Rectangular Obstacles Research Articles

Heat transfer and flow structure through a backward and forward-facing step micro-channels equipped with obstacles

This study presents 2-D simulations of a flow-through a sudden expansion/contraction micro-channel with the existence of obstacles. The bottom wall is maintained at constant flux, while the other walls are adiabatic. Rectangular adiabatic obstacles are mounted before the expansion region on the upper and lower wall of the channel used. The finite element method was used to discretize the equations that govern the physical model. Results indicate the apparition of a separate vortex, situated in the corner after the sudden expansion of the micro-channel for low Reynolds numbers. For higher values and expansion ratios, the vortex separation length increases. The obtained results show that the obstacles have a considerable effect on the dynamics of the flow and enhancement of heat transfer.

Meshfree modeling of near field two-liquid mixing process in the presence of different obstacles

In this research two-liquid dam break induced mixing process in the presence of different obstacles was modeled using δ-SPH method. Water and polyetilenoxid (PEO) were used as two different Newtonian fluids. The model was validated using laboratory data, including single-liquid dam break over wet bed and over triangular and rectangular obstacles as well as two-liquid dam break. Then, the effect of various parameters such as ambient water depth and gate motion characteristics on mixing pattern and front propagation of water-PEO interface were investigated. The results show the necessity of considering the gate in numerical simulation. Furthermore, a two-step formula for gate motion consisting accelerated phase and a uniform velocity phase was used leading to increasing the accuracy of the results. Finally, the flow simulation was performed to evaluate and compare the mixing pattern, front propagation of water-PEO solution interface as well as maximum flow height in the presence of three different obstacles.

Large eddy simulation of turbidity currents in a narrow channel with different obstacle configurations

Turbidity currents are frequently observed in natural and man-made environments, with the potential of adversely impacting the performance and functionality of hydraulic structures through sedimentation and reduction in storage capacity and an increased erosion. Construction of obstacles upstream of hydraulic structures is a common method of tackling adverse effects of turbidity currents. This paper numerically investigates the impacts of obstacle’s height and geometrical shape on the settling of sediments and hydrodynamics of turbidity currents in a narrow channel. A robust numerical model based on LES method was developed and successfully validated against physical modelling measurements. This study modelled the effects of discretization of particles size distribution on sediment deposition and propagation in the channel. Two obstacles geometry including rectangle and triangle were studied with varying heights of 0.06, 0.10 and 0.15 m. The results show that increasing the obstacle height will reduce the magnitude of dense current velocity and sediment transport in narrow channels. It was also observed that the rectangular obstacles have more pronounced effects on obstructing the flow of turbidity current, leading to an increase in the sediment deposition and mitigating the impacts of turbidity currents.

Experimental dataset and numerical simulation of floating bodies transport in open-channel flow

Abstract Numerical models trying to faithfully represent the movement of floating bodies transport in open-channel flow require experimental data for validation. In order to provide an adequate dataset, flume experiments were carried out to analyse the transport of singular and grouped rigid bodies floating on the water surface. Both cylindrical and spherical samples were employed: they were released in a rectangular channel under steady conditions in one-dimensional (plain channel) and two-dimensional (2D) configurations using one rectangular side obstacle, one smooth side obstacle or two rectangular alternate obstacles. The outcomes of the experiments are the planar displacement and the rotation of the samples, which are related to the flow field in the different configurations. The detailed experimental analysis of the floating body motion provides information for the calibration of numerical models simulating floating bodies transport. This dataset is thus employed for the validation of the Eulerian–Lagrangian model ORSA2D_WT, highlighting its strengths and improvable aspects. Similar applications could be carried out with any 2D model which performs the simulation of discrete elements moving on the water surface.

Design and Simulation of an Integrated Centrifugal Microfluidic Device for CTCs Separation and Cell Lysis.

