Fluid Flow Field Research Articles

Combined electromagnetohydrodynamic flow in microchannels with consideration of the surface charge-dependent slip

In microscale systems, hydrodynamic slip is considered to significantly influence the fluid flow field. Existing theories of electromagnetohydrodynamic flow in hydrophobic microchannels have postulated a constant slip length and ignored the effect of the surface charge on slip. In this study, we extended prior models by considering a combined pressure-driven and electromagnetohydrodynamic flow in microchannels with consideration of surface charge-dependent slip. An analytical solution for this simple model was derived. After a detailed discussion of the obtained results, we demonstrate that the more realistic surface-charge-dependent case has smaller velocities and flow rates than the surface-charge-independent slip case. Considering the effect of the surface charge on slip, the flow rate can be reduced by up to 7% in the currently selected parameter range. Our results are useful for optimizing electromagnetohydrodynamic flow models in microchannels.

Design and optimization of dry powder jet cleaning nozzles for airport navigation lights

The research of this work is based on the nozzle design and optimization of dry powder (NaHCO3) jet cleaning system for airport navigation aid lamps. In this cleaning system, compressed air drives dry powder (NaHCO3) abrasive, and a gas-solid mixed high-speed jet is sprayed onto the surface of the luminaire through the nozzle to scour and clean the dirt attached to the surface of the luminaire. Based on the computational fluid dynamics and flow field theory, three types of nozzle structures, namely tapered nozzle, Laval nozzle, and flat nozzle, were studied; the DPM (Deformable part model) model in Fluent was used to analyze the internal and external flow fields of the nozzle mixed with the gas-solid two-phase flow to obtain the velocity field, pressure field and nozzle wear rate of the mixed gas, and the flat nozzle was selected and the nozzle parameters were optimized. The optimized level combination of flat type nozzle structure is obtained with a flat width of 4mm, flat height of 24.5mm, and flat length of 55mm.

Geothermal geological characteristics and exploitation potential in Nanyang Basin

Based on the geothermal geological conditions and the geothermal resources development and utilization data of Nanyang Basin for many years, the geothermal fields in the basin are divided according to the study of fault structures. According to the pumping test data of geothermal wells, the permeability coefficients of the thermal storage aquifers of the geothermal wells were calculated using the steady-flow Dupuit formula and Kusakin's empirical formula. In this paper, the water conductivity of thermal reservoir is calculated by using the method of line diagram and recovery water level, and the characteristics of thermal reservoir aquifer group, geothermal fluid flow field, and hydrochemistry are described systematically. Based on the analysis method of groundwater exploitation potential index, the development and utilization potential of geothermal resources is studied, which has certain reference significance for the development and utilization of geothermal resources of sedimentary basins.

FVM-RANS Modeling of Air Pollutants Dispersion and Traffic Emission in Dhaka City on a Suburb Scale

The present study aims to investigate the impact of air pollutants dispersion from traffic emission under the influence of wind velocity and direction considering the seasonal cycle in two major areas of Dhaka city: namely, Tejgaon and Gazipur. Carbon monoxide (CO) mass fraction has been considered as a representative element of traffic-exhausted pollutants, and the distribution of pollutants has been investigated in five different street geometries: namely, single regular and irregular, double regular and irregular, and finally, multiple irregular streets. After the grid independence test confirmation as well as numerical validation, a series of case studies has been presented to analyze the air pollutants dispersion, which mostly exists due to the traffic emission. The popular Reynolds-averaged Navier–Stokes (RANS) approach has been considered, and the finite volume method (FVM) has been applied by ANSYS FluentTM. The k−ϵ turbulence model has been integrated from the RANS approach. It was found that the wind velocity as well as wind direction and the fluid flow fields can play a potential role on pollution dispersion in the Dhaka city street canyons and suburbs. Inhabitants residing near the single regular streets are exposed to more traffic emission than those of single irregular streets due to fewer obstacles being created by the buildings. Double regular streets have been found to be a better solution to disperse pollutants, but city dwellers in the east region of double irregular streets are exposed to a greater concentration of pollutants due to the change of wind directions and seasonal cycles. Multiple irregular streets limit the mobility of the pollutants due to the increased number of buildings, yet the inhabitants near the multi-irregular streets are likely to experience approximately 11.25% more pollutants than other dwellers living far from the main street. The key findings of this study will provide insights on improving the urbanization plan where different geometries of streets are present and city dwellers could have less exposure to traffic-exhausted pollutants. The case studies will also provide a template layout to map pollutant exposure to identify the alarming zone and stop incessant building construction within those regions by creating real-time air quality monitoring to safeguard public safety.

