Two-dimensional Flow Model Research Articles

Investigation of the Influence of the Computational Grid for Turbulent Flow

The article provides basic information about the principles of calculations based on the solution of the system of Navier-Stokes equations by the control volume method, and the relationship between velocities and pressure was found using the SIMPLE procedure. For the numerical solution of this problem, schemes against the flow of A.A. Samarsky and McCormack were applied. The results were compared with each other and with experimental data. The Spalart-Allmares model is used for turbulence. On the example of a two-dimensional flow model in a straight channel, the influence of the quality of the grid and turbulence models on the distribution of flow parameters inside the calculated zone and the integral characteristics of the flow is studied.

Numerical study of inhomogeneous deformation of gas diffusion layers on proton exchange membrane fuel cells performance

Gas diffusion layers play a critical role in the operation of proton exchange membrane fuel cells. As the most compressible component in proton exchange membrane fuel cells, the non-uniform deformation mainly occurs on the interface between bipolar plates and gas diffusion layers caused by the special channel-rib geometry of the flow field, which results in a non-uniform variation of physical properties of gas diffusion layers, such as porosity, effective electrical conductivity, and gas diffusivity, consequently affects the cell performance. In this paper, a two-dimensional, across-the-channel, multi-physics and two-phase flow model based on the spherical agglomerate assumption is developed to investigate the complicated relationships between the non-uniform deformation and variation of physical properties of the gas diffusion layers, as well as the cell performance. A modified diffusion coefficient is introduced to describe the effect of the variation of species concentration on the effective diffusion coefficient based on the Bruggeman formula. Simulation results show that an optimal cell performance can be achieved by balancing the variation of porosity, effective electrical conductivity, and effective gas diffusion coefficient with respect to different degrees of deformation of gas diffusion layers.

A numerical study on thermal management of a lithium-ion battery module via forced-convective air cooling

• Air-cooled thermal management of battery module has been explored numerically. • Thermal performance for inline and staggered cell arrangement was examined. • Negligible effect of cell arrangement occurs beyond a critical number of cells. • For small number of cells, the staggered arrangement slightly improves thermal uniformity. Global environmental concerns over increased emissions from the transportation vehicles have driven research instincts towards development of clean energy vehicles. Pure and hybrid electric vehicles coupled with lithium-ion batteries for energy storage are environmental friendly options to realize the future dream of low carbon emissions. However, an efficient battery thermal management system (BTMS) is a prerequisite for safe operation of such high voltage batteries to avoid thermal runaway and degradation, thereby maintaining the temperature uniformity in the battery pack. Thus, the present work numerically investigates the performance of an air cooled battery module for efficient removal of heat generated during the discharge process at different values of air-flow velocity, cell configuration and the number of cells in the battery module. A coupled electrochemical-thermal model is employed to model the discharge behaviour of the battery in conjunction with the two-dimensional flow and heat transfer model to monitor the temperature in and out of each battery cell. A correlation is developed for the maximum temperature in the module as a function of the number of cells in the system. The flow configuration (inline or staggered arrangement) of cells in the stack is observed to have no influence over the velocity and thermal field beyond a critical value of number of cells in the module.

Stabilized finite element computations with a two-dimensional continuum model for disorderly traffic flow

A two-dimensional continuum model of traffic flow is proposed. The model incorporates disorderly traffic, lane indiscipline, streamwise variation of the width of the road, as well as the impact of edges of the road, on the traffic. A stabilized finite element formulation is employed to solve the governing equations. The performance of the model is demonstrated using numerical experiments. Several features that are commonly observed in high speed flow of fluids, such as oblique shocks, normal shocks, slip lines, and expansion fans, are observed in the traffic flow simulated via the proposed model. The model is utilized to predict the traffic capacity of a road with varying road width. It is found that the narrow section behaves as a throat in a converging diverging nozzle in high speed fluid flow. The proposed model explains several phenomena observed in real traffic streams.

