Two-dimensional Unsteady Flow Research Articles

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.

Adaptive water management in response to tidal inundation and sea level rise on tidal agricultural lowlands of Katingan, Central Kalimantan

Decreased water management systems and sea level rise cause inundation in the Katingan tidal agricultural lowland. Excessive and prolonged inundation can decrease rice production or even loss of rice land. A study was conducted to provide adaptive water management for controlling water levels in canals and rice crop fields inundation. For this purpose, a combined one- and two-dimensional unsteady flow method was used in HEC-RAS. The scenario of water level control uses sluice and flap gates in secondary canals. Under spring tide conditions, water level control with gates decreases the inundation area by 95.62%. Likewise, in the 25 and 50-year sea level rise scenarios, inundation decreased by 88.51% and 82.25%. In the spring tide condition, the duration of inundation is decreased from 3.5 to 0.9 days. Under 25 and 50-year sea level rise scenarios, the duration of inundation was decreased from 3.7 to 3 days and from 4.3 to 4.1 days. The use of gates significantly decreases inundation in the spring tide condition, but under sea level rise in 25 and 50-year, the depth and duration of inundation are still dangerous for rice crops; therefore, it is necessary to advance water management control for the sustainability of rice fields.

Predictive modelling of flow dynamics in micropolar hybrid nanofluids subjected to magnetic dipole influence using nonlinear autoregressive artificial neural networks with exogenous input

In the present research article, we explore the intelligence-based numerical computation of a nonlinear autoregressive artificial neural network with exogenous input using the Levenberg-Marquardt algorithm (ANN-LMA) trained to analyze the unsteady two-dimensional micro-polar flow of an incompressible hybrid nanofluid (Al 2 O 3−Fe 3 O 4/Ethylene Glycol) under the impact of the magnetic field introduced by the magnetic dipole on a nonlinear stretched sheet. In the first step of the research, partial differential equations are converted into nonlinear ordinary differential equations using appropriate transmission and then solved numerically via the Successive Over Relaxation method after applying the finite difference method. The impact of numerous emerging parameters on the solutions is displayed graphically, and the physical significance is discussed. The results show that the concentration profile displays a dwindling trend for the Brownian motion parameter, and the opposite trend is witnessed for the thermophoretic parameter. Moreover, for increasing values of the dimensionless distance parameter and ferromagnetic interaction parameter, the temperature and velocity profiles exhibit the opposite tendency. In the second step of the study, we validated the Successive Over Relaxation outcomes with an ANN-LMA. For this purpose, the suggested ANN-LMA is trained for six different scenarios of the reference dataset points of the given flow model. The analysis shows that Successive Over Relaxation and LM-SNNs yield similar results, with a decreasing trend for the Brownian motion parameter and an opposite trend for the thermophoretic parameter.

A cluster analysis-based shock wave pattern recognition method for two-dimensional inviscid compressible flows

Compressible flows typically exhibit multiple shock waves which interact with each other, making the detection of these shock waves crucial for various aspects of flow studies including construction of high-order numerical schemes (e.g., shock-fitting), adaptive grid refinement, and flow visualization. This study aims to effectively identify and localize multiple shock waves and their interaction points in two-dimensional inviscid steady and unsteady flows. A novel shock wave pattern recognition method based on cluster analysis is proposed, including three processes. First, a series of grid-cells located at the transition zones of captured shock waves are extracted using a shock wave detection approach based on local flow variation. Subsequently, these grid-cells are grouped into numerous clusters using the classical K-means clustering algorithm, with categorization based on nearest neighbor features. Finally, a strategy is introduced to merge relevant adjacent clusters and further localize the points where shock waves interact. The Bézier curve fitting technique is then employed to obtain the high-quality shock-lines. Several numerical cases demonstrate that this method achieves high localization accuracy for shock-lines while being minimally affected by grid type and scale variations. Moreover, it enables clear and effective identification of the shock interaction patterns in both steady and unsteady flows, providing an effective visualization means for analyzing the motion and evolution of shock wave configurations.

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.

