Steady Flow Model Research Articles

Evaluation of the PG method for modeling unsteady flows in complex bathymetries

The performance graph (PG) hydraulic routing method has been shown to be accurate, numerically efficient, and robust for unsteady flow routing. However, up to present, the PGs are constructed using one-dimensional (1D) steady flow models only, which are often questioned when simulating flows through complex bathymetries. This paper investigates whether the PG method can still be used when utilizing two-dimensional (2D) models for the construction of PGs. The test case is a stretch around an island in the Fraser River in British Columbia. The results show that the PG method is still applicable when utilizing a 2D steady flow model. The results also show that once the PGs are constructed, the PG routing method (1D and 2D) is computationally more efficient than the unsteady HEC-RAS model and can be several orders of magnitude faster than TELEMAC-2D.

A hydrodynamic analysis of thermocapillary convection in evaporating thin liquid films

Evaporation in a thin film induces pronounced temperature gradient and surface tension gradient along the liquid-vapor interface and in turn engenders thermocapillary flow. This study aims to investigate the fluid flow characteristics attributed to the thermocapillarity in an evaporating thin liquid film of polar and nonpolar liquids. A numerical steady-flow model is derived based on the fundamental principles of fluid flow and heat transfer by applying the long-wave evolution technique. To scrutinize the underlying physical transport phenomena associated with the significance of thermocapillary effect in an evaporating thin liquid film, we investigate the hydrodynamic characteristics of thermocapillary convection which is typically characterized by the recirculation flow patterns. The two-dimensional recirculation flow patterns in different excess-temperature regimes are analyzed and a critical turning point at where the flow is reversed due to the thermocapillary action can be identified. Compared to other working fluids, water depicts a unique thermocapillary flow characteristic where its flow lines manifests in the form of swirls along the liquid-vapor interface. The normal and the shear stress distributions further provide a clearer picture on the strength of thermocapillarity to identify the manifestation of thermocapillary flow. The analysis of flow patterns and hydrodynamic behaviors of evaporating thin liquid films provide essential insights in discerning the occurrence of thermocapillary flow as well as the significance of thermocapillarity in polar and nonpolar liquids.

On a Certified Smagorinsky Reduced Basis Turbulence Model

In this work we present a reduced basis Smagorinsky turbulence model for steady flows. We approximate the nonlinear eddy diffusion term using the empirical interpolation method (cf. [M. A. Grepl et al., ESAIM Math. Model. Numer. Anal., 41 (2007), pp. 575--605; Barrault et al., C. R. Acad. Sci. Paris Ser. I Math., 339 (2004), pp. 667--672]) and the velocity-pressure unknowns by an independent reduced-basis procedure. This model is based upon an a posteriori error estimation for a Smagorinsky turbulence model. The theoretical development of the a posteriori error estimation is based on [S. Deparis, SIAM J. Sci. Comput., 46 (2008), pp. 2039--2067] and [A. Manzoni, ESAIM Math. Model. Numer. Anal., 48 (2014), pp. 1199--1226], according to the Brezzi--Rappaz--Raviart stability theory, and adapted for the nonlinear eddy diffusion term. We present some numerical tests, programmed in FreeFem++ (cf. [F. Hecht, J. Numer. Math., 20 (2012), pp. 251--265]), in which we show a speedup on the computation by factor larger...

High-order exact solutions for pseudo-plane ideal flows

A steady pseudo-plane ideal flow (PIF) model is derived from the 3D Euler equations under Boussinesq approximation. The model is solved analytically to yield high-degree polynomial exact solutions. Unlike quadratic flows, the cubic and quartic solutions display reduced geometry in the form of straightline jet, circular vortex, and multipolar strain field. The high-order circular-vortex solutions are vertically aligned and even the non-aligned multipolar strain-field solutions display vertical concentricity. Such geometry reduction is explained by an analytical theorem stating that only straightline jet and circular vortex have functional solutions to the PIF model.

