Simulation Of Two-dimensional Flow Research Articles

Numerical simulation on the condensation heat transfer and flow characteristics outside smooth and enhanced tubes

Most of the current studies only conducts two-dimensional simulations of condensation heat transfer and flow outside enhanced tubes, which cannot accurately reflect the flow and heat transfer characteristics of liquid film outside enhanced tubes. In order to provide theoretical support for the design optimization of enhanced tubes, this study adopts the VOF multiphase model and Lee condensation model to simulate the condensation heat transfer(HTC) of refrigerants outside smooth and enhanced tubes. The instantaneous film flow characteristics of the liquid film outside the horizontal smooth and enhanced tubes are analyzed, and the thickness of the liquid film and the relationship with the condensation heat transfer coefficient of the smooth and enhanced tubes under different working conditions are calculated. The refrigerants are compared under the same working conditions, and the results are shown: The simulation results are in good agreement with the experimental data and the Nusselt analytical solution, and the error is all within 15%; the distribution of liquid film is highly sensitive to the magnitude of local condensation heat transfer coefficients, and the condensation HTC outside the enhanced tube is approximately six times of that of smooth tube. Combining the distribution of the liquid film and the thermophysical properties of the refrigerants, it was determined that R410A has the highest HTC, while R1234yf has the lowest HTC.

A fourth-order compact finite volume method on unstructured grids for simulation of two-dimensional incompressible flow

This paper introduces a novel and efficient compact reconstruction procedure for high-order finite volume methods applied to unstructured grids. In this procedure, we establish a set of constitutive relations that ensure the continuity of the reconstruction polynomial and its normal derivatives between adjacent elements at control points. The paper delves into the details of the fourth-order compact reconstruction method specifically designed for two-dimensional triangular grids. This method can be considered an extension of the one-dimensional compact scheme and cubic spline interpolation methods to two-dimensional triangular unstructured grids. In the cubic polynomial reconstruction, a two-dimensional cubic polynomial is reconstructed using the cell averages of elements in the standard stencil and the function values at control points. The determination of function values at control points is achieved by adhering to the constraint of normal derivative continuity. This reconstruction is solved using a relaxation iteration method and has been verified to be solvable for triangular grids. Compared to other fourth-order implicit compact polynomial reconstructions, our method requires solving a smaller number of unknowns, which means less computational cost in reconstruction. By applying this method to solve the Poisson equation, the linear convection equation, and incompressible flow benchmarks, it demonstrates that the proposed method exhibits the expected high-order accuracy and performs well in incompressible flow problems.

DEM analysis of cohesive granular shear flow using dynamic adhesion force model – Model validation for contact-dominated regime

When the DEM simulations are performed, the particle stiffness of the Discrete Element Method (DEM) is often reduced to reduce the computational cost. The Dynamic Adhesion/Cohesion Force Model (DAFM/DCFM) was proposed for adhesive/cohesive particles to make the effect of adhesion/cohesion force on the collisional motion of a particle with a reduced particle stiffness equivalent to that of the original system.This study validates the applicability of DCFM to the contact-dominated regime by means of a series of DEM simulations of two-dimensional simple shear flow of cohesive spherical particles. The results demonstrate that DCFM accurately represents the cohesive nature of the original system with respect to the fluid-to-solid phase transition of granular medium due to a reduction in shear rate, as well as the shear stress of the granular medium. It is demonstrated that the bond-breaking model proposed in the present study describes well the validity of DCFM in the contact-dominated regime.

Radiation and outflow properties of super-Eddington accretion flows around various mass classes of black holes: Dependence on the accretion rates