Characteristics of Heat Transfer and Turbulent Flow in a Baffled Pipe with Different Arrangements

In the heat transfer, fluid flow and energy fields, baffles are an advanced enhancer to improve heat transfer and fluid mixing by working as an obstacle to the flow particles and then increasing the turbulence. The present paper numerically investigates the thermal performance of a circular pipe with a centralized baffle in two arrangements, with a Reynolds number (Re) (ranging from 10,000-50,000) under constant wall heat flux boundary conditions. Ansys Fluent software is used to solve the flow field considering six conical baffles with different Pitch ratios (PR) (from 1 to 5). Results show that baffles shape, arrangement, and PR have a significant impact on the properties of flow and heat transfer. The obtained results show an effective role for the baffles to promote thermal performance when it is used in heated pipes. Heat transfer rate is increased for the baffled pipe by 1-2 compared with the smooth pipe. Moreover, the best value of friction factor, thermal performance, and Nusselt number is recorded at PR= 5 at Re=30000 in the baffled pipe for the second arrangement.

Numerical evaluation of thermal and hydrodynamic effects caused by heat production well on geothermal Phlegraean Fields

This study describes the geothermal response of the Phlegraean Fields as well as the impact of changes in its thermal and hydrodynamic properties brought on by a deep borehole heat exchanger (DBHE). For this purpose, we have developed a specialized model based on the Galerkin Method (GM) and the iterative Newton–Raphson algorithm to perform a transient simulation of heat transfer with fluid flow in porous media by solving the related system of coupled non-linear differential equations. A two-dimensional domain characterized with an anisotropic saturated porous media and a non-uniform grid is simulated. Extreme characteristics, such as non-uniformity in the distribution of the thermal source, are implemented as well as the fluid flow boundary conditions. While simulating the undisturbed geothermal reservoir and reaching the steady temperature, stream function, and velocity components, a DBHE is placed into the domain to evaluate its impact on the thermal and fluid flow fields. This research aims to identify and investigate the variables involved in the Phlegraean Fields and provide a numerical approach to accurately simulate the thermodynamic and hydrodynamic effects induced in a reservoir by a DBHE. The results show a maximum temperature change of 107.3°C in 200 years of service in the study area and a 65-year time limit is set for sustainable geothermal energy production.

Break the superheat temperature limitation of induction skull melting technology

Overcoming the limitation of low superheat temperature problem is key for the applications of the induction skull melting technology in many important high melt point metals used in fields such as aerospace. The present paper presents an advanced numerical study to explain the mechanism of melt superheat temperature. A coupling model between electromagnetic, thermal, phase and fluid flow fields was established, which accurately predict the temperature and meniscus shape in the research domain. The simulation results show that the forced convective heat transfer caused by electromagnetic force in the melt and the current passing through phenomenon between molten melt and crucible were the key to influence the superheat temperature and electrical efficiency. Furthermore, it was discovered that convection suppression in the melt by employing an external DC coil and increasing the thermal resistance between the skull and the crucible could increase the melt superheat temperature effectively. Increasing the thermal resistance between the skull and the crucible also leads to an increase in the superheat temperature, which could be achieved by enhancing the interface roughness. The present work would shed lights on the design of new generation induction crucible to obtain high superheat temperature melt.

