Simulation Of Two-dimensional Flow Research Articles

Can Minkowski tensors of a simply connected porous microstructure characterize its permeability?

We show that the permeability of periodic simply connected porous media can be reliably predicted from the Minkowski tensors (MTs) describing the pore microstructure geometry. To this end, we consider a large number of two-dimensional simulations of flow through periodic unit cells containing complex-shaped obstacles. The prediction is achieved by training a deep neural network using the simulation data with the MT elements as attributes. The obtained predictions allow for the conclusion that MTs of the pore microstructure contain sufficient information to characterize the permeability, although the functional relation between the MTs and the permeability could be complex to determine.

Two-dimensional numerical simulations of soil-water and heat flow in a rainfed soybean field under plastic mulching

Abstract Numerical simulation can help understanding water- and heat-flow systems through plastic-mulched soils. An effective simulation approach is crucial to know the role of plastic mulch in a soil ecosystem, which can save water in agriculture. A field experiment was conducted at Gifu University in a rainfed soybean cultivation under plastic mulch and bare soil treatments to clarify the soil water and heat flow mechanism. Furthermore, the two-dimensional numerical software HYDRSUS-2D model with different boundaries at the soil surface was used to simulate water and heat flows. Firstly, soil hydraulic parameters were estimated by inverse solution using laboratory-measured data and then coupled soil-water and heat flows were simulated by optimizing soil thermal parameters by inverse solution. The HYDRUS-2D model simulated water and heat flow through the root zone depths satisfactorily. The root-mean square error (RMSE) was 0.015–0.030, and 0.046–0.055 cm3 cm−3 for the plastic mulch, and bare soil, respectively, in estimating soil moisture and 0.66–1.28, and 0.70–1.54 °C, respectively in estimating soil temperature. Water infiltration was 61% lower in the plastic-mulched soil, which reduced soil evaporation as well as soil-moisture storage changes compared to bare soil. This study can be applied to design and manage different plastic mulching patterns in rain-fed crop cultivation.

The effects of Prandtl number on the nonlinear dynamics of Kelvin–Helmholtz instability in two dimensions

Abstract

Effect of Upstream Side Flow of Wind Turbine on Aerodynamic Noise: Simulation Using Open-Loop Vibration in the Rod in Rod-Airfoil Configuration

Adaptive and flexible control techniques have recently been examined as methods of controlling flow and reducing the potential noise in vertical axis wind turbines. Two-Dimensional (2D) fluid flow simulation around rod-airfoil is addressed in this study as a simple component of the wind turbine by using Unsteady Reynolds Averaged Navier–Stokes (URANS) equations for prediction of noise using Ffowcs Williams-Hawkings (FW-H) analogy. To control the flow and reduce noise, the active controlling vibration rod method is utilized with a maximum displacement ranging from 0.01 C to 1 C (C: airfoil chord). Acoustic assessment indicates that the leading edge of the blade produces noise, that by applying vibration in cylinder, blade noise in 0.1 C and 1 C decreases by 22 dB and 35 dB, respectively. Applying vibration is aerodynamically helpful since it reduces the fluctuations in the airfoil lift force by approximately 48% and those in the rod by about 46%. Strouhal assessment (frequency) shows that application of control is accompanied by 20% increase. Applying vibration in the rod reduces the flow fluctuations around the blade, thus reduces the wind turbine blade noise. This idea, as a simple example, can be used to study the incoming flow to turbines and their blades that are affected by the upstream flow.

A Numerical Study on Heat Transfer Performance in a Straight Microchannel Heat Sink with Standing Surface Acoustic Waves

There has been a remarkably increasing interest in applying acoustofluidics in micro-electro-mechanical systems and lab-on-a-chip systems in the past decades. This paper investigated the heat transfer performance in a straight microchannel heat sink which applies standing surface acoustic waves (SSAW) to disturb the flow. Two-dimensional numerical simulations of the SSAW-driven flow are performed by employing perturbation theory on basis of COMSOL platform. The elasticity of microchannel material is taken into account by applying the impedance boundary conditions. Parametric effects on heat transfer performance including the SSAW wavelength and the dimensions of microchannel heat sink are investigated. It is found that the introduction of SSAW can greatly enhance the overall heat transfer. Moreover, with a constant channel height, shorter SSAW wavelength and narrower microchannel are found to be more beneficial to the overall thermal performance. Keeping both the microchannel width and the SSAW wavelength unchanged, a “wide” configuration of the microchannel cross section is recommended to achieve higher heat transfer efficiency. Finally, we elucidate the underlying mechanisms of heat transfer enhancement peculiar to the excitation of SSAW in microchannel, which is attributed to the appearance of acoustic vortices and the disruption of thermal boundary layer induced by acoustic streaming.