Analysis of muzzle flow field characteristics of gun fired in different media

To study the muzzle flow field created by a sealed launch of an underwater gun and the distribution characteristics of the muzzle flow field in different media, a two-dimensional axisymmetric numerical model for the muzzle multiphase flow created by an underwater sealed launch is established. The volume of fluid numerical model, standard k- \begin{document}$\varepsilon $\end{document} turbulence model, user-defined function (UDF) and dynamic mesh technology are used to numerically analyze and compare the evolution process of the muzzle flow field between underwater sealed launch and air launch. The calculation results show that the muzzle flow field is notably different from that in air when the gun is launched under water. The maximum chamber pressure of the underwater sealed launch is basically the same as that in air. The muzzle velocity of the projectile is reduced by 32 m/s compared with launching in air, while the pressure and temperature of the muzzle are significantly increased. The Mach disc of the underwater sealed launch is initially formed at about 140 μs, while the Mach disc of the air launch is formed later, at about 320 μs. Compared with launching in air, the core area of shock wave in underwater launch is smaller, and there is no coronal shock wave around the head of the projectile. In the case of underwater sealed launch, the axial displacement of the Mach disc from the muzzle increases exponentially with time, while in the case of air launch, the axial displacement of the Mach disc from the muzzle increases linearly with time.

A Stabilized Finite Element Formulation of Non-Newtonian Fluid Model of Blood Flow in A Bifurcated Channel with Overlapping Stenosis

A stabilized form of finite element formulation known as the Galerkin least-squares (GLS) method is implemented here for solving the two-dimensional incompressible non-Newtonian fluid model of blood flow in a diseased artery. The modelling for this type of flow is based on the conservation of mass and momentum equations, coupled with the generalised Newtonian liquid (GNL) constitutive equation characterized by the generalised power law (GPL) model. The flow of blood in this present study are assumed as steady, laminar and fully developed. The finite element algorithms considered herein are first solved for the Newtonian fluid in a straight artery with a bell shaped stenosis for validation purposes. As the efficiency and validity of the proposed algorithms are obtained through comparison with the findings from existing literature and COMSOL Multiphysics 5.2 software. Then, the algorithms are being implemented to the generalised power law fluid model of blood flow in a bifurcated artery with overlapping stenosis located at the parent's arterial lumen. The numerical results illustrate the arising of distinct sizes of vortex shedding downstream of the stenotic region for each generalised power law index.

Extended shallow-water theories with thermodynamics and geometry

Driven by growing momentum in two-dimensional geophysical flow modeling, this paper introduces a general family of “thermal” rotating shallow-water models. The models are capable of accommodating thermodynamic processes, such as those acting in the ocean mixed layer, by allowing buoyancy to vary in horizontal position and time as well as with depth, in a polynomial fashion up to an arbitrary degree. Moreover, the models admit Euler–Poincaré variational formulation and possess Lie–Poisson Hamiltonian structure. Such a geometric property provides solid fundamental support to the theories described with consequences for numerical implementation and the construction of unresolved motion parametrizations. In particular, it is found that stratification halts the development of small-scale filament rollups recently observed in a popular model, which, having vertically homogeneous density, represents a special case of the models presented here.

Numerical investigation of heat transfer and water infiltration characteristics within two-dimensional granular packed beds

This study used numerical analysis to determine the transport phenomena of hot water infiltration in a two-dimensional granular packed bed. The present study aims to investigate the parameter that affects the water saturation and temperature distribution in the two-dimensional porous packed bed. For this purpose, the problem was solved numerically using two-dimensional unsaturated flow and heat transfer models of hot water infiltration. Novel studies on the simultaneous heat and moisture transfer during hot water infiltration in partially saturated porous materials were investigated. The study illustrated the characteristics of heat and moisture transfer during the water infiltration process in various testing conditions. The results of the numerical model were validated with the results from previous research. It was found that the water flux supplied, and particle size have significant effects on the distribution of water saturation and temperature in the packed bed. The water saturation and heating area of the fine particles tended to expand in the lateral direction faster than the downward direction. The increase in supplied water flux resulted in a deeper and larger zone of water saturation and heating area. Furthermore, the heating area was found to be expanding slower than the water saturation front in all conditions.

Impact of the Magnetic Field on the Performance of Heat Pipes Driven by a Photovoltaic–Thermal Panel with Nanofluids

A two-dimensional dynamic heat transfer and fluid flow model was developed to describe the behavior of photovoltaic cells and the performance of a hybrid solar collector photovoltaic–thermal solar panel system. The system was assessed under different magnetic field Gauss forces. Nanofluids were used to drive the heat pipes in a thermal panel under different conditions, such as levels of solar irradiance and different boundary conditions. The model was developed based on the equations of the dynamic conservation of mass and energy, coupled with the heat transfer relationships and thermodynamic properties, in addition to the material properties under different magnetic Gauss forces. Comparisons were made with the literature data to validate the predictive model. The model reliably predicted the key parameters under different nanofluid conditions and magnetic fields, and compared well with the existing data on the subject.