Perbandingan Hasil Pemodelan Aliran Satu Dimensi Unsteady Flow dan Steady Flow pada Banjir Kota

One dimensional flow is often used as a flood simulation for the planning capacity of the river. Flood is a type of unsteady non-uniform flow, that can be simulated using HEC-RAS. HEC-RAS software is often used for flood modeling with a one-dimensional flow method. Unsteady flow modeling results in HEC-RAS sometimes refer to error and warning due to unstable analysis program. The stability program among others influenced bend in the river flow, the steep slope of the river bottom, and changes in cross-section shape. Because the flood handling required maximum discharge and maximum flood water level, then a steady flow is often used as an alternative to simulate the flood flow. This study aimed to determine the advantages and disadvantages of modeling unsteady non-uniform and steady non-uniform flow. The research location in the Kanal Banjir Barat, in the Semarang City. Hydraulics modeling uses HEC-RAS 4.1 and for discharge the plan is obtained from the HEC-HMS 3.5. Results of the comparison modeling hydraulics the modeling of steady non-uniform flow has a tendency water level is higher and modeling of unsteady non-uniform flow takes longer to analyze. Results of the comparison the average flood water level maximun is less than 15% (± 0,3 meters), that is 0.27 meters (13.16%) for Q50, 0.25 meters (11.56%) for Q100, dan 0.16 meters (4.73%) for Q200. So the modeling steady non-uniform flow can still be used as a companion version the modeling unsteady non-uniform flow.

Integrated approach of geospatial visualization and modeling for groundwater management in hard rock terrains in Nagpur Urban Area, India

Groundwater management requires complete visualization of aquifer characteristics to understand scientific aspects and hence remains a challenge, especially in hard rock terrains. In the present research paper, a comprehensive approach using 3D stratigraphic model, fence diagrams and numerical modeling has been proposed to understand the groundwater status for effective recharge. The stratigraphy, groundwater flow, and groundwater fluctuations for the period 1999–2010 were analyzed. The total volume of formations, volume of voids, storage capacity, and quantities of recharge of unconfined aquifer system in the Nagpur urban area were estimated. The steady state groundwater flow model of Basalt formation was calibrated to evaluate the subsurface system using Processing Modflow (PMWIN 5.3.2). The calibrated hydraulic head is compared with field observed head. The comparative spatial analysis presents a simple integrated approach in identifying zones with falling groundwater trends suitable for groundwater recharge in hard rock terrain in Nagpur urban area.

Two-Fluid Model for Blood Flow Through a Tapered Arterial Stenosis: Effect of Non-zero Couple Stress Boundary Condition at the Interface

The present paper concerns a mathematical model for steady flow of blood through tapered stenosed arteries with peripheral plasma layer near the wall. The model consists of a core region of suspension of all the erythrocytes assumed to be a couple stress fluid and a peripheral layer of plasma as a Newtonian fluid. A non-zero couple stress boundary condition at the interface is introduced. The values of velocity, wall shear stress and the flow resistance with respect to the non-zero couple stress condition at the interface for normal blood and diseased [polycythemia, plasmal cell dyscrasias and HBSS (sickle cell)] blood are computed. It is observed that the introduction of the non-zero couple stress boundary condition at the interface helps to increase the velocity and significantly reduces the resistive impedance which, in turn, improves or normalizes the blood flow in diseased state. This information of blood flow could be useful for the development of new diagnosis tools and medicines for many diseases.

Dynamic wetting failure in surfactant solutions

The influence of insoluble surfactants on dynamic wetting failure during displacement of Newtonian fluids in a rectangular channel is studied in this work. A hydrodynamic model for steady Stokes flows of dilute surfactant solutions is developed and evaluated using three approaches: (i) a one-dimensional (1D) lubrication-type approach, (ii) a novel hybrid of a 1D description of the receding phase and a 2D description of the advancing phase, and (iii) an asymptotic theory of Cox (J. Fluid Mech., vol. 168, 1986b, pp. 195–220). Steady-state solution families in the form of macroscopic contact angles as a function of the capillary number are determined and limit points are identified. When air is the receding fluid, Marangoni stresses are found to increase the receding-phase pressure gradients near the contact line by thinning the air film without significantly changing the capillary-pressure gradients there. As a consequence, the limit points shift to lower capillary numbers and the onset of wetting failure is promoted. The model predictions are then used to interpret decades-old experimental observations concerning the influence of surfactants on air entrainment (Burley & Kennedy, Chem. Engng Sci., vol. 31, 1976, pp. 901–911). In addition to being a computationally efficient alternative for the rectangular geometries considered here, the hybrid modelling approach developed in this paper could also be applied to more complicated geometries where a thin air layer is present near a contact line.

