Unsteady aerodynamical effect of accelerated or decelerated two-dimensional airfoil (NACA0012) wa... more Unsteady aerodynamical effect of accelerated or decelerated two-dimensional airfoil (NACA0012) was numerically examined using a grid-free vortex method. The flow characteristics and aerodynamical forces were compared among various accelerated or decelerated conditions. The results showed that flow separation occurred under decelerated condition and the lift-drag ratio decreased as the decelerated velocity became high and increased as the accelerated velocity became high.
In this study, numerical simulation on acceleration characteristics of a cold gas jet through uti... more In this study, numerical simulation on acceleration characteristics of a cold gas jet through utilization of an arcjet was conducted, where the supersonic free jet was accelerated through an interaction in a shear layer between the free jet and arcjet. In this analysis, the governing equations including two–dimensional compressible Reynolds– averaged Navier–Stokes equations (RANS) were calculated with a commercial code, ANSYS Fluent v.14.5. As for the turbulence model, a k–ε realizable turbulence model was employed. In this paper, when an arc flow is used for the center nozzle, the velocity is higher especially in potential core part than in the case of unheated flow because of a hot core flow of the arcjet.
In this study, a grid-free vortex method was developed and applied to turbulent flows in order to... more In this study, a grid-free vortex method was developed and applied to turbulent flows in order to validate the scheme. In order to satisfy the boundary condition for internal flow calculation, the direct boundary element method (BEM) was employed. The grid-free redistribution model proposed by Fukuda and Kamemoto [3] and vortex reconnection model was also introduced and the spatial resolution was improved for high strain regions. From the results, it was confirmed that the unsteady feature of the turbulent boundary layer in the turbulent internal flow and its development were successfully captured. Furthermore, comparisons of the calculated mean velocity and the calculated rms value of the axial velocity fluctuation in the turbulent internal flow with experimental data showed that the method provided an accurate velocity profile and axial velocity fluctuation in turbulent boundary layers. In the vortex rings interaction calculation, reconnection process was reasonably simulated and ...
The exhaust gas from rocket motors generates severe acoustic waves. The acoustic waves reflected ... more The exhaust gas from rocket motors generates severe acoustic waves. The acoustic waves reflected from the ground and launch facility is cause of vibration of the payload in the fairing. Therefore, prediction and reduction of acoustic level at the lift-off is quite important. Traditionally, acoustic level has been predicted by an empirical method, NASA SP-8072 [1] or subscale tests [2] . In recent, prediction of acoustic level by CFD is required, because an empirical methods does not have enough accuracy. The alumina particles released from solid rocket motors might attenuate acoustic wave, but the mechanism is not well known. Therefore, a new model for prediction of drag force at the highMach-number and low-Reynolds-number condition is necessary, in order to perform high accuracy prediction on acoustic wave generated by exhaust gas from solid rocket motors. In this study, the high-Mach-number and low-Reynolds-number flow analysis of the around a sphere by direct numerical simulation...
In this study, unsteady aerodynamical effect of accelerated or decelerated two-dimensional airfoi... more In this study, unsteady aerodynamical effect of accelerated or decelerated two-dimensional airfoil (NACA0012) was numerically examined using a grid-free vortex method. The flow characteristics and aerodynamical forces were compared among various accelerated or decelerated conditions. The results showed that large flow separation occurred under decelerated condition than accelerated condition and constant condition. Furthermore, the lift-drag ratio decreased as the decelerated velocity became high and increased as the accelerated velocity became high.
One of the crucial problems for turbulent flow analyses via computational fluid dynamics (CFD) is... more One of the crucial problems for turbulent flow analyses via computational fluid dynamics (CFD) is how to analyze the unsteady motion and deformation of vortical structures. The Navier-Stokes flow solvers with the finite element method, the finite difference method, or the finite volume method can capture the vortical structures explicitly, but when the computational grid is not sufficiently small, the vortices are diffused due to the numerical diffusion. In the vortex methods, vorticity distributions are represented by using discrete vortex elements. When compared to other schemes, vortex methods have the advantage that the nonlinear distortion of vortical structures is directly calculated without the numerical diffusion. The vortex methods are divided into two types. The first one is vortex-in-cell (VIC) method in which stream function is calculated on the fixed grid. Another is the grid-free vortex method, in which the velocity field is calculated by the Biot-Savart law, without u...
