Steady Flow Simulations Research Articles

Numerical simulation and modelling of steady convective Hiemenz flow of a dissipative micropolar fluid through stretching sheet

ABSTRACT The ongoing objective is to expand the mathematical model for steady convective Hiemenz flow on radiative dissipative micropolar fluid transport in a stretching sheet with Joule heating impacts and boundary conditions are influenced by slip velocity. Effectively a micropolar formulation combining different novel effects model is deployed. Navier-Stokes-based flow equations are rendered into non-dimensional form using some influential similarity transformations. The transmuted system of ordinary derivative equations has been solved through the Runge–Kutta Fourth order (RKF) along with the shooting technique. The outcome solutions are offered for velocity, angular velocity and temperature in tables, further engineering interest like shear stresses and Nusselt number are computed and discussed extensively to foremost parameters. Validation with prior results are established and found to agree quantitatively with others. The detailed analysis explores that, results produce notable hold upon boundary layer distributions.

Application of vanishing diffusion stabilization in Oldroyd-B fluid flow simulations

Two different methods of artificial diffusion stabilization of the numerical simulations of steady Oldroyd-B fluids flows are presented. They are based on the idea of vanishing in time added stabilization terms which are only present during the initial stage of time-marching process towards the steady state solution. These extra terms naturally vanish and do not affect the final result. The numerical simulations are built on a simple steady 2D case of Oldroyd-B fluid flow in a symmetrical corrugated channel. Numerical solver uses finite element discretization in space and characteristic Galerkin method for pseudo-time discretization. Numerical results are presented in the form of isolines and graphs of selected flow variables, to assess the possible efficiency of the different stabilization techniques used.

Determination of the maximum allowable active powerflow in the section taking into account the thermal conditions of power transmission lines

Subject of research: This paper assesses the possibility of introducing into the task of calculating maximum and emergency allowable active power flow, taking into account the thermal modes of overhead lines when planning electric power regimes. 
 Purpose of research: determine the effect of thermal processes in power lines on the maximum allowable active power flow in controlled sections of electric power systems.
 Methods and objects of research: Such factors influencing active power flow as ambient air temperature, which is currently corrected by the Russian Power System Operator, wind speed, solar radiation and direct heating from flowing current are considered. Simulation of steady state flow in the software package RastrWin3 and Mathcad for a 2-bus scheme with mode only taking into account the ambient temperature and the calculations of steady state flow were already taking into account variations in weather parameters, taking into account possible restrictions on the maximum load due to the modes of operation of the power system (technical feasibility generating equipment was not taken into account in the work under consideration).
 Main results of research: the result of calculation, it is clearly seen that when taking into account the thermal conditions of overhead power lines, the allowable active power flows differ by 1626 % from the values determined only when taking into account the ambient temperature.

Numerical simulation of ideal and non-ideal under-expanded supersonic jets with adaptive grids

This paper numerically investigates the effect of flow non-ideality on the Mach disk pattern occurring in axisymmetric under-expanded supersonic jets. The explored conditions are found in the non-ideal gas region close to the liquid–vapor saturation curve and the critical point, where involved thermodynamics cannot be accurately described by the ideal gas law. Numerical simulations of steady inviscid compressible flows are carried out by adopting the polytropic ideal gas model and improved Peng–Robinson thermodynamic model, via the open-source computational fluid dynamics code SU2. To properly resolve the Mach disk position and radius, a mesh adaptation procedure is used. An assessment of the most suitable mesh adaptation criteria for the considered ideal and non-ideal flow configurations is carried out, considering isotropic and anisotropic mesh adaptation criteria. The best mesh adaptation criterion for ideal and non-ideal under-expanded jets results to be the anisotropic criterion based on the Hessian of the density and Mach number field. Then, the effects of the flow non-ideality on the Mach disk are investigated by simulating different operating conditions of under-expanded nozzle jets of five different vapors. For nitrogen, oxygen, carbon dioxide, the Mach disk moves downstream and has a smaller radius with a higher level of non-ideality. Conversely, for siloxanes MM and MDM, the Mach disk moves upstream and has a larger radius as the non-ideality of the flows increases.

