Flow Situations Research Articles

Effect of drag force modeling on the flow of electrostatically charged particles

In CFD simulations of two-phase flows, accurate drag force modeling is essential for predicting particle dynamics. However, a generally valid formulation is lacking, as all available drag force correlations have been established for specific flow situations. In particular, these correlations have not been evaluated for particle-laden flows subjected to electrostatic forces. The paper reports the effect of drag force modeling on the flow of electrically charged particles. To this end, we implemented different drag force correlations to the open-source CFD tool pafiX. Then, we performed highly-resolved Direct Numerical Simulations (DNS) using the Eulerian–Lagrangian approach of a particle-laden channel flow with the friction Reynolds number of 180. The simulations generally revealed a strong influence of the precise drag correlation on particles in the near-wall region and a minor effect on the particles far from the walls. Due to their turbophoretic drift, particles accumulate close to the channel walls. For uncharged particles, the simulations show large deviations of the particle concentration profile in the near-wall region depending on the drag force correlation. Therefore, the disturbance of the flow surrounding a particle by a nearby wall or other particles is important for its drag. Driven by electrostatic forces, charged particles accumulate even closer to the wall. Contrary to the uncharged cases, when the particles carry a high charge (in our case one femto-coulomb), we found minor effects of drag force modeling on particle concentration profiles. In conclusion, for the investigated conditions, we propose to account for the effect of nearby particles and walls on the drag of low- or uncharged particles.

Bulk Viscosity of Dilute Gases and Their Mixtures

In this work, we use the Green–Kubo method to study the bulk viscosity of various dilute gases and their mixtures. First, we study the effects of the atomic mass on the bulk viscosity of dilute diatomic gas by estimating the bulk viscosity of four different isotopes of nitrogen gas. We then study the effects of addition of noble gas on the bulk viscosity of dilute nitrogen gas. We consider mixtures of nitrogen with three noble gases, viz., neon, argon, and krypton at eight different compositions between pure nitrogen to pure noble gas. It is followed by an estimation of bulk viscosity of pure oxygen and mixtures of nitrogen and oxygen for various compositions. In this case, three different composition are considered, viz., 25% N2 + 75% O2, 50% N2 + 50% O2, and 78% N2 + 22% O2. The last composition is aimed to represent the dry air. A brief review of works that study the effects of incorporation of bulk viscosity in analysis of various flow situations has also been provided.

Analysis of buoyancy assisting and opposing flows of colloidal mixture of titanium oxide, silver, and aluminium oxide nanoparticles with water due to exponentially stretchable surface

Energy is essential for a nation's economic growth. Energy is recognized in contemporary society as being crucial to the development of quality of life and sustainability. The environment transforms/absorbs heat and sunlight in a variety of ways. Some of these transitions lead to the flow of renewable energy sources like wind and biomass. Solar energy has become one of the promising alternative energy sources in the future because to the improvements made to enhance its performance. In this context, the impact of solar radiation on modified nanofluid flowover an exponential stretching sheet is examined. Using the proper similarity transformations, the governing equations for the flow assumptions are reduced to ordinary differential equations. The numerical simulation of these simplified equations is then performed using the Runge-Kutta Fehlberg method and the shooting methodology. With the aid of graphs and tables, the effects of numerous parameters on the involved fields are described. Results reveal that the modified nano liquid shows increased heat transport for opposing flow situation than the assisting flow situation for incremented values of porosity parameter and volume fraction. The modified nanoliquid shows increased heat transport for opposing flow situation with respect to augmented values of radiation parameter.

Role of bioconvection on the dynamics of chemically active Casson nanofluid flowing via an inclined porous stretching sheet with convective conditions

ABSTRACT Nanofluids are emerging as a revolutionary replacement for traditional cooling agents. In addition to this, the motile microorganism helps to stabilize the nanofluid. In this direction, the present investigation addressed Casson fluid flow immersed with gyrotactic microorganisms due to an inclined surface. This flow is controlled by incorporating magnetic forces and restricted to passing through porous media. The influence of the chemical activities and heat convection is examined to complete the mathematical description of the flow situation. The total energy involvement is obtained by the addition of resistive heating and viscous dissipation terms in the energy equation. The current flow situation of equations of said physical condition is renovated into the ordinary differential equations (ODEs) with the implementation of proper similarity variables. The numerical solution is developed with the Runge-Kutta scheme. Graphical illustration for respective physical parameters is obtained via MATLAB. The numerical discussion of the present work is validated with previously published literature. The flow motion is controlled by strengthening the magnetic strength. Boost in the Schmidt number and bioconvection Schmidt number reduces the boundary layer thickness.