Numerical Investigation of a Mixed Convection Flow in a Lid-Driven Cavity

This study is devoted to the computational fluid dynamics (CFD) modeling of steady laminar mixed convection flow and heat transfer in lid driven cavity (10 ≤ Re ≤ 1000). The ratio of the height to the width of the cavity is ranged over H/L = 0.5 to 1.5. The governing equations are solved using commercial finite volume package FLUENT to visualize the nature of the flow and estimate the heat transfer inside the cavity for different aspect ratio. The simulation results are presented in terms of average Nusselt number of the hot wall, velocity profile, and temperature contours. It was found that the average Nusselt number inside the cavity is strongly governed by the aspect ratio as well as the Reynolds number. A parametric study is conducted to demonstrate the effect of aspect ratio on the flow and heat transfer characteristics. It is found that heat transfer enhancement was obtained by decreasing the aspect ratio and/or increasing the Reynolds number.

Novel experimental/numerical approach to evaluate the permeability of cement-caprock systems

This study presents a novel laboratory-scale experimental/numerical approach that contributes to our understanding of micro-annular flow paths in cement-caprock interfaces. The approach is based on studying single-phase fluid flow in composite specimens with imperfect bonding between cement and caprock. Imperfect bonding and defect zones in the cement were initially characterized by X-ray micro computed tomography. Subsequently, the bulk permeability of the specimens was determined through single-phase fluid permeability measurements. Permeability was also evaluated numerically by finite-element modelling of steady single-phase flow in the specimens. The numerical modelling revealed that the average permeability of defect zones mapped from μ-CT images was likely to be within 1–10D (0.1×10−11 to 1×10−11m2). If a connected region of elevated permeability is established in situ, it can create a potential well integrity risk by providing a flow path up the annulus of the well. The integrated experimental and numerical framework employed in this study can form the basis for future systematic evaluation of leakage risks related to well integrity issues during underground CO2 storage, as well as in other applications such as drilling and completion of geothermal wells.

Optimal conditions in converting methanol to dimethyl ether, methyl formate, and hydrogen utilizing a double membrane heat exchanger reactor

Following importance of investigating new sources of energy with highly efficient processes, a new configuration for simultaneous production of high purity dimethyl ether (DME), hydrogen and methyl formate (MF) is numerically studied in this work. In this regard, a catalytic heat-exchanger reactor assisted with two different membranes for methanol conversion and in-situ separation of products is simulated. The interesting feature of this system is utilizing only one feedstock (i.e. methanol) to produce different valuable products. Methanol is dehydrated through an exothermic reaction and supplies required energy for the methanol dehydrogenation reaction. Produced water in the exothermic side and produced hydrogen in the endothermic side are separated by permeation to particular membranes. A steady state one-dimensional plug flow model is developed to evaluate molar and thermal behavior of the system. Optimum operating conditions are determined applying genetic algorithm as a powerful optimization method. The proposed configuration working under optimum conditions promotes methanol conversion to DME to % 95.1 and methanol conversion to MF to % 99.6 providing high purity products in the output streams.

Simulation of Groundwater-Surface Water Interactions under Different Land Use Scenarios in the Bulang Catchment, Northwest China

Groundwater is the most important resource for local society and the ecosystem in the semi-arid Hailiutu River catchment. The catchment water balance was analyzed by considering vegetation types with the Normalized Difference Vegetation Index (NDVI), determining evapotranspiration rates by combining sap flow measurements and NDVI values, recorded precipitation, measured river discharge and groundwater levels from November 2010 to October 2011. A simple water balance computation, a steady state groundwater flow model, and a transient groundwater flow model were used to assess water balance changes under different land use scenarios. It was shown that 91% of the precipitation is consumed by the crops, bushes and trees; only 9% of the annual precipitation becomes net groundwater recharge which maintains a stable stream discharge in observed year. Four land use scenarios were formulated for assessing the impacts of land use changes on the catchment water balance, the river discharge, and groundwater storage in the Bulang catchment. The scenarios are: (1) the quasi natural state of the vegetation covered by desert grasses; (2) the current land use/vegetation types; (3) the change of crop types to dry resistant crops; and (4) the ideal land use covered by dry resistant crops and desert grasses, These four scenarios were simulated and compared with measured data from 2011, which was a dry year. Furthermore, the scenarios (2) and (4) were evaluated under normal and wet conditions for years in 2009 and 2014, respectively. The simulation results show that replacing current vegetation and crop types with dry resistant types can significantly increase net groundwater recharge which leads to the increase of groundwater storage and river discharges. The depleted groundwater storage during the dry year could be restored during the normal and wet years so that groundwater provides a reliable resource to sustain river discharge and the dependent vegetations in the area.