Calculation method of short-duration rainstorm intensity formula considering nonstationarity of rainfall series: impacts on the simulation of urban drainage system

AbstractThe changing nature of the Earth's climate and rapid urbanization lead to the change of rainfall characteristics in urban areas, the stability of rainfall series is destroyed and it is a difficult challenge to consider this change in urban drainage simulation. A generalized additive model (GAMLSS) with time as covariant was established to calculate and predict the design values of extreme rainstorm return period, and the nonstationary short-duration rainstorm intensity formula of three periods was fitted and compared with the stationary formula. The urban water simulation model and the MIKE 21 two-dimensional surface flow model are coupled to simulate the urban flood under different formulas and different return periods. The results show that the nonstationary results are worse in the same period. In the 5-year return period rainfall–runoff simulation performance, the nonstationary inundation area is 18.5% more than the stationary, and inundation water is 23.5% more than the stationary. The nonstationary simulation results show higher inundation depth and slower flood recession process. These gaps will widen in the future, but they will become less significant as the return period increases. It can provide a reference for the study of flood control work and the design of existing drainage infrastructure in the region.

Balance in non-hydrostatic rotating shallow-water flows

Unsteady nonlinear shallow-water flows typically emit inertia-gravity waves through a process called “spontaneous adjustment-emission.” This process has been studied extensively within the rotating shallow-water model, the simplest geophysical model having the required capability. Here, we consider what happens when the hydrostatic assumption underpinning the shallow-water model is dropped. This assumption is in fact not necessary for the derivation of a two-dimensional or single-layer flow model. All one needs is that the horizontal flow field be independent of height in the fluid layer. Then, vertical averaging yields a single-layer flow model with the full range of expected conservation laws, similar to the shallow-water model yet allowing for non-hydrostatic effects. These effects become important for horizontal scales comparable to or less than the depth of the fluid layer. In a rotating flow, such scales may be activated if the Rossby deformation length (the ratio of the characteristic gravity-wave speed to the Coriolis frequency) is comparable to the depth of the fluid layer. Then, the range of frequencies supporting inertia-gravity waves is compressed, and the group velocity of these waves is reduced. We find that this change in wave properties has the effect of strongly suppressing spontaneous adjustment-emission and trapping inertia-gravity waves near regions of relatively strong circulation.

Revisiting simplified model of a single-well push–pull test for estimating regional flow velocity

Simplified analytical models of the single-well push–pull (SWPP) test have been widely used to estimate the regional flow velocity and the aquifer porosity, where the simplifications refer to that the dispersion effect is negligible, and the flow is steady state during the entire SWPP test. However, the errors caused by such assumptions have not been investigated thoroughly. In this study, numerical modeling of the SWPP test without above-mentioned simplifications and the field experimental data will be employed to test the applicability of the simplified analytical models. The numerical simulation is based on a mathematical model composed of a two-dimensional transient flow and transport model, which will be solved by the finite-element method. The results indicate that errors increase with the increasing dispersivity when using the simplified analytical models to estimate both regional flow velocity and porosity. The errors refer to the relative difference between the input parameters of the numerical modeling and the estimated parameters by the simplified models. Such errors also depend on the input values of regional groundwater velocity, drift time of the SWPP test, and aquifer porosity. Specifically, the errors caused by the simplified models of estimating regional groundwater velocity decrease with increasing input regional groundwater velocity, increasing input drift time, and decreasing input porosity. The errors produced by the simplified models of estimating porosity decrease with increasing input regional groundwater velocity, increasing input drift time, and decreasing input porosity. Field in-situ experiments show that the fitness of the observed breakthrough curves (BTCs) by the numerical modeling is far better than the simplified analytical models. The estimated regional flow velocity by the numerical modeling of this study is closer to the estimated values by previous other studies.