Investigation of pressure wave propagation and attenuation characteristics in managed pressure drilling by fast switching throttle valve

Pressure waves possess many significant applications in the oil and gas drilling engineering field, such as mud pulse telemetry (MPT) and measurement while drilling (MWD). The focus of this research is to study the pressure wave propagation and attenuation characteristics of wellbore liquid-phase flow in managed pressure drilling (MPD) by fast switching throttle valve (FSTV). First, a mathematical model of transient pressure wave propagation along the wellbore in both upstream and downstream directions is proposed in MPD by FSTV based on the one-dimensional transient flow theory. The model considering the frictional shear effect between the pipe walls is solved by utilizing the method of characteristics. Meanwhile, boundary conditions at the drill string inlet and annulus outlet, at the throttle valve, at the junction of drill bit, and at the reducer are adequately taken into account according to the actual situation of fluid flow. Second, a laboratory experiment of excited pressure waves in a vertical wellbore is conducted to measure the variation of the pressure fluctuation with different pump rates by FSTV. Comparing with the measurement result, the calculation result is discovered that the overall change is consistent, where the maximum absolute relative error at the peak of the pressure wave is only 4.5%. Finally, it further analyzes influential factors affecting the propagation and attenuation behaviors of wellbore pressure waves in liquid-phase flow based on the model. The results indicate that pressure waveforms present sinusoidal wave propagation, and pump rates, pressure wave speed, excitation time, fluid type, mud density, fluid viscosity, and borehole size exert varying degrees of influence on downhole pressure fluctuations. The proposed model achieves accurate quantitative interpretation and analysis of downhole pressure wave in MPD by FSTV, which has important significance for the realization of safe and efficient drilling.

Validation of boundary layer solution for assessing mixing zone dynamics of saltwater wedge in a coastal aquifer

In saltwater intrusion problems of coastal regions, the dynamics of narrower mixing zones are influenced by the amount of dispersive entrainment and its associated marine discharges. Modelling low-fresh water recharge and high-Peclet-number scenarios gives inaccurate results with the available methods. In this study, the physical accuracy of the BL solution provided by Paster and Dagan (2007) and Paster (2010) for such conditions is validated for discharge at outflow face and width of mixing zone (WMZ) with experimentally created datasets and further extended with numerical analysis to quantify the influence of dispersive entrainment on marine discharge and saline circulation. By comparing the measured and estimated saltwater outflows, the average transverse dispersion for all dimensionless freshwater flux rates (a) was calculated, and it ranged from 0.005 cm to 0.062 cm. The study showed that, for buoyancy-dominated, high Peclet number flow circumstances, the boundary layer solutions can be effectively used to predict the marine discharges up to a = 0.5. The combined effects of water flux and dispersion revealed that buoyant force has a considerable impact on the rate of saline circulation as it suppresses the dispersion. The findings lend credence to simplicity of the boundary layer solution in reducing numerical model convergence issues for field problems caused by low recharge and low transverse dispersion flow situations.

Film-Cooling Effectiveness Downstream of a Single Row of Holes With Numberical Modeling in ANSYS-Fluent

With the increasing thrust of aero-engine, the temperature of turbine leading edge gradually exceeded the limit that materials can bear. Therefore, it is a common way to cool the turbine blades with a reasonable structure of film cooling. In this paper, the single exhaust film hole is taken as the main research object, and the effects of jet mass flow ratio, different temperature of mainstream and jet flow on the cooling effect are studied. The main research method is numerical modeling, and the modeling results are compared with the existing experimental results. The results show that the results have some error in jet’s flow situation and fluctuation in cooling efficiency, but there are still some errors in the calculation of heat transfer efficiency, which may be related to boundary layer separation phenomenon and the accuracy of the corresponding turbulence model.

