Rectangular Obstacles Research Articles

Effects of impacted dynamic hollows and extending dense drops on the concave surface with practical obstacles

In this study, the center of a concave surface was analytically studied using the volume of fluid approach to simulate hollow and dense droplets on a variety of solid obstacles. OpenFoam software was used to carry out the numerical simulations. The hollow droplet’s fluid phase, Glycerine, has an outer diameter of 5.25 mm and its gas phase, air, has a diameter of 4 mm. We looked at the laminar flow of an incompressible Newtonian fluid phase. Jet characteristics and droplet collision hydrodynamic behavior were investigated. Due to the interaction between droplets and shells on the obstacle’s surface and the concave surface, which causes a pressure difference and improves fluid movement, the largest jet size is consequently produced in rectangular obstacles. The sharp obstacle, on the other hand, molds the jet’s shortest length and height.

Optimization Method of RFID Reader Antenna Deployment in Obstacle Environment Based on Improved FA

The aim of this study is to solve the problem of RFID reader antenna deployment when an obstacle in the environment or the material itself is an obstacle. The article establishes a new reader antenna constraint model based on the rectangular obstacle RFID antenna deployment optimization environment model and the reader antenna sensing model containing Gaussian distribution noise probability and applies the improved firefly algorithm to find the optimum with coverage rate, interference degree, and load balance function as multiobjective functions. First, to obtain a uniform traversal of the target space, and a cube mapping is applied for chaos initialization. Second, a weighting model is proposed to control the speed of firefly variation and combine the variable step strategy of elite individuals to expand the movement step of elite individuals and reduce the movement step of nonelite individuals to improve population diversity. Finally, to improve the algorithm’s continuous optimality-seeking ability, a Gaussian variation operation strategy based on elite fireflies is introduced to ensure the algorithm’s optimality-seeking throughout the process.

Learning by neural networks under physical constraints for simulation in fluid mechanics

The Physical Informed Neural Networks (PINN) model is one of the emerging and promising Deep Learning approaches to predict physical phenomena governed by PDEs such as fluid flow dynamics. The PINN model is indeed of great importance for improving the accuracy of machine learning methods for predicting mass transfer problems. However, it is sensitive to the accuracy of input datasets, and also struggles to predict phenomena occurring in complex geometries. These two weaknesses could limit the application of the PINN model. In this article, we improve the use of the PINN model by combining it with a One-hot matrix model to better take into account the boundary conditions on complex geometries. The use of the One-hot matrix is also investigated with non-uniform weights from physics. We indeed used the Q-criterion as a non-uniform weight to enforce the vortical structure location by the neural network. The proposed model more accurately predicts the two-dimensional flow around sharp rectangular obstacles from low-resolution datasets.

Significance of Aspect Ratio Parameter on a Solid Oxide Fuel Cell with Rectangular, Trapezoidal, and Triangular Obstacles in the Flow Channel

Significance of Aspect Ratio Parameter on a Solid Oxide Fuel Cell with Rectangular, Trapezoidal, and Triangular Obstacles in the Flow Channel

Analytical Solution for Wave Scattering by a Surface Obstacle above a Muddy Seabed

We present an analytical solution for the scattering of linear progressive waves by a surface rectangular obstacle above a muddy seabed. The bottom cohesive mud is assumed to act as a Newtonian fluid, and the thickness of the mud layer is considered to be comparable to the Stokes boundary layer thickness. Our analytical results based on the matched eigenfunction expansions incorporate the combined effects of obstacles and a fluid mud bottom. By reducing the mud layer thickness or the dimensions of the obstacle to zero, the present study recovers the classical solution for wave scattering by a surface obstacle above a solid bed or wave propagation over a layer of fluid mud. Our analytical predictions of wave amplitudes and wave forces acting on the bottom of the obstacle agree satisfactorily with the available numerical results. The most prominent effect of a muddy seabed is a strong damping of wave amplitude. Parameter study reveals that the obstacle submerged depth, mud layer thickness, and wave frequency can have significant impacts on the attenuation of wave amplitude due to the presence of a muddy seabed.

Gas-liquid hydrodynamics with different liquid viscosities in a split-and-recombine microchannel

Split-and-recombine (SAR) technology has shown great potential in the passive intensification of mass transfer. However, the gas-liquid flow is rarely encountered in the SAR microdevices. In this work, the flow regime, void fraction, and pressure drop of gas-liquid flow were experimentally studied in a common SAR microchannel designed with a curved divergence-convergence channel and rectangular obstacles. Parameter studies were conducted by varying the flow rates of nitrogen/glycerol aqueous solutions and glycerol contents. Four flow regimes, namely, total breakup, partial breakup, abnormal breakup, and annular flow are observed with a high-speed camera. The flow map and correlations to predict the regime transitions are presented based on the liquid-phase Capillary number (0.0022-1.016) and gas/liquid rate (0.5-5). Furthermore, the modified frictional factor is correlated with Capillary and Reynolds numbers based on the flow regimes. Overall, the SAR microchannel is a promising candidate as the high-efficient gas-liquid contactor in terms of mass transfer rate, product selectivity, and energy efficiency for highly viscous liquids. A reasonable match of bubble length and the number of SAR units for the total breakup of bubbles is required. This study can contribute to the design, optimization, and regulation of the SAR microchannel for gas-liquid flows.