Impact of Magnetic Field on the Dynamic Performance of Photovoltaic-Thermal Panel with Nanofluids

The performance of a hybrid solar collector photovoltaic-thermal solar panel system under a magnetic field using nanofluids was presented hereby. A two-dimensional dynamic heat transfer and fluid flow model was developed to describe the behavior of the photovoltaic cell-thermal panel at different conditions such as solar irradiance, nanoparticles, different magnetic field gauss forces. different material properties, and boundary conditions. The model has been established after the dynamic mass and energy equations coupled with the heat transfer relationships, and thermodynamic properties as well as material properties under different magnetic gauss forces. Comparisons were made against literature data for validation purposes of the predictive model. The model fairly predicted the key parameters under different nanofluids conditions, magnetic fields, and compared well with existing data on the subject.

Experimental and Theoretical Study on The Flame Stabilization by Recirculation behind a Bluff - Body.(Dept.M)

An experimental investigation and analytical description have been carried out on the flame stabilization by recirculation behind a bluff-body flame holder. The blowout limits of flames and the length of the recirculation zone have been investigated for cylindrical and spherical bluff-body flame holders. Also, measurements of the influence of the flame holder geometry on the lean blowout limits as well as on the rich blowout limits have been carried out. In the theoretical study, a two-dimensional flow model to describe the mechanism of the flame stabilization by recirculation behind a bluff-body has been developed. In this model, the process of flame stabilization is governed by the balance between the rates of turbulent nixing and chemical reactions in the shear layer at the recirculation zone boundary. The predicted blowout limits of flames have shown a qualitatively agreement with the observed ones.

Piezoelectric rod sensors for scour detection and vortex-induced vibration monitoring

As extreme events increase in frequency, flow-disrupting large-scale structures become ever more susceptible to collapse due to local scour effects. The objective of this study was to validate the functionality of passive, flow-excited scour sensors that can continue to operate during an extreme event. The scour sensors, or piezo-rods, feature continuous piezoelectric polymer strips embedded within and along the length of slender cylindrical rods, which could then be driven into the soil where scour is expected. When scour erodes away foundation material to reveal a portion of the piezo-rod, ambient fluid flow excitations would cause the piezoelectric element to output a voltage response corresponding to the dynamic bending strains of the sensor. The voltage response is dependent on both the structural dynamic properties of the sensor and the excitation fluid’s velocity. By monitoring both shedding frequency and flow velocity, the exposed length of the piezo-rod (or scour depth) can be calculated. Two series of experimental tests were conducted in this work: (1) the piezo-rod was driven into sediment around a mock pier to collect scour data, and (2) the piezo-rod was used to monitor its own structural response by collecting vortex-shedding frequency data in response to varied flow velocities to establish a velocity–frequency relationship. The results showed that the piezo-rod successfully captured structural vortex-shedding frequency comparable to state-of-practice testing. A one-dimensional numerical model was developed using the velocity–frequency relationship to increase the accuracy of voltage-based length prediction of the piezo-rod. Two-dimensional flow modeling was also performed for predicting localized velocities within a complex flow field. These velocities, in conjunction with the velocity–frequency relationship, were used to greatly improve length-predictive capabilities.

Two-phase flow characteristics of different charging structure in ignition and flame-spreading

To study the influence of flame-spreading behaviour in the ignition process of different charging structures in high-density charge chambers, a visualisation device was designed, and the ignition process of the two charging structures was researched. The flame-spreading process was observed by a high-speed digital camera system and the pressure data was recorded by a data acquisition instrument. According to the experiment, a two-dimensional axisymmetric internal ballistic two-phase flow model was established to simulate the flow process of gas in particle bed based on the Weighted Essentially Non-Oscillatory (WENO) Scheme. The results show that the flow field and flame-spreading status in different charging structures are different. In the full charging structure, the development of the flow field is regular, the flow field in the entire chamber has less fluctuation areas, and velocity vortices only generate during the development of the flow field and when it reaches the wall. However, in the partially charging structure with free space, there are many pressure fluctuation areas in the flow field in the chamber, and the flow field development is also uneven. Pulsating propagation occurs at the interface between particles and free space, which has a great influence on the whole combustion and ignition process. The research results reveal the characteristics of two-phase flow in different charging structures and provide a reference for the actual charging process.