International Journal for Numerical Methods in Fluids
In the present study, we proposed a simple collision algorithm, which can be handled arbitrarily ... more In the present study, we proposed a simple collision algorithm, which can be handled arbitrarily shaped objects, for flow solvers using the immersed boundary method (IBM) based on the level set and ghost cell methods. The proposed algorithm can handle the collision of the arbitrarily shaped object with little additional computational costs for the collision calculation because collision detection and calculation are performed using the level set function and image point, which are incorporated into the original IBM solver. The proposed algorithm was implemented on the solid-liquid IBM flow solver and validated by simulations of the flow over an isolated cylinder and sphere. Also, grid and time step size sensitivity on the total energy conservation of objects were investigated in cylinder-cylinder, cylinder-red-blood-cells-shaped (RBC-shaped) objects, sphere-sphere, and sphere-flat plate interaction problems. Through validation, good agreement with previous studies, grid and time step size convergence, and sufficient total energy conservation were confirmed. As a demonstration, the drafting, kissing, and tumbling processes were computed, and it was confirmed that the present result by the proposed method is similar to the previous computations. In addition, particle-laden flow in a channel including obstacles with collision and adhesion phenomena and the interaction of cylinders and wavy-wall were computed. The results of these simulations reveal the capability of solving a flow containing arbitrarily shaped moving objects with collision phenomena by a simple proposed method.
International Journal of Computational Methods and Experimental Measurements
We investigated gas-particle flows by using the three-dimensional incompressible Navier-Stokes eq... more We investigated gas-particle flows by using the three-dimensional incompressible Navier-Stokes equation with the immersed boundary method (IBM) to treat particles-wall collisions. We compared flow structures from the two-way coupled simulation with the one-way simulation that is usually used in the industrial simulation. In this study, all objectives, which are particles and walls, are defined by the level-set function for the ghost-cell method of the IBM. The proposed algorithms to represent particle-particle and particle-wall collisions are simple and stable for the coupling simulation. Moreover, flow structures obtained with the coupled simulation of the moving, colliding and rebounding particles are in good agreement with the previous numerical and experimental results. The one-way and two-way coupling simulations were carried out based on a number of particles of 50, 100 and 200, respectively. As a result, the one-way scheme indicated more frequently collisions on the particle and wall than the two-way scheme. The reason is that the one-way scheme ignored the particle-flow interactions.
We investigated particulate flows by coupling simulations of the three-dimensional incompressible... more We investigated particulate flows by coupling simulations of the three-dimensional incompressible Navier–Stokes equation with the immersed boundary method (IBM). The results obtained from the two-way coupled simulation were compared with those of the one-way simulation, which is generally applied for clarifying the particle kinematics in industry. In the present flow simulation, the IBM was solved using a ghost–cell approach and the particles and walls were defined by a level set function. Using proposed algorithms, particle–particle and particle–wall collisions were implemented simply; the subsequent coupling simulations were conducted stably. Additionally, the wake structures of the moving, colliding and rebounding particles were comprehensively compared with previous numerical and experimental results. In simulations of 50, 100, 200 and 500 particles, particle–wall collisions were more frequent in the one–way scheme than in the two-way scheme. This difference was linked to differ...
Unsteady aerodynamical effect of accelerated or decelerated two-dimensional airfoil (NACA0012) wa... more Unsteady aerodynamical effect of accelerated or decelerated two-dimensional airfoil (NACA0012) was numerically examined using a grid-free vortex method. The flow characteristics and aerodynamical forces were compared among various accelerated or decelerated conditions. The results showed that flow separation occurred under decelerated condition and the lift-drag ratio decreased as the decelerated velocity became high and increased as the accelerated velocity became high.
In this study, numerical simulation on acceleration characteristics of a cold gas jet through uti... more In this study, numerical simulation on acceleration characteristics of a cold gas jet through utilization of an arcjet was conducted, where the supersonic free jet was accelerated through an interaction in a shear layer between the free jet and arcjet. In this analysis, the governing equations including two–dimensional compressible Reynolds– averaged Navier–Stokes equations (RANS) were calculated with a commercial code, ANSYS Fluent v.14.5. As for the turbulence model, a k–ε realizable turbulence model was employed. In this paper, when an arc flow is used for the center nozzle, the velocity is higher especially in potential core part than in the case of unheated flow because of a hot core flow of the arcjet.
In this study, a grid-free vortex method was developed and applied to turbulent flows in order to... more In this study, a grid-free vortex method was developed and applied to turbulent flows in order to validate the scheme. In order to satisfy the boundary condition for internal flow calculation, the direct boundary element method (BEM) was employed. The grid-free redistribution model proposed by Fukuda and Kamemoto [3] and vortex reconnection model was also introduced and the spatial resolution was improved for high strain regions. From the results, it was confirmed that the unsteady feature of the turbulent boundary layer in the turbulent internal flow and its development were successfully captured. Furthermore, comparisons of the calculated mean velocity and the calculated rms value of the axial velocity fluctuation in the turbulent internal flow with experimental data showed that the method provided an accurate velocity profile and axial velocity fluctuation in turbulent boundary layers. In the vortex rings interaction calculation, reconnection process was reasonably simulated and ...
