Numerical simulation for magnetized non-isothermal nanofluid flow in hexagonal curved cavity with heated obstacle

Analysis of recent research and publications. It is known that the presence near the body of another body or a solid wall in a flow can significantly change both the overall flow pattern and the aerodynamic characteristics of bodies in a group. Studies of the interaction of bodies in the flow are conducted for a long time. In [6], the results of a study of changes in the overall flow pattern and the form of interaction of vortices behind tandem-arranged circular cylinders are presented. Further, experimental studies of the flow around a group consisting of two cylinders were aimed at classifying flow patterns depending on the position of the group in the flow, the distance between the cylinders and the Reynolds number [1, 2, 9]. A rather complete identification and classification of the pattern of flow was performed in [6, 7]. Studies on the classification and analysis of flow patterns are still being conducted [1]. Studies on the classification of patterns of the flow around group of spheres are currently performed mainly with the help of numerical simulation. In [3, 4, 5], simulation of the flow around spheres on the side-by-side position was performed. In [8], the classification of typical patterns of the flow around two spheres (Re = 300) with considering of different positions of the spheres relative to the flow direction was made. The authors of [8] describe nine typical patterns of the flow around two spheres in analogy with the patterns of the flow of the two cylinders.The purpose of the study. The main goal of this work is study the mutual influence of two bodies in a flow of a viscous incompressible fluid and a change in the flow structure with a change in the position of the bodies in the group relative to the incoming flow. Also, the aim of the work was to study the influence of the mutual arrangement of bodies in a group on the non-stationary and time-averaged aerodynamic characteristics of bodies in a group.Modeling of the flow around groups of cylinders and spheres. Numerical simulation of the flow around the group of cylinders was carried out with the values of the angle θ = 0°, 15°, 30°, 45°, 60°, 75°, 90° and the gap between the cylinders h = 0.2D, 0.4D, 0.6D, 0.8D, 1.0D, 2.0D, 3.0D, 4.0D, 5.0D. The flow parameters was corresponded to the flow around a circular cylinder at Re = 80 and 1.66 105. Eight patterns (regimes) of flow around a group of two cylinders at Re = 80 were found. Regimes 1 and 2 are steady state flows. In regime 1, the drag coefficient is Cx2 <0, and for regime 2, Cx2> 0. Regimes 3-8 are unsteady flows. Regime 8 is an aperiodic change in Cx, Cy. Regimes 3 - 7 are periodic, characterized by different values of the coefficients Cx, Cy, as well as those oscillations of Cx and Cy that occur in phase or antiphase. Simulation of the turbulent flow around a group of two cylinders took place at the tandem and the side-by-side positions at distances between cylinders centers 1.435D and 3.7D.Similarly, in this work, was performed the parametric study of the flow around two spheres for Reynolds number 750 with the distances between the centers of the spheres along axis Δx = 0.0, 1.0, 2.0, 3.0 and Δy = 0.0, 1.0, 2.0, 3.0. The drag and lift coefficients were obtained, as well as the patterns of flow around two spheres were analyzed.Conclusions. Depending on the position of the group relative to the flow, the average drag coefficient of the cylinders and spheres in the group can be both smaller and larger than the drag coefficient of a single body with the same parameters of the free flow. With a tandem arrangement, the second cylinder has a stabilizing effect and with a decrease in the gap of less than three diameters, the flow becomes steady state. For all cases with staggered arrangement of spheres the symmetry restoration of vortex structures is observed. In the case of the tandem arrangement of spheres, the separation of loop-shaped vortex structures is realized as in the case of a flow around a single sphere.

The numerical simulation of a flow through a duct requires an externally specified forcing that makes the fluid flow against viscous friction. To this end, it is customary to enforce a constant value for either the flow rate (CFR) or the pressure gradient (CPG). When comparing a laminar duct flow before and after a geometrical modification that induces a change of the viscous drag, both approaches lead to a change of the power input across the comparison. Similarly, when carrying out direct numerical simulation or large-eddy simulation of unsteady turbulent flows, the power input is not constant over time. Carrying out a simulation at constant power input (CPI) is thus a further physically sound option, that becomes particularly appealing in the context of flow control, where a comparison between control-on and control-off conditions has to be made. We describe how to carry out a CPI simulation, and start with defining a new power-related Reynolds number, whose velocity scale is the bulk flow that can be attained with a given pumping power in the laminar regime. Under the CPI condition, we derive a relation that is equivalent to the Fukagata–Iwamoto–Kasagi relation valid for CFR (and to its extension valid for CPG), that presents the additional advantage of naturally including the required control power. The implementation of the CPI approach is then exemplified in the standard case of a plane turbulent channel flow, and then further applied to a flow control case, where a spanwise-oscillating wall is used for skin-friction drag reduction. For this low-Reynolds-number flow, using 90 % of the available power for the pumping system and the remaining 10 % for the control system is found to be the optimum share that yields the largest increase of the flow rate above the reference case where 100 % of the power goes to the pump.