Abstract We perform axisymmetric two-dimensional radiation-hydrodynamic simulations of super-Eddington accretion flow and outflow around black holes to examine the properties of radiation and outflow as functions of the black hole mass and the accretion rate on to the black hole ($\dot{M}_{\rm BH}$). We find that the $\dot{m}_{\rm BH} ({\equiv} \dot{M}_{\rm BH}c^2 /L_{\rm Edd})$ dependence of $L_{\rm rad}/L_{\rm Edd}$ and $L_{\rm mech}/L_{\rm Edd}$ found for a stellar-mass black hole can apply to the high-mass cases, where $L_{\rm rad}$ is the radiation luminosity, $L_{\rm mech}$ is the mechanical luminosity, c is the speed of light, and $L_{\rm Edd}$ is the Eddington luminosity. Such universalities can appear in the regime in which electron scattering opacity dominates over absorption opacity. Further, the normalized isotropic mechanical luminosity $L_{\rm mech}^{\rm ISO}/L_{\rm Edd}$ (evaluated by normalized density and velocity at $\theta =10^\circ$) exhibits a broken power-law relationship with ${\dot{m}}_{\rm BH}$; $L_{\rm mech}^{\rm ISO}/ L_{\rm Edd} \propto {\dot{m}}_{\rm BH}^{2.7}$ (or $\propto {\dot{m}}_{\rm BH}^{0.7}$) below (above) ${\dot{m}}_{\rm BH}\sim 400$. This is because the radial velocity stays nearly constant (or even decreases) below (above) the break with increase of $\dot{m}_{\rm BH}$. We also find that the luminosity ratio is $L_{\rm mech}/L_{\rm rad}^{\rm ISO} \sim 0.05$ at ${\dot{m}}_{\rm BH} \sim 100$, which is roughly consistent with the observations of NLS1, 1H 0323+103.

Review paper on applications of the HEC-RAS model for flooding, agriculture, and water quality simulation

ABSTRACT The Hydrologic Engineering Center (HEC) of the United States Army Corps of Engineers (USACE) has developed the HEC-River Analysis System (RAS) hydraulic channel flow model as part of its portfolio of hydrologic and hydraulic modeling tools. HEC-RAS is a new version with capabilities to model flooding, modeling for agriculture production computations for water quality, and many more related to hydraulic modeling. The analysis components of the HEC-RAS system include one-dimensional steady flow water surface profile computations, one-dimensional and or two-dimensional unsteady flow simulation, one-dimensional and two-dimensional computations of quasi-unsteady or fully unsteady flow movable boundary sediment transport, and one-dimensional water quality analysis. The main objective of this paper is to review the use of HEC-RAS on flooding, agriculture, and water quality. The three primary components of the data input are plan data, geometry data, and flow data. Three of these scenarios applied to HEC-RAS and were proven by previous reviewers.

Suitability of 2D depth-averaged simulations to support predictions of cyprinids passage through Vertical Slot Fishways

Fishways are a key measure to recover longitudinal connectivity. Among them, Vertical Slot Fishways (VSFs) have undergone extensive studies. However, very few numerical studies have included coupled hydrodynamics and ecological simulations. We investigated the impact of using three-dimensional (3D RANS) and two-dimensional (2D SWE) flow simulations in a Eulerian Lagrangian Agent-based Model (ELAM) for VSFs. Spatial distribution of turbulent kinetic energy ( k ), velocity magnitude ( | u i | ) , and velocity strain rate ( S ij ) were evaluated. While the | u i | was consistent across simulations, k was overestimated by the 2D SWE simulations. The frequency of S ij highest values was different between 3D RANS and 2D SWE. Also, the influence of these variables on the agent’s cognitive response was inconsistent. 2D SWE displayed an influence of around 0%, 35%, and 25% for k , | u i | and S ij , respectively. 3D RANS resulted in percentages of around 80% of k , 10–20% of | u i | and 0–10% of S ij . All cases were validated, demonstrating that both approaches are suitable to reproduce experimental observations. We demonstrated that the 2D SWE might serve as a good input to simulate fish movement in VSF. Nonetheless, hydrodynamic variables’ influence on agents’ decision making might be biased from real fish experience.

Comparison between processing time for groundwater flow of fractured porous media via analytic element method

The aim of our work is to study two-dimensional fractured flow simulations for groundwater by using non-identical aperture of fractures via Analytic Element Method, and make a comparison between processing time of both techniques i.e. iterative and matrix method. Numerical solutions for the considered problems are totally based on series expansions, whereas the effects of every fracture are expressed as a series which obey Laplace's equation. In all examined cases, it is evident that the iterative method is not able to converge, while by introducing the matrix method, the expected results are obtained with minimum computational cost (processing time).

