocturnal cooling. The experiment was instrumented with temperature sensors and an air velocity sensor, inspired by works reported in the literature. The numerical model involved solving the equations governing natural convection, considering turbulent bi-dimensional and three-dimensional flow in a transient state. This research allowed the selection of an appropriate turbulence model and evaluated the performance of the two-dimensional and three-dimensional approaches in simulations. Results showed that the k-omega SST model performed best in predicting velocity, while the standard k-omega model performed best in predicting temperature for the two-dimensional simulation, and the RNG k-epsilon model performed best for the three-dimensional simulation. Additionally, the three-dimensional simulation more accurately reproduced the chaotic fluctuations observed in experimental velocity data, demonstrating up to 30 % better estimation during periods of high velocities. The study identified the reversal of convective cells in the cavity, with an approximate duration of 2 h and 40 min in a real case. This study contributes to improving the understanding of turbulent natural convection in a differentially heated cavity with oscillatory boundary conditions. These findings have significant implications for various environmental and engineering applications, including the design of thermally comfortable buildings.

An experimental and numerical study of propyl acetate laminar combustion characteristics

The laminar burning characteristics of propyl acetate were investigated using the constant volume combustion experimental unit at the working conditions of 1, 2, and 4 bar and 390, 420, and 450 K over a wide range of equivalence ratios (0.7–1.4). Both experimental and numerical investigations were used to study the laminar combustion characteristics of propyl acetate. Also, a chemical mechanism was proposed in this work to numerically investigate the laminar combustion of propyl acetate. A comparison of this study and literature experimental burning velocity data with the proposed mechanism laminar burning velocity showed satisfactory agreement. Sensitivity investigations of the burning velocity and production rate analysis of the reactions revealed that the reaction that mostly produces OH, H, and O radicals significantly drives the combustion of propyl acetate and increases the laminar burning velocity. Moreover, fuel-related reaction R1086: H + PA ⇔ H2 + PA2J increased the laminar burning velocity but fuel-related reaction R1098: OH + PA ⇔ H2O + PAMJ decreased the burning velocity. The reaction pathway study showed that propyl acetate mainly decomposes to PAMJ radical, PA2J radical, PAEJ radical, propene, and acetic acid before it converts into other radicals. Also, it was shown that ally radicals and ketene are essential intermediates in the fuel conversion process of propyl acetate.

Active microparticle propulsion pervasively powered by asymmetric AC field electrophoresis

HypothesisSymmetry breaking in an electric field-driven active particle system can be induced by applying a spatially uniform, but temporally non-uniform, alternating current (AC) signal. Regardless of the type of particles exposed to sawtooth AC signals, the unevenly induced polarization of the ionic charge layer leads to a major electrohydrodynamic effect of active propulsion, termed Asymmetric Field Electrophoresis (AFEP). ExperimentsSuspensions containing latex microspheres of three sizes, as well as Janus and metal-coated particles were subjected to sawtooth AC signals of varying voltages, frequencies, and time asymmetries. Particle tracking via microscopy was used to analyze their motility as a function of the key parameters. FindingsThe particles exhibit field-colinear active propulsion, and the temporal reversal of the AC signal results in a reversal of their direction of motion. The experimental velocity data as a function of field strength, frequency, and signal asymmetry are supported by models of asymmetric ionic concentration-polarization. The direction of particle migration exhibits a size-dependent crossover in the low frequency domain. This enables new approaches for simple and efficient on-chip sorting. Combining AFEP with other AC motility mechanisms, such as induced-charge electrophoresis, allows multiaxial control of particle motion and could enable development of novel AC field-driven active microsystems.