Overturning and rollover characteristics of a tractor through dynamic simulations: Effect of slope angle and obstacles on a hard surface

The lateral overturning and backward rollover characteristics of a tractor driven on a hard surface were analysed depending on the ground slope angle and the shape and height of obstacles. The size and material properties of a tractor were used to create a 3D simulation model using a commercial dynamic simulation program. The simulation model was verified using tractor certification test results. For the simulations, ground slope was set to a maximum of 50° and four heights were applied to three different shapes of obstacle. Tractor driving speeds at which lateral overturning and backward rollover occurred were determined using each condition. The results revealed that the factor that contributed the most to the overturning and rollover of the tractor was ground slope, followed by the obstacle height and then obstacle shape. As the obstacle height and ground slope increased, the tractor became vulnerable to lateral overturning and backward rollover based on the height of its centre of mass and angular velocity in the rolling direction. Backward rollover occurred when the slope was mild and lateral overturning occurred above a certain slope angle. Depending on the obstacle shape, the sensitivity to lateral overturning and backward rollover varied with sinusoidal-shaped obstacles making the tractor relatively vulnerable to lateral overturning, whereas rectangular obstacles made it vulnerable to backward rollover. Therefore, on steep slopes, where lateral overturning occurs, sinusoidal-shaped obstacles are more risky, whereas on flat ground, where backward rollover occurs, rectangular obstacles are more risky. • Lateral slope angle and obstacle shape selected as main influencing factors. • Comprehensive analysis conducted on impact of slope angle and obstacle. • Three different obstacle shapes used: rectangular, right-triangular, and sinusoidal. • Ground slope maximum 50° and obstacle height maximum of 400 mm. • Speed of the tractor when overturning and rollover occurred determined.

Existence and uniqueness result for a fluid–structure–interaction evolution problem in an unbounded 2D channel

In an unbounded 2D channel, we consider the vertical displacement of a rectangular obstacle in a regime of small flux for the incoming flow field, modelling the interaction between the cross-section of the deck of a suspension bridge and the wind. We prove an existence and uniqueness result for a fluid–structure-interaction evolution problem set in this channel, where at infinity the velocity field of the fluid has a Poiseuille flow profile. We introduce a suitable definition of weak solutions and we make use of a penalty method. In order to prevent the obstacle from going excessively far from the equilibrium position and colliding with the boundary of the channel, we introduce a strong force in the differential equation governing the motion of the rigid body and we find a unique global-in-time solution.

Numerical treatment of finite difference method for solving dam break model on a wet-dry bed with an obstacle

In this paper, we propose four different numerical methods for solving the Non-Linear Shallow Water Equations (NSWE), which are used to study dam-break flow over an obstacle. The discrete equations are formulated by applying various finite difference methods with filter involving wet-dry procedure. To validate our numerical model, several benchmark tests are carried out. Comparison of the computed results with the analytical and experiment data shows that our numerical model reproduces the flow with high accuracy. Moreover, we examine the effect of the shape and dimensions of the obstacle on downstream water height. Rectangular obstacles reduce downstream water height more significantly than triangular and trapezoidal ones. Downstream water height decreases non-linearly as obstacle height and width are increased.

Impacts of Rectangular Obstacle Lengths on Premixed Methane–Air Flame Propagation in a Closed Tube

Impacts of Rectangular Obstacle Lengths on Premixed Methane–Air Flame Propagation in a Closed Tube

3D numerical simulation of dam-break flow over different obstacles in a dry bed

Abstract In this research, a numerical investigation was carried out on the effect of obstacle presence on the water flow during the dam-break in a dry bed. The validity of the numerical simulations was confirmed after comparing the results with the experimental evidence. Rectangular, trapezoidal and triangle obstacles were simulated numerically to explain the obstacle effect on the water flow. Water surface tracking and turbulent flow were modeled using the Volume of Fluid (VOF) method and the standard k-ω model, respectively. Pressure and velocity variations during the dam-break flow are presented and analyzed.