A CUDA Fortran GPU-parallelised hydrodynamic tool for high-resolution and long-term eco-hydraulic modelling

Eco-hydraulic models are wide extended tools to assess physical habitat suitability on aquatic environments. Currently, the application of these tools is limited to short river stretches and steady flow simulations. However, this limitation can be overcome with the application of a high-performance computing technique: graphics processing unit (GPU) computing. R-Iber is a GPU-based hydrodynamic code parallelised in CUDA Fortran that, with the integration of a biological module, performs as an eco-hydraulic numerical tool. R-Iber was validated and applied to real cases by using an optimised instream flow incremental methodology in long river reaches and long-term simulations. R-Iber reduces the computation time considerably, reaching speed-ups of two orders of magnitude compared to traditional computing. R-Iber allows for overcoming the current limitations of the eco-hydraulic tools with the simulation of high-resolution numerical models calculated in a reasonable computation timeframe, which provides a better representation of the hydrodynamics and the physical habitat.

Numerical Analysis of Transfer of Heat by Forced Convection in a Wavy Channel

Convective heat transfer of laminar forced convection in a wavy channel is studied in this paper. Numerical simulations of the 3D steady flow of Newtonian fluid and heat transfer characteristics are obtained by the finite element method. The effects of the Reynolds number (10 ≤Re≤1000), number of oscillations (0 ≤N≤5) and amplitude of the wall (0.05 ≤A≤0.2) on the heat transfer have been analyzed. The results show that the average Nusselt number is elevated as the Reynolds number is raised, showing high intensity of heat transfer, as a result of the intensified effects of the inertial and zones of recirculation close to the hot wavy wall. The rate of heat transfer increases about 0.28% with the rise of the number of oscillations. In the transfer of heat along a wavy surface, the number of oscillations and the wave amplitude are important factors. With an increment in the number of oscillations, the maximal value of the average velocity is elevated, and its minimal value occurs when the channel walls are straight. The impact of the wall amplitude on the average Nusselt number and dimensionless temperature tends to be stronger compared to the impact of the number of oscillations. An increase of the wall amplitude improves the rate of heat transfer about 0.91% when the Reynolds number is equal 100. In addition, when the Reynolds number is equal 500, the rate of heat transfer grows about 1.1% with the rising of the wall amplitude.

Computing intracoronary blood flow rate under incomplete boundary conditions: Combing coronary anatomy and fractional flow reserve.

Accurate measurement of intracoronary blood flow rate is of great significance for the diagnosis of ischemic heart disease (IHD). Computational fluid dynamic (CFD) method, combining coronary angiography images and fractional flow reserve (FFR), provides a new way to calculate the mean flow rate. However, due to the incomplete boundary conditions obtained by FFR, side branches were ignored which was likely to have a significant impact on the accuracy. In this paper, a novel CFD based method for calculating the mean intracoronary flow rate under incomplete pressure boundary conditions was proposed, in order to improve the accuracy by including the side branches. A pressure-flow curve based flow resistance model was employed to model resistance of the epicardial arteries. A series of steady flow simulations were performed to extract the parameters of the flow resistance model, which implicitly specified constraints for splitting flow between branches and thus enabled the mean intracoronary blood flow rate to be calculated in two or more branches under incomplete pressure boundary conditions. Simulation experiments were designed to validate the proposed method in both idealized and reconstructed 3D models of coronary branches, and the impact of the assumed coefficient of the Murray's Law for splitting flow between branches was also investigated. The mean percentage error of the proposed method was +2.05%±0.04% for idealized models and +2.24%±0.01% for reconstructed models, and it was much lower than that of the method ignoring side branches (+38.48%±10.45% for idealized models and +30.54%±6.12% for reconstructed models). When the assumed coefficient of the Murray's Law was inconsistent with the real blood flow condition, the percentage errors still maintained less than about 3.00%. The proposed method provided an easy and accurate way to measure the mean intracoronary flow rate and would facilitate the accurate diagnosis of IHD.