Bayesian parameter estimation and evaluation of the K-ω shear stress transport model for plane impinging jets

Numerical simulations with semi-empirical turbulence models are commonly used to model impinging jets, often used for cooling solid surfaces. In this work, the constants in the k-ω shear stress transport model in ANSYS FLUENT are calibrated to experimental velocity and heat transfer data for a plane turbulent impinging air jet to determine if Kennedy-O’Hagan calibration (Kennedy and O’Hagan 2001 J. R. Stat. Soc. B 63 425–64) can improve predictions of near-surface velocities and surface Nusselt numbers for similar flows. Impinging jets have been proposed to cool the target plates of the divertor in future magnetic fusion energy reactors, where simulations are used to estimate divertor performance. The flat-plate divertor (Wang et al 2009 Fusion Sci. Technol. 56 1023–7) uses a plane jet of helium issuing from a B = 0.5 mm slot to cool a surface with radius of curvature of 44B at a distance 4B from the slot. Predictions from the calibrated numerical model are compared with independent experimental data at different flow conditions, as well as surface temperature data for a flat plate divertor test section. The contribution of this work is evaluation of the accuracy of a calibrated turbulence model for modest extrapolations in flow geometry and flow conditions for a plane impinging jet.

Analytical solutions for airborne droplet trajectory: Implications for disease transmission

Airborne droplets containing viruses from infected persons can present long range disease transmission risks. In this study, we examine the trajectory of an airborne droplet based on a point force model. The interplay between gravity, drag, inertia and deformation are factored in, for drop sizes ranging from micrometer to millimeter size. In particular, we propose an expression for the drag force which enables analytical solutions for cases of practical interest, such as the transient velocity behavior and spreading distances. This allows us to obtain physical insights which are not obvious from direct numerical simulations. Effects such as droplet deformation, breakup and evaporation are also considered. Our analytical solutions compare favorably with numerical and experimental data. The evaporation rate was determined experimentally with a levitating device and some experimental drop velocity versus time data were obtained with falling millimeter sized droplets.

Acoustic wave velocities and effective Debye temperature in potassium alum KAl(SO4)2·12H2O crystal

The acoustic wave velocity along principal propagation directions and polarization orientations was computed for potassium alum KAl(SO4)2·12H2O crystals at 295 K, using elastic constants derived from ultrasonic resonance experiments. The mean elastic Debye temperature was subsequently determined. The temperature dependency of elastic Debye temperature was assessed, based on Brillouin scattering measurements of the longitudinal acoustic (LA) phonon propagating in the [100] direction. Comparison between the elastic Debye temperature extrapolated to T → 0 from the high-temperature phase and the calorimetric Debye temperature determined below the transition temperature (Tc = 59.7 K) revealed an 18 % disparity, primarily attributed to insufficient experimental data of velocity above and below Tc.

A Theoretical and Experimental Approach to Ultrasonic Velocities, Densities, and Refractive Indices in Benzene and Aniline Mixture

The study investigates the theoretical velocities of binary liquid mixtures comprising Aniline and Benzene under 2MHz ultrasonic waves at temperatures of 303.15K, 308.15K, and 313.15K, examined in relation to mole fraction. Experimental data is compared with various theoretical models, including Nomoto theory (NOM), Ideal mixing relation (IMR), Impedance Relation (IR), Rao’s Specific Velocity Method (R), and Junjie’s relations (JR). The work reflects the changes in refractive index with varying liquid density across different mole fractions, explaining observed impacts on ultrasonic velocities. To assess the goodness of fit, Chi-square tests and average percentage errors are employed, allowing for an evaluation of the relative applicability of these theories within the studied systems. The study also explores how the thermos-acoustical characteristics of the systems evolve concerning the mole fraction of a common molecule, shedding light on molecular interactions. Furthermore, various parameters for the binary mixture, such as discrepancies in ultrasonic velocity, excess isentropic compressibility, surplus acoustic impedance, excess intermolecular free length, and molar refraction deviation, are computed using experimental data of density, refractive index, and ultrasonic velocities at different mole fractions of benzene in the aniline-benzene mixture. These calculations serve to reflect the intermolecular interactions present in the binary liquid mixture.