Hydraulic conductivity tensor of anisotropic soils: the impact on seepage flow

Natural or artificial changes in soil stratigraphic-plane (i.e., the deposition of soil and sediments into distinct layers) orientation can cause variations in hydraulic conductivity in different direction. Hydraulic conductivity must, therefore, be considered – in this case – as a nondiagonal, full tensor to appropriately represent the effect of the orientation of soil stratigraphic planes on the seepage flow pattern. This paper introduces the derivation of the formula for the three-dimensional nondiagonal hydraulic conductivity full tensor calculation in terms of azimuth and vertical angles. Furthermore, two-dimensional numerical simulations of the seepage flow beneath a concrete dam are presented to demonstrate the need to account for the nondiagonal elements of the hydraulic conductivity tensor in anisotropic soils of varying degrees of stratigraphic tilt with respect to the coordinate system.

Enhanced parallel computation for time-fractional fluid dynamics: A fast time-stepping method with Newton-Krylov-Schwarz solver

This paper presents a sum-of-exponentials domain decomposition method for the numerical simulation of two-dimensional unsteady fluid flow and heat transfer using a time-fractional fluid model. We employ a fast time-stepping approach to discretize the time-fractional derivatives, followed by the application of a parallel Newton-Krylov-Schwarz algorithm to solve the resulting discrete nonlinear system. The numerical experiments demonstrate a superior performance of the fast time-stepping method compared to the traditional L1 scheme, particularly in the context of parallel computation, as it substantially reduces the computational complexity and memory usage. The algorithm exhibits robust performance across a wide range of model parameters and solver settings. Notably, it achieves 60% parallel efficiency with the use of 768 processor cores. This study underscores the efficacy of parallel processing as a potent computational strategy for addressing the challenges in solving time-fractional partial differential equations.

Simulation of two-dimensional flow around an elliptical cylinder at high Reynolds numbers

The modified viscous vortex domains method is used for direct numerical simulation of two-dimensional flow around an elliptical cylinder at the Reynolds number up to Re = 106. The modified method is based on the use of a conformal mapping from the outer region of an ellipse to the outer region of a circle. Transformed Navier–Stokes equations under an arbitrary conformal mapping are derived. These equations are solved in the mapped plane. An efficient algorithm for calculating boundary elements, previously developed to calculate the flow around a circular cylinder, is applied. The application of this algorithm makes it possible to reduce the calculation time by orders of magnitude and significantly expands the possibilities of flow simulation at high values of the Reynolds number. The method developed in this work can be implemented in other vortex methods.

Back-Calculation of Manning’s Roughness Coefficient by 2D Flow Simulation and Influence of In-Channel Physical Parameters in a Mountain River, Japan

This study attempts to back-calculate Manning’s roughness coefficients by repeating a two-dimensional flow simulation to fit the spatially and temporally dense river water-level data observed in Japan’s Yamatsuki River, a typical mountainous river with an average riverbed gradient of 1/50 and an average river width of 17.9 m. Furthermore, we aim to clarify the influence of the in-channel physical parameters on the coefficient of roughness obtained through the above method. In the Yamatsuki River, 16 water-level gauges were installed at intervals of about 40~80 m in the longitudinal direction in the study reach. Manning’s roughness coefficients were back-calculated by repeating two-dimensional flow simulations to match the observed water levels of a flood in 2021 (the estimated maximum flow rate is 11.5 m3/s). The back-calculated roughness coefficients approached a constant value in the range of 0.05 to 0.1 s/m1/3 as the relative water depth increased, indicating that the roughness coefficient can be considered a constant value when performing plane two-dimensional flow calculations for flooding. The roughness coefficient during flooding was found to be correlated with the slope and step height (H)-step length (L)- channel slope (S) ratios (H/L/S). An equation for predicting the roughness coefficient during flooding based on the physical parameters of the channel is also proposed.

Optimizing flow control with deep reinforcement learning: Plasma actuator placement around a square cylinder

This study introduces a deep reinforcement learning-based flow control approach to enhance the efficiency of multiple plasma actuators on a square cylinder. The research seeks to adjust the control inputs of these actuators to diminish both drag and lift forces on the cylinder, ensuring flow stability in the process. The proposed model uses a two-dimensional direct numerical simulation of flow past a square cylinder to represent the environment. The control approach involves adjusting the AC voltage across three specific configurations of the plasma actuators. Initially tested at a Reynolds number (ReD) of 100, this strategy was later applied at ReD of 180. We observed a 97% reduction in the mean drag coefficient at ReD = 100 and a 99% reduction at ReD = 180. Furthermore, the findings suggest that increasing the Reynolds number makes it harder to mitigate vortex shedding using plasma actuators on just the cylinder's rear surface. However, an optimized configuration of these actuators can fully suppress vortex shedding under the proposed control scheme.