Separation of circulating tumor cells (CTCs) from blood samples and subsequent DNA extraction from these cells play a crucial role in cancer research and drug discovery. Microfluidics is a versatile technology that has been applied to create niche solutions to biomedical applications, such as cell separation and mixing, droplet generation, bioprinting, and organs on a chip. Centrifugal microfluidic biochips created on compact disks show great potential in processing biological samples for point of care diagnostics. This study investigates the design and numerical simulation of an integrated microfluidic device, including a cell separation unit for isolating CTCs from a blood sample and a micromixer unit for cell lysis on a rotating disk platform. For this purpose, an inertial microfluidic device was designed for the separation of target cells by using contraction–expansion microchannel arrays. Additionally, a micromixer was incorporated to mix separated target cells with the cell lysis chemical reagent to dissolve their membranes to facilitate further assays. Our numerical simulation approach was validated for both cell separation and micromixer units and corroborates existing experimental results. In the first compartment of the proposed device (cell separation unit), several simulations were performed at different angular velocities from 500 rpm to 3000 rpm to find the optimum angular velocity for maximum separation efficiency. By using the proposed inertial separation approach, CTCs, were successfully separated from white blood cells (WBCs) with high efficiency (~90%) at an angular velocity of 2000 rpm. Furthermore, a serpentine channel with rectangular obstacles was designed to achieve a highly efficient micromixer unit with high mixing quality (~98%) for isolated CTCs lysis at 2000 rpm.

Effect of Obstacle’s Length-to-Height Ratio on Aerodynamic Quantities of Rarefied Hypersonic Flow

The DSMC method was used to calculate and analyse the flow field structure and the surface aerodynamic quantities when the hypersonic rarefied gas flow passing obstacle at a height of 70km. The changes of surface aerodynamic quantities such as skin friction coefficient, heat transfer coefficient, and pressure coefficient when the length-to-height ratio of the rectangular obstacle is 1/1, 1/2, 1/3, and 1/4 are analysed. The results show that under the above aspect ratio of the obstacle, a recirculation region is formed at each corner of the obstacle. A bow shock will be formed on the windward side of the obstacle, and with the increase of the obstacle’s height, the bow shock will be superimposed on the separated shock wave in front. A strong expansion wave will be formed on the backside of the obstacle, which affects the downstream flow field structure and aerodynamic quantities. When the obstacle’s height increases, the maximum value of the aerodynamic quantities on each surface of the obstacle will increase significantly. It is calculated that the quantities such as heat transfer coefficient and pressure coefficient reach the maximum at the convex point of the windward surface.

A New Parallel Framework of SPH-SWE for Dam Break Simulation Based on OpenMP

Due to its Lagrangian nature, Smoothed Particle Hydrodynamics (SPH) has been used to solve a variety of fluid-dynamic processes with highly nonlinear deformation such as debris flows, wave breaking and impact, multi-phase mixing processes, jet impact, flooding and tsunami inundation, and fluid–structure interactions. In this study, the SPH method is applied to solve the two-dimensional Shallow Water Equations (SWEs), and the solution proposed was validated against two open-source case studies of a 2-D dry-bed dam break with particle splitting and a 2-D dam break with a rectangular obstacle downstream. In addition to the improvement and optimization of the existing algorithm, the CPU-OpenMP parallel computing was also implemented, and it was proven that the CPU-OpenMP parallel computing enhanced the performance for solving the SPH-SWE model, after testing it against three large sets of particles involved in the computational process. The free surface and velocities of the experimental flows were simulated accurately by the numerical model proposed, showing the ability of the SPH model to predict the behavior of debris flows induced by dam-breaks. This validation of the model is crucial to confirm its use in predicting landslides’ behavior in field case studies so that it will be possible to reduce the damage that they cause. All the changes made in the SPH-SWEs method are made open-source in this paper so that more researchers can benefit from the results of this research and understand the characteristics and advantages of the solution proposed.