On the estimation of the bed-material transport and budget along a river segment: application to the Middle Loire River, France

Sediment load and budgets are a fundamental component of the process-based hydromorphological framework developed by the REFORM project, and are needed to accurately assess the current condition of a river, its sensitivity to change, and its likely future evolutionary trajectory. This paper presents an evaluation of three different methods for estimating both bedload sediment transport and bed-material budget within river channels, using the Middle Loire River as a case study. The first method is based on the stream power concept and does not need any hydraulic calculations. It yields estimates of the sediment transport in the same order of magnitude as measurements but poor results for the bed-material budget in terms of magnitude and tendency. For the second method, hydraulic parameters are computed using the Manning–Strickler equation (or a 1D hydraulic model for steady flow). It provides useful indicators for understanding river dynamics but does not yield significant improvements compared to the first method. The third method uses 1D numerical software for water flow and river bed evolution. It yields the most accurate results for both sediment transport and bed evolution but requires more data and overall more work to construct the model. Guidance is provided on the amount of data required, the competence needed to build the models, and the predictive capability of each of the methods.

Numerical solution of viscous and viscoelastic fluids flow through the branching channel by finite volume scheme

This work deals with the numerical modelling of steady flows of incompressible viscous and viscoelastic fluids through the three dimensional channel with T-junction. The fundamental system of equations is the system of generalized Navier-Stokes equations for incompressible fluids. This system is based on the system of balance laws of mass and momentum for incompressible fluids. Two different mathematical models for the stress tensor are used for simulation of Newtonian and Oldroyd-B fluids flow. Numerical solution of the described models is based on cetral finite volume method using explicit Runge-Kutta time integration.

Numerical and experimental study of Boussinesq wall horizontal turbulent jet of fresh water in a static homogeneous environment of salt water

This paper investigates a numerical and experimental study about buoyant wall turbulent jet in a static homogeneous environment. A light fluid of fresh water is injected horizontally and tangentially to a plane wall into homogenous salt water ambient. This later is given with different values of salinity and the initial fractional density is small, so the applicability of the Boussinesq approximation is valid. Since the domain temperature is assumed to be constant, the density of the mixture is a function of the salt concentration only. Mathematical model is based on the finite volume method and reports on an application of standard k – ɛ turbulence model for steady flow with densimetric Froude numbers of 1-75 and Reynolds numbers of 2 000-6 000. The basic features of the model are the conservation of mass, momentum and concentration. The boundaries of jet body, the radius and cling length are determined. It is found that the jet spreading and behavior depend on the ratio between initial buoyancy flux and momentum, i.e., initial Froude number, and on the influence of wall boundary which corresponds to Coanda effect. Laboratory experiments were conducted with photographic observations of jet trajectories and numerical results are described and compared with the experiments. A good agreement with numerical and experimental results has been achieved.

Comparison Between Bench-Top and Computational Modelling of Cerebral Thromboembolism in Ventricular Assist Device Circulation

Despite improvements in ventricular assist devices (VAD) design, VAD-induced stroke rates remain remarkably high at 14-47%. We previously employed computational fluid dynamics (CFD) to propose adjustment of VAD outflow graft (VAD-OG) implantation to reduce stoke. Herein, we present an in-vitro model of cerebral vessel embolization in VAD-assisted circulation, and compare benchtop results to CFD predictions. The benchtop flow-loop consists of a 3D printed aortic bed using Accura 60 polymer driven by a continuous-flow pump. Three hundred spherical particles simulating thrombi of 2, 3.5, and 5 mm diameters were injected at the mock VAD-OG inlet. A water and glycerin mixture (3.8 cP viscosity) synthetically mimicked blood. The flowrate was adjusted to match the CFD Reynolds number. Catch cans were used to capture and count particles reaching cerebral vessels. VAD-OG geometries were evaluated using comparison of means Z-score range of -1.96 ≤ Z ≤ 1.96 to demonstrate overall agreement between computational and in-vitro techniques. Z-scores were: (i) Z = -1.05 for perpendicular (0°), (ii) Z = 0.32 for intermediate (30°), and (iii) Z = -0.52 for shallow (60°) anastomosis and confirmed agreement for all geometries. This study confirmed added benefits of using a left carotid artery bypass-graft with percent embolization reduction: 22.6% for perpendicular, 21.2% for intermediate, and 11.9% for shallow anastomoses. The shallow anastomosis demonstrated lower degrees of aortic arch flow recirculation, consistent with steady-flow computations. Quantitatively and qualitatively, contemporary steady-flow computational models for predicting VAD-induced cerebral embolization can be achieved in-vitro to validate the CFD equivalent.