Aerodynamic force by Lamb vector integrals in unsteady compressible flows

Purpose This study aims to propose an aerodynamic force decomposition which, for the first time, allows for thrust/drag bookkeeping in two-dimensional viscous and unsteady flows. Lamb vector-based far-field methods are used at the scope, and the paper starts with extending recent steady compressible formulas to the unsteady regime. Design/methodology/approach Exact vortical force formulas are derived considering inertial or non-inertial frames, viscous or inviscid flows, fixed or moving bodies. Numerical applications to a NACA0012 airfoil oscillating in pure plunging motion are illustrated, considering subsonic and transonic flow regimes. The total force accuracy and sensitivity to the control volume size is first analysed, then the axial force is decomposed and results are compared to the inviscid force (thrust) and to the steady force (drag). Findings Two total axial force decompositions in thrust and drag contributions are proposed, providing satisfactory results. An additional force decomposition is also formulated, which is independent of the arbitrary pole appearing in vortical formulas. Numerical inaccuracies encountered in inertial reference frames are eliminated, and the extended formulation also allows obtaining an accurate force prediction in presence of shock waves. Originality/value No thrust/drag bookkeeping methodology was actually available for oscillating airfoils in viscous and compressible flows.

A numerical investigation on forced convection heat and mass transfer performance in a right triangular cavity

The objective of this numerical study is to examine how different Reynolds numbers impact heat and mass transfer in an unsteady forced convective two-dimensional flow within a right-angle triangular cavity. The lowest surface of the enclosure is held at a fixed temperature and concentration, whereas the slanted surface is taken to be a cool surface. Furthermore, the cavity's left wall is adiabatically positioned to move in two directions: upwards (aiding flow) and downwards (opposing flow), with a constant speed being maintained. The partial differential equations that govern the system are converted into a non-dimensional form through a straightforward transformation. The finite-element scheme is employed to solve these dimensionless equations. The analysis facilitates the investigation of the belongings of the Reynolds number on the heat and mass transfer appearances by using streamlines, isotherms, and isoconcentration lines. It is initiated that the temperature spreading as well as concentration within the cavity depends strongly on the Reynolds number. Moreover, the motion of the moving wall influences the patterns of fluid flow, temperature, and concentration fields. This study provides a comprehensive investigation into heat and mass transfer behavior occurring within a lid-driven right-angled triangular cavity moving in two opposite directions for aiding flow and opposing flow respectively.

Investigation of Magnetized Casson Nanofluid Flow along Wedge: Gaussian Process Regression

An unsteady two-dimensional magnetized Casson nanofluid flow model is constructed over a wedge under the effect of thermal radiation and chemical reaction. The multiple slip effects are also assumed near the surface of the wedge along with the convective boundary restrictions. This study investigates the application of soft computing techniques to address the challenges posed by the complexity of problem modeling and numerical methods. Traditional approaches incorporating various model factors may struggle to provide accurate solutions. To resolve this issue, Gaussian process regression (GPR) is employed to predict the solution of the proposed flow model. With the help of the numerical shooting method together with Runge–Kutta–Fehlberg fourth-fifth-order (RKF-45) reference data, the GPR model is trained. The numerical simulation illustrated that the Casson fluid parameter β and the unsteadiness parameter S strengthen the friction factor, and the heat transfer rate is enhanced as the radiation parameter Rd becomes larger. In addition, the Biot numbers Bi1 & Bi2 lead to strengthen nanoparticle temperature; an opposite behavior is noticed with the skin friction coefficient S˜fxRex0.5, heat transfer rate H˜tx Rex0.5, and nanoparticle transfer rate C˜txRex0.5. The GPR model with the exponential Kernel function provided better performance than other functions on both training and checking datasets to predict S˜fxRex0.5,H˜tx Rex0.5, and C˜txRex0.5. Statistical metrics including RMSE, MAE, MAPE, MSE, R2, and R are employed to check the accuracy and convergences of the predicted and numerical solutions obtained through GPR and RKF-45. It is observed that all three GPR models had an R2 value of higher than 0.9. The proposed study demonstrates the advantages of employing soft computing methods (GPR) to effectively analyse the behavior of complex flow models.

Unsteady Two-Dimensional Natural Convection Fluid Flow in a Valley Shaped Cavity

Unsteady Two-Dimensional Natural Convection Fluid Flow in a Valley Shaped Cavity

Unsteady magneto-hydrodynamic behavior of TiO2-kerosene nanofluid flow in wavy octagonal cavity