On the Scope of Lagrangian Vortex Methods for Two-Dimensional Flow Simulations and the POD Technique Application for Data Storing and Analyzing.

The possibilities of applying the pure Lagrangian vortex methods of computational fluid dynamics to viscous incompressible flow simulations are considered in relation to various problem formulations. The modification of vortex methods—the Viscous Vortex Domain method—is used which is implemented in the VM2D code developed by the authors. Problems of flow simulation around airfoils with different shapes at various Reynolds numbers are considered: the Blasius problem, the flow around circular cylinders at different Reynolds numbers, the flow around a wing airfoil at the Reynolds numbers and , the flow around two closely spaced circular cylinders and the flow around rectangular airfoils with a different chord to the thickness ratio. In addition, the problem of the internal flow modeling in the channel with a backward-facing step is considered. To store the results of the calculations, the POD technique is used, which, in addition, allows one to investigate the structure of the flow and obtain some additional information about the properties of flow regimes.

Time-dependent study of blood flow in an aneurysmic stenosed coronary artery with inelastic walls

Coronary arteries are a family of arteries that are indulged in the supply of oxygenated blood to the muscles of the heart. These blood vessels envelop the entire heart. These blood vessels encounter a common disturbance in which the vessel wall gets thickened leading to the blockage of the vessel lumen. Also, an uncommon condition seen is the development of a protruding bulging structure outward the lumen. The common disturbance seen is the stenosis of the artery whereas the uncommon bulging is the aneurysm. In the present paper, a discussion on the two-dimensional simulation of blood flow across the computationally constructed coronary arterial domain with clinical measurements is made. The arterial segment is assumed to have an aneurysm protrusion as well as a plaque developed due to stenosis. The velocity profile, pressure profile, and the wall shear stress patterns observed are enunciated by treating blood as a classical Newtonian fluid. The results show that the spots below the aneurysm are prone to develop new sacs and lesions. The main innovations of this study are: a) identifying the most probable spots for new plaque development; b) the interrelation between the flow characteristics due to the presence of stenosis and the aneurysm sac.

High-order gas kinetic flux solver for simulation of two dimensional incompressible flows

Within the framework of the high-order finite volume (FV) method, a high-order gas kinetic flux solver (GKFS) is developed in this work for simulation of two-dimensional incompressible flows. Generally, in the conventional high-order FV method, the inviscid and viscous fluxes are treated separately. However, different from the conventional high-order FV method, the high-order GKFS evaluates the inviscid and viscous fluxes simultaneously from the local asymptotic solution to the Boltzmann equation, which consists of the equilibrium distribution function and its substantial derivative at the cell interface. By introducing a difference scheme with the high-order accuracy in space to discretize the substantial derivative, a high-order accurate local asymptotic solution to the Boltzmann equation can be obtained. The numerical flux of the Navier–Stokes equations can then be calculated by the moments of the local asymptotic solution. Since this local asymptotic solution is relatively simple, the numerical fluxes of the Navier–Stokes equations can be given explicitly for the high-order GKFS, which is the function of the left and the right states and their first-order derivatives. Numerical results showed that the developed solver can achieve the desired accuracy on both the quadrilateral mesh and the triangular mesh and its efficiency is higher than the second-order counterpart when achieving comparable accuracy of solution.

The Barnes — Hut-type algorithm in 2D Lagrangian vortex particle methods

The Lagrangian vortex particle method for two-dimensional flow simulation around airfoils is considered. Generally, the most time-consuming operation in the vortex method is vortex particles interaction simulation, especially if it is performed directly “point-to-point” for all pairs of particles. The result of such operation is vortex particles convective velocities. This problem is similar to the N-body problem and has squared computational complexity O(N2). The only efficient approach for its solution in a reasonable time for large N is to use approximate fast algorithms. The fast method suggested by Barnes and Hut having logarithmic computational complexity is considered for the mentioned problem of convective velocities computation. It also has been adapted for other operations in the vortex method such as a system of algebraic equations iterative solution and efficient right-hand side computation. As the result, the Barnes — Hut method allows reducing the whole time of calculations by several tens of times.

