Semi-circular Obstacle Research Articles

Expression of Concern: Examine the Lattice Boltzmann Method for the Mixed Convection Simulation of Water/Al2O3 Nanofluid in a 2D Rectangular Cavity under Radiation with Isothermal Semicircular Obstacles

Expression of Concern: Examine the Lattice Boltzmann Method for the Mixed Convection Simulation of Water/Al2O3 Nanofluid in a 2D Rectangular Cavity under Radiation with Isothermal Semicircular Obstacles

Fiber reorientation due to obstacles in open channel flow

A model along with experimental validation is presented for fiber re-orientation within the flow of a thin fluid layer down an inclined plane. Unlike the usual approach (Jeffery), the model accommodates the fast-changing velocity gradient defying linearization and the flow constraints due to the thin thickness of the fluid film. Model equations are formulated, and the algorithm for the fiber rotation is developed. The velocity field within the channel is obtained, using COMSOLTM multiphase simulation. The formulated model equations are used to track the orientation of a single fiber. The spatial fiber orientation state is described in terms of the second order tensor by tracking multiple individual fibers with different initial orientations. To validate the model's predictions, an experimental setup was fabricated to record individual fiber kinematics during the flow and to describe the orientation of fibers in the open channel. A novel benchmark for assessing fiber re-orientation models is presented, wherein the dynamics of fiber orientation is observed in response to a semicircular obstacle within the fluid flow. The experimental results are compared to model predictions and are in reasonable agreement. Despite the simplified approach, both the dynamic of single fiber and the development of fiber orientation distribution due to the obstacle can be reasonably predicted.

Experimental study on the flow field geometry of the PEM fuel cell bipolar plates: The effects of various shaped blocks embedded in serpentine pattern on cell performance

The flow field pattern is crucial in many aspects such as cost-efficiency (in terms of excessive fuel consumption), water management on the cathode side, and achieving a high cell performance. The studies on the reconnaissance of much more effective flow field design have been continuing for years. As a matter of fact, it may be succeeded with some manipulations on the flow area. The current research proposes to investigate the effects of blocks in various shapes and positions on the net power output by changing the shape of the channels in the flow field (FF). For this reason, semicircular and triangular blocks were machined on the serpentine channels and their short-term performances were compared with the conventional serpentine pattern. In addition to the related new FF designs, performance evaluation was made by using nickel foam placed to fill the inner part of the serpentine FF. First, ultimate operating conditions were optimized with the traditional serpentine FF. Then, the performance outputs of the proposed FF designs were compared under the same conditions assigned in the previous section. The single-cell performance tests yielded that the highest power density was ensured with nickel foam (NF)-serpentine FF with 0.267 W/cm2. This increment corresponds to a 38 % enhancement in the power output when compared to the classical serpentine-type FF. Triangular (T) and semicircular (S) obstacles increased the performance significantly. Each manipulation on the traditional serpentine FF affected the power output positively, essentially. The pattern structures of the diagonal semicircle (DS) and diagonal triangular (DT) FFs reduced both water evacuation ability and performance increase rate. NF-serpentine FF contact highly decreased the ohmic resistance level of the cell when compared to the other designs according to the impedance (EIS) measurements. In addition, a correlation was observed between the performance and pressure drop test results. The highest-pressure drop was recorded with NF-serpentine FF (4.225 kPa) whereas the lowest is conventional serpentine FF (0.55 kPa). Traditional serpentine pattern is famous for with high-pressure drop structure. Consecutively, the pressure drop tests proved that the manipulations increased the pressure level of the system directly.

