Velocity Profiles Research Articles

Flow analysis of MHD ternary hybrid nanofluid over a permeable wedge with variable surface temperature and slip effect

A comparative flow analysis of a water based- ternary hybrid nanofluid has been studied in this article over a moving permeable wedge in the presence of variable wedge surface temperature. The model has been developed keeping in mind magnetic, velocity slip, buoyancy, and suction effects. The primary nanoparticle was Nimonic 80A, Fe 3 O 4 being the secondary nanoparticle and Graphene Oxide ( GO ) ternary nanoparticle. The velocity, temperature, heat transfer rate, and shear drag profiles for various parametric values of the magnetic parameter ( M ), velocity ratio parameter ( R ) , velocity slip parameter ( h ) , buoyancy parameter ( γ ) and suction parameter ( S ) was investigated. MATLAB bvp4c code was utilized for obtaining the numerical results by solving the nondimensional differential equations obtained using similarity transformations. All the results and graphs were formulated after a positive outcome of our results with that available in existing literature. An increase in the velocity slip parameter ( h ) and velocity ratio parameter ( R ) resulted in an increase in velocity profiles and local Nusselt number graphs while a reverse trend was observed for temperature and skin friction profiles. Also, the velocity graphs faced an increase by 0.09% with an increment in M = 0.4 to M = 0.8 . The present study finds its extensive applications in medical industries, water heaters, and forging of hot exhaust valve heads.

Modeling and simulation of biodiesel synthesis in fixed bed and packed bed membrane reactors using heterogeneous catalyst: a comparative study

In this study, modeling and simulation of biodiesel synthesis through transesterification of triglyceride (TG) over a heterogeneous catalyst in a packed bed membrane reactor (PBMR) was performed using a solid catalyst and compared with a fixed bed reactor (FBR). The kinetic data for the transesterification reaction of canola oil and methanol in the presence of solid tungstophosphoric acid catalyst was extracted from the published open literature. The effect of reaction temperature, feed flow rate, disproportionation of the reactants, and reactor length on the product performance was investigated. Two-dimensional and heterogeneous modeling was applied to PBMR and the resultant equations were solved by the Matlab software. Moreover, the velocity profile in the membrane reactor was obtained. The results showed the best conditions for this reaction are 180 °C, the molar ratio of methanol to oil equal 15:1, and the input flow rate of 0.5 mL/min. In this condition, a conversion of 99.94% for the TG can be achieved in the PBMR with a length of 86 cm while a length of 2.75 m is required to achieve this conversion of the FBR. Finally, the energy consumption for the production of 8000 ton/y biodiesel in a production plant using the PBMR and the FBR was obtained as is 1313.24 and 1352.44 kW, respectively.

Brownian motion and thermophoresis effects on radiative polar fluid flow with higher-order chemical reaction along a vertical porous plate

The unsteady simulation of hydromagnetic radiative polar fluid, including thermophoresis, Brownian motion, and higher-order chemical reactions across a perpendicular permeable plate with heat radiation, is performed numerically. The nonlinear PDEs are solved by the explicit finite difference technique and studio developer FORTRAN. The stability and convergence of the present model and a comparison are done to obtain accuracy. The effects of various parameters such as Brownian motion, thermophoresis, radiative heat transfer, and higher-order chemical reactions on the velocity, temperature, and concentration fields are investigated. It is found that the parameters have a significant influence on velocity and temperature profiles, angular velocity, concentration, shear stress, angular momentum density, and Nusselt and Sherwood numbers. In addition, the local share stress rises with the chemical reaction, Eckert number, and thermophoresis, whereas it decreases with the magnetic field and porous medium. In addition, the Nu (local) intensifies with higher order chemical reactions and porous mediums, whereas it falls with Eckert number, Brownian effects, micro-rotation, and thermophoresis. The concentration profile decreases with higher radiation, and the Lewis number whereas it augments with higher radiation. With an Eckert number and thermophoresis, the temperature and velocity increase. Additionally, the higher order of chemical reaction and Brownian motion augment the Sherwood number, whereas the chemical reaction, magnetic field, and porous medium reduce it. Moreover, the study may help to understand the dynamics of flow and heat transfer for the design and optimization of various engineering applications such as heat exchangers, pollutant dispersion models, energy systems, biomedical, and so on.