The aim of this study is to mathematically model the behavior of magneto-hydrodynamics (MHD) in a two-dimensional unsteady flow, specifically focusing on natural convection (NC) and heat transfer (HT) within a wavy octagonal cavity. The study investigates how heat is transferred and fluid flows within this cavity under specific conditions. In particular, it examines the impact of various parameters, such as the Hartmann number (Ha), Rayleigh number (Ra), and the volume fraction of nanoparticles (ϕ) on the flow and HT patterns. This cavity includes a rectangular vertical wall (RVW) at the center of its bottom wall, filled with kerosene-TiO2 nanofluid of spherical shape. Within this setup, the RVW is maintained at a high temperature (T = Th), while the wavy wall is kept at a lower temperature (T = Tc, where Tc <Th). All other boundaries of the domain are assumed to be adiabatic. The finite element method (FEM) is employed as the solver for the relevant partial differential equations in numerical simulations. The results show excellent agreement with previously published research papers. The numerical solution transitions from an unsteady state to a steady state in approximately 0.68 dimensionless time units during the HT process. Throughout the study, various parameters are explored, including Ha, ranging from 0 to 100, Ra, ranging from 103 to 106, and ϕ, ranging from 0 to 0.05. The findings reveal distinct patterns in streamlines and isotherms. Specifically, a reduction in the rate of HT is observed as the Lorentz force increases, while the rate of HT is enhanced with increasing buoyancy force. Additionally, an expansion in ϕ led to an increase in the rate of HT. The study's findings could contribute to our understanding of fluid dynamics, heat transfer, and the behavior of nanofluids in complex geometries, potentially leading to improvements in various engineering and industrial applications.

Dual solutions of unsteady flow of copper-alumina/water based hybrid nanofluid with acute magnetic force and slip condition

Suspending particles of tiny solid in a fluid used to transport energy can enhance its thermal conductivity and heat transport properties. Our main goal of this examination is to study the radiative unsteady two-dimensional (2D) flow on a continuously diminishing, horizontal sheet. with suction for the hybrid water-based nanofluid and an aligned field of magnetic, including the combined suction, magnetic, and velocity slip conditions effect. The Tiwari & Das model of nanofluid equations is used, which takes into consideration the solid volume percentage. Equations of similarity are derived by employing the transformations of similarity, and the associated equations have been simplified numerically by employing the bvp4c method in MATLAB software for a variety of values of the nanoparticle volume fraction, the unsteadiness, and the wall mass suction in water. It is discovered that, within the given the unsteadiness parameter range, two solutions exist. Moreover, it is found that the fluid velocity slows down in 1st solution as volume fraction of copper nanoparticles rises but speeds up in the second solution at first before slowing down again. Using a temporal stability analysis, it is found that only one of the dual branches is stable over the long run, while the other is unstable.

Effect of Magnetic field on Unsteady Mixed convection Micropolar Nanofluid flow in the Presence of Non-Uniform Heat Source/Sink.

: The idea of the current investigation is to study the two-dimensional unsteady mixed convection MHD flow of a micro-polar nanofluid with non-uniform heat source/sink. Effects of radiation, reaction, thermo-diffusion, and viscous dissipation are considerednanoparticles are suspended in water base fluid. The governing non-linear system of PDEs is transformed into a system of ODEs using the similarity transformation and HAM is employed for obtaining solutions. Effects of different physical parameter on momentum, microrotation, energy, and concentration profiles are discussed through graphs. From graphical results, it is concluded that the unsteady parameter and magnetic parameter tend to improve the motion of the fluid. It is also seen that microrotation is raised in the shrinking sheet and reduced in the stretching sheet with the increase in the unsteady parameter. The mass transfer process improved with thermal diffusion parameter while delayed with chemical reaction.

Численное исследование двухмерного симметричного течения несжимаемой жидкости с зависящей от координат вязкостью между частично неровными плоскостями

The structure of a symmetric two-dimensional unsteady flow between two planes having a periodic step-like irregularity is investigated by numerical methods using the finite element package Freefem++. The kinematic viscosity of the fluid is chosen as typical for turbulent flows, depending on the coordinates as 𝜇 = 𝜇0(𝜂2(𝑥) − 𝑧2), 𝜂(𝑥) = ℎ(𝑥) + 𝛿, where 𝜇0 is the characteristic viscosity, 𝛿 is the roughness, ℎ(𝑥) is the function defining the boundary 𝑧 = 𝜂(𝑥) (profiles of planes mirror-symmetric with respect to 𝑧 = 0), 𝑥, 𝑧 are longitudinal and transverse coordinates along the main flow. In contrast to the usual parabolic profile of the Poiseuille flow between the planes, with the specified choice of viscosity, the flow profile is logarithmic and has a singularity at the boundary of the region, to prevent which the roughness of the boundary is introduced. A distinctive feature of the problem under study is the setting of boundary conditions on an irregular part of the boundary. On plane sections of the boundary, we maintain the usual non-slip conditions for a viscous liquid, but on the irregular part of the boundary we set only the impermeability conditions of the boundary for the liquid (no sticking!). Computational experiment - numerical solution of the Navier-Stokes equations for a viscous incompressible fluid using a modified penalty method, showed that for a wide set of parameters, the structure of the flow described by the initial non-stationary complete problem and the quasi-stationary flow described by the asymptotic model constructed in the presented paper, for which there is an exact solution, are in good agreement - in the non-stationary flow, a stable regular system of vortices is established concentrated near those surface irregularities for which the boundary has a negative curvature (`deepening’of boundary).