Preface

This Proceedings arose from 2023 International Conference on Applied Statistics, Modeling and Advanced Algorithms (ASMA 2023), which was held via hybrid form in Qingdao, China from July 28th to 30th, 2023. ASMA 2023 marks the first time that this series of conference had been successfully held.The scientific and social program for the meeting ran over three days with more than 60 delegates from over 10 countries gathering on July 28th and departing on July 30th, including plenary, keynote speeches, oral presentations, poster presentations, and academic communication.In all there were five keynote speeches during the meeting. Prof. Le Fang addressed a speech on Hexagonal Periodic Condition in the Simulation of Two-Dimensional Flows. In order to simulate numerically the isotropic turbulence, traditional methods are to use periodic boundary conditions. However, using periodic conditions will involve problems of background anisotropy at large scales, which prevents to generate the truly isotropic turbulence. According to qualitative calculations, he showed that this background anisotropy is principally related to the shape of the energy spectrum. In two-dimensional cases, he designed a fast Fourier transfer (FFT) algorithm for hexagonal periodic conditions, which can be used in pseudo-spectral methods. Using this algorithm, the hexagonal periodic conditions were involved to reduce the large-scale background anisotropy.Topics that were the focus of invited presentations and contributed papers at ASMA 2023 included: Statistical Mechanics, Data Mining, Modeling Simulation Input, Numerical Analysis, Application-driven Numerical Parallel Algorithms, etc. All submissions were gone through rigorous review and process by performing double blind review to check their quality of content, level of innovation, significance, originality and legibility.The Conference could not have occurred without the generous support of our Conference sponsors. It would also not have been possible without the hard work of the Technical Program Committee members. We are most grateful for the staff of Journal of Physics: Conference Series for their help and kindness in the preparation of this volume. Finally, we would like to thank all the attendees at ASMA 2023 for their scientific contributions to the Conference, and for their warm spirit of engagement which characterized the scientific discussions and social occasions.The Committee of ASMA 2023List of Committee Member is available in the pdf.

Construction and Verification of Two-dimensional Surface Hydraulic Calculation Model

Accurate calculation and prediction of the surface water flow process in the substation and surrounding area is of great significance for on-site flood control and disaster reduction of the substation. Aiming at the dynamic process of surface water flow, this paper simulated the spatial and temporal distribution characteristics of surface water flow by establishing a two-dimensional hydrodynamic calculation model. Based on the N-S equation, a finite volume integral method is used to discrete the governing equations. On this basis, a hydrodynamic model for two-dimensional numerical simulation of surface water flow is constructed, and the basic governing equations for two-dimensional surface shallow water movement are derived. Based on the Toce River physical model and water flow control experiment, the corresponding conceptual model is established. On this basis, the measured data are used to verify the constructed two-dimensional surface hydrodynamic calculation model. The results show that the model can better simulate the process of surface water flow and describe its temporal and spatial distribution characteristics. The research results will provide effective technical support for substation site flood warning and prevention.

Numerical Simulation of Two-Dimensional Turbulent Dilatable Flows in a Fire

Numerical simulations, based on the theories of computational fluid dynamics and combustion, are currently a powerful tool in the field of fire engineering. Field models allow us to analyze key aspects such as the integrity of buildings and safety. However, it is fundamental to define strategies that allow engineers to obtain a balance between the precision of the results and the computational cost. One of the most relevant sub-models is the turbulence model. This paper presents the research carried out in the field of two-dimensional computational simulations of turbulent dilatable flows to evaluate the behavior of diffusion flames, hot gases, and smoke produced in accidental fires. Several computational simulations have been performed using direct numerical simulations and large eddy simulation turbulence models in the two-dimensional field, analyzing the ability of the models to correctly characterize the transport of hot gases and the behavior of the thermal plumes if the grid resolution is adequate to the physics of the problem. Additionally, several three-dimensional models have been developed to contrast and validate the results obtained in the two-dimensional simulations. In order to validate the capacity to develop a qualitative analysis of two-dimensional models in fire engineering, an evaluation criterion is presented based on the frequency spectral analysis to study the capacity of each type of turbulence model to accurately capture the vorticity of these dilatable flows.