Vertical-Axis Wind Turbine Blade-Shape Optimization Using a Genetic Algorithm and Direct-Forcing Immersed Boundary Method

The aim of this study was to prove that an optimization method combining genetic algorithms with a direct-forcing immersed boundary method as a distinguished numerical method could improve the performance of vertical-axis wind turbine blades. The proposed direct-force immersed boundary (DFIB) flow solver was tested using the benchmark laminar flow problems (lid-driven flow, flow over a stationary cylinder, and vortex-induced vibration of the circular cylinder). Two cases were analyzed, one of a stationary airfoil and another of a rotating airfoil in a vertical-axis wind turbine. The analysis was carried out using two-dimensional flow simulations in a laminar flow regime. A NACA 0012 airfoil was used as the original airfoil cross section of the vertical-axis wind turbine. The proposed method successfully simulated the moving blade in the flow field, and the results revealed that the optimized wind turbine blade designed using the proposed method had an efficiency improvement of 5.61% compared to the original airfoil.

Evaluating Efficiency Improvement of Deep-Cut Curb Inlets for Road-Bioretention Stripes

Making a deep cut on the curb inlet has been used in some sponge-city (SPC) projects for road-bioretention stripes to manage stormwater runoff since they were easily implemented in the field. The efficiencies of the deep-cut curb inlets in those projects were unknown for lacking equation to evaluate their efficiencies. Two kinds of retrofit scenarios are commonly used: (1) The curb-cut cases when the deep cut is made only over the width of the curb inlet; (2) the road-curb cut cases when both the curb inlet and a small part of the road surface have a deep cut. An updated two-dimensional flow simulation program, FullSWOF-ZG, was used to determine two important parameters in road curb inlet design: The 100% interception curb inlet lengths (LT) and the curb inlet efficiencies (Eci). Eight-hundred retrofit modeling cases were compared with the no-cut cases to quantify the efficiency improvement of the deep-cut curb inlets. The simulation results show both LT and Eci of the curb-cut cases do not improve much. This case study with limited combinations of longitudinal and cross slopes and inlet lengths demonstrated that Eci of the road-curb cut cases improves to a large extent so that they can be used in the SPC projects and other urban drainage projects to reduce the flooding potentials. A general equation used to design and evaluate the road-curb cut inlets can be developed based on more simulation cases with a wide range of input parameters in a future study.

Dam breach analysis: a case of Gidabo dam, Southern Ethiopia

Gidabo dam provides flood control and irrigation water supply for sugarcane and rice cultivation. The dam has 25.8 m height and 335 m crest length with side ogee spillway to pass 10,000 years’ flood. There were different economic developments downstream of the dam including irrigation command area and irrigation structures. Since Nature is full of uncertainties, it is likely that Gidabo dam can be subjected to sudden breaches due to the probable maximum flood. Therefore, dam breach analysis and flood inundation map preparation should be conducted. The Hydrologic Engineering Center’s River Analysis System new version was used to analyze the dam breach for overtopping failure. River analysis system Mapper which is Geographic information system tool of Hydrologic Engineering Center’s River Analysis and Geographic information system were used to develop flood inundation map. Dam breach parameters were calculated within the Geographic information system model by using beach parameter calculator tab. A two-dimensional unsteady flow simulation of the dam breach was performed by using the inflow hydrograph as upstream boundary condition. From the rainfall data analysis, the probable maximum precipitation resulting probable maximum flood was found 277 mm results a peak inflow of 6387 m3/s. It was found that the breach bottom width was 143 m while the breach side slope (horizontal: vertical) was 1.4:1 and 2.7 h breach formation time. The peak breach outflow was found to be 15,848.85 m3/s which covers 2050 hectares with maximum depth of 12.14 m.

Understanding hydrothermal behavior of the Maneadero geothermal system, Ensenada, Baja California, Mexico

A hydrogeological conceptual model has been developed that describes the geothermal system located at the Maneadero region in Ensenada, Baja California, Mexico. In addition, a two-dimensional steady state simulation of water flow and heat transfer of a model profile using COMSOL Multiphysics software is also presented. The proposed hydrogeological conceptual model considers that the old local anoxic subsurface seawater feeds the system, and a remnant magmatic intrusion in the surface from past volcanism at 2 km of depth works as heat source. The intersection between the south Agua Blanca Fault and the L3 alignment promote the fluids ascent to the submarine hydrothermal vent. The results of the simulation show a reservoir temperature of 164 °C and an affluent temperature of 105 °C, varying between 1 °C and 3 °C, respectively, with previous studies. Moreover, a geothermal potential of 0.48 MW was estimated for the simulated profile. The current policy of exploitation of geothermal resources in Mexico makes the development of these models particularly relevant, serving as a tool for their evaluation and management.