FlowSRNet: A multi-scale integration network for super-resolution reconstruction of fluid flows

A wide range of research problems in physics and engineering involve the acquisition of high-resolution data. Recently, deep learning has proved to be a prospective technique for super-resolution (SR) reconstruction of fluid flows. General deep learning methods develop temporal multi-branch networks to improve SR accuracy while ignoring computational efficiency. Further, the generalization ability of the deep learning model in different fluid flow scenarios is still an unstudied issue. In this article, we propose an efficient multi-scale integration network called FlowSRNet to reconstruct the high-resolution flow fields. Specifically, we elaborately design a lightweight multi-scale aggregation block (LMAB) to capture multi-scale features of fluid data, which contains a parallel cascading architecture and feature aggregation module. The residual backbone of FlowSRNet is built by cascading the LMABs (cascaded blocks number N = 8) in a serial manner. Also, we present a small architecture LiteFlowSRNet (cascaded blocks number N = 2) for comparison. In addition, a corresponding SR dataset is constructed to train and test the proposed model, which contains different kinds of fluid flows. Finally, extensive experiments are performed on different fluid data to evaluate the performance of the proposed model. The results demonstrate that our approach achieves state-of-the-art SR performance on various fluid flow fields. Notably, our method enjoys merit of lightweight, which facilitates the development of the complicated calculation in computational fluid dynamics.

Hydrodynamic Analysis and Cake Erosion Properties of a Modified Water-Based Drilling Fluid by a Polyacrylamide/Silica Nanocomposite during Rotating-Disk Dynamic Filtration.

In this study, the potential of using a polyacrylamide-silica nanocomposite (PAM-S) to control the filtration properties of bentonite water-based drilling muds under different salinity conditions was evaluated. Static filtration tests under low-pressure/low-temperature (LPLT) conditions accompanied by rheological measurements have been carried out to analyze the role of silica nanoparticles (NPs) and nanocomposites (NCs) in the base fluid properties. Moreover, high-pressure/high-temperature (HPHT) static filtration was also investigated to evaluate the thermal stability of PAM-S. Afterward, dynamic filtration has been conducted in a filtration cell equipped with an agitating system with a disk-type impeller to investigate the hydrodynamic and formation of a filter cake under shear flow conditions. Fluid flow velocity and wall shear stress (WSS) distribution over the filter cake were analyzed using an exact 3D computational fluid dynamic (CFD) simulation. A transparent filtration cell with a camera was used to accurately record the fluid flow field inside the filter press and validate the CFD results. The obtained results indicated that adding silica NPs at a concentration of less than 2 wt % increases the fluid loss due to reducing rheological properties such as yield point. While silica NPs could not significantly change the mud properties, the experimental results showed that, under both LPLT and HPHT conditions, the PAM-S NC could reduce the total filtration loss by 70% at a low concentration of 0.75 wt %. Moreover, during dynamic filtration, the results indicated that there is a linear relationship between the cake thickness and the inverse of WSS at different operating pressures. However, no correlation could be found between predeposited mud cake erosion and WSS. At a rotating disk speed of 1000 rpm, more than 60% of the predeposited mud cake was eroded after 30 min for a saline mud sample while for the NC-treated mud sample cake erosion is considerably reduced and reaches up to 20% at 1.5 wt % PAM-S.

Numerical investigation of dynamic characteristics of debris bed formation based on CFD-DEM method

In a severe accident in nuclear reactor, the core meltdown occurs when nuclear fuel rods cannot be sufficiently cooled, thus forming debris beds with specific shapes on the lower head of the Reactor Pressure Vessel (RPV). In this paper, the fluid–solid interaction during debris bed formation is studied based on Computational Fluid Dynamics method coupled with Discrete Element Method (CFD-DEM). The CFD models are used to simulate the flow and pressure field of fluid, the DEM models are used to calculate the collision between solids and the collision between solids and wall, as well as the fluid–solid interaction force can be calculated by the two-way coupling models. The DEM models and CFD-DEM models were validated by different experiments. Based on the above models, the DEFOR-E7 test was simulated, and a conical debris bed formed by irregular debris with a static angle of 35° and a porosity of 72% was obtained. Therefore, the method and findings in this paper are significative on theory and application for the study of nuclear severe accidents.