Microfluidic fabrication using cyclic olefin copolymer and hydrocarbon solvents

Cyclic olefin copolymer (COC) is a promising material in microfluidic applications due to their unique physical, chemical, and optical properties. This study implements a new and versatile fabrication process to fabricate COC microchannels, combining the fabrication and bonding processes in a single step, taking advantage of COCs’ swelling behavior in linear non-polar hydrocarbon solvents and their chemical compatibility with photolithography. Dodecane was selected as the hydrocarbon solvent based on the degree of swelling and Flory-Huggins interaction parameter, which resulted in the highest degree of swelling and affinity to COC. The effect of dodecane immersion time on the COC microchannel height was investigated, achieving a maximum average height of 50 ± 3 µm after 180 min. Bonding quality was quantified by a leakage test (maximum flow rate of 1730 ± 205 µL/min (Re = 237)), and a tensile test (800 ± 90 kPa). Furthermore, the effectiveness of the implemented process was demonstrated through the successful execution of three highly diverse microfluidic applications. These applications included a serpentine microchannel featuring semicircular obstacles that facilitated passive mixing, pinched flow fractionation which enabled the separation of a system of three different sizes of microparticles, and droplet microfluidics that allowed for the efficient generation of water in oil droplets.

Motion of a neutrally buoyant circular particle in a lid-driven square cavity with a semicircular obstacle

Understanding, predicting and controlling the motion of the solid particles in the square cavity with obstacles are important. This work performs a lattice Boltzmann study on the motion of a neutrally buoyant circular particle in a lid-driven square cavity with a semicircular obstacle, where the effects of Reynolds numbers and initial positions of the circular particle on the motion of the circular particle are investigated. The motion of the circular particle is affected significantly by the semicircular obstacle, which is quite different from the case without obstacles. With the increase of the Reynolds number, the motion of the circular particle is divided into three stages. At low Reynolds numbers ([Formula: see text]), similar to the case without obstacles, no matter where the initial position of the circular particle is, the limit cycle of the circular particle is the same. Beyond a critical Reynolds number (between 800 and 900), the limit cycle of the circular particle is dependent on the initial position of the circular particle obviously, which is attributed to the opposing centrifugal and wall-repulsion forces.

Examine the lattice Boltzmann method for the mixed convection simulation of water/Al2O3 nanofluid in a 2D rectangular cavity under radiation with isothermal semicircular obstacles

The present study simulated the mixed convection (MCXN) of the water/Al2O3 nanofluid (NFs) in a two-dimensional rectangular cavity in the presence of radiation. The top and bottom walls were assumed to be cold and hot, respectively, with the lateral walls being insulated. A magnetic field (MGF) with a Hartmann number (Ha) of 0–40 was applied to the NFs within the cavity. The simulations were carried out at a Richardson number (Ri) of 1 and a Rayleigh number (Ra) of 105 for cavity heights of 0.5–2.0 to evaluate heat transfer (HTF) on the walls and analyze fluid rotation within the cavity. The lattice Boltzmann method (LBM) was used to perform the simulations. It was found that the incorporation of radiation into the system reversed the flow rotation in the cavity and increased the Nu. A rise in the radiation parameter from 0 to 0.2 led to a 2.8-fold larger Nu on the cold wall. A rise in the cavity height decreased the Nu, and a further increase in the height increased the Nu on the wall. An increased Ha had an insignificant effect on the Nu at small cavity heights but decreased the Nu on the wall at large cavity heights.

RETRACTED: Utilization of machine learning and neural networks to optimize the enclosure angle, magnetic field, and radiation parameter for mixed convection of hybrid nanofluid flow next to assess environmental impact