CFD simulation of bubbly flow in a long coaxial heat exchanger

The numerical investigation of a two-phase bubbly flow inside a long vertical counterflow heat exchanger has been performed in this study. The heat transfer was running from the steam moving inside the tubing to the two-phase bubbly water in the annulus. A two-dimensional steady-state heat transfer and fluid flow model are based on the coupling of a probability density function (PDF) coupled with a k-epsilon turbulence model is determined to be the best computation technique in this large-scale case. The k-epsilon model was used to analyze the carrier fluid (water or steam) and the PDF model to calculate bubble flow. The authors desired to receive practical results of the heat transfer process rather than paying attention to the formation of bubbles, their coalescence, tracking flow regimes, and other turbulence-related features that are useless in industrial applications. The article explored two cases: short (800 m) and long heat exchanger (8000 m). Several thermodynamic parameters were on track: flow velocities, pressure, temperature, and concentration of the bubbles in the radial direction. Einstein's correction equation adjusted the viscosity of the bubbles. Solution converged with non-uniform grid spacing in the longitudinal and radial directions. The results gave satisfactory conclusions about the validity of the obtained data with theoretical and experimental results. This article opens a new way on computational fluid dynamics (CFD) application to a large-scale simulation of long vertical or horizontal pipelines and coaxial heat exchangers with the coupled bubbly flow and heat transfer applicable to geothermal and petroleum industry problems.

Particle-Resolved Computational Fluid Dynamics as the Basis for Thermal Process Intensification of Fixed-Bed Reactors on Multiple Scales

Process intensification of catalytic fixed-bed reactors is of vital interest and can be conducted on different length scales, ranging from the molecular scale to the pellet scale to the plant scale. Particle-resolved computational fluid dynamics (CFD) is used to characterize different reactor designs regarding optimized heat transport characteristics on the pellet scale. Packings of cylinders, Raschig rings, four-hole cylinders, and spheres were investigated regarding their impact on bed morphology, fluid dynamics, and heat transport, whereby for the latter particle shape, the influence of macroscopic wall structures on the radial heat transport was also studied. Key performance indicators such as the global heat transfer coefficient and the specific pressure drop were evaluated to compare the thermal performance of the different designs. For plant-scale intensification, effective transport parameters that are needed for simplified pseudo-homogeneous two-dimensional plug flow models were determined from the CFD results, and the accuracy of the simplified modeling approach was judged.

Testing of an Optimization-Simulation Model for Real-Time Flood Operation of River-Reservoir Systems

A new methodology was developed for the real-time determination gate control operations of a river-reservoir system to minimize flooding conditions. The methodology is based upon an optimization-simulation model approach interfacing the genetic algorithm within MATLAB with simulation software for short-term rainfall forecasting, rainfall–runoff modeling (HEC-HMS), and a one-dimensional (1D), two-dimensional (2D), and combined 1D and 2D combined unsteady flow models (HEC-RAS). Both real-time rainfall data from next-generation radar (NEXRAD) and gaging stations, and forecasted rainfall are needed to make gate control decisions (reservoir releases) in real-time so that at time t, rainfall is known and rainfall over the future time-period (Δt) to time t + Δt can be forecasted. This new model can be used to manage reservoir release schedules (optimal gate operations) before, during, and after a rainfall event. Through real-time observations and optimal gate controls, downstream water surface elevations are controlled to avoid exceedance of threshold flood levels at target locations throughout a river-reservoir system to minimize the damage. In an example application, an actual river reach with a hypothetical upstream flood control reservoir is modeled in real-time to test the optimization-simulation portion of the overall model.

Eddy formation in the bays of Kamchatka and fluxes to the open ocean

The Eastern Kamchatka Current (EKC) is the western boundary current of the North Pacific subpolar gyre. Southeast of the Kamchatka Peninsula lies a large anticyclonic eddy, the Kamchatka Eddy (KE). This eddy is quasi-stationary. More generally, the oceanic region east of the EKC contains many eddies, several of them large and long lasting. Using surface currents derived from altimetry, particle tracking and a simple two-dimensional numerical model of fluid flow, we investigate the variability of this eddy field, the generation of eddies in the bays of Kamchatka by the EKC and fluxes of water to and from these bays. Firstly, we recover in our analysis of long-lasting eddies, the main eddies of the region. Among strong eddies, the parity bias favors anticyclones. Our numerical simulations give a possible explanation for the process of eddy creation in the bays of the peninsula and show that the northernmost bay produces most anticyclones. Then, we track forward the water particles from these bays and we determine their fate in the open ocean; southeastward and southwestward trajectories are the most frequent. We also track water particles backward from the KE site; they often drift near the Kamchatka coast, but others drift south of this site and remain there, a priori trapped in other eddies. This study confirms the complexity of mesoscale motions and water exchanges in this region.