Spatial–temporal analysis of magnetohydrodynamics flow and energy flux of power-law nanofluid in a confined domain

Energy flux analysis of power-law fluid is a novel contribution to recent developments in computational fluid dynamics. The study of the unsteady two-dimensional flow with double diffusive effect inside a complex enclosure exhibits great potential in optimizing the heat transfer rate due to the wavy nature of the side walls. The enclosure is confined with the flow circulation due to the thermal and solutal gradients acting along the left and right wavy walls. The computational time and accuracy in results are estimated and compared by implementing the finite volume method and element-free Galerkin technique. The results are obtained in terms of streamlines, isotherms, isoconcentrations, average Nusselt number, Sherwood number, and total entropy generation due to the effect of conventional parameters, namely, power-law index, Rayleigh number, buoyancy ratio parameter, thermophoresis parameter, Brownian motion parameter, and Lewis number with a fixed Prandtl number throughout the computation. The optimized double-diffusive natural convection analysis is based on entropy generation and a calculated Bejan number. The novelty of this paper lies in the implementation of a mesh-free approach, which may be useful for the further analysis of elliptical/semi-elliptical structures.

Comparison of Adomian Decomposition Method with Differential Transformation Method for Unsteady MHD Flow and Heat Transfer Over a Stretching/Shrinking Permeable Sheet with Ohmic Heating

In this paper, two semi-analytical techniques were implemented to solve a two-dimensional unsteady MHD fluid flow and heat transfer through a stretching/shrinking permeable sheet with ohmic heating and viscous dissipation. The governing flow equations in PDE form were reduced to ordinary differential equations using appropriate similarity transformation. We obtained approximate expressions for the velocity and temperature profiles. Comparative results obtained employing Adomian decomposition method and differential transformation method were benchmarked against a numerical solution using Keller box scheme. Our findings revealed that the approximate analytical solution obtained using DTM is more dependable with fast convergence, highly accurate with minimal calculations and computationally convenient. However, the requirement of Adomian polynomials to tackle the nonlinear terms in ADM makes its execution sometimes cumbersome and difficult.

Compressibility effects on the secondary instabilities of the circular cylinder wake

With a growing interest in low Reynolds number compressible flows, compressibility effects on the secondary instabilities developing on the circular cylinder periodic wake are investigated. The unsteady and time-averaged two-dimensional flows are characterised for Reynolds numbers ${{Re}} \in [200;350]$ and Mach numbers up to ${{M}}_{\infty }=0.5$ , revealing different flow structures which influence the characteristics of the secondary unstable modes. The two-dimensional time-periodic solution is used as the base state for a global linear stability analysis performed by means of Floquet theory coupled with a time-stepping finite-difference approach of the nonlinear operator. The influence of compressibility on mode A and mode B secondary instabilities which are responsible for the three-dimensionalisation of the two-dimensional periodic wake is analysed. A stabilising or a destabilising effect of compressibility is observed on mode A, depending on the Reynolds number and the spanwise wavelength of the mode, while mode B is stabilised by the increase of the Mach number. Compressibility is indeed found to decrease the mode kinetic energy production due to base flow shear conversion, which drives the growth of mode B. This results in a delay of the three-dimensionalisation process of the wake due to compressibility.