Household flow detection using FEAT (flow estimating accelerometer-thermometer) device

The use of IoT devices in water end use disaggregation verification is an emerging field which offers benefits over conventional approaches, in terms of cost, accuracy and scalability. Having reliably disaggregated water appliance consumption data will enable smart water meter data to be used in household water conservation approaches and for understanding water consumption behaviours. The FEAT device provides a low cost, easily applied and scalable solution that is demonstrated to work even for very low flow conditions of 0.03 l/s. The FEAT device is a combination of a battery, Wi-fi board and MPU6050 sensors providing multi-modal accelerometer and thermometer data. The study places 7 of these FEAT devices onto hot and cold water pipes leading to a shower, which is operated 4 times in a high flow situation, 0.13 l/s, and 4 times in a low flow situation, 0.03 l/s. The data is then analysed and compared with a flow logger to determine if the FEAT device can detect when a domestic appliance is using water. There are limiting cases where the level of noise or external interference limits distorts the data, obscuring the distinguishable peaks in the data due to the similarity of the values. By using high and low pass filtering methods it was possible to enhance the peaks but there are still situations where peaks cannot be detected: for example, if a rigid pipe is not able to vibrate easily or if a hot water boiler is not triggered due to the low flow rate. However, the results show it should be possible to overcome these limiting cases, as it is much less likely for both the vibration and temperature data to be adversely affected by noise or external influences simultaneously, therefore decreasing the effect of noise and external influences. In conclusion, this research paper demonstrates that FEAT devices are a low cost, easily applied and scalable solution for detecting flow. By using high and low pass filtering, placing sensors on freely moving pipes and through the use of multi-modal verification, the FEAT device is shown to work on both metal and plastic pipes even in the lowest flow situations of 0.03 l/s. Therefore the FEAT device is a suitable solution for appliance identification in disaggregation verification datasets.

Investigation on performance of a marine centrifugal pump with broken impeller

As an important auxiliary equipment for ships, the stable operation of centrifugal pumps has a significant impact on the safe operation of ships, so monitoring the operation of marine centrifugal pumps is particularly urgent. In this paper, a marine centrifugal pump is studied for four cases: the normal state, the initial stages of broken state, the intermediate stages of broken state, and the late stages of broken state. The Delayed Detached Eddy Simulation (DDES) with a nonlinear eddy viscosity model is used for the nonstationary calculation of the whole channel, aiming to study the performance of the centrifugal pump in the broken state. A comprehensive analysis of the hydrodynamic characteristics of the centrifugal pump, such as external characteristics, flow situation, pressure pulsation, and flow analysis based on the proper orthogonal decomposition (POD) method, was carried out. Taken together, these results suggest that as the number of broken blades increases, the corresponding head and efficiency gradually decrease. Blade loss mainly affects the uniformity and stability of the flow field, so that the centrifugal pump performance loss increases, which in turn causes the centrifugal pump head and efficiency to decline. It also leads to an increase in radial force during operation, which in turn causes an increase in the amplitude of pump vibration. The results of the study provide some references for the fault diagnosis of centrifugal pumps.

Mixed convection in a lid driven square cavity using lattice Boltzmann method: Effects of thermal gradient direction and moving lid length

This numerical study investigates the effect of thermal boundary conditions and moving lid length on the mixed convective heat transfer and flow regime dynamics in a square top-lid driven cavity. The numerical simulations are performed using an in-house developed thermal lattice Boltzmann solver. Here, the two cavity walls are defined using the opposite pairs of hot and cold isothermal walls. The rest walls are set as adiabatic with zero thermal flux conditions such that a thermal gradient is established either in the vertical or horizontal direction. Additionally, we have varied the size of the moving top-lid to couple the inertia effect with the thermal gradient and investigated how the mixed convective heat transfer and flow regime are affected in the square lid-driven cavity. Here, the Richardson number () is varied as 0.1, 1.0, and 10.0 to cover a wide range of mixed convective flow situations in the lid-driven cavity. is fixed at 106 in all the cases. Qualitative results of the flow regime and heat transfer characteristics are presented as isotherms and streamline patterns. The quantitative information is analyzed by the conduction-convection characteristics along the cavity centerlines and on the boundary walls. It is intuitive to say that the rate of heat transfer or Nusselt number will be higher for larger moving lid lengths, but this is achieved at the cost of higher driving force estimated by the line integral of the shear stress at the moving wall. Additionally, we have defined an efficiency parameter that can relate the heat transfer rate (Nuhot ) with the fluid friction (Cf ). Furthermore, η helps identify the effective and energy-efficient way to achieve the optimized heat transfer in the lid-driven cavity in the considered parametric range.