Optimisation of initial velocity distribution of jets for entrainment and diffusion control using deep reinforcement learning

The control of the entrainment and diffusion of the heat and mass ejected along the jet flow requires the control of fluid motion. In the present study, optimal initial velocity distributions for suppressing and promoting jet entrainment and diffusion were identified using deep reinforcement learning under constant initial jet flow rate conditions. Two-dimensional jet flow simulations using OpenFOAM were combined with a deep Q-network as the learning algorithm. The spatial distribution of the initial jet (velocity and ejection angle) changed. The results show that to suppress the entrainment of the jet, an optimal initial velocity distribution shape in which the velocity in the centre is almost 0, with an inward velocity just outside of it, and a large outward velocity at the outer edge, is desirable. However, to promote entrainment, a shape with a large velocity in the centre portion and small velocity at the outer edge, with an overall inward angle, is desirable. To suppress the diffusion of the jet, an optimal initial velocity distribution shape with a large velocity in the centre portion, a small velocity at the outer edge, and an overall inward angle is desirable. Conversely, to promote diffusion, a shape with a large outward velocity at both the centre and outer edges is desirable. It is also indicated that, when the initial velocity distribution of the jet has a special shape, and the relationship between flow rate, centre velocity, and centre temperature that is normally observed in a jet flow may not hold. In other words, by changing the initial velocity distribution, the entrainment and diffusion of the jet can be separated and controlled, which is usually difficult to achieve using conventional engineering methods.

Modulation and hysteresis in vortex-induced vibration of a spring-mounted cylinder in a slowly varying oscillatory stream

The response of a spring-mounted circular cylinder constrained to vibrate with a single degree of freedom transverse to an oscillating stream is investigated using two-dimensional flow simulations. The Keulegan–Carpenter number was set at large values with the ratio of the oscillatory flow frequency fo to the natural frequency of the cylinder fn assuming values of fo/fn=0.01, 0.02, and 0.04, so as to investigate the effect of very-slowly-varying reduced velocity on the transient response. A maximum reduced velocity of 5, corresponding to a maximum Reynolds number of 150, was employed in all cases. Under these conditions, the cylinder underwent intermittent vortex-induced vibration (VIV) with amplitude modulations at the period of the oscillatory flow. Maximum VIV amplitudes of approximately half diameter occurred near the end of the flow acceleration stage. Pronounced hysteresis was observed in the plots of the ensemble-averaged amplitude and frequency, both being greater during the deceleration stage than during the acceleration stage at the same instantaneous reduced velocity over a significant part of the flow half period. The hysteresis was found to be related to ‘transient’ operating points that, in the space of normalized amplitude and frequency, join smoothly the distinct branches of steady-VIV where operating points do not exist (for the same system with varying the reduced velocity). The main deterministic VIV features were similar at all three frequency ratios examined but the stochastic features became more pronounced as fo/fn was increased. We also found that the cylinder motion and the driving fluid force sometimes were not synchronized around the point of maximum flow velocity, although this point corresponds to well within the synchronization range in steady-VIV.

Numerical Simulation and Computational Fluid Dynamics Analysis of Two-Dimensional Lid-Driven Cavity Flow Within the Weapon Bay of an Autonomous Fighter Drone