This paper examines the mixed convective heat transfer (HTR) of nanofluid (NFD) flow in a rectangular enclosure with the upper moving wall numerically. The lower wall has a high temperature and a number of semi-circular obstacles with the same temperature are installed on it. The upper moving wall has a low temperature and the other two walls are insulated. The enclosure can change from horizontal to vertical. Radiation HTR is considered in the enclosure and there is a magnetic field (MGF) that can change the angle from horizontal to vertical affecting the NFD. This study is carried out for different angles of the enclosure and MGF from horizontal to vertical for radiation parameters (RDP) of 0 to 3 and a constant MGF with Hartmann number of 20 and Richardson number of 10. The aim is to estimate the Nusselt number (Nu), entropy generation (ETG), and Bejan number (Be). The SIMPLE algorithm is utilized using FORTRAN software, and optimization is done using artificial intelligence to find the maximum and minimum output values. The results demonstrate that the maximum value of Nu and Bes corresponds to the MGF angle and enclosure angle of 90°. The minimum value of the Nu and the maximum amount of ETG corresponds to the horizontal MGF and horizontal enclosure when the RDP is 1.5. An increment in the RDP enhances the amount of Nu. The maximum amount of ETG, i.e. 12.87, corresponds to the enclosure with an angle of 45° for the horizontal MGF and the absence of RDP. corresponds to the enclosure with an angle of 45° for the horizontal MGF and the absence of RDP. It was also found that most environmental impacts, and hence values for different environmental factors, arise from the production of nanoparticles; thus, it is a significant contributor to environmental impacts.

Statistical Analysis of Hydrodynamic Forces in Power-Law Fluid Flow in a Channel: Circular Versus Semi-Circular Cylinder

This numerical study is about the steady incompressible non-Newtonian fluid flow in a channel with static obstacles. The flow field is governed by the Generalized Navier-Stokes equations incorporating the constitutive relation of power-law fluids. Three cases are considered: 1) circular obstacle(C1), 2) semicircular obstacle(C2), and 3) both circular and semicircular obstacles. A range of values of the power-law index0.3≤n≤1.7are considered atRe=20to check the impact of shear-thinning and shear-thickening viscosity on the drag and lift coefficients. The correlation between drag and lift coefficients is calculated against the power-law index. The simulated results of velocity and pressure are investigated at different sections of the channel. Benchmark results of drag and lift for the Newtonian fluid are reproduced as a special case. A strong positive correlation is observed between drag and lift coefficients in the case of a single obstacle, while in the case of dual obstacles and inverse correlation, drag and lift coefficients have been found.

Downstream semi-circular obstacles' influence on floods arising from the failure of dams with different levels of reservoir silting

Dam-break wave propagation in a debris flood event is strongly influenced by accumulated reservoir-bound sediment and downstream obstacles. For instance, the Brumadinho dam disaster in Brazil in 2019 released 12 × 106 m3 of mud and iron tailings and inflicted 270 casualties. The present work was motivated by the apparent lack of experimental or numerical studies on silted-up reservoir dam-breaks with downstream semi-circular obstacles. Accordingly, 24 dam-break scenarios with different reservoir sediment depths and with or without obstacles were observed experimentally and verified numerically. Multiphase flood waves were filmed, and sediment depths, water levels, and values of front wave celerity were measured to improve our scientific understanding of shock wave propagation over an abruptly changing topography. Original data generated in this study is available online in the public repository and may be used for practical purposes. The strength of OpenFOAM software in estimating such a complex phenomenon was assessed using two approaches: volume of fluid (VOF) and Eulerian. An acceptable agreement was attained between numerical and experimental records (errors ranged from 1 to 13.6%), with the Eulerian outperforming the VOF method in estimating both sediment depth and water level profiles. This difference was most notable when more than half of the reservoir depth was initially filled by sediment (≥0.15 m), particularly in bumpy bed scenarios.