Numerical simulation of the flow around kayak hull

The purpose of this study was to determine the total resistance and investigate the flow around a full-scale kayak. Utilizing Computational Fluid Dynamics(CFD), it was deter-mined how the presence of a rudder affects the kayak hydrodynamic performance. To an-alyse the flow, computational fluid dynamics based on the RANS-VOF solver was em-ployed. The fluid volume approach and the k-ω turbulence model were used in two-phase steady flow simulations around the kayak hulls.

Implementation of Artificial Compressibility Method for Steady and Unsteady Incompressible Flows Based on Finite Volume Method of Unstructured Grids

The development of a new computational fluid dynamics solver for simulating incompressible flows is described. Unlike traditional pressure-based solvers, the artificial compressibility method simulates both steady and unsteady states. Some classical numerical examples are used to validate the solvers. These findings show that the artificial compressibility method’s LES/DNS and steady flow simulations are competitive with the best previously reported methods. The following characteristics make this paper unique: (1) We implement the artificial compression method in OpenFOAM for the first time and show the detailed mathematical process of the algorithm so that readers can easily reproduce and improve it; (2) steady flow simulation case, the convergence time of the present method is 52% of the pressure base solver; (3) to accelerate the convergence rate of each time step to the incompressible state, the L-stable Singly Diagonal Implicit Runge-Kutta method is introduced into the pseudo-time advance, which enlarges the limit of maximum Courant number to accelerate convergence.

Thermo‐Hydro‐Chemical Simulation of Mid‐Ocean Ridge Hydrothermal Systems: Static 2D Models and Effects of Paleo‐Seawater Chemistry

AbstractDecades of research have resulted in characterization of the ocean floor manifestations of mid‐ocean ridge (MOR) hydrothermal systems, yet numerical models accounting for the connections between heat transfer, hydrology and geochemistry have been slow to develop. The Thermo‐hydro‐chemical code ToughReact can be used to describe the coupled effects of fluid flow, heat transfer, and fluid‐rock chemical interactions that occur in MOR systems. We describe the results of 2‐dimensional simulations of steady state flow in fractured diabase with mineral‐fluid chemical reactions. Basal heating and specified permeability yield maximum temperature of 400°C. Total fluid flux and high fracture flow velocities are in accord with observations. Fluid chemistry, mineralogical changes and 87Sr/86Sr ratios can be compared to observations to assess and calibrate models. Simulated high temperature fracture fluids have Mg and SO4 near zero, elevated Ca and 87Sr/86Sr of about 0.7040. Total alteration is 10%–50% for simple models of spreading. Anhydrite forms mainly near the base of the upwelling zone and results in substantial local fracture porosity reduction. A calibrated model is used to predict how Sr isotopes and other features of altered oceanic crust would be different in the Cretaceous (95 Ma) early Proterozoic (1,800 Ma) and Archean (3,800 Ma), when seawater may have had high Ca and Sr concentrations, lower pH, higher temperature, and lower Na, Mg, and SO4. The simulations are offered as a start on what ultimately may require a longer‐term community effort to better understand the role of MOR thermo‐hydro‐chemical systems in Earth evolution.

Analysis of Turbomachinery Averaging Techniques

Abstract In this paper, various averaging techniques commonly used in turbomachinery applications are analyzed. It is shown how the work average relates to Miller’s mechanical work potential and that it is, in a certain way, consistent with Hartsel’s cooled turbine efficiency. It is found that a key to understand these approaches is to analyze the impact that entropy variations at inflows have on them. Second-order asymptotics of mixing entropy are used to establish a close relationship between flux and work averages. It is found that the mixing entropy asymptotic due to entropy modes is identical for both averages. The work average, along with Miller’s mechanical work potential analysis, is as optimistic as the entropy average for vorticity and acoustic modes, but as pessimistic as the flux averaging for entropy variations. This explains why mechanical work potential-based analysis is pessimistic about the inflow and thus optimistic about the efficiency of a turbine for high entropy variations in the inflow, e.g., in the presence of hot streaks or film cooling. Radial averaging techniques are discussed and their impact on turbine performance is shown. Our findings are illustrated by means of the analysis of steady and unsteady flow simulations of a 1.5 stage turbine configuration.