Bubble dynamics and mass transfer enhancement in split–and–recombine (SAR) microreactor with rapid chemical reaction

In this study, a split–and–recombine (SAR) microreactor which is composed of convergent–divergent arc channel and rectangular obstacles was designed, and its enhancement characteristics in gas–liquid rapid chemical absorption system were explored. In the SAR microreactor, the deformation, splitting, stretching and breakup of bubbles are monitored by a high–speed camera. Accordingly, the bubble velocity pulsation caused by SAR structure is analyzed. The squeezing mechanism for bubble breakup located on the front surface of the obstacle is revealed. Two breakup patterns, namely complete and partial breakup, are observed, and the mass transfer performance is highly related to them. The mass transfer enhancement factor (Eka) of SAR structure increases with gas/liquid flow rate in complete breakup pattern while decreases in partial breakup pattern. The increase of gas–liquid flow rates and the number of SAR units, or slower reaction rate strengthens the velocity fluctuation and bubble breakup, resulting in an increase in Eka, with a maximum value of 2.74. Overall, the SAR microreactor performs comparable to Corning Advanced Flow Reactor in term of mass transfer energy efficiency. This work guides the application of SAR microreactor in rapid gas–liquid chemical reaction system.

New application of MOL-PACT for simulating buoyancy convection of a copper-water nanofluid in a square enclosure containing an insulated obstacle

<abstract> <p>In this study, we have simulated transient and steady state free convection flow and heat transfer inside a square enclosure filled with a copper-water nanofluid of spherical shape nanoparticles following Tiwari-Das model. The cavity containing an insulated rectangular obstacle of height ranging from 0% to 50% of the cavity side-length. The vertical sides of the enclosure are kept at different temperatures, while the flat sides are assumed to be adiabatic as the obstacle. The combined method of lines/penalty-artificial compressibility technique (MOL-PACT) has been applied to solve the dimensional time dependent mathematical model after converting it into a non-dimensional structure. The combined method of lines/penalty-artificial compressibility technique is recently successfully applied to simulate free convection of MHD fluid in square enclosure with a localized heating. The extension of this promising technique for studying heat transfer of nanofluids is one of the objectives of this paper. Another objective of the study is to inspect the impact of several model parameters such as, the obstacle height, nanoparticles volume-fraction, nanoparticles radius and Rayleigh number on streamlines, temperature distribution and Nusselt number as an expression of heat transfer inside the enclosure. The results have been discussed and shown graphically. Comparisons with former results for related cases in the literature are made and reasonably good agreements are observed.</p> </abstract>

Impacts of Rectangular Obstacle Lengths on Premixed Methane-Air Flame Propagation in a Closed Tube

Impacts of Rectangular Obstacle Lengths on Premixed Methane-Air Flame Propagation in a Closed Tube

Near Source Modeling of Pollutant Emissions From an Elevated Source Over an Urban Area Under Cross High Ventilation

Abstract Due to the rapid urbanization of many cities around the world, industrial manufacturing plants have grown rapidly, thus leading to the release of large amounts of pollutants into the environment. This is the main reason for the degradation of the local air quality, resulting in an increased risk of unfavorable sanitary conditions for city dwellers. Understanding the dispersion of pollutants in local population environments, meteorological conditions and other physical characteristics is fundamental for predicting and evaluating air quality. This paper provides comprehensive details on the study of flow patterns and pollutant dispersion processes in urban areas. Several factors which include building geometry, local atmospheric effects, structural obstructions, and velocity of exhaust pollutants are examined considering field data, wind tunnel tests, operational simulation techniques, and computational fluid dynamics. Good agreements are noticeable. Simultaneous evolutions of the velocity, thermal and scalar mass fraction fields of the pollutant emitting from a three-dimensional elevated source around a rectangular obstacle placed on a turbulent boundary layer wall, and also downstream the obstacle, have been successfully carried out. The most serious pollutant levels in urban areas under various high wind velocities are identified.

Computational Investigation of Micro-channel Heat Sink with Rectangular Shape Obstacles

Nowadays a lot of interest is given to the geometrical modification of heat sink systems to cool down the electronic components. To improve the performance index of the heat sinks, the use of geometrical features with different shapes and at different locations on the surface can be a valuable approach. In this paper, the effect of rectangular shape obstacles on the micro channel heat sink (MCHS) performance is studied. Due to surface features, vortex is developed which helps to increase the heat transfer rate. Numerical modeling software Comsol Multiphysics with heat transfer in fluid physics is used to investigate the characteristics of a micro-channel heat sink. The numerical result shows that the heat transfer rate can be improved through an appropriate arrangement of rectangular shape obstacles, on the heat sink. Numerical analysis and the comparison is carried out for micro-channel heat sink with and without obstacles. In this paper, various parameters like temperature rise, cell Peclet number and Mean effective thermal conductivity are studied.