The tip clearance flows of transonic compressor rotors are important because they have a significant impact on rotor and stage performance. While numerical simulations of these flows are quite sophisticated, they are seldom verified through rigorous comparisons of numerical and measured data because these kinds of measurements are rare in the detail necessary to be useful in high-speed machines. In this paper we compare measured tip-clearance flow details (e.g. trajectory and radial extent) with corresponding data obtained from a numerical simulation. Recommendations for achieving accurate numerical simulation of tip clearance flows are presented based on this comparison. Laser Doppler Velocimeter (LDV) measurements acquired in a transonic compressor rotor, NASA Rotor 35, are used. The tip clearance flow field of this transonic rotor was simulated using a Navier-Stokes turbomachinery solver that incorporates an advanced k-ε turbulence model derived for flows that are not in local equilibrium. Comparison between measured and simulated results indicates that simulation accuracy is primarily dependent upon the ability of the numerical code to resolve important details of a wall-bounded shear layer formed by the relative motion between the over-tip leakage flow and the shroud wall. A simple method is presented for determining the strength of this shear layer.

Numerical simulation of a turbulent flow of air with dispersed particles through a cyclonic separator is presented. Because of a high streamline curvature in the separator it is difficult to simulate the flow by using the conventional turbulent models. In this work the curvature correction term was included into the k – ω – SST turbulence model implemented in the OpenFOAM® software. Experimental data and results of numerical simulation by the commercial ANSYS Fluent® solver for a turbulent flow in a U-duct were used to validate the model. The numerical simulation of the flow in the cyclonic separator demonstrates that the implemented turbulence model successfully predicts the cyclonic separator efficiency.

The paper is concerned with the experimental and numerical simulations of the viscous flows in 3D planar cylindrical bifurcations and in a bypass configuration. The main goal of the study is to investigate the influence of the angle between the main and secondary branches of the bifurcation on the flow pattern and the wall stresses distributions. Numerical simulations of the flows in a bypass are also performed. The flow rate distribution between the branches in the presence of a stenosis is determined, as function of the Reynolds number. The results are expected to give value information about the functioning of cardiovascular bifurcation and bypass configuration in the pre-stenosis and stenosis regimes.

On the use of the open boundary condition method in the numerical simulation of nonisothermal viscoelastic flow

This numerical study was conducted to investigate the flow properties in a model scramjet configuration of the experiment in the T4 shock tunnel. In most numerical simulations of flows in shock tunnels, the inflow conditions in the test section are determined by assuming the thermal equilibrium of the gas. To define the inflow conditions in the test section, the numerical simulation of the nozzle flow with the given nozzle reservoir conditions from the experiment is conducted by a thermochemical nonequilibrium computational fluid dynamics (CFD) solver. Both two-dimensional (2D) and three-dimensional (3D) numerical simulations of the flow in a model scramjet were conducted without fuel injection. Simulations were performed for two types of inflow conditions: one for thermochemical nonequilibrium states obtained from the present nozzle simulation and the other for the data available using the thermal equilibrium and chemical nonequilibrium assumptions. The four results demonstrate the significance of the modelling approach for choosing between 2D or 3D, and thermal equilibrium or nonequilibrium.

The aerodynamic characteristics of launch vehicles separable elements, which are cylindrical and conical shells, in supersonic airflow are presented in this paper. Numerical simulation of the flow around shells in the plane of their symmetry is performed for flow Mach numbers from 2.0 to 4.0 using an open-source software package OpenFoam. We got the aerodynamic coefficients of the axial, normal forces and pitch moment, and the structure of the flow around shells. We compared the numerical simulation results with the results of experimental studies conducted in the BMSTU supersonic wind tunnel. The complex nature of the flow around shells with the formation of shock waves, areas of flow separation, and circulation flow are established. We compared the aerodynamic characteristics of cylindrical and conical shells with the characteristics of a solid cone and cylinder, and with the characteristics of rectangular and triangular plates. We found that the flow around the shells (except for the hollow cone) is accompanied by a through flow, the aerodynamic force is created by all the shell surfaces. The flow around the hollow cone is accompanied by the formation of a stagnant area inside the cavity. Features in the flow structures are reflected in the shells’ aerodynamic characteristics, which differ from the solid bodies and plates characteristics.