New insights into the breathing physiology from transient respiratory nasal simulation

The flow characteristics and heat transfer during nasal breathing in the complete human upper airway were investigated through the respiratory cycle using transient numerical simulations. We postulate that the complete airway from the nasal cavity to the trachea most accurately represents dynamic airflow patterns during inhalation and exhalation as they are likely to be affected by downstream anatomical structures. A 3D model was constructed from a healthy adult computed tomography scan. Computational fluid dynamics simulations were performed with Ansys Fluent software [ANSYS Fluent, R1 User's Guide (ANSYS, Inc., 2020)] using the stress-blended eddy simulation turbulence model looking at airflow patterns, velocity, mucosal temperature, and humidity (H2O fraction). One and a half breathing cycles were simulated for a total of 5.65 s, where the first inhalation cycle was discarded to avoid start-up effects. The results demonstrated that airway geometry structures, including the turbinates, the soft palate, and the glottic region, affect the flow patterns differently during inspiration and expiration. It also demonstrated phenomena not seen in steady flow simulations or in those without the lower respiratory tract geometry, including the nasopharyngeal temperature imprint during inhalation, the nasopharyngeal jet during exhalation, and the flow structures of the larynx and laryngeal jet. The inclusion of the exhalation phase demonstrates airflow preconditioning before inhalation, which we postulate contributes to achieving alveolar conditions. Alveolar temperature and humidity conditions are not achieved by the nasal cavity alone, and we demonstrate the contribution of the nasopharynx and larynx to air conditioning. Including the complete airway with realistic anatomy and using transient airflow modeling provided new insights into the physiology of the respiratory cycle.

Self-diffusion in inhomogeneous granular shearing flows.

In this Letter, we discuss how flow inhomogeneity affects the self-diffusion behavior in granular flows. Whereas self-diffusion scalings have been well characterized in the past for homogeneous shearing, the effect of shear localization and nonlocality of the flow has not been studied. We, therefore, present measurements of self-diffusion coefficients in discrete numerical simulations of steady, inhomogeneous, and collisional shearing flows of nearly identical, frictional, and inelastic spheres. We focus on a wide range of dense solid volume fractions, that correspond to geophysical and industrial shearing flows that are dominated by collisional interactions. We compare the measured values first with a scaling based on shear rate and, then, on a scaling based on the granular temperature. We find that the latter does much better than the former in collapsing the data. The results lay the foundations of diffusion models for inhomogeneous shearing flows, which should be useful in treating problems of mixing and segregation.

Nano-CT measurement of pore-fracture evolution and diffusion transport induced by fracturing in medium-high rank coal

Fracturing, as a common fracture-making technique, can improve the permeability of coal seams to enhance fluid transport efficiency. To quantitatively evaluate the microscopic characteristics of medium-high rank coal, the loaded pore-fracture system was characterized by computerized tomography (CT) scanning under triaxial loading, followed by the analysis of stress-strain evolution, stress sensitivity and three-dimensional (3D) fractal dimension. Combined with snow algorithm and incompressible steady laminar flow simulation, the heterogeneous distribution of fluid pressure is investigated, focusing on the diffusion effect of gas transport. The results show that the strain of the high-rank coal Chengzhuang (CZ) in the linear elastic stage increases from 0.25% to 1.25%, greater than that of the medium-rank coal Qiyi (QY) from 0.75% to 1.63%, demonstrating a slight lag of the high-rank coal from the linear elastic stage into the yielding stage. The porosity of CZ changes from 1.66% to 13.58% and that of QY varies from 1.74% to 22.28% after fracturing, reflecting that the primary and secondary pores of the medium- and high-rank coals form a complex network structure for fluid transport through continuous connection-expansion. When the strain is between 0.75% and 1.25%, the stress sensitivity coefficient of CZ decreases from 0.13 to 0.02. Moreover, there are many mutation points in the 3D fractal dimension of coal samples after fracturing, mainly due to the generation of new pore-fractures at different locations of the computational domain. For fluid transport, the pressure of QY after fracturing spreads in a wider range than CZ, accompanied by more distribution of high fluid pressure. The diffusion coefficient of the fractured CZ is 350 times higher than that of the original coal under the gas pressure condition of 0.5 MPa, which provides the possibility for more gas to be converted from Knudsen diffusion to transition diffusion or Fick diffusion in the channel.