Моделирование движения обвальной массы горной породы с использованием двухжидкостной математической модели

Introduction. Rock falls are considered to be very dangerous slope processes that can lead to serious consequences. In addition to real observations, numerical (mathematical) or experimental (physical) modeling methods are used to study slope processes. Mathematical modeling is used in the cases where experimental data is insufficient. There are quite a lot of models to describe slope processes. The choice of model to describe a particular slope process lies in the approach on which the model is based. In this work, the debris flow taking into account the fluidization of the collapse mass during its movement along the hillside was described. We used a two-fluid model based on the continuum approach and the kinetic theory of granular gas. The model takes into account the fluidization of the collapse mass, and its implementation does not require the use of powerful computing resources. Purpose of the study. Investigation of the collapse mass motion along a hillside using a two-fluid model based on continuum approach and kinetic theory of granular gas. Estimation of the maximum height of the collapse mass flow layer and the average flow velocity. Materials and methods. The two-fluid model based on the continuum approach and the kinetic theory of granular gas was used for theoretical study of the collapse mass flow. The motion of the collapse mass flow consisting of rock granules (average diameter 7.5 cm) along the hillside (slope angle of 30 degrees) was considered. The 3D simulation results obtained using the two-fluid model were compared with experimental data and calculated data obtained using the discrete element method. The results and discussion. Three-dimensional modeling was applied to study the motion of the collapse mass flow along the hillside using the two-fluid model. The obtained calculations of the maximum height of the flow layer and the average flow velocity are compared with experimental data and calculated data using the discrete element method. The comparison showed that the averaged value (obtained as the arithmetic mean) of the experimental data of the average flow velocity coincides with the result of calculations using the two-fluid model. And the average value of the calculated data using the discrete element method differs slightly from the calculated value using the two-fluid model. The paper proposes a method for calculating the maximum height of the flow layer using graphs of the distribution of the particles volume fraction along the normal to the inclined surface. Using this technique, the maximum value of the layer height was obtained. This value coincides with the maximum value obtained using the discrete element method and differs only slightly from the maximum value obtained in the experiments. Using the two-fluid model, additional calculations were carried out at different values of the slope angle in the range from 20 to 60 degrees. The calculation results of the maximum height of the flow layer and average flow velocity were compared with the calculated data obtained using a model based on the discrete element method. It was found that the calculation results obtained using two different models agree better with each other when the dependence of the average flow velocity on the slope angle is studied. Conclusion. In general, it can be concluded that the results of calculations of the maximum layer height and average flow velocity obtained using the two-fluid model are in fairly good agreement with experimental data and calculated data obtained using the discrete element method. It can also be concluded that the two-fluid model can be used to describe the motion of the flows of the collapse mass with a relatively low liquid content (up to 18 %) and fine inclusions (up to 27 %). Resume. The research results can be useful in estimating the maximum height of the flow layer of the collapse mass and the average flow velocity. The direction of future research is to improve the two-fluid model based on the continuum approach and the kinetic theory of granular gas for describing of real slope processes.

Thymoquinone-Micellar Interactions: A physico-chemical investigation at molecular level

Thymoquinone (TQ) is considered the most-active component of the well-known essential oil of the black cumin/seeds (Nigella sativa L.), also known for its wide-spectrum anticancer and other pharmacological potentials since ancient times. Apart from its thermo- and photo-sensitive nature, TQ has also been reported to demonstrate strong hydrophobicity and low bioavailability. These physico-chemicals, properties hinder the development of a successful oral dosage formulation. Interaction of the pharmacologically active molecule with biological membranes is crucial step to manifest health-related effects. However, further insight into the biophysical interactions of “active” natural chemotherapeutics with cellular membranes can play a vital role in designing and developing new anti-cancer regimens. In this context pseudo-membrane models comprising ionic and non-ionic micelles offer a useful way to explore in vitro drug-membrane interactions at the molecular level. The present study focuses on the physicochemical interactions of a thymoquinone (TQ) with micelles of ionic (dodecyl trimethylammonium bromide, DTAB; and sodium dodecyl sulfate, SDS) and non-ionic (tween-80 and TX-100) surfactants at the molecular level in aqueous medium. Volumetric and acoustic parameters (apparent molar volume (ɸV), isentropic compressibility (Ks), apparent molar isentropic compressibility (ɸk), specific acoustic impedance (Z), relative association (RA), intermolecular free length (Lf)) are calculated from experimental data of density and sound velocity and interpreted in terms of solute/solvent–solute/solvent interactions using the co-sphere overlap model and the electrostriction effect. Further, UV spectroscopy and conductivity studies are used to predict the locus of TQ in the micelles, binding constant (Kb), partition coefficient (Kc), and free energy changes of TQ-micelle systems in the presence of surfactants. The results show that the binding and partitioning of TQ is more significant with TX-100 as compared with other ionic and non-ionic surfactants used.