Numerical and asymptotic solutions of the unsteady mixed convection boundary-layer flow over an expanding/contracting vertical cylinder

PurposeThe purpose of this study is to obtain both the numerical and asymptotic solutions of the unsteady mixed convection flow and heat transfer over an expanding or contracting cylinder which is placed vertically.Design/methodology/approachSolutions of the governing ordinary (similarity) differential equations for the fluid flow and temperature field are obtained using the function bvp4c from MATLAB. The problem involves the Prandtl number σ, the mixed convection parameter λ and unsteadiness parameter S that characterize an expanding or contracting cylinder. This solution approach is capable of producing multiple solutions once the necessary assumptions are provided.FindingsIt is found that solutions exist for all negative values of S, expanding cylinder, and only for small positive values of S, contracting cylinder. Further, more than one solution is observed; numerical computation shows that the critical point of S becomes singular as λ approaching zero. For the case of expanding cylinder, the mixed convection parameter has a significant effect on both the flow and heat transfer characteristics. Asymptotic analysis also shows that when σ is large, dual solutions exist for some values of S and λ.Originality/valueThe present results are new and original for the study of the unsteady mixed convection flow and heat transfer over an expanding/contracting cylinder where numerical solutions are obtained for representative values of the involved parameters. Asymptotic solutions for large λ and large σ are derived.

Numerical and experimental flow investigation using ultrasonic PIV for optimizing mechanically agitated lab-scale anaerobic digesters

In this article, a non-invasive ultrasonic flow field measurement method is studied to investigate its applicability to resolve fluid flow in bio- and chemical engineering reactors. In detail, the proposed flow field investigation method is applied to mechanically agitated lab-scale reactors for the validation of anaerobic digester mixing simulations. Two reactors with different geometries, which are cold models of real-life anaerobic digesters, are studied. Since conventional non-invasive flow field measurement techniques are not suitable for the investigated reactor geometries, the applicability of ultrasonic measurement is demonstrated. The experimental results are compared to Computational Fluid Dynamics (CFD) simulations using the Finite Volume Method with multiple reference frames to account for the stirrer-induced mixing. It is shown that ultrasonic measurement is an easily applicable non-invasive method for resolving flow fields of opaque fluids found in chemical, mechanical and biological engineering. The study highlights the benefits of the non-invasive measurement approach and also demonstrates the suitability of this flow measurement technique for further applications such as the optimization of the mixing time characteristics of paints and coatings or silicone production. The resolved flow fields are in accordance with numerical reference results with minor deviations of up to 9% for velocity measurements aligned with the main axis of the ultrasound probe. The validated CFD model can be used as a template for modelling similar chemical engineering processes where the mixing time characteristic is critical. It is further shown that the accuracy of this flow measurement method decreases with increased offsets from the main axis. In addition to the axis alignment, the impact of different fluid properties and reactor geometries is also discussed.

Flow-induced self-sustained oscillations in a straight channel with rigid walls and elastic supports

This work considers the two-dimensional flow field of an incompressible viscous fluid in a parallel-sided channel. In our study, one of the walls is fixed whereas the other one is elastically mounted, and sustained oscillations are induced by the fluid motion. The flow that forces the wall movement is produced as a consequence that one of the ends of the channel is pressurized, whereas the opposite end is at atmospheric pressure. The study aims at reducing the complexity of models for several physiological systems in which fluid-structure interaction produces large deformation of the wall. We report the experimental results of the observed self-sustained oscillations. These oscillations occur at frequencies close to the natural frequency of the system. The vertical motion is accompanied by a slight trend to rotate the moving mass at intervals when the gap height is quite narrow. We propose a simplified analytical model to explore the conditions under which this motion is possible. The analytical approach considers asymptotic solutions of the Navier–Stokes equation with a perturbation technique. The comparison between the experimental pressure measured at the midlength of the channel and the analytical result issued with a model neglecting viscous effects shows a very good agreement. Also, the rotating trend of the moving wall can be explained in terms of the quadratic dependence of the pressure with the streamwise coordinate that is predicted by this simplified model.

Computational rheometry of yielding and viscoplastic flow in vane-and-cup rheometer fixtures