A combined multiscale finite element method based on the LOD technique for the multiscale elliptic problems with singularities

In this paper, we construct a combined multiscale finite element method (MsFEM) using the Local Orthogonal Decomposition (LOD) technique to solve the multiscale problems which may have singularities in some special portions of the computational domain. For example, in the simulation of steady flow transporting through highly heterogeneous porous media driven by extraction wells, the singularities lie in the near-well regions. The basic idea of the combined method is to utilize the traditional finite element method (FEM) directly on a fine mesh of the problematic part of the domain and using the LOD-based MsFEM on a coarse mesh of the other part. The key point is how to define local correctors for the basis functions of the elements near the coarse and fine mesh interface, which require meticulous treatment. The proposed method takes advantages of the traditional FEM and the LOD-based MsFEM, which uses much less DOFs than the standard FEM and may be more accurate than the LOD-based MsFEM for problems with singularities. The error analysis is carried out for highly varying coefficients, without any assumptions on scale separation or periodicity. Numerical examples with periodic and random highly oscillating coefficients, as well as the multiscale problems on the L-shaped domain, and multiscale problems with high-contrast channels or well-singularities are presented to demonstrate the efficiency and accuracy of the proposed method.

On Boussinesq and Coriolis coefficients and their derivatives in transient pipe flows

A rigorous analytical justification is developed for a simplification that is widely used in one-dimensional simulations of steady and unsteady flows in pipes, namely treating the flow as a 'plug flow' in which cross-sectional variations in axial velocity are neglected except for consequential shear forces on pipe walls. The proof is obtained without assuming that the flow is nearly incompressible flow and, indeed, it is found that the plug flow approximation remains good even for compressible flows at moderate, subsonic speeds. In more general analyses, explicit allowance is sometimes made for the influence of (i) the Boussinesq coefficient β and (ii) its axial rate of change ∂β/∂x. Typically, such analyses discard the terms in ∂β/∂x in the basic equations and proceed using β alone. This is done on the grounds that no method of evaluating ∂β/∂x is available. It is shown in this paper that discarding ∂β/∂x is not only unnecessary, but that it actually leads to less accurate outcomes than simply assuming plug flow. The process used to derive the analytical justification has a spin-off benefit of shedding light on alternative methods of integrating source terms over the pipe cross-section. Although the primary purpose of the paper is to demonstrate that the use of plug flow approximations can be justified rigorously for most flows, brief attention is also paid to cases where it has potential to mislead.

Energetics and Mixing of Stratified, Rotating Flow over Abyssal Hills

Abstract One of the proposed mechanisms for energy loss in the ocean is through dissipation of internal waves, in particular above rough topography where internal lee waves are generated. Rates of dissipation and diapycnal mixing are often estimated using linear internal wave generation theory and a constant value for mixing efficiency. However, previous oceanographic measurements found that nonlinear dynamics may be important close to topography. To investigate the role of nonlinear interactions, we conduct idealized 3D direct numerical simulations (DNS) of steady flow over 1D topography and vary the topographic height, which correlates to the degree of flow nonlinearity. We analyze the spatial distribution of energy transfer rates between internal waves and the nongeostrophic portion of the time-mean flow, and of dissipation and diapycnal mixing rates. In our simulations with taller, more nonlinear topographies, energy transfer rates are similar to previously unexplained oceanographic observations near topography: internal waves gain energy from time-mean flow through horizontal straining and lose energy through vertical shearing. In the tall topography simulations, buoyancy fluxes also play a significant role, consistent with observations but contrary to linear wave theory, suggesting that quasigeostrophy-based approximations and linear theory may not hold in some regions above rough topography. Both dissipation and mixing rates increase with topographic height, but their vertical distributions differ between topographic regimes. As such, the vertical profile of mixing efficiency is different for linear and nonlinear topographic regimes, which may need to be incorporated into parameterizations of small-scale processes in models and estimates of ocean energy loss.