Estimating ski orientation using IMUs in alpine skiing

Ski-snow interaction is the essential component of alpine skiing. To understand how a skier manipulates his ski to turn, we need to develop methods to measure the orientation of the ski throughout a complete run. Recent studies tried to use IMUs to estimate edge angle (EA) during skiing. We introduce and validate a method on how to calibrate and employ IMUs to precisely and accurately measure roll angles (RA) as a matter of changing orientation of the ski around its longitudinal axis in 3D space during skiing. Static orientation measurements on an inclined plane perfectly correlate (r2 = 1) with 3D motion capturing: RMSE = 0.18° and 0.24° respectively. Bland Altman showed a mean bias of 0.23° (95% CI: -0.16°, 0.63°) and 0.21° (95% CI: -0.3°, 0.73°). Accuracy and drift tests against constant standardised rotational velocities showed no drift behaviour over time, but RA estimation accuracy is reduced with increasing angular velocities (SD @ ±300°/s: 0.57°, max. difference from average at ±300°/s: 2.7°). During skiing on a ski ergometer the comparison of maximum RA against Vicon showed a mean bias of 0.13° (95% CI: -0.86° to 1.1°). Even though ski ergometer skiing has a similar frequency and angular velocity profile like outdoor skiing, there are more rotational degrees of freedom in outdoor skiing. The foundation is provided in this paper. To understand how a skier manipulates the ski on snow and to understand RA and EA progression during a turn in detail, further research should validate the method in the field and additionally look into RA progression within individual turns.

Image-processing-based ultrasonic velocimetry development with high applicability to flows in microparticle dispersion

This study presents the development of a novel methodology, image-processing-based ultrasonic velocimetry (IPUV). For evaluating flow velocity, we present a new perspective utilizing image processing for spatiotemporal echo images instead of conventional ultrasonic analysis methods such as pulse compression and quadrature detection. In addition to traditional tracer particle size O(100 μm), IPUV has a high applicability for measuring the velocity of microparticle dispersion of the particle size O(1 μm) and dilute concentration O(0.001 wt.%). Velocimetry utilizing microparticles has significant merit: Velocity measurements can be conducted under conditions with less influence on the flow and higher traceability to fluid flow than the size conventionally used as a tracer particle. The accuracy and effectiveness of velocity analysis based on the IPUV principle are verified numerically and experimentally. In the experiments, IPUV was applied to Couette flow and stirring flow. In the former, the validity of the velocity profiling by IPUV was confirmed compared to the theoretical profiles of Couette flow. In the latter, IPUV measured velocity profiles in the stirring flows with different dispersions [spherical particle O(100 μm) and mica O(1 μm)]. Differences in the ability of dispersed particles to follow turbulent fluctuations in stirring water flow appeared in the frequency spectrum of IPUV velocity profiles.

Velocity Measurements of Powdered Rock at Low Confining Pressures and Comparison to Lunar Shallow Seismic Velocity

AbstractSeismic methods will be useful for future lunar near‐surface characterization, and high‐fidelity elastic models will be required to aid interpretation of seismic observations. To develop an elastic lunar near‐surface model, we performed ultrasonic velocity measurements of lunar regolith simulant at low confining pressure and developed a rock physics model calibrated to these measurements. Grain contact models based on Hertz‐Mindlin theory produce accurate results at high confining pressure (i.e., several hundred meters or more burial depth) but historically fail to predict observed velocities in unconsolidated media at low pressure. Therefore, we heuristically modified existing models to fit our measured data over a range of porosities and confining pressures. To compare with Apollo 14 and 16 active seismic experiments, we used our new heuristic rock physics model to produce lunar subsurface velocity profiles. We performed ray tracing through our velocity profiles to calculate seismic traveltime, which results in good agreement with first arrivals interpreted from the Apollo experiments. Our model suggests a slightly higher velocity‐pressure dependence than inferred from in situ measurements, which may be due to porosity reduction in the lunar regolith from impact‐induced and natural vibrations.