A Review of Vision-Based Traffic Semantic Understanding in ITSs

A semantic understanding of road traffic can help people understand road traffic flow situations and emergencies more accurately and provide a more accurate basis for anomaly detection and traffic prediction. At present, the overview of computer vision in traffic mainly focuses on the static detection of vehicles and pedestrians. There are few in-depth studies on the semantic understanding of road traffic using visual methods. This paper aims to review recent approaches to the semantic understanding of road traffic using vision sensors to bridge this gap. First, this paper classifies all kinds of traffic monitoring analysis methods from the two perspectives of macro traffic flow and micro road behavior. Next, the techniques for each class of methods are reviewed and discussed in detail. Finally, we analyze the existing traffic monitoring challenges and corresponding solutions.

A novel theoretical model of gas–solid two-phase flow mixed dielectric discharge

A theoretical physical model of gas–solid two-phase flow mixed dielectric discharge in a uniform field based on Townsend's discharge theory is presented. This model extends the classical Townsend's theory to be applicable to the quantitative analysis of dielectric discharge questions related to gas–solid two-phase flow environments, reveals the influence mechanism of flowing gases and solid-phase particles on discharge, and provides a theoretical basis for expanding the application of discharge plasma technology in various fields. In the model, based on the basic physical process of gas discharge and our previous studies, the effects of the attraction and obstructive factors of solid-phase particles on the number density of electrons or ions and the local space electric field in the inception and development of gas discharge were taken into account. On this basis, the analytical expression of the breakdown voltage in a gas–solid two-phase flow mixed dielectric is obtained, Paschen's law of gas breakdown is modified, and Townsend's breakdown criterion for gas–solid two-phase flow situation is proposed. It is shown that the breakdown voltage of the gas–solid two-phase flow mixed dielectric decreases with increasing gas flow velocity. The gas flow velocity is the main factor affecting the variation trend of the breakdown voltage. The concentration and size of solid-phase particles determine the values of breakdown voltage. The breakdown voltage of the smaller size and higher concentration of solid-phase particles is greater, which has a stronger suppression effect on the discharge.

Analysis of entropy generation for Magnetohydrodynamics peristaltic motion of Carreau-Yasuda nanofluid through a curved channel with variable thermal conductivity and Joule heating

Present communication investigates the effects of entropy generation on the MHD peristaltic motion of Carreau–Yasuda nanofluid through a curved geometry with temperature-dependent thermal conductivity. Considered non-Newtonian model depicts the thermophysical properties of graphene nano-powder and Ethylene glycol. The assumed flow situation is modeled considering viscous dissipation, heat absorption/generation, Joule heating, thermophoresis effects, Brownian motion, and slip conditions using lubrication approximation. Numerical computations of resulting non-linear system of equations subject to the related boundary conditions are carried out using NDSolve. Physical behaviors of velocity profile, Bejan number, temperature profile, concentration profile, stresses at the wall, entropy production, mass, and heat transfer rates are computed and presented through graphs and tables. The results indicate that temperature rises and concentration of nanofluids reduces for larger values of thermal slip parameter. In the curved channel, the velocity of fluids decreases by enhancing the Hartman number. Entropy generation is reduced by increasing thermal conductivity parameter. Temperature distribution increases when the Eckert number is assigned higher values. Furthermore, the Hartman number and curvature parameter are observed to enhance the rates of mass and heat transfer at the wall. Additionally, the straight channel results can be obtained for the higher values of the curvature parameter.