Linear global and asymptotic stability analysis of the flow past rectangular cylinders moving along a wall

The primary instability of the steady two-dimensional flow past rectangular cylinders moving parallel to a solid wall is studied, as a function of the cylinder length-to-thickness aspect ratio ${A{\kern-4pt}R} =L/D$ and the dimensionless distance from the wall $g=G/D$ . For all ${A{\kern-4pt}R}$ , two kinds of primary instability are found: a Hopf bifurcation leading to an unsteady two-dimensional flow for $g \ge 0.5$ , and a regular bifurcation leading to a steady three-dimensional flow for $g &lt; 0.5$ . The critical Reynolds number $Re_{c,2\text{-}D}$ of the Hopf bifurcation ( $Re=U_\infty D/\nu$ , where $U_\infty$ is the free stream velocity, $D$ the cylinder thickness and $\nu$ the kinematic viscosity) changes with the gap height and the aspect ratio. For ${A{\kern-4pt}R} \le 1$ , $Re_{c,2\text{-}D}$ increases monotonically when the gap height is reduced. For ${A{\kern-4pt}R} &gt;1$ , $Re_{c,2\text{-}D}$ decreases when the gap is reduced until $g \approx 1.5$ , and then it increases. The critical Reynolds number $Re_{c,3\text{-}D}$ of the three-dimensional regular bifurcation decreases monotonically for all ${A{\kern-4pt}R}$ , when the gap height is reduced below $g &lt; 0.5$ . For small gaps, $g &lt; 0.5$ , the hyperbolic/elliptic/centrifugal character of the regular instability is investigated by means of a short-wavelength approximation considering pressureless inviscid modes. For elongated cylinders, ${A{\kern-4pt}R} &gt; 3$ , the closed streamline related to the maximum growth rate is located within the top recirculating region of the wake, and includes the flow region with maximum structural sensitivity; the asymptotic analysis is in very good agreement with the global stability analysis, assessing the inviscid character of the instability. For cylinders with $AR \leq 3$ , however, the local analysis fails to predict the three-dimensional regular bifurcation.

Entropy analysis of unsteady MHD nanofluid flow over a stretching surface with effects of variable viscosity and nonuniform heat generation

An unsteady two-dimensional nanofluid flow across a permeable stretched sheet is examined in terms of thermodynamic analysis. Water is utilized as the basic fluid, together with four distinct types of nanoparticles: copper (Cu), copper oxide (CuO), aluminum oxide (Al2O3), and titanium dioxide (TiO2). An external source is used to describe the heat transfer phenomena. The effects of heat generation and absorption are also taken into account. The nonlinear partial differential equations are transformed into a system of nonlinear ordinary differential equations via a similarity transformation. The spectral quasi-linearization approach is then used to numerically integrate the altered equations. Except when otherwise noted, the findings are provided for copper nanoparticle situations. A visual and detailed explanation of the effects of several physical factors on the profiles of dimensionless velocity, temperature, average entropy generation function, skin friction, and the Nusselt number are discussed. As exceptional circumstances of the current findings, there is a strong agreement between the current conclusion and the findings of the other researchers. The average entropy generation number, temperature, and velocity profiles are shown to be strongly influenced by regulating factors. It is concluded that the average entropy generation decreased in the presence of a temperature- and space-dependent heat source/sink, but it improves with enhanced viscosity parameter. The significance of the present study has frequent applications in the major area of heat transfer enhancement in renewable energy systems, industrial thermal management, and also materials processing.

Numerical Simulation of a Two-Dimensional Spatial Unsteady Flow Past Thick Airfoils and Low-Aspect-Ratio Wings with Slot Suction in a Vortex Cell as Applied to Hybrid Aerostatic Aircraft

Numerical Simulation of a Two-Dimensional Spatial Unsteady Flow Past Thick Airfoils and Low-Aspect-Ratio Wings with Slot Suction in a Vortex Cell as Applied to Hybrid Aerostatic Aircraft

Prediction of Near-Wake Velocity in Laminar Flow over a Circular Cylinder Using Neural Networks with Instantaneous Wall Pressure Input

In the present study, to predict the transverse velocity field in the near-wake of laminar flow over a circular cylinder at the Reynolds numbers of 60 and 300, we construct neural networks with instantaneous wall pressures on the cylinder surface as the input variables. For the two-dimensional unsteady flow at Re=60, a fully connected neural network (FCNN) is considered. On the other hand, for a three-dimensional unsteady flow at Re=300 having spanwise variations, we employ two different convolutional neural networks based on an encoder–FCNN (CNN-F) or an encoder–decoder (CNN-D) structure. Numerical simulations are carried out for both Reynolds numbers to obtain instantaneous flow fields, from which the input and output datasets are generated for training these neural networks. At the Reynolds numbers considered, the neural networks constructed accurately predict the transverse velocity fields in the near-wake over the cylinder using the information of instantaneous wall pressures as the input variables. In addition, at Re=300, it is observed that CNN-D shows a better prediction ability than CNN-F.