A planar two-dimensional computational analysis is presented to qualify traditional and fractal vane-in-cup geometries for accurate rheometry of simple viscoplastic fluids with and without slip. Numerical simulations based on an adaptive augmented Lagrangian scheme are used to study the two-dimensional flow field of yield-stress fluids within and around vane tools with N=3 to 24 arms for a wide range of Bingham numbers, B (i.e. the ratio of the yield stress over the characteristic viscous stress). This allows for accurate calculations of the velocity and stress fields around vanes with various geometries, as well as direct comparison to experimental observations of the output torque measured by a rheometer, revealing sources of variation and error. We describe the impact of the vane structure on the fluid velocity field, from few-arm cruciform vanes (N≤6) that significantly perturb the flow away from ideal azimuthal kinematics, to many-arm fractal vanes (N≥12) in which the internal structural features are successfully “cloaked” by a yield surface. This results in the shearing of an almost-circular ring of viscoplastic fluid that is indistinguishable from the annular ring of fluid deformed around a slip-free rotating cylindrical bob and leads to more accurate rheometric measurements of the material flow curve. Moreover, in direct comparison with data from previous literature, we show that slip conditions on the vane surface do not impact the velocity field or measured overall torque T, whereas slip conditions on the smooth outer wall have significant impact on data, even when using a vane geometry. Finally, we describe the impact of vane topography and Bingham number, B, on the measured torque and rheometric accuracy of vane-in-cup geometries for “simple” (inelastic) yield-stress fluids described by either the Bingham plastic or Herschel–Bulkley constitutive model.

Local investigation of the dynamic and thermal fields to characterize the transition onset from steady to unsteady laminar flow in a complex geometry

The present work investigated numerically the onset of the transition from steady to unsteady laminar flow regime in a three dimensional complex geometry. The behavior of the dynamic and thermal fields of the chaotic fluid flow has been analyzed for numerous Reynolds numbers ranging from 190 to 550. Several parameters were used during this study to verify the fluid pattern such as; velocity and temperature profiles, secondary flow, flow intensity, helicity and the Nusselt number. It is found that at Re = 400, the symmetry of the flow is destroyed in the second and the third geometric periods whereas it still remains present in the first period which indicates the first step towards the transition. While at Re = 445, the symmetry is still preserved in the first period of the geometry, but the velocity begins to be unsteady with periodic variation at a single frequency where a clear impression can be given on the transition from the steady laminar regime to the unsteady regime. Results illustrate that the flow goes through intermediate steps to reach the unsteady domain before exiting the laminar zone. Moreover, the flow in the geometry of interest is not of the same nature so it can be totally or partially unsteady where different stages can be cited as; stable and symmetric flow, stable asymmetric flow, unstable flow with one or more frequencies and finally erratic flow.

Simulation and experimental research on magnetorheological finishing under dynamic pressure with a gap-varying

Magnetorheological finishing (MRF) is a novel machining method used to obtain ultra-smooth and even surfaces. To improve the material removal rate (MRR) while attaining smooth and undamaged surfaces, an MRF method with a varying machining gap between the polishing disks and workpieces is proposed to increase the polishing efficiency and improve the surface quality. According to the computational fluid dynamics (CFD) method, the behaviors of MRF fluids under the effect of magnetic fields are measured using a rheometer. Furthermore, a simulation model for fluids based on the gap-varying MRF is established to evaluate the influence of the varying machining gap on the behaviors of the flow field of MRF fluids. The results show that the flow field formed during gap-varying MRF presents a periodic dynamic change and formation of turbulence. Both the fluid pressure and velocity on the workpiece surface show a periodic change and the maximum fluid velocity on the workpiece surface in the x-direction is much greater than that in the z-direction; the transverse shear velocity contributes to the material removal and abrasive update. Under the same polishing time and rotational speed, the surface roughness is reduced from Ra 6.36 nm to Ra 0.155 nm after MRF without varying gaps for 5 h; in contrast, the surface roughness decreases from Ra 6.44 nm to Ra 0.104 nm after MRF with a varying gap, attaining an atomic step-structure. Properly increasing the frequency and amplitude of gap variations is conducive to achieving a better polishing effect. By conducting real-time force measurement and establishing a material removal function, it is shown that the simulation results match the test results. MRF with a varying gap can increase the polishing efficiency and surface quality by changing the behaviors of the flow field.

Radial Flow Field of Spiral Cochlea and Its Effect on Stereocilia.