Two explicit schemes of the finite difference method are presented and analyzed in the paper. The applicability of the Lax-Wendroff and McCormack schemes for modeling unsteady rapidly and gradually varied open channel flow is investigated. For simulation of the transcritical flow the original and improved McCormack scheme is used. The schemes are used for numerical solution of one dimensional Saint-Venant equations describing free surface water flow. Two numerical simulations of flow with different hydraulic characteristics were performed - the first one for the extreme flow of the dam-break type and the second one for the simplified flood wave propagation problem. The computational results are compared to each other and to arbitrary solutions.

The alkaline water electrolysis is one of the methods of large-scale hydrogen production, and it is required to improve its efficiency. Experimental approach and numerical studies have been conducted to improve the efficiency [1,2]. Abdelouahed et al. [3] confirmed that bubbles strongly influence the flow field pattern and mix the local electrolyte near the electrodes. Ehrl et al. [4] conducted a numerical simulation of electrochemical systems with natural convection and solved both multi-ion transportation and flow in the cell. In these studies, macroscopic (mm scale) hydrodynamical behavior have been discussed, however, the size of the bubbles in water electrolysis can be micro scale and microscale flow can be induced. We have been studied about the microscale hydrodynamical effect on the alkaline water electrolysis with two-phase flow, electrochemical, and electromagnetic coupling numerical simulations. In our previous studies [1,2], numerical simulations of flow around the aligned bubbles with a cyclic boundary condition are conducted and it is revealed that the rising bubbles suppress the cell overpotential and this suppression is enhanced by a bubble atomization, however, there is a strong limitation to the bubble movement and it had been difficult to discuss the bubble-bubble interaction and the influence of that on the efficiency of the alkaline water electrolysis cell. From the background mentioned above, in this study, large-scale coupling numerical simulations are conducted to elucidate the influence of the bubble-bubble interactions on the cell overpotential. Strength of the interaction depends on dispersibility of bubbles. So, we also discuss the influence of the dispersibility of multiple bubbles on the cell overpotential.In this study, electrochemical, two-phase flow, electromagnetic field coupling numerical simulation are conducted with the same procedure as previous studies [1,2]. The analysis area is expanded to calculate the bubble-bubble interaction and the number of grids is 16 million. Graphical Processing Unit (GPU) are used in this calculation for Large-scale parallel analysis to realize this simulation. The average applied current density is 400 mA/cm2, the bubble size of oxygen bubbles is 500μm and four bubbles are set close to the anode at initial condition. The numerical simulations are conducted with changing the dispersibility from 0.25 to 0.92. Dispersibility is 1 when bubbles are equally spaced and is 0 when bubbles are concentrated and in touched.Figure 1 shows the influence of the dispersibility (D) on the cell overpotential. From D = 0.25 to 0.43, the overpotential is almost decreased with the increase in D, and it increased with the increase in D from D = 0.43 to 0.92. Fig.2 shows concentration distribution, iso-surface (1.7 mol/L) and bubbles position with dispersibility of (a) D = 0.25, (b) D = 0.43 and (c) D = 0.92. In the case of low dispersibility (D = 0.25, Fig.2 (a)), the overpotential is high and some bubbles are combined and remain close to the anode. These bubbles close to the anode, make shielding effect and increase the ohmic loss. The anodic activation overpotential is also high because fewer bubbles reduce the flow and decrease the concentration near the anode. With the increasing in D, the overpotential is suppressed (D = 0.43, Fig.2 (b)). In this case of optimum dispersibility, some bubbles locate far from the anode. This is because, the upper bubble leaves from the anode because of the lift force against the anode [5] and induces repulsive force to the lower bubble [6]. This upper bubble far from the anode, reduces shielding effect and suppresses the ohmic loss. The anodic activation overpotential is also suppressed because the interaction between the bubbles enhance the flow which facilitate the ion transportation and increase the concentration near the anode. In the case of high dispersibility (D = 0.92, Fig.2 (c)), many bubbles remain close to the anode. These bubbles make shielding effect and increase the ohmic loss. The anodic activation overpotential is also increased because there is little interaction between bubbles to generate strong flow and the concentration near the anode are decreased. In conclusion, this study reveals that the interaction between bubbles affects the cell overpotential, and bubbles in optimum dispersibility, the cell overpotential can be suppressed. Acknowledgement This study is partially supported by Nissin Sugar Found and Japan High Performance Computing and Networking plus Large-scale Data Analyzing and Information Systems. Figure 1