Non-linear radiative flow of unsteady Oldroyd-B nanofluid subject to Arrhenius activation energy

It is generally known that the inclusion of nanoparticles improves the thermal conductivity of liquids. Because of their improved thermophysical and rheological properties, these are appropriate for energy transport. The objective of the current analysis is to investigate the thermal transport analysis of unsteady magnetohydrodynamic (MHD) Oldroyd-B nanofluid generated by an impermeable stretching cylinder. An important aspect of this endeavor is to add the effects of Arrhenius activation energy for modified Buongiorno's model of nanofluid. In an axisymmetric flow situation, boundary layer approximations are used to simulate the model equations of thermal energy, momentum, and, concentration for Oldroyd-B nanofluid. To convert the leading PDEs into a nonlinear ODEs system, dimensionless quantities are utilized. The physical consequences of the dimensionless constraints on nanofluid velocity, temperature, and concentration are discussed and revealed via graphs. It is worth noting that enhancing the estimation of the activation energy parameter results in an increase in the nanoparticles concentration field. These findings also provide the impression that as the reaction rate parameter is increased, the rate of heat transfer over the surface of the cylinder drops. Additionally, with enhancing values of the temperature difference parameter, the thickness of the nanoparticle's concentration layer depreciates.

Influence of dedicated lanes for connected and automated vehicles on highway traffic flow

AbstractThe introduction of Connected and automated vehicles (CAVs) promises various social and economic benefits, but safety issues are encountered when CAVs are mixed with human‐driven vehicles (HDVs). This study presents three scenarios as lane operation alternatives for situations in which CAVs and HDVs are mixed. The proposed lane operation scenarios for CAVs are the operation of dedicated lanes (DLs) for CAVs, operation of a DL for CAVs and buses, and the operation of DLs for buses. For each scenario, the effects of the market penetration rate (MPR) on traffic efficiency and safety were evaluated. The following findings were obtained from the results: CAVs had a potential effect on each lane according to the lane operation scenario; traffic efficiency and safety improved in a traffic flow situation where CAVs and HDVs were mixed; traffic efficiency and safety were higher when operating DLs for CAVs than when operating a mixed traffic flow; and efficiency and safety were optimal when operating Scenario 2 (DL for CAVs and Buses) in the early stages of introducing CAV (MPR 10–30%) and operating Scenario 1 (DL for CAVs) in the mid‐ to long‐term stages (MPR 40–80%). These findings provide a basis for preparing new policy alternatives to the current policy of adopting DLs for buses. Furthermore, the evaluation of the effects of each DL operation in the transition period where CAVs and HDVs are mixed will contribute to the operation of an efficient and safe CAV‐based road traffic system.

Validation and evaluation of the CPFD modeling of dense particle flow velocity: Taking particle flow around an obstacle as an example

The computational particle fluid dynamic (CPFD) method is a common approach to simulating dense particle flow, but the direct validation of the CPFD model using the particle velocity distribution is lacking. Taking particle flow around an obstacle as an example, the accuracy of the CPFD method in the simulation of the dense particle velocity field was validated and evaluated in the present study. The particle flow field was experimentally visualized using a quasi-2D flow channel and the particle velocity distribution was measured by a newly-proposed stained-particle image velocimetry technique. The simulated particle velocity using the CPFD method was compared with the measured data and the results indicated that the CPFD method was capable of accurately predicting the particle flow velocity distribution as well as the overall parameters such as the apparent mass flux if the CPFD model parameters were properly adopted. The sensitivity analysis of the simulated particle velocity to the key CPFD parameters was conducted and the results showed that the simulated particle velocity distribution was quite sensitive to the particle pack volume fraction, while the particle stress model parameters and particle-to-wall restitution coefficients show less and close sensitivity in the dense particle flow situations. The recommended model parameters were given in the present study. It is also found that multiple choices of the model parameter combinations could all give accurate overall mass flow predictions but might lead to very different flow velocity distributions with a prediction error even higher than 45%. One should directly verify the CPFD simulated flow velocity using the experimental data if the flow field study was desired.