The efficient deployment of weapons in military operations is critical for mission success, and the flow of air within the weapon bay of an autonomous fighter drone plays a vital role in achieving this objective. In this paper, we present a comprehensive numerical simulation and computational fluid dynamics (CFD) analysis of the three-dimensional lid-driven cavity flow within the weapon bay of an autonomous fighter drone. To address this challenging problem, we employ CFD analysis and a multigrid approach to solve the Navier-Stokes equations for the aerodynamic problem. Our simulations include high Reynolds numbers of up to 10,000, which demonstrates the potential of CFD analysis in optimizing the design of autonomous fighter drones for military operations. We evaluate the effectiveness of the linked strongly implicit multigrid technique in estimating high-Re fine-mesh flow solutions using the vorticity-stream function formulation of the two-dimensional incompressible Navier-Stokes equations. The model issue is the driven flow in a square cavity, and we consider meshes up to 1024 x 1024 points and combinations with Reynolds numbers as high as 1000. To further improve the accuracy of our simulations, we employ one-dimensional grid clustering coordinate transformations instead of uniform mesh refinement, as the flow field exhibits one or more secondary vortices. Our findings demonstrate that CFD analysis can provide valuable insights into the complex flow dynamics within the weapon bay of autonomous fighter drones, which can lead to the optimization of their design for enhanced mission capabilities. Overall, our study highlights the significance of numerical simulations and CFD analysis in the design and optimization of autonomous fighter drones for military applications. Our results can serve as a basis for future research in the field of UAV aerodynamics and contribute to the development of more efficient and effective military operations.

Flood risk mapping for the area with mixed floods and human impact: a case study of Yarkant River Basin in Xinjiang, China

Flooding has been causing severe consequences worldwide, including loss of human life and damage to property. Flood risk mapping, as a nonstructural measure, is efficient for flood protection and disaster alleviation. This study aims at completing the flood risk mapping of the region located at the middle reaches of the Yarkant River Oasis in western China, which has a dry climate and suffers from mixed flooding consisting of glacial outburst floods (GLOFs) and many other floods. In view of the complexity of flooding in the area, the study adopts two typical types of scenarios, namely overflow scenarios and dike-break scenarios, to complete the flood risk mapping. The MIKE FLOOD 1D/2D coupled model is used for two-dimensional flood flow simulation to compute the inundation depths and duration for flood risk assessment. The spatial overlay analysis was then used to combine the modeling results and land use/land cover layers with socioeconomic data to generate flood risk maps and damage losses under different scenarios. It is noted that evaporation and infiltration losses in the study area are not negligible because of the long flood process, the low precipitation, and dry surface/subsurface conditions. Due to the insufficient evaporation and infiltration data, a new method of synthesis loss rate is proposed to compute the evaporation/infiltration loss rate. Based on the water balance principle, the upstream and downstream flow data is utilized to calculate the water attenuation, which is then used to estimate the evaporation/infiltration loss rate. The proposed method can solve the problem of calculating evaporation/infiltration loss rates during the flooding process in such data-scarce areas. The flood risk mapping results indicate that the flood risk is high along the Yarkant River and that floods can cause severe inundation losses.

Remediation of multilayer soils contaminated by heavy chlorinated solvents using biopolymer-surfactant mixtures: Two-dimensional flow experiments and simulations.

To assess the efficiency of remediating dense non-aqueous phase liquids (DNAPLs), here heavy chlorinated solvents, through injection of xanthan solutions with or without surfactant (sodium dodecylbenzenesulfonate: SDBS), we conducted a comprehensive investigation involving rheological measurements, column (1D) and two-dimensional (2D) sandbox experiments, as well as numerical simulations on two-layers sand packs. Sand packs with grain sizes of 0.2-0.3mm and 0.4-0.6mm, chosen to represent the low and high permeable soil layers respectively, were selected to be representative of real polluted field. The rheological analysis of xanthan solutions showed that the addition of SDBS to the solution reduced its viscosity due to repulsive electrostatic forces and hydrophobic interactions between the molecules while preserving its shear-thinning behavior. Results of two-phase flow experimentsdepicted that adding SDBS to the polymer solution led to a reduced differential pressure along the soil and improvements of the DNAPL recovery factor of approximately 0.15 and 0.07 in 1D homogeneous and 2D layered systems, respectively. 2D experiments revealed that the displacement of DNAPL in multilayer zones was affected by permeability difference and density contrast in a heterogeneous soil. Simulation of multiphase flow in a multilayered system was performed by incorporating non-Newtonian properties and coupling the continuity equation with generalized Darcy's law. The results of modeling and experiments are very consistent. Numerical simulations showed that for an unconfined soil, the recovery of DNAPL by injection of xanthan solution can be reduced for more than 50%. In a large 2D experimental system, the combination of injecting xanthan with blocking the contaminated zone led to a promising remediation of DNAPL-contaminated layered zones, with a recovery of 0.87.