Model for Longitudinal Perch Maneuvers of a Fixed-Wing Unmanned Aerial Vehicle

Aerodynamicists with a vision for birdlike aircraft systems must move beyond steady flow models toward new ways of characterizing motion of agile flight systems. One such system is a fixed-wing aircraft that performs a deep stall maneuver commonly referred to as a perch. Described herein is a mathematical model for perch maneuvers of a small aircraft with fixed, positively cambered wings. The modeling approach does not rely on resource-heavy forms of system identification but rather employs a minimalist approach, whereby insights gleaned from previous high-angle-of-attack research are applied to individual components of the aircraft. Using the model that results from this approach, three aggressive, longitudinal perch maneuvers are computer-simulated, and results of the simulations are compared to laboratory flight measurements obtained using high-speed video tracking. Notwithstanding its simplicity, the model predicts position, velocity, and pitch orientation of the aircraft with significant accuracy.

Numerical and experimental study of horizontal round turbulent forced plume in a static homogeneous environment

This paper investigates a numerical and experimental study about horizontal round turbulent forced plume injected into a static homogeneous environment. Helium–air plume is an example of non-Boussinesq forced plume in which a low-density binary gas mixture is injected into a high density ambient of air. Since the domain temperature is assumed to be constant, the density of the mixture is a function of the concentration only. Numerical model is based on the finite volume method and reports on an application of standard k–e model for steady flow with densimetric Froude numbers of 30–300 and Reynolds numbers of 2000–6000. The basic features of the model are: the conservation of mass, momentum and concentration. The boundaries of plume body, the centerline trajectory, the radius plume and the centerline mixture density are determined. It is found that the plume spreading and behavior depend on the ratio between buoyancy flux and momentum, i.e. Froude number. Laboratory experiments have been conducted for photographic observations of plumes trajectories for different mixture (helium–air) densities with different velocities and injection nozzle diameters. Numerical results are described and compared with the experiments and good agreement has been achieved.

A perspective on fifty years of natural ventilation research

A brief history is given of research into natural ventilation over the first fifty years of the Journal, from the personal perspective of the author. One of my aims is to give an indication of the contribution that the Journal has made to reporting research on this subject. Another aim is to provide a background for researchers who are starting out in research. There are nine areas of research that I have identified, namely:- steady envelope flow models; flow characteristics of openings; unsteady envelope flow models; internal air motion, zonal models and stratification; contaminant transport; age of air; CFD and its applications; scale modelling; full-scale measurements. For reasons given in the text, some of these topics are only very briefly mentioned. For example, the sections on contaminant transport and CFD are relatively brief, partly because they are the subject of other papers in this issue. (Similarly, the feasibility of natural ventilation relies on the adaptability of the occupants to be comfortable, but thermal comfort is not covered at all here, because it too is the subject of other papers.) The paper concludes with a few personal comments on the design process, since the underlying aim of research is to minimise the risks associated with naturally ventilated buildings.

Investigation of sheet-flow processes based on novel acoustic high-resolution velocity and concentration measurements

AbstractA new dataset of uniform and steady sheet-flow experiments is presented in this paper. An acoustic concentration and velocity profiler (ACVP) is used to measure time-resolved profiles of collocated 2C velocity ($u,w$) and sediment concentration and to measure the time evolution of the bed interface position. Ensemble averaging over 11 similar experiment realisations is done to evaluate the mean profiles of streamwise velocity, concentration, sediment flux and Reynolds shear stress. The repeatability, stationarity and uniformity of the flow are carefully checked for a Shields number${\it\theta}\approx 0.5$and a suspension number of$S=1.1$. The mean profile analysis allows to separate the flow into two distinct layers: a suspension layer dominated by turbulence and a bed layer dominated by granular interactions. The bed layer can be further subdivided into a frictional layer capped by a collisional layer. In the suspension layer, the mixing length profile is linear with a strongly reduced von Karman parameter equal to 0.225. The Schmidt number is found to be constant in this region with a mean value of${\it\sigma}_{s}=0.44$. The present results are then interpreted in terms of existing modelling approaches and the underlying assumptions are discussed. In particular, the well-known Rouse profile is shown to predict the concentration profile adequately in the suspension layer provided that all the required parameters can be evaluated separately. However, the strong intermittency of the flow observed in the bed layer under the impact of turbulent large-scale coherent flow structures suggests the limitations of averaged steady two-phase flow models.