Mechanical characteristics of short fiber composite samples located behind circle, rectangle, triangle obstacles

The article investigates the influence of the weld line on the mechanical characteristics of flat samples on tensile strength according to ISO-527-2, cut from a plate with an obstacle, molded from polyamide-6, reinforced from 30% short glass fibers. There are considered circular, rectangular, triangular obstacles. Melt front, weld line location and reinforcing fiber orientation are calculated in Moldex3D. The stiffness and strength of the samples were predicted in ANSYS using an anisotropic nonlinear composite material model obtained in the Digimat by reverse engineering method. The transversely isotropic criterion of Tsai Hill in the first pseudo-grain failure statement was used for predict strength. The paper presents the influence of the weld line on the stress, deformation and first pseudo-grain failure strength criterion. The greatest contribution to the samples mechanical characteristics was made by the rectangular obstacle.

Experimental study on the influence of obstacle aspect ratio on ethanol liquid vapor deflagration in a narrow channel

A series of experimental tests were conducted in a narrow obstructed channel to investigate the influence of obstacle distribution mode (unilateral and bilaterally symmetrical distribution) and obstacle aspect ratio (the width-to-height ratio in flame propagation direction) on vapor deflagration. Rectangular obstacles with different aspect ratios 0.9–2.1 were used. The flame propagation speed, flame front structure, overpressure and local temperature near obstacles were recorded and analyzed. The results indicated that different obstacle distribution modes would not fundamentally alter the propagation mechanism of deflagration flame and overpressure. The shear action of obstacle edges and the confined space structural form between the obstacle and the channel boundaries both exerted a significant effect on deflagration flame propagation. And two acceleration stages existed in the deflagration, and the flame speed peaks appeared above obstacle and near the channel portal, respectively. Specifically, when aspect ratio was 1.8, the maximum flame speed peaked to 102.5 m/s. Moreover, obstacle aspect ratio has shown a significant influence on flame front, and the flame front structure experienced complex changes as it passed through obstacle. What's more, an interesting reverse flame phenomenon was observed, which resulted in a larger area of violent flame combustion. The maximum length of reverse flame decreased firstly and then increased with the increase of obstacle aspect ratio, which probably ascribed to the inertial force of fluid. Accordingly, a simple empirical equation was proposed to predict the reverse flame length during flame propagation in the narrow obstructed channel. This equation performs well in prediction of reverse flame length in current application range. Meanwhile, the local temperature peak is closely related to the local deflagration reaction intensity affected by obstacle aspect ratio. In addition, it is also found that the deflagration overpressure and flame propagation involved the obvious coupling mechanism. Deflagration overpressure and flame speed reached peaks almost simultaneously. This coupling mechanism could significantly expend the impact range of deflagration.

Single-Layer Obstacle-Aware Substrate Routing via Iterative Pin Reassignment and Wire Assignment

It is known that single-layer obstacle-aware substrate routing is necessary for modern IC/Package designs. In this article, given a set of two-pin nets and a set of rectangular obstacles inside a single-layer routing plane, a two-phase routing algorithm including an iterative routing phase and a rip-up-and-reroute phase can be proposed to maximize the number of the routed nets in single-layer obstacle-aware substrate routing. In the iterative routing phase, based on the pin and path distribution of the routing nets and the locations of the obstacles inside a single-layer routing plane, the start or target pins on some routing nets inside dense obstacle regions may be firstly reassigned to complete the partial wiring paths on the nets. Based on the region extraction of two intersected nets in single-layer routing, the private regions of some routing nets inside sparse obstacle regions can be extracted and the nets inside the extracted regions can be further routed by using maze routing. In the rip-up-and-reroute phase, the routability of the routing nets can be improved by ripping up some routed nets and rerouting the unrouted nets. Compared with Liu's modified algorithm and Yan's flow-based algorithm in single-layer obstacle-aware substrate routing, the experimental results show that the proposed algorithm can use less CPU time to increase 3.4% and 1.8% of the routability on the routing nets for eight tested examples on the average. Additionally, the percentage of the tested examples with the 100% routability of the routing nets on the eight tested examples has been improved from 25% to 62.5%.