The flow field characteristics around a square cylinder determine particle concentration distribution in environmental air. This paper introduces the application of the numerical simulation in the research of flow around an environmental square cylinder, improves the numerical simulation method, and uses the Unsteady Reynolds-average Numerical Simulation (URANS) to research the flow around an environmental square cylinder. Result shows that unsteady RANS k-ε model achieved a better conclusion than the steady simulation. In the numerical simulation of the flow around a square cylinder, especially in the simulation of the Karman vortex at the end of the square cylinder, the unsteady RNG k-ε model clearly shows the fall-off and reattachment process of eddy; and the result in same phase matches well with the average result achieved by the large eddy simulation. Compared with the large eddy simulation, the calculation results using URANS are more close to experiment results in separation-points-fixed circular square cylinder. This paper will be an essential basis for practical applications.

On the Numerical Simulation of Viscoplastic Fluid Flow

Numerical simulation is an important tool for understanding the physics of flows in porous media and for making predictions. The state of the art of multiscale modeling and simulation of turbulent flows in porous media is reviewed in this paper. Numerical simulations of flows in porous media can be classified as microscopic simulations, in which both macroscopic and pore-scale flows are directly resolved, and macroscopic simulations, in which the pore-scale motions are modeled while the volume-averaged equations are solved. Studies in the past few years have shown that microscopic simulations improve the understanding of turbulent flows in porous media considerably; this motivates the development of more efficient and more accurate turbulence models for macroscopic simulations. On the basis of this review, we believe that simulation of flows with higher Reynolds numbers, understanding the transport of macroscopic turbulence, modeling of turbulent flows in inhomogeneous and anisotropic porous media, simulation of compressible and multiphase turbulent flows in porous media, and fluid–structure interaction in deformable porous matrices are important topics to be studied in the future.

This paper presents and discusses the results of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory events” aimed at assessing the ability of different computational codes and turbulence models to reproduce the flow generated by a rapid prototypical exhalation and the dispersion of the aerosol cloud it produces. Given a common flow configuration, a total of 7 research teams from different countries have performed a total of 11 numerical simulations of the flow dispersion by solving the Unsteady Reynolds Averaged Navier–Stokes (URANS) or using the Large-Eddy Simulations (LES) or hybrid (URANS-LES) techniques. The results of each team have been compared with each other and assessed against a Direct Numerical Simulation (DNS) of the exact same flow. The DNS results are used as reference solution to determine the deviation of each modeling approach. The dispersion of both evaporative and non-evaporative particle clouds has been considered in 12 simulations using URANS and LES. Most of the models predict reasonably well the shape and the horizontal and vertical ranges of the buoyant thermal cloud generated by the warm exhalation into an initially quiescent colder ambient. However, the vertical turbulent mixing is generally underpredicted, especially by the URANS-based simulations, independently of the specific turbulence model used (and only to a lesser extent by LES). In comparison to DNS, both approaches are found to overpredict the horizontal range covered by the small particle cloud that tends to remain afloat within the thermal cloud well after the flow injection has ceased.

The tip clearance flows of transonic compressor rotors are important because they have a significant impact on rotor and stage performance. A wall-bounded shear layer formed by the relative motion between the overtip leakage flow and the shroud wall is found to have a major influence on the development of the tip clearance flow field. This shear layer, which has not been recognized by earlier investigators, impacts the stable operating range of the rotor. Simulation accuracy is dependent on the ability of the numerical code to resolve this layer. While numerical simulations of these flows are quite sophisticated, they are seldom verified through rigorous comparisons of numerical and measured data because these kinds of measurements are rare in the detail necessary to be useful in high-speed machines. In this paper we compare measured tip-clearance flow details (e.g., trajectory and radial extent) with corresponding data obtained from a numerical simulation. Laser-Doppler Velocimeter (LDV) measurements acquired in a transonic compressor rotor, NASA Rotor 35, are used. The tip clearance flow field of this transonic rotor is simulated using a Navier–Stokes turbomachinery solver that incorporates an advanced k–ε turbulence model derived for flows that are not in local equilibrium. A simple method is presented for determining when the wall-bounded shear layer is an important component of the tip clearance flow field. [S0889-504X(00)02504-6]