A Numerical Technique for Determining Aerodynamic Derivatives of a Suspension Bridge Deck

A novel two-dimensional numerical solution methodology based on variable wind angle of attack for numerical simulation of fluid-structure interaction associated with rotations of bridge deck section is proposed. In this methodology, the deck is considered fixed in the computational domain, while incremental inclination of flow approach and wind angle attack are applied to far-field boundaries of the initial mesh. The numerical simulation is carried out to calculate aerodynamic flutter derivatives of Great Belt East Bridge deck using commercial computational fluid dynamic code of ANSYS FLUENT combined with a developed MATLAB code for post-processing of the aerodynamic derivatives. The utilized finite volume flow solver is applied for two-dimensional flow simulation around structural sections. Aerodynamic flutter parameters of a thin flat plate and bridge deck are determined based on the proposed methodology. Comparison between the analysis results with simulated values and the measurements of wind tunnel tests or the Theodorsen’s solution shows that the accuracy of the present modeling strategy in prediction of the aerodynamic derivatives is promising.

Effect of Cylinder Arrangement on Fluid Flow and Heat Transfer Characteristics past Four Elliptic Cylinders

Fluid flow and heat transfer characteristics past four elliptic cylinders arranged in square configuration are numerically investigated in this study. An in-house finite element method code based on streamline upwind Petrov - Galerkin algorithm has been used for simulations of two-dimensional, incompressible and laminar flow of air. Analyses are carried out by changing geometric parameters such as spacing ratio, axis ratio and incident angle. Results in terms of vorticity and temperature contours, Strouhal number, drag and lift coefficients and Nusselt number are studied for all cases. These results show that fluid flow patterns are strongly influenced by geometric parameters, based on which flow can be categorized into different types. A critical spacing ratio is found for some of the configurations, where a steep increase in drag coefficient is encountered. From this study, it is observed that incident angle 22.5 degree gives a higher heat transfer rate compared to the other two configurations (0 and 45 degree). Also, elliptic cylinders (axis ratio of 0.8 and 0.5) have similar Nusselt number value with less drag force compared to circular cylinders (axis ratio of 1.0) which justifies the utilization of elliptic cylinders as an alternative for circular ones.

Direct Simulation of Fluid–Structure Interaction in a Hypersonic Compression-Ramp Flow

Sustained flight at hypersonic speeds presents an enduring challenge to vehicle design and control. An extreme aerothermal environment acting on geometrically thin, multifunctional structures can result in the significant structural response of key aerodynamic surfaces. Specifically, the oscillations of a compression corner shock-wave/boundary-layer interaction, which models a control surface deflection, can couple with the lowest natural frequencies of a proximal compliant surface, leading to a range of undesirable outcomes from reduced service life to structural failure. The present work investigates these phenomena through time-accurate high-fidelity aeroelastic simulations of a laminar two-dimensional flow at over a 35 deg compression ramp featuring an embedded compliant panel. Surface pressure, skin friction, and heat transfer associated with the corner shock-wave/boundary-layer interaction are directly compared between rigid and compliant configurations. The upstream separation zone is observed to synchronize with the compliant-panel deflection. A reduction in surface heat flux is observed for a majority of compliant cases relative to the rigid case, whereas entirely new flow features are observed in response to large-scale panel deflections. A modification is proposed to the local piston-theory aerodynamic model to improve the accuracy of surface pressure predictions.

Numerical simulation of groyne placement in minimising Krueng Aceh river bank erosion

This paper presents the prediction of the flow velocity in a 575 meters-long reach of the Krueng Aceh river. It focused on the part of the riverbank where erosion occurred due to the pillars and bridge abutments. One alternative to reduce erosion is using groynes for regulation. The simulations were conducted using the Surface Water Modelling System program (SMS 11.2). The effects of the groynes on the flow changes causing erosion were determined by mathematical simulation of two-dimensional flow using RMA2. The calibration of RMA2 was undertaken by determining the Root-Mean-Square (RMS) error between the measured and mathematical model velocities. Nine scenarios of simulations have been done to investigate the effect of the groyne installation in reducing erosion in the river bend, in term of its length (L), and angle (α), according to river condition. From the simulation results, it can be concluded that the distribution of flow velocities towards the outer river bend for the perpendicular groyne of 9.0m long was smaller compared to the 7.0m one. The groyne with the angle of 10° and length of 7.0m was better in reducing the velocities at the outer riverbank than the 9.0m one. Whereas the groyne with 30° orientation and 9.0m long is better in reducing the eddy than that of the 7.0 m.