Development of a Compact Skeletal Mechanism for Thermally Cracked Hydrocarbon Fuels

ABSTRACT The construction of a compact kinetic mechanism for thermally cracked hydrocarbon fuels holds great importance for developing advanced engine with regenerative cooling. In the present study, a skeletal oxidation mechanism consisting of 104 species and 373 reactions, which can be divided into two parts, i.e. a core mechanism for pyrolysis gas, and a skeletal sub-mechanism for pyrolysis liquid, was developed by a decoupling method. The combustion process of pyrolysis gas and its pure constituents was depicted by incorporating detailed reaction pathways of H2/CO/C1-C4 molecules, and variations of hydrocarbon classes, as well as carbon number distributions were also considered by introducing eight skeletal sub-mechanisms for heavy hydrocarbons which covered chain alkanes, cycloalkanes, and monocyclic aromatics in pyrolysis liquid, thus the newly developed mechanism was suitable for thermally cracked hydrocarbon fuels over a wide range of pyrolysis temperatures. The skeletal mechanism was extensively validated by experimental data of laminar burning velocities and ignition delay times, confirming its applicability for reproducing the flame characteristics of pyrolysis gases, pyrolysis liquids, and thermally cracked fuels. Sensitivity analyses showed that laminar burning velocities of thermally cracked fuels were only affected by reactions involving small radicals when the pyrolysis temperature was lower than 600°C, while reactions involving benzene rings started to dominate the flame propagation of thermally cracked fuel at 650°C under fuel-lean, stoichiometric, and fuel-rich conditions. Reactions of small radicals and heavy hydrocarbons both affected the ignition process of thermally cracked fuels.

Data-driven estimation of scalar quantities from planar velocity measurements by deep learning applied to temperature in thermal convection

The measurement of the transport of scalar quantities within flows is oftentimes laborious, difficult or even unfeasible. On the other hand, velocity measurement techniques are very advanced and give high-resolution, high-fidelity experimental data. Hence, we explore the capabilities of a deep learning model to predict the scalar quantity, in our case temperature, from measured velocity data. Our method is purely data-driven and based on the u-net architecture and, therefore, well-suited for planar experimental data. We demonstrate the applicability of the u-net on experimental temperature and velocity data, measured in large aspect ratio Rayleigh–Bénard convection at Pr=7.1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{Pr} =7.1$$\\end{document} and Ra=2×105,4×105,7×105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{Ra} =2\ imes 10^5,4\ imes 10^5,7\ imes 10^5$$\\end{document}. We conduct a hyper-parameter optimization and ablation study to ensure appropriate training convergence and test different architectural variations for the u-net. We test two application scenarios that are of interest to experimentalists. One, in which the u-net is trained with data of the same experimental run and one in which the u-net is trained on data of different Ra\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{Ra}$$\\end{document}. Our analysis shows that the u-net can predict temperature fields similar to the measurement data and preserves typical spatial structure sizes. Moreover, the analysis of the heat transfer associated with the temperature showed good agreement when the u-net is trained with data of the same experimental run. The relative difference between measured and reconstructed local heat transfer of the system characterized by the Nusselt number Nu\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{Nu}$$\\end{document} is between 0.3 and 14.1% depending on Ra\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{Ra}$$\\end{document}. We conclude that deep learning has the potential to supplement measurements and can partially alleviate the expense of additional measurement of the scalar quantity.

Wave Velocities and Poisson Ratio in a Loose Sandy Martian Regolith Simulant Under Low Stresses: 2. Theoretical Analysis

AbstractThis paper presents a theoretical analysis of the data on wave velocity measurements at small stresses presented in a companion paper describing the experimental results on a Martian regolith loose sandy simulant (Fontainebleau sand) of the soil at the InSight landing site on Mars (Elysium Planitia). Experimental data of wave velocities and Poisson's ratio are interpreted in the light of a granular contact mechanics theory and completed accounting for rugosity effects that are suspected to have stronger effects in sands under low stresses. The asperities of a grain of Fontainebleau sand were investigated through Atomic Force Microscopy, but larger asperities had to be adopted so as to better fit the model prediction with experimental data. A good agreement between the experimental data and the model predictions is obtained for stress above 10 kPa. Below 5 kPa, an area in which asperities are suspected to have a stronger influence, the model is not fully satisfactory, showing that further experimental and theoretical investigation is necessary in a stress zone particularly relevant to surface soils in planets, with probably enhanced effects of asperities on the intergrain contact mechanics.