Thermal and hydrodynamic analysis of non-Newtonian nanofluid in wavy microchannel

In this study, hydrodynamic and heat transfer of non-Newtonian nanofluid behavior is investigated in a wavy microchannel with rectangular obstacles. Aluminum oxide as nanoparticles (Al2O3) with 0.5% and 1.5% volume fractions and three different diameters (25, 45 and 100 nm) are added to pure water as a base phase to form a nanofluid structure. In order to form the non-Newtonian nanofluid, 0.5% carboxy methyl cellulose (CMC) is added to the nanofluid structure. Up and down walls of microchannels at the middle section where obstacles are located have constant 50,000 W⁄m2 heat flux. Inlet temperature is constant and equal to 298 K with different Reynolds numbers varying as 5, 50, 150 and 300. Rib heights varying between 3 and 7 μm for five cases with different nanoparticle volume fractions, nanoparticle diameters and Reynolds numbers are investigated. Nusselt number, friction factor and pressure drop are studied. Results indicated that the average Nusselt number is increased by increasing the volume fraction of Al2O3 nanoparticles. Also, the results show the largest friction factor value is obtained in the case with the highest obstacle height. It is observed that MC-3 case has maximum outlet temperature, and therefore is the best case among investigated cases.

Three-dimensional numerical simulation of a turbulent flow around an obstacle

In this work we study the influence of the inclined shape of the lover and downstream edge of a rectangular obstacle. We analyze the dimensions of the recirculation zones, the velocity field, the kinetic energy and the pressure. A three-dimensional study was conducted using the ansys cfx calculation code. The turbulence model k-ԑ is used to model turbulence, and the governing equations are resolved by the finite volume method.

Localization of a combined pulse discharge within a gas with a rectangular obstacle on the channel wall

Analysis of plasma energy redistribution was conducted on the basis of experimental study of combined volume discharge of submicrosecond duration at its initiation in a gas-dynamic flow in rectangular channel with an obstacle. Shock wave diffraction on the obstacle (parallelepiped) on the channel wall was visualized. Effects of plasma localization at upward facing step and backward facing step were experimentally discovered and studied. CFD simulation patterns of the gas dynamic non stationary flow were compared to instant flow glow images.

Effect of inserting obstacles in flow field on a membrane humidifier performance for PEMFC application: A CFD model

In this study, the numerical models are developed to investigate the influence of obstacle shape and number on performance of a planar porous membrane humidifier for proton exchange membrane fuel cell (PEMFC) application. Dew point of dry side outlet and water transfer rate are applied as evaluation parameters of the performance regardless of pressure drop. A dimensionless number named performance evaluation criteria (PEC) is calculated for all models. The higher value of PEC indicates the higher heat transfer rate with lower pressure drop. In humidifier with one rectangular obstacle compared with the simple humidifier, water transfer rate increases by 7.28%. The highest values of water transfer rate, dew point and PEC, also the greatest values of pressure drop are in humidifiers with rectangular, triangular and circular obstacles, in that order. When there is restriction in securing pumping power in fuel cell system, circular obstacle is the best choice. With considering the pressure drop, using one obstacle does not offer any advantage because the PEC is less than one (0.898). At least two obstacles are needed to have PEC number greater than one, consequently an efficient performance. An increment in number of obstacles causes an increment in water transfer rate, dew point and PEC.

Bond graph approach for dynamic modelling of the biped robot and application to obstacle avoidance

This paper deals with the modelling and obstacle avoidance of a biped robot. At first, the bond graph-based three-dimensional model of the biped is proposed. The robot walking scheme depends upon the oscillating cylinder mechanism. Two DC motors are actuating the prismatic leg of the robot. Then, bond graph model is converted into the Simulink block which is further used for obstacle avoidance application. The physical model of the biped robot is also fabricated. The second part of the work deals with the development of the hybrid obstacle avoidance algorithm by using the merits of the line following, tangent bug and wall following algorithm. The practicability of algorithm is validated on two cases depend upon the positions of the obstacle. The coding of the algorithm is developed by using MATLAB software. The single rectangular shape obstacle is considered for obstacle avoidance by the robot during experimentation work. At last, the validation of the simulation and experimentation work is considered.