Numerical Computation of Low Reynolds Number Viscous Flow Past Bluff Bodies

This article presents a two-dimensional steady viscous flow simulation past circular and square cylinders at low Reynolds numbers (based on the diameter) by the finite volume method with a non-orthogonal body-fitted grid. Diffusive fluxes are discretized using central differencing scheme, and for convective fluxes upwind and central differencing schemes are blended using a ‘deferred correction’ approach. A simplified pressure correction equation is derived, and proper under-relaxation factors are used so that computational cost is reduced without adversely affecting the convergence rate. The governing equations are expressed in Cartesian velocity components and solution is carried out using the SIMPLE algorithm for collocated arrangement of variables. The mesh yielding grid-independent solution is then utilized to study, for the very first time, the effect of the Reynolds number on the separation bubble length, separation angle, and drag coefficients for both circular and square cylinders. Finally, functional relationships between the computed quantities and Reynolds number (Re) are proposed up to Re = <i>40</i>. It is found that circular cylinder separation commences between Re= <i>6.5-6.6</i>, and the bubble length, separation angle, total drag vary as Re, Re<i>−0.5</i>, Re<i>−0.5</i> respectively. Extrapolated results obtained from the empirical relations for the circular cylinder show an excellent agreement with established data from the literature. For a square cylinder, the bubble length and total drag are found to vary as Re and Re<i>−0.666</i>, and are greater than these for a circular cylinder at a given Reynolds number. The numerical results substantiate that a square shaped cylinder is more bluff than a circular one.

Self-sustained elastoinertial Tollmien–Schlichting waves

Direct simulations of two-dimensional plane channel flow of a viscoelastic fluid at Reynolds number Re = 3000 reveal the existence of a family of attractors whose structure closely resembles the linear Tollmien-Schlichting (TS) mode, and in particular exhibits strongly localized stress fluctuations at the critical layer position of the TS mode. At the parameter values chosen, this solution branch is not connected to the nonlinear TS solution branch found for Newtonian flow, and thus represents a solution family that is nonlinearly self-sustained by viscoelasticity. The ratio between stress and velocity fluctuations is in quantitative agreement for the attractor and the linear TS mode, and increases strongly with Weissenberg number, Wi. For the latter, there is a transition in the scaling of this ratio as Wi increases, and the Wi at which the nonlinear solution family comes into existence is just above this transition. Finally, evidence indicates that this branch is connected through an unstable solution branch to two-dimensional elastoinertial turbulence (EIT). These results suggest that, in the parameter range considered here, the bypass transition leading to EIT is mediated by nonlinear amplification and self-sustenance of perturbations that excite the Tollmien-Schlichting mode.

Fluid Dynamics of Flow Around Side-by-Side Arranged Cylinders

Flow past four side-by-side identical square cylinders arranged normal to the flow have been found to show interesting and important flow features which are very difficult to get through experiments. Lattice Boltzmann method (LBM) is used for numerical simulations of two-dimensional (2D) flow around four side-by-side arranged cylinders. In this study, the Reynolds number (Re) is chosen to be 60, 80, 100, 120 and 140 and the spacing ratio g* (= g/D, where D is the size of cylinder and g is the distance between the cylinders) is set at 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 3.5 and 4. Based on the flow characteristics, seven distinct and unique flow regimes are identified for different ranges of Re and g*. Physical features of each flow regime such as wake structures, vortex dynamics, gap flow behavior, time histories of lift coefficients, shedding frequencies and hydrodynamic forces are thoroughly discussed. The Reynolds numbers strongly affect the flow, especially at 0 ≤ g* ≤ 2, in terms of vortex-shedding frequency. A significant secondary frequency is also found other than the primary frequency in the base-bleed and flip-flopping flow regimes. It is observed that for g* ≥ 2.5 primary shedding frequency strongly affects the flow dynamics and the mutual interaction of the wakes behind the cylinders decreases with an increase in the Reynolds number. The Strouhal value is same for the outer and inner cylinders in inphase–antiphase weak interaction flow regime and different for base-bleed and flip-flopping flow regimes. In inphase asynchronous weak interaction flow regime, the Strouhal number is same for all four cylinders.