Optimization of photochemical machining process for fabrication of microchannels with obstacles

ABSTRACT The microchannels are one of the most prominent components used in Lab on a chip device for mixing applications. For effective mixing, microchannels with obstacles are commonly used. Design and fabrication of a microchannel with obstacles (micro features) is a crucial one. By considering this motivation, a study on optimization of control parameters for fabrication of different microfeatures on copper and brass using photochemical machining (PCM) is carried out. The control parameters such as etchant concentration, etching temperature and time were considered to measure material removal rate (MRR), surface roughness (Ra) and the edge deviation (ED). In order to have better PCM performance, MRR desired to be higher, while Ra and ED are desired lesser. To obtain optimum conditions for attaining the higher MRR with lesser ED and Ra, Overall Evaluation Criteria (OEC) was articulated. Further, characterization has been carried out employing scanning electron microscopy. Finally, as an application of the study, different master molds of microchannels without and with triangular, semi-circular, and square obstacles were fabricated and using these molds, Polydimethylsiloxane (PDMS) microchannels were fabricated employing soft lithography technique. On the basis of fluid flow analysis, fabricated microchannels found to be suitable for the various microfluidic applications.

Characteristics of thermal transpiration effect and the hydrogen flow behaviors in the microchannel with semicircular obstacle

The thermal transpiration effect has great potential applications for the hydrogen energy. In this paper, the thermal transpiration effect and the hydrogen flow behaviors are studied in the microchannel with the semicircular obstacles. Firstly, the slip boundary model is used in the simulation of the flow performance in the microchannel. The validity of the model at different Kn is verified by comparing with some previous work. Then, the hydrogen flow characteristics of the thermal transpiration effect with the semicircular obstacle are investigated. The result shows that as the size of the semicircular obstacle increases, the hydrogen flow path of the thermal transpiration effect becomes longer, and the temperature gradient decreases. As the characteristic length of the hydrogen flow decreases, there is an obviously negative influence on the thermal transpiration flow. A deeper analysis shows that the thermal driven flow and the pressure driven flow will produce y-component velocity, which leads to a backflow under the effect of semicircles, and the semicircular obstacles make the Knudsen layer spread to the channel center.

Numerical and experimental investigations on the performance of a serpentine microchannel with semicircular obstacles

This paper focuses on computational and experimental analysis of a simple serpentine microchannel without obstacles and serpentine microchannel with semicircular obstacles of different sizes. The work has been performed in three phases- computational analysis, experimentation and flow physics study. The 3D models of a simple serpentine microchannel (without obstacles) and serpentine microchannels with semicircular obstacles (with radius as 50, 100, 150 and 200 µm) have been developed using COMSOL Multiphysics software. The effect of obstacle size on pressure drop and mixing length for achieving index 1 has been analyzed. A simple serpentine qmicrochannel and a serpentine microchannel with 150 µm radius semicircular obstacles have been fabricated with polydimethylsiloxane using soft lithography process. The experimental analysis for pressure drop as well as mixing index has been performed. A good agreement has been observed between experimental and computational results. The validated computational model is then used to study the mixing index for the same microchannels for different flow conditions, i.e. for different Reynolds numbers. The mixing lengths are observed to be lesser for Re 0.28 and 30. Further, the effect of diffusion and generation of secondary flow due to advection on mixing length for the considered Reynolds numbers are analyzed through the flow physics study.

Self-healing of tightly focused scalar and vector Bessel–Gauss beams at the focal plane

The property of self-healing at the focal plane for both scalar and vector Bessel-Gauss (BG) beams is investigated in the tight focusing condition. For the BG beam, which is partially obstructed at the pupil plane, the spatial intensity distribution at the focal plane is well recovered. Furthermore, recovery of not only intensity but also polarization distribution is observed for an obstructed vector BG beam. This self-healing effect for both the intensity and polarization components is recognized even when the half of the beam is obstructed by a semicircular obstacle. The effect of the size of the obstacle on recovery of polarization and intensity distribution is studied. The role of the beam size at the pupil plane is also discussed.