Convective drying of iron ore fines: A CFD model validated for different air temperatures and air velocities

In this research, a granular Eulerian multiphase model coupled with heat and mass transfer was used to simulate the convective drying process of iron ore fines. The CFD model was validated with experimental data for different air temperatures and air velocities. Convective drying experiments were performed using laboratory-scale equipment in order to obtain drying kinetics data for iron ore fines at air temperatures up to 140 °C and air velocities up to 15 m/s. The drying system had combined characteristics of fluidized bed and pneumatic transport. Numerical results showed good agreement with experimental data (average RMSE of 3.9 × 10−3) for the moisture content for nine drying air conditions. Since the coupled momentum, heat and mass transfer model could accurately and validly estimate the drying rate for iron ore fines according to the local conditions of the drying air in laboratory-scale equipment, it has potential for application in CFD simulations of industrial-scale equipment.

Ultrasonic Velocity and Attenuation of Low-Carbon Steel at High Temperatures.

On-stream inspections are the most appropriate method for routine inspections during plant operation without undergoing production downtime. Ultrasonic inspection, one of the on-stream inspection methods, faces challenges when performed at high temperatures exceeding the recommended 52 °C. This study aims to determine the ultrasonic velocity and attenuation with known material grade, thickness, and temperatures by comparing theoretical calculation and experimentation, with temperatures ranging between 30 °C to 250 °C on low-carbon steel, covering most petrochemical equipment material and working conditions. The aim of the theoretical analysis was to obtain Young's modulus, Poisson's ratio, and longitudinal velocity at different temperatures. The experiments validated the theoretical results of ultrasonic change due to temperature increase. It was found that the difference between the experiments and theoretical calculation is 3% at maximum. The experimental data of velocity and decibel change from the temperature range provide a reference for the future when dealing with unknown materials information on site that requires a quick corrosion status determination.

Comparative study of droplet and liquid film velocities in sprays

This study presents a comparative analysis of droplet and conical liquid film velocities in sprays by a pressure swirl injector with Abramovich geometric constant K = 1.986. The velocities were measured simultaneously by schlieren image velocimetry and sequential images of the liquid film, using a high-speed camera with 8192 fps and shutter of 2 μs. Other parameters, such as discharge coefficients, spray cone angles and breakup lengths were also determined, using water as test fluid, for injection pressures from 0.05 to 0.5 MPa. Experimental velocity data were compared to results from different semi-empirical equations. The breakup lengths decreased continuously from around 20 mm to 15 mm for injection pressures from 0.1 to 0.5 MPa, while spray cone angles increased continuously from about 42°–53°, for pressures from 0.2 to 0.5 MPa. Mean axial droplet velocities varied from 4.7 m s−1 to 14.5 m s−1, while the mean total droplet velocities varied from 5 m s−1 to 16.2 m s−1 and the total liquid film velocity increased from 5.7 m s−1 to 20.2 m s−1, approximately, for increasing injection pressure. Liquid film velocities were about 15%–28% higher than the droplet velocities in the pressure range considered, due to the energy required for liquid film breakup and the air drag on the droplets. The current findings underscore that significant discrepancies may arise when relying on inadequate velocity data, particularly when employed in the computation of key parameters such as the Reynolds and Weber numbers.