Numerical Simulation of the Electromagnetic Dross Removal Technology Applied in Zinc Pot of Hot-Dip Galvanizing Line

The forming of zinc dross floating on the surface of molten zinc in zinc pot is inevitable during hot-dip galvanizing production. The cleaning of zinc dross has always been a challenge and a difficult problem to solve. Based on the electromagnetic field theory and its application, a new electromagnetic dross removal technology was proposed, and the zinc dross driven by flowing molten zinc was possible to remove in an electromagnetic field circumstance. Through the coupling simulation of electromagnetic field and flow field, the electromagnetic force acting on molten zinc and the flow situation of molten zinc were simulated. The results showed that electromagnetic field can effectively act on the top surface of molten zinc and affect the flow of molten zinc. Different load conditions of electromagnetic field and the distance between the bottom surface of the iron core and the top surface of molten zinc related to zinc dross removal effect were discussed. Finally, the optimal application parameters of the electromagnetic dross removal technology were put forward.

Temperature Dependence on Transient Hydrodynamic Gravity Driven Flow Down an Inclined Plane

Transient hydrodynamic gravity driven flow of a viscous incompressible fluid down an inclined plane occupying a semi-infinite region of space bounded by an infinite hot plate is studied. The effect of modified Froude number plays an important role in determining the flow situation. Exact solution is obtained by employing Laplace transform method. This problem is concerned with a car – following theory subjected to traffic flow with a decisive importance to a variation of depth with a slope leading to a flood wave. A reducible influence of a frictional drag has an active influence to the flow reversal characteristics with time variation satisfying the separation due to the existance of a modified Froude number. The stabitity of a roll wave is determined by the critical Froude number in a time varying flow. Numerical results of velocity distributions and frictional shear stress are depicted graphically for different values of flow parameters. Numerical results of a critical Froude number are presented in tables. Temperature analysis has been presented analytically with a view to point out the expression of Nusselt number at the plate.

Evaluation of Commercial Corrosion Sensors for Real-Time Monitoring of Pipe Wall Thickness under Various Operational Conditions.

In this study, we investigated the performance and reliability of commercial corrosion sensors for monitoring the integrity of piping systems in various fluid environments as an alternative to ultrasonic transducers. To this end, we investigated pipes’ wall-thinning using commercial electrical resistance (ER), linear polarization resistance (LPR), and ultrasonic transducer (UT) sensors under various operating environments. A pilot-scale closed-loop test bed was built to simulate a real pipeline flow situation, from which the sensor data were collected and analyzed. Experimental results indicate that, in the case of the LPR sensor, it is challenging to accurately measure the corrosion rate when a specific measure exceeds the threshold in a severe corrosion environment. In contrast, the ER sensor could measure metal loss under all conditions and reflect the corresponding characteristics. The metal loss (about 0.25 mm) of the real pipe after the experiment was confirmed to be equal to the metal loss (0.254 mm) measured by the sensor. Furthermore, the regression analysis revealed a high correlation between the results obtained from the ER and UT sensors. Thus, evaluating the remaining thickness of the piping system using the commercial ER sensor is deemed to be effective and reliable.

Shape optimization during design for improving outdoor wind comfort and solar radiation in cities

This paper delivers an idea of weather-based optimization as a sustainable design strategy addressing the changing climate. An environment-driven design technique is introduced and tested at the urban and architectural scale. Utilizing the interplay between the architectural intention and weather influences (specifically solar radiation and wind effects), the optimal design solution for the urban configuration and architectural shape emerges. An exploratory case study near the amphitheater in Kosice, Slovakia, demonstrates the proposed approach. Through the real-time iterative analysis of the environmental performance of multiple design variants, an urban concept of offices/apartment blocks, reacting to the local wind and sun situation, is formed. The wind flow situation and comfort are investigated in a design loop, blending the newly developed AI-driven simulation prediction models of InFraRed11InFraRed: AI-based real-time analysis of wind, sun, and thermal comfort in the streets developed by the CIL of the AIT in Vienna, Austria. and the sun hours analysis in Ladybug with the Galapagos optimization within Grasshopper. The final step of this method is the design and subsequent wind and sun analysis of fluid-shaped lamellae in three variants acting as wind catchers/shading systems. Improved pedestrian wind comfort for outdoor sitting (more than 30% increase in areas suitable for short and prolonged sitting) and optimum sunlight hours (25% gain in sunlight during winter solstice) is achieved using the proposed technique.