MULTIPHASE MODELING OF WAVE PROPAGATION OVER SEMICIRCULAR OBSTACLES USING WENO AND LEVEL SET METHODS

Wave propagation over a semicircular obstacle is studied. This problem is related to the design of semicircular breakwaters. These breakwaters are expected to have enhanced stability and were constructed in various places in China. Enhanced numerical modeling is done taking viscosity into account. The fifth order space accurate weighted essentially non-oscillatory (WENO) method is used to discretize the convection terms. As a result accurate results are obtained using simple options (uniform Cartesian grid, level set method). Wave generation is done using a numerical piston wave maker that is analogous to the real experiment. The model results are compared with free surface visualization and pressure measurements. Various features of the problem including wave drag and the flow field are revealed.

Multiphase Modeling of Wave Propagation Over Submerged Obstacles Using Weno and Level Set Methods

A new numerical multiphase model is presented to study wave propagation over arbitrary shaped submerged obstacles. The high order space accurate weighted essentially non-oscillatory (WENO) method is adopted along with relatively coarse Cartesian uniform grids. Viscosity effects are included and the free surface is tracked using the level set method. The model is validated via application to solitary and progressive wave motion over rectangular, trapezoidal and semicircular obstacles. The complex flow field features induced near a large sized obstacle, including separation vortices and large free surface deformations, are accurately reproduced. Compared to other relatively complicated models, the present model is efficient and produces enhanced results.

Truncation Approximations for Gravity-capillary Free-surface Flows

Gravity-capillary free-surface flows past disturbances in a channel of finite depth are considered. These flows are usually assumed to extend from x = −∞ to x = ∞ where the x-axis is parallel to the bottom. Many numerical schemes truncate this infinite domain to the interval −B < x < A where A and B are large positive numbers. These truncations introduce inaccuracies, especially when the effect of surface tension is included. In this paper numerical methods are presented which remove these inaccuracies. This is achieved by taking into account the contributions from −∞ to −B and from A to ∞. Explicit computations are presented for a semi-circular obstacle at the bottom of the channel.

Open Channel Flow Over Submerged Obstructions: An Experimental and Numerical Study

This paper reports on experimental and computational investigations of water flow over two-dimensional obstacles in an open channel. Both triangular and semi-circular obstacles are considered in order to study the effects of obstacle type and size on the flow. The upstream flow is subcritical while the downstream flow is supercritical in all the cases discussed. The results of the experiments indicate that the downstream Reynolds number increases and appears to approach an asymptotic value as the obstacle height is increased. The upstream Reynolds number, on the other hand, decreases linearly as the obstacle height is increased. For the cases involving triangular obstacles, comparisons are presented between the results of the experimental measurements and the computational simulations as well as with available analytical solutions for inviscid flow. The comparisons point to the conclusion that the fluid rotational activity has a negligible effect on the overall flow in the open channel.

38 半円柱まわりの流れの振舞について

The fluid motion past a semicircular cylindar is visualized by means of alminum dust method in the water tank of NDA. Many photograph of flow pattern around a semicircular obstacle are taken at Reynolds numbers ranging 0.7×103 to 5.7×103 The separation points and the stagnation points are analyzed at the various angle of attack.

Critical free-surface flow over a semi-circular obstruction

Numerical solutions are presented for the problem of two-dimensional “critical” flow of an ideal fluid over a semi-circular obstacle attached to the bottom of a running stream. The upstream Froude number and downstream flow speed are known in advance, and are therefore computed as part of the solution. The dependence of flow behaviour on obstacle size is discussed.

Free-surface flow over an obstruction in a channel

Two-dimensional steady potential flow over a semicircular obstacle at the bottom of a channel is considered. The problem is solved numerically by using an integrodifferential equation formulation derived by Forbes and Schwartz [J. Fluid Mech. 114, 299 (1982)]. This equation is reduced to a set of algebraic equations by a difference method and solved by Newton’s method together with parameter variation. The numerical results for subcritical flows agree with those of Forbes and Schwartz. However, it is found that supercritical solutions exist only for values of the Froude number greater than some particular value. Furthermore, for some values of the Froude number, there are two supercritical solutions. One is a perturbation of a uniform stream whereas the other is a perturbation of a solitary wave.