Extraction of flow features around a bridge pier with an evolving scour hole using Lagrangian coherent structures

Local scouring around a bridge pier poses a severe threat to the safety of the bridge. A better understanding of flow features around the bridge piers is necessary for accurate prediction of the scour depth. The ridges of the finite-time Lyapunov exponent, called Lagrangian coherent structures (LCSs), were used to extract the flow features around a circular bridge pier with an evolving scour hole. The velocity field required for the LCSs computation was obtained using a three-dimensional Reynolds-averaged Navier–Stokes simulation. The simulation results were validated with the published experimental and numerical findings. The computed LCS stretching field extracted all the flow features around the bridge pier that were previously reported in the literature. In addition, the LCSs extracted the region of flow acceleration on both sides of the pier. The forward LCSs upstream of the pier extracted a particle trapping region, providing insight into the volume of fluid converting into the downflow. They extracted anchor-like structures inside the scour hole upstream of the pier. The analysis of velocity variations along the width and depth of the flow domain revealed that a change in the velocity profile is triggering the formation of LCS. The behavior of non-inertial particles released and integrated into the flow field revealed the significance of LCSs in particle transport. Using the LCS method, the study extracted the flow features that were difficult to extract with traditional flow visualization methods.

Shear rate dependency on flowing granular biomass material

The commercialization of bioenergy has been significantly limited by various material handling issues due to the poor flowability of granular biomass materials. Addressing these issues demands a fundamental understanding of flow physics and robust models to predict the multi-regime flow behavior of biomass particles. In this study, we investigated the multi-regime flow behavior of loblolly pine chips, a widely used bioenergy feedstock, through combined experiments and simulations. A quasi-static hypoplastic model and a cross-regime Drucker–Prager (DP)-μ(I) model were utilized and validated against inclined plane flow experiments to understand the quasi-static and dense flow behavior of milled pine chips. The results show that along the inclined plane, loblolly pine chips mainly present in heap flow (varying thickness along the plane), and in plane flow (iso-thickness along the plane) only when the inclination closes to the material’s critical state internal friction angle. The results also show that the multi-regime DP-μ(I) model predicts a completely different velocity profile from the hypoplastic model. DP-μ(I) model can capture the flow behavior of pine chips in both flow regimes well but at the cost of extra parameter determination, and the shear-rate dependent rheology model can successfully capture the flow of elongated high-frictional particles. These findings advance the scientific understanding of the multi-regime flow behavior of granular biomass materials and shed light on formulating novel constitutive models to assist granular biomass handling in the bioenergy industry.

Multiple Outflows around a Single Protostar IRAS 15398−3359

We present the results of our mosaic observations of a single Class 0 protostar IRAS 15398−3359 with the Atacama Compact Array in the CO J = 2–1 line. The new observations covering a ∼2′ square region reveal elongated redshifted and blueshifted components, which are located at distances of ∼30″–75″ on the northern and southern sides of the protostar, respectively, in addition to the previously observed primary and secondary outflows. These elongated components exhibit Hubble-law-like velocity structures, i.e., an increase of velocity with increasing distance from the protostar, suggesting that they comprise the third outflow associated with the protostar. Besides, a new redshifted component is detected at radii of ∼40″–75″ on the northwestern side of the protostar. This redshifted component also exhibits a Hubble-law-like velocity profile, which could be a counterpart of the secondary outflow mostly detected at blueshifted velocities in a previous study. The three outflows are all misaligned by ∼20°–90°, and the dynamical timescale of the primary outflow is shorter than those of the other outflows, approximately by an order of magnitude. These facts hint that the outflow launch direction has significantly changed with time. The outflow direction may change if the rotational axis and the magnetic field are misaligned or if the dense core is turbulent. We favor the second scenario as the origin of the multiple outflows in IRAS 15398−3359, based on a comparison between the observational results and numerical simulations.