The opening of the ion channels ultimately depends on the movement and energy conversion of the microstructural organization. But the role was not yet clear how the active sound amplification function is generated by the microstructure in the cochlear characteristic spiral shape. In this paper, an analytical model of the spiral cochlea is developed to investigate the radial flow field generated by the spiral shape of the cochlea and its effect on the outer hair cell stereocilia, and to analyze the effect of the spiral shape on the micromechanics of the cochlea. The results show that the spiral shape of the cochlea exerts a radial shear force on the hair cell stereocilia by generating a radial flow field, causing the stereocilia to deflect in the radial flow field, with the maximum deflection occurring at the apex of the cochlea. This finding explains from the microscopic mechanism that cochlear spiral shape can enhance low-frequency hearing in humans, which provides a basis for further studies on the contribution of the movement of stereocilia applied by the radial flow field of lymphatic fluid to activate ion channels for auditory production.

Flow Field Measurements Of The Grinding Cooling Liquid Jet

The workpiece cooling by metalworking fluids, which has a significant influence on the workpiece surface layer quality, is not fully understood for industrial grinding processes. This necessitates a significant effort in determining optimal cooling conditions empirically, raising part manufacturing costs. As a solution, a measurement method for the metalworking fluid flow field near the grinding wheel is desired to close the knowledge gap. However, the fluctuating curved surfaces of the coolant cause unpredictable light deflections and reflections, making optical flow measurements difficult. To evaluate the effect of light deflections on the coolant flow measurements, particle image velocimetry is applied in combination with background-oriented schlieren and a ray-tracing approach. Here we study coolant flow measurements in a grinding machine for in-process supply conditions, at first without a working piece and with a focus on the measurability and reliability of the coolant flow from the nozzle exit to the interaction with the rotating grinding wheel. As a result, for the nozzle flow, a systematic measurement deviation of up to 2 % is identified and after the correction, a plausible flow behaviour is obtained. Furthermore, the in-situ measurements of the coolant flow in interaction with the grinding wheel reveal a detailed description of the fluid-workpiece interaction.

Thermal analysis on mutual interaction of temperature stratification and solutal stratification in the presence of non-linear thermal radiations

The mutual interaction of thermal stratification and solutal stratification in mixed convection flow regimes claims many thermal engineering standpoints in daily life and so holds the interest of researchers in the thermal science of fluid flows. Owning to such interest, the current attempt contains a comparative thermal case study on a non-Newtonian fluid flow field subject to inclined surfaces. The stagnation point temperature flow regime is manifested with non-linear radiations, magnetic field, and heat generation/absorptions effects. The physical problem is translated mathematically in terms of a non-linear coupled differential system. The solution is reported by using the shooting method for Jeffrey fluid flow. The surface quantities namely are Sherwood and Nusselt numbers are evaluated for various important physical domains namely radiative flow field, non-radiative flow field, stratified and non-stratified fields, magnetic and non-magnetic fields. We observed that the thermophysical characteristics of stagnation point flow of Jeffrey fluid are enriched in magnitude for the cylindrical surface. Further, the heat transfer normal to the cylindrical surface is higher in magnitude with temperature stratification in comparison with the flow regime without temperature stratification.

Simulation Analysis of Power Consumption and Mixing Time of Pseudoplastic Non-Newtonian Fluids with a Propeller Agitator

In order to study the effect of a high twist rate propeller on the flow field characteristics of pseudoplastic non-Newtonian fluids, the numerical simulation method was used to analyze the mixing flow field of pseudoplastic non-Newtonian fluids at different concentrations in this paper. By changing the rotational speed and the blade installation height, the vorticity, turbulent energy, mixing power consumption, mixing time and mixing energy of the flow field were analyzed. By analyzing and comparing the research results, it was found that increasing the mixing propeller speed can effectively improve the mixing effect. Single-layer arrangement of mixing propeller is not suitable to be placed close to the bottom of the tank, and the mixing of the upper flow field is weaker. Under the same conditions, when the viscosity of pseudoplastic non-Newtonian fluid is increased, the high vorticity and high turbulence energy area is reduced to the mixing propeller area, and the time required for mixing 1.25% CMC solution is 246 times longer than that for mixing 0.62% CMC solution and the required mixing energy also increases sharply. The accuracy of the numerical simulation was verified by experiments. Considering the mixing effect and the mixing power consumption, the single-layer arrangement propeller is more suitable for mixing pseudoplastic non-Newtonian fluids with mass fraction of 0.62% CMC or below. This study can provide a reference for the practical application of propeller mixers to mix pseudoplastic non-Newtonian fluids.