An experimental study on turbine vane Leading-Edge film cooling with deposition

• Impacts of particle deposition on film cooling at turbine leading-edges are highlighted. • Early-stage deposition effects are experimentally simulated by injecting molten wax droplets. • Dynamic deposition process is documented by a transient infrared thermography technique. • Effects of deposit thickness on leading-edge film cooling are coupled with coolant blowing ratios. Deposition of particles ingested into the hot turbine component of an aircraft engine could lead to degradation of turbine cooling performance and thus reduces service lifetime. It is thereby critical to gain basic knowledge of the deposition effects on the turbine cooling, of which cooling for the vane leading edge, where hot gas stagnates, is intricate. In this work, liquid wax is air-atomized into micro droplets to simulate a particle-laden flow condition where a vane leading-edge model cooled by five rows of staggered holes is immersed. To take circumferential pressure gradient at the leading edge of a real turbine vane into consideration, a rectangular obstacle is designed ahead of the test model and is shifted towards one side to form pressure and suction sides around the leading edge. Particularly, cooling effectiveness is measured by using an infrared thermography (IR) technique at an early-stage deposition for blowing ratios of 0.5–1.6. Additionally, an array of real-time IR images of surface temperatures is gathered to document the dynamic changings of film cooling with the accumulation of deposits on the leading edge for a longer exposure. Comparisons between the deposition and non-deposition cases reveal that for the incipient deposition, the deposits are helpful to improve cooling effectiveness except for the optimum blowing ratio of 0.8 at which film cooling on the non-deposition model has the best performance. Because of the high-pressure surroundings, the hole rows on the pressure side are more sensitive to deposition, where increases of 0.05–0.15 in cooling effectiveness are found due to deposition. Moreover, dynamic deposition shows that the heavy deposits and heating effects of the warm particles could generate a reduction of cooling effectiveness up to 76% for a longer exposure. The added value of this study lies in providing a better understanding of the deposition effects on film cooling at the turbine vane leading edge, which is helpful to design a robust cooling scheme for this region to withstand the deposits.

Numerical analysis for the effects of heat transfer in modified square duct with heated obstacle inside it

This article deals with numerical analysis of two-dimensional viscous fluid in modified square duct. A rectangular obstacle with constant temperature at walls is placed inside it. Flow duct is depicted in Figs. 1 and 2. Influence of Prandtl number and geometry on heat transfer of working fluid is studied in two cases. Computation for the present model is made in commercial package ANSYS-Fluent. Calculations are carried at two different values of Reynolds numbers i.e., Re 40 and 200 for each of the cases. Liquid water (H20) and Liquid Aniline (C6H5NH2) are taken as working fluids. Stream functions, isotherms, vorticity, velocity and pressure profiles are examined. Graphical data for Cf and Nu is presented to analyze the effect of Reynolds number and Prandtl number on heat transfer. Thermal boundary layers are discussed in each of the cases. It is shown that heat transfer has high dependance on Reynolds number and Prandtl number. Geometry of the problem has noticeable effect on heat transfer.

Off-line exploration of rectangular cellular environments with a rectangular obstacle

In this paper, we consider exploring a known rectangular cellular environment that has a rectangular obstacle using a mobile robot. The robot has to visit each cell and return to its starting cell. The goal is to find the shortest tour that visits all the cells. We give a linear-time algorithm that finds the exploration tour of optimal length. While the previous algorithms for environments with obstacles are approximation, the algorithm is presented in this paper is optimal. This algorithm also works for L-shaped and C-shaped environments. The main idea of the algorithm is, first, to find the longest simple exploring cycle, then extend it to include the unvisited cells.

An improved CIP-based numerical model for simulating free-surface flow with adaptive mesh

In this paper, an improved CIP (constrained interpolation profile)-based numerical model, which combines with Afivo (Adaptive Finite Volume quadtree/Octree mesh, an adaptive mesh framework), has been presented to simulate free-surface flow. In the CIP-based model, the constrained interpolation profile (CIP) method, a high-order finite difference method, is employed as the base flow solver and THINC/SW (Tangent of Hyperbola for Interface Capturing with Slope Weighting) method, a volume of fluid method, is applied to capture the flow interface. In this present model, an adaptive mesh technique is introduced to reduce the computational cost and multigrid technique is used to improve the solution efficiency. In the adaptive mesh system, new spatial interpolation schemes are provided, which have better performance in mass conservation compared with schemes provided in Afivo. Lid-driven cavity flow test was carried out to validate the accuracy of the flow solver with adaptive mesh and two/three-dimensional interface benchmark tests were performed to test the reliability of the interface capturing scheme and spatial interpolation schemes. Then two/three-dimensional applications (dam-break flow case, tank sloshing case and dam-break flow over a rectangular obstacle case) were investigated to demonstrate the model accuracy. The numerical results were compared with the previous experimental and numerical results, and good agreements were observed. It is demonstrated that the present numerical model has good applicability in modeling the free-surface flow.