Potential flow over a submerged rectangular obstacle: Consequences for initiation of boulder motion

AbstractSteady two-dimensional fluid flow over an obstacle is solved using complex variable methods. We consider the cases of rectangular obstacles, such as large boulders, submerged in a potential flow. These may arise in geophysics, marine and civil engineering. Our models are applicable to initiation of motion that may result in subsequent transport. The local flow depends on the obstacle shape, slowing down in confining corners and speeding up in expanding corners. The flow generates hydrodynamic forces, drag and lift, and their associated moments, which differ around each face. Our model replaces the need for ill-defined drag and lift coefficients with geometry-dependent functions. We predict smaller flow velocities to initiate motion. We show how a joint-bound boulder can be transported against gravity, and analyse the influence of a wake region behind an isolated boulder.

Shock wave attenuation using rigid obstacles with large- and small-scale geometrical features

Explosions and their resulting shock waves may pose a large threat to both humans and structures alike. The previous research concludes that a logarithmic spiral configuration is effective in focusing shock waves to a focal point. This research outlines shock tube experiments conducted on two types of solid rectangular obstacles placed in a logarithmic spiral shape. The obstacles have a square cross-sectional area, with one set of obstacles being normal square shapes, but the other set of obstacles have three grooves cut out on every side of the obstacle, thus reducing the cross-section area by 10%. High-speed schlieren photography is used to visualize the shock waves and numerical simulations provide supporting data. A comparison in regards to shock wave attenuation between the two obstacle sets is presented. Results conclude that the three-groove obstacle geometry was successful in attenuating the peak pressure and pressure impulse of a reflected shock wave; however, the results for the transmitted shock wave between the two configurations are again inconclusive.

Experimental Investigation of Two-phase Fluid Flow over a Rectangular Obstructions Located Inside Enlarged Rectangular Channel

Experimental Investigation of Two-phase Fluid Flow over a Rectangular Obstructions Located Inside Enlarged Rectangular Channel

Data-Driven Detection of Needle Buckling Events in Robotic Needle Steering

In robotic needle steering, flexible asymmetric-tip needles can steer around obstacles to reach targets deep within tissue. Due to tissue inhomogeneity and needle flexibility, needle buckling can occur, preventing accurate placement. This paper focuses on detecting needle buckling using axial force and needle-tip position readings from sensors. Our algorithm uses errors between the force readings and a predictive force model generated from those readings to track rapid changes in the measured forces. Using this prediction error and needle-tip position, the algorithm detects unexpected force increase, strict needle buckling, and buckling with sliding events at the needle-tip. The metrics for the detections are derived using a standard three-sigma rule and a sigmoid function to ensure generalizability of this method to a variety of tissue types. Our algorithm was tested using insertions into a gelatin tissue with an embedded rectangular obstacle designed to elicit buckling events. Needle buckling was detected at a maximum of 2[Formula: see text]mm after collision with the obstacle. Our algorithm was tested for robustness with insertions in an ex vivo tissue under different boundary conditions. Our algorithm was also able to detect buckling events 1–2[Formula: see text]s sooner than human detection times, showing significance for future autonomous control.

Numerical investigation of flow and heat transfer in a channel with different configurations and alternately order obstacles

In the present study, a numerical investigation has been made to predict the laminar flow and heat transfer through a rectangular channel with adiabatic, different configuration obstacles which are arranged alternately on the upper and lower walls of the channel. These walls are subjected to a constant heat flux 500 W/m2. The effect of obstacles number, and obstacles shape on the flow and heat transfer characteristics with different Reynolds number (100,200,300,400,500,600and 700) have been studied. The continuity, momentum, and energy governing equations are solved by the finite volume method. The results of this study reveal that the obstacles have an obvious effect on parameters of the flow and heat transfer enhancement. The heat transfer is improved more as the obstacle's number increase. Further that, using rectangular obstacle leads to increase heat transfer rate higher than the rest of shapes for all Reynolds number tested.