Analysis of Fluid-Structure Coupling Dynamic Characteristics of Centrifugal Pump Rotor System

Safety and reliable operation is one of the most important research areas for centrifugal pump systems, due to the interaction of complex flow, large structural load, and vibration caused by the operation of the impeller. To analyze the internal flow and impeller deformation of the centrifugal pump, the single-stage single-suction centrifugal pump titled IS100-80-160 was selected as the research object. Under the principle of single variable, the turbulent flow and structural response of three impellers designed by different parameters were calculated by CFX and ANSYS Workbench. A numerical simulation of steady flow at different flow rates of the centrifugal pump was carried out, and its hydraulic performance is consistent with the corresponding experimental results. By comparing the deformation of the impeller rotor system, it was found that the closed impeller has the worst stability with the best hydraulic performance; the impeller with split blades has the worst stability with the best hydraulic performance. This study could enhance the understanding of impeller FSI on centrifugal pump stability and provide a reference for improving the operational stability of centrifugal pumps.

Early River Flood-Warning System Based on Embedded Systems

This paper details the design and construction of a Flood Warning System (FWS) for River Nyamwamba that has been prone to floods of a greater magnitude. The idea was developed on the principle that floods are a meteorological event that develops over time, and thus a need for sufficient time for people to evacuate, and to protect their lives and property. However, the range of existing FWSs have a tangle of conflicting requirements in terms of cost and reliability and have challenges from factors as diverse as technological and social. Built on Computer Embedded Systems, this study provides a cheaper and reliable FWS for a country like Uganda. River Nyamwamba flow was modelled with DEM, Topography sheets, river map, imageries, flow data, stage data, land use maps, and rainfall data. The data sets were conditioned and processed in a GIS environment using ArcGIS software and exported to the HECRAS program to perform a steady flow simulation of the river. High-risk areas were visualized that provided reliable river flow parameters that were used as input values for the design of the FWS. An Arduino programmed microcontrollers were used to control all input and output values regarding the modelled river. An ultrasonic sensor was used to monitor the normal flow, intermediate flow, and peak flood water levels. From this, the river stage was displayed onto an LCD screen at all times, an electronic SMS is sent to operators at intermediate flow, while an alarm is sounded at flood level.

SENSITIVITY ANALYSIS OF ANGLE, LENGTH AND BRIM HEIGHT OF THE DIFFUSER FOR THE SMALL DIFFUSER AUGMENTED WIND TURBIN

This paper presents the performance of the diffuser augmented wind turbine (DAWT) with the various diffuser shapes using the numerical investigations. DAWT is also a type of wind turbine and the diffuser shapes, the nozzle shapes and the cylindrical shapes are commonly inserted around the horizontal axis wind turbine (HAWT) to become the more efficient wind turbine. The aim of this study is to find the more efficient design of the diffuser for the horizontal axis wind turbine using the numerical investigations. In this research, the converging and diverging diffuser shape is inserted and the airfoil design is calculated by using the Blade Elementary Momentum Theory. The airfoil type NACA 4412 is chosen because it is suitable for the low wind speed area and easy to produce. The turbulent model k-ω is combined with the Navier Stoke equation to solve the 3-dimensional steady flow simulation of the diffuser augmented wind turbine using the Computational Fluid Dynamics (CFD) simulations. The numerical investigation is used to compare and predict the power coefficient of the DAWT with various shapes. The baseline design of the diffuser (L = 170 mm, H = 57 mm and α = 11̊) is firstly investigated. To predict the power coefficient of the various diffuser shapes, the range of the length of the diffuser is (L/D = 0.5 to 1.5), the range of the brim height of the diffuser (H/D = 0.1 to 0.35) and the range of the angle of the diffuser (α = 5̊ to 15̊ ) are also investigated. The parameters of the diffuser shapes are assigned by using the Central Composite Design Face Centered Method. The response surface method is also used to predict the most efficient diffuser design. The performance of the horizontal axis wind turbine, that of the diffuser augmented wind turbine and that of the diffuser augmented wind turbine with various shapes of diffuser are compared. The performance of new diffuser augmented wind turbine (IND_009) is 50% and 55% higher than the baseline diffuser augmented wind turbine and the horizontal axis wind turbine at rated velocity. The flow visualization of the HAWT, DAWTs are also discussed.