Entropy Analysis of Hall Effect with Variable Viscosity and Slip Conditions on Rotating Hybrid Nanofluid Flow Over Nonlinear Radiative Surface

PurposeWith possible uses in engineering and industrial processes, this work aims to further our knowledge of fluid dynamics and heat transfer in complicated flow configurations. This study looks at how Al2O3−Cu/H2O hybrid nanofluids move across a nonlinear radiative 3D unsteady surface. It tries to figure out what happens when the Hall current, variable viscosity, viscous dissipation, velocity and thermal slip conditions work together. The goal of this analysis is to provide insight into the system's thermodynamic behavior and the ways in which these elements affect the flow's entropy generation. MethodologyThe controlling system is converted into nonlinear nondimensional partial differential equations (PDEs) by applying suitable non-similar transformations. In this work, the governing equations are simulated using the local non-similarity (LNS) approach up to the second truncation level using the numerical technique bvp4c in MATLAB. FindingsThe temperature, velocity, entropy production, skin friction in both directions, and Nusselt number profiles of the nanofluid and hybrid nanofluid are detailed in many figures. The tabular form contains the results of computing the local Nusselt number for linear, nonlinear, and radiation-free scenarios. The velocity profiles in both directions and the temperature profile grow as the rotation parameter and nanoparticle volume fraction parameter increase. Conversely, the velocity profiles drop when the variable viscosity parameter falls, while the temperature profile increases. When the unsteadiness parameter A is set to 0.5 and the nanoparticle volume fraction is 1%, hybrid nanofluid has 4.26% lower x-direction skin friction than nanofluid and 3.62% greater y-direction friction. When the unsteadiness parameter A = 0.5 and the nanoparticle volume percentage is 1%, a hybrid nanofluid has a 2.77% higher Nusselt number than a nanofluid. The generation of entropy was also enhanced by an increase in the volume fraction of nanoparticles, radiation, temperature ratio, and Brinkman number. We evaluate and contrast the results of this study with those of earlier research.

Optimization-based planning of speech articulation using general Tau Theory

This paper presents a model of speech articulation planning and generation based on General Tau Theory and Optimal Control Theory. Because General Tau Theory assumes that articulatory targets are always reached, the model accounts for speech variation via context-dependent articulatory targets. Targets are chosen via the optimization of a composite objective function. This function models three different task requirements: maximal intelligibility, minimal articulatory effort and minimal utterance duration. The paper shows that systematic phonetic variability can be reproduced by adjusting the weights assigned to each task requirement. Weights can be adjusted globally to simulate different speech styles, and can be adjusted locally to simulate different levels of prosodic prominence. The solution of the optimization procedure contains Tau equation parameter values for each articulatory movement, namely position of the articulator at the movement offset, movement duration, and a parameter which relates to the shape of the movement’s velocity profile. The paper presents simulations which illustrate the ability of the model to predict or reproduce several well-known characteristics of speech. These phenomena include close-to-symmetric velocity profiles for articulatory movement, variation related to speech rate, centralization of unstressed vowels, lengthening of stressed vowels, lenition of unstressed lingual stop consonants, and coarticulation of stop consonants.

Investigation of nonlocal granular fluidity models using nuclear magnetic resonance

Nonlocal rheology models describe features in granular flows, such as scale dependence and flow below the yield point, that are not captured by local rheology models. It has been proposed that these features may be described by the transport of a property known as the granular fluidity. In this article, we studied an annular Couette shear cell of lobelia seeds using nuclear magnetic resonance to collect detailed measurements of the velocity distribution and volume fraction. These data were used to study nonlocal granular rheology models. We found that the nonlocal granular fluidity model was capable of accurately describing the decay in the velocity profile along the shear gradient direction. We also measured the dimensionless fluidity and validated the general form of the relation between this quantity and the volume fraction.

Electroosmotic flow in graphene nanochannels considering steric effects

Graphene nanochannels are excellent channels for electroosmotic flow (EOF) due to their larger slip length. In this study, the fully developed EOF in graphene nanochannels is investigated numerically, where the influence of surface charge mobility on the Navier-slip boundary conditions and the influence of steric effect on the electric potential distribution are considered. In addition, an analytical solution is provided for the scenario with low zeta potential. Detailed investigations are conducted on the impact of slip length, surface charge density, surface charge mobility, effective ion size, solution concentration, and channel height on velocity profiles. The findings indicate that the velocity increases with slip length, surface charge density, and effective ion size. Yet, accounting for surface charge mobility (αs = 0.815) leads to a reduction in slip velocity. It is noteworthy that our investigation focuses on quantifying the velocity decline due to surface charge mobility, as well as the velocity enhancement resulting from the steric effect. By adjusting parameters, such as channel height, bare slip length, and solution concentration, we achieve a maximum velocity increase of approximately 48%. These insights are valuable for optimizing the design of efficient electro-osmotic pumping systems.