Magnetic Resonance Velocimetry Measurements of Internal Blade Cooling Flow and Computational Fluid Dynamic Validation by Data Matching With the Experimental Data

Abstract The optimal Reynolds-averaged Navier–Stokes (RANS) turbulence model to be used in a Computational Fluid Dynamics (CFD) simulation varies depending on the application. Conventionally, the model is selected from benchmark tests and experience, but its performance is difficult to predict. For this reason, this study presents a cost-effective CFD validation routine, which uses three-dimensional experimental velocity data obtained in replicas of the specific flow system. Magnetic Resonance Velocimetry is used as the measurement technique. Since the objective is only the validation of the turbulence model, the experiment and the simulation are performed with simplified flow conditions, hence stationary isothermal isovolumetric flow without inertial forces. The routine applies a data-matching routine to align the two three-dimensional data sets before they are interpolated on a common grid. Various error metrics are presented, which provide the degree of the CFD modeling error and indicate its source. For demonstration, the validation routine is used to evaluate RANS-CFD results of a three-pass internal cooling system of a high-pressure turbine airfoil used in a small industrial gas turbine. The simulations are performed with the eddy-viscosity-based turbulence model k–ω shear stress transport (SST), the Reynolds-stress Speziale, Sarkar and Gatski (SSG), and baseline-Explicit algebraic Reynolds stress model turbulence (BSL-EARSM) models. The results indicate strong local errors in the examined turbulence models. None of the models performed well enough, underlining that every RANS-CFD application needs to be validated.

On the ballistic performance of Weldox steel plates impacted by blunt projectiles

We present a numerically based study concerning the perforation of high strength Weldox steel plates by blunt projectiles. Our study focuses on an ongoing discrepancy between experimental data for the ballistic limit velocities of these plates and their numerical simulation results. We show that this discrepancy can be eliminated by applying a proper failure model for these steels, which accounts for the failure strains at pure shear states. We also highlight several inherent difficulties in the numerical simulations of shear bands, arising from uncertainties in the estimated temperatures inside these narrow bands.

Proprioceptive wake classification by a body with a passive tail

The remarkable ability of some marine animals to identify flow structures and parameters using complex non-visual sensors, such as lateral lines of fish and the whiskers of seals, has been an area of investigation for researchers looking to apply this ability to artificial robotic swimmers, which could lead to improvements in autonomous navigation and efficiency. Several species of fish in particular have been known to school effectively, even when blind. Beyond specialized sensors like the lateral lines, it is now known that some fish use purely proprioceptive sensing, using the kinematics of their fins or tails to sense their surroundings. In this paper we show that the kinematics of a body with a passive tail encode information about the ambient flow, which can be deciphered through machine learning. We demonstrate this with experimental data of the angular velocity of a hydrofoil with a passive tail that lies in the wake generated by an upstream oscillating body. Using convolutional neural networks, we show that with the kinematic data from the downstream body with a tail, the wakes can be better classified than in the case of a body without a tail. This superior sensing ability exists for a body with a tail, even if only the kinematics of the main body are used as input for the machine learning. This shows that beyond generating ‘additional inputs’, passive tails modulate the response of the main body in manner that is useful for hydrodynamic sensing. These findings have clear application for improving the sensing abilities of bioinspired swimming robots.

Experimental estimation of the settling velocity and drag coefficient of the hollow cylindrical particles settling in non‐Newtonian fluids in an annular channel

AbstractThe drag coefficient data of particles settling in an annular channel is very much essential for designing different solid–fluid handling equipment, such as the fluidized bed. Experimental settling velocity, wall factor, and drag coefficient data of the hollow‐cylinder particle are presented. Carboxymethyl cellulose solution has been used as the working fluid with a flow index of 0.64 ≤ n ≤ 0.91 and a consistency index of 0.31 ≤ K ≤ 1.81. The experimental results covered a wide diameter ratio range (0.14 ≤ deq/L ≤ 0.46), hollow cylinder inner to outer diameter ratio (0.2 ≤ di/do ≤0.8), and Reynolds number (0.05 ≤ Re ≤ 51 and 0.09 ≤ Re∞ ≤ 55). deq, di, and do are the equivalent inner and outer diameters of the particle, L is the annular gap, and Re and Re∞ are the Reynolds numbers in the presence and absence of the wall effect, respectively. The wall factor decreased, and the drag coefficient increased with deq/L and di/do ratios. The above parameters declined with the Reynolds number. The hollow cylinder experienced a lesser wall effect than the spherical particles settling in a non‐annular channel. In some cases, the wall factor of the hollow cylinder is found to be equal to the spherical particles settling in an annular channel. The developed correlations have successfully predicted the drag coefficients of the hollow cylinder.