Intelligent Neural Computing to Investigate the Heat and Mass Transmission in Nanofluidic System between Two Rotating Permeable Disks: Supervised Learning Mechanism

The prime objective of the present study is to investigate the effectiveness and accuracy of a single-trained artificial neural network. The Levenberg-Marquardt Backpropagated networks are tested for heat and mass transmission in magnetized hybrid nanofluid flow between the rotating permeable system. The reference data to generate different cases for distinct scenarios has been obtained using the Adams method in Mathematica using the ND-Solver function. Additionally, the system of highly nonlinear PDE's is achieved and transformed into ODE's. The effect of body forces such as thermophoresis particle diffusion and Brownian motion are incorporated in the hybrid nanofluid system. Configuration under observation is permeable and under constant impact of the magnetic field. Rosseland thermal radiation approximation relation is utilized to investigate the linear impact of radiation on velocity and temperature profile. The accuracy and effectiveness of the proposed ANNLMB are depicted with performance demonstrations. Mean square error, histogram error, and regression plots are generated for all the scenarios to discuss the varying impact of different key study parameters on the performance of the proposed ANNLMB. Furthermore, the generated reference data is distributed in the following manner 82%, 9%, and 9% for training, testing, and validation, respectively.

Integral solution method of the laminar conjugated natural convection heat transfer from a hollow cylinder

The laminar conjugated natural convection heat transfer from a hollow cylinder is a common problem in engineering. The accurate calculation of the hot-spot temperature helps to monitor and evaluate the operating status of the equipment. In this paper, first, a mathematical model of the conjugated natural convection from a hollow cylinder is established. The boundary layer integral equations under arbitrary heat flux distribution on the surface are derived, and the optimal velocity and temperature profiles corresponding to different Prandtl numbers are determined. By combining the integral equations and the thermal network model, the hot-spot temperature and the average surface temperature of a hollow cylinder are solved iteratively. Subsequently, a computational fluid dynamic (CFD) simulation based on finite volume method is carried out to verify the accuracy of the integral solution method. The maximum relative error of the computed results of the two methods is 1.35%. The integral solution method performs much better in computation speed, increasing by 90 times. It is also found that as the thermal conductivity of solid materials decreases, although the hot-spot temperature increases, the average surface temperature remains basically unchanged. Finally, based on the lumped thermal equivalent circuit, the correlation of the Nusselt number corresponding to the hot-spot temperature is predicted. The parameters in the correlation are estimated by regression orthogonal design. The results show that under a wide range of solid thermal conductivity and fluid Prandtl numbers, the maximum error of the correlation is 6.02%. Therefore, this novel method is feasible and significant for calculating hot-spot temperature.

Investigation of the local apparent viscosity in a stirred tank with a shear-thinning fluid through Particle Image Velocimetry.

The local apparent viscosity in a cylindrical stirred tank was investigated using Particle Image Velocimetry in a shear-thinning fluid. Two impellers were studied, a Rushton turbine for validation and an axial impeller HTPG4, for three Reynolds numbers corresponding to the transition regime between laminar and turbulent flows. Mean and instantaneous velocity contours and profiles are analysed. Then, the different contributions to the mean total kinetic energy are investigated with the HTPG4 impeller. The sensitivity of the mean apparent viscosity to the method of determining the shear rate is discussed. This work shows that the mean apparent viscosity is highly sensitive to the method of determining the shear rate. Future work will focus on improving the measurement of the local shear rate.

Direct numerical simulation of mechanism and control of secondary instability induced transition in a supersonic boundary layer

Mechanisms and control of secondary-instability-induced-transition in a supersonic boundary layer are studied numerically via direct numerical simulation. The aim is to investigate and compare the transition mechanisms of fundamental, subharmonic, asymmetric subharmonic, and detuned resonances, and to control these secondary instabilities using a local wall cooling strip. The results indicate that the nonlinear interaction between the high-amplitude primary mode and low-amplitude secondary modes is the main contributor to transition. The mutual- and self-interactions of the primary and secondary modes generate other harmonic modes with laminar breakdown soon appearing. The asymmetric subharmonic resonance induces the earliest transition, while the fundamental subharmonic has the latest. Wall cooling effects are also studied. The results show that a lower wall temperature significantly suppresses the secondary instabilities, and steady modes become dominant and lead to obvious streamwise vortexes. Numerical data demonstrate that all secondary-instability-induced transitions result in fully developed turbulent boundary layers, as supported by the skin friction and scaled velocity profiles. The transition control cases indicate that the local wall cooling strip can significantly delay the transition by suppressing the growth of the primary mode. An upstream control strip is found to have a more obvious suppression effect. The fundamental and asymmetric subharmonic resonances are sensitive to the location of the local wall cooling strip and show a stronger transition delaying effect.

Wire coating and melt elasticity

In modern wire coating, the polymer is dragged through a round cylindrical die. Onto this drag flow, we superpose pressure-driven extrusion. We devote this paper to analyzing this extrusion in eccentric cylindrical coordinates. We find that, when the molten polymer is an elastic liquid, a recentring force, Fx, is exerted on the wire. This is how the wire is then coated concentrically. The lateral force acting on the wire thus matters. This also explains why the wire cannot be coated with Newtonian or nearly Newtonian polymer. The axial force on the wire, Fz, is always positive, and we find that the die eccentricity decreases Fz. This determines the required pulling force. Thus, the axial force acting on the wire also matters. We follow the method of Jones (1964) called polymer process partitioning, to obtain the coating velocity profile, v⌣z(ξ,θ), from which we get the coating thickness profile. We integrate this profile to get the flow rate, and thus, the average thickness. We also obtain the stresses in the extrudate. We include one detailed dimensional worked example to help engineers design coating dies.

A study on the impact of solar radiations and activation energy effects in existence of nanofluid over stretching solar sheets

In this paper, we study the effects of activation energy and solar radiation on expanding solar sheets, as well as non-Newtonian nanofluid dynamics, which are important in these applications and are driving efforts to find solutions to the world’s energy problems. We provide numerical solutions to physical flow problems by solving partial differential equations. We utilise the MATLAB-integrated bvp4c methodology after applying similarities to turn these PDEs model into ODEs. By investigating dimensionless momentum, concentration, and thermal profiles under different conditions, our research delves into the physical relevance of nanofluids. Important flow field components have also been numerically and tabulatively studied and displayed graphically. The rates at which heat is transferred is 29.06% and 37.99%, respectively. The rate of heat transport rose by 13.93% as a result. At greater values for the Maxwell fluid parameter, the velocity profiles improved while the temperature profiles decreased. This paper contributes significant new information to the ongoing discussion in this area, which is in line with earlier findings.

Tunable viscoelastic size-based particle separation in straight microchannels with triangular cross-sections

In recent years, viscoelastic particle manipulation within microfluidic systems has received much attention due to the ease with which micron-sized objects may be maneuvered and isolated on the basis of size. While several factors, including both fluid and particle properties, regulate the precise locations and trajectories of micron-sized species flowing along a microchannel, the role of channel cross-section shape is critical, since it directly influences the fluid velocity profile and thus the direction and magnitude of hydrodynamic forces. It is therefore surprising that this parameter has not been comprehensively investigated for cell-based separations, especially since most viscoelastic microfluidic systems are only able to efficiently sperate cells over limited size ranges. To address this shortcoming, we present a viscoelastic microfluidic system integrating a triangular cross-section microchannel, for efficient and tunable size-based separations of micron-sized species. We find that particle focusing patterns can be controlled by simple variation of volumetric flow rates, which allows for the efficient separation of particles and cells of variable size. To showcase the efficacy of the approach, we present a size-based separation of various blood components, including white blood cells, platelets, and rare cells. By quantifying the number of particles collected at the outlets, we achieve recovery efficiencies of over 98%.