The exhaust gas from rocket motors generates severe acoustic waves. The acoustic waves reflected ... more The exhaust gas from rocket motors generates severe acoustic waves. The acoustic waves reflected from the ground and launch facility is cause of vibration of the payload in the fairing. Therefore, prediction and reduction of acoustic level at the lift-off is quite important. Traditionally, acoustic level has been predicted by an empirical method, NASA SP-8072 [1] or subscale tests [2] . In recent, prediction of acoustic level by CFD is required, because an empirical methods does not have enough accuracy. The alumina particles released from solid rocket motors might attenuate acoustic wave, but the mechanism is not well known. Therefore, a new model for prediction of drag force at the highMach-number and low-Reynolds-number condition is necessary, in order to perform high accuracy prediction on acoustic wave generated by exhaust gas from solid rocket motors. In this study, the high-Mach-number and low-Reynolds-number flow analysis of the around a sphere by direct numerical simulation...
In this study, unsteady aerodynamical effect of accelerated or decelerated two-dimensional airfoi... more In this study, unsteady aerodynamical effect of accelerated or decelerated two-dimensional airfoil (NACA0012) was numerically examined using a grid-free vortex method. The flow characteristics and aerodynamical forces were compared among various accelerated or decelerated conditions. The results showed that large flow separation occurred under decelerated condition than accelerated condition and constant condition. Furthermore, the lift-drag ratio decreased as the decelerated velocity became high and increased as the accelerated velocity became high.
One of the crucial problems for turbulent flow analyses via computational fluid dynamics (CFD) is... more One of the crucial problems for turbulent flow analyses via computational fluid dynamics (CFD) is how to analyze the unsteady motion and deformation of vortical structures. The Navier-Stokes flow solvers with the finite element method, the finite difference method, or the finite volume method can capture the vortical structures explicitly, but when the computational grid is not sufficiently small, the vortices are diffused due to the numerical diffusion. In the vortex methods, vorticity distributions are represented by using discrete vortex elements. When compared to other schemes, vortex methods have the advantage that the nonlinear distortion of vortical structures is directly calculated without the numerical diffusion. The vortex methods are divided into two types. The first one is vortex-in-cell (VIC) method in which stream function is calculated on the fixed grid. Another is the grid-free vortex method, in which the velocity field is calculated by the Biot-Savart law, without u...
International Journal for Numerical Methods in Fluids
In the present study, we proposed a simple collision algorithm, which can be handled arbitrarily ... more In the present study, we proposed a simple collision algorithm, which can be handled arbitrarily shaped objects, for flow solvers using the immersed boundary method (IBM) based on the level set and ghost cell methods. The proposed algorithm can handle the collision of the arbitrarily shaped object with little additional computational costs for the collision calculation because collision detection and calculation are performed using the level set function and image point, which are incorporated into the original IBM solver. The proposed algorithm was implemented on the solid-liquid IBM flow solver and validated by simulations of the flow over an isolated cylinder and sphere. Also, grid and time step size sensitivity on the total energy conservation of objects were investigated in cylinder-cylinder, cylinder-red-blood-cells-shaped (RBC-shaped) objects, sphere-sphere, and sphere-flat plate interaction problems. Through validation, good agreement with previous studies, grid and time step size convergence, and sufficient total energy conservation were confirmed. As a demonstration, the drafting, kissing, and tumbling processes were computed, and it was confirmed that the present result by the proposed method is similar to the previous computations. In addition, particle-laden flow in a channel including obstacles with collision and adhesion phenomena and the interaction of cylinders and wavy-wall were computed. The results of these simulations reveal the capability of solving a flow containing arbitrarily shaped moving objects with collision phenomena by a simple proposed method.
International Journal of Computational Methods and Experimental Measurements
We investigated gas-particle flows by using the three-dimensional incompressible Navier-Stokes eq... more We investigated gas-particle flows by using the three-dimensional incompressible Navier-Stokes equation with the immersed boundary method (IBM) to treat particles-wall collisions. We compared flow structures from the two-way coupled simulation with the one-way simulation that is usually used in the industrial simulation. In this study, all objectives, which are particles and walls, are defined by the level-set function for the ghost-cell method of the IBM. The proposed algorithms to represent particle-particle and particle-wall collisions are simple and stable for the coupling simulation. Moreover, flow structures obtained with the coupled simulation of the moving, colliding and rebounding particles are in good agreement with the previous numerical and experimental results. The one-way and two-way coupling simulations were carried out based on a number of particles of 50, 100 and 200, respectively. As a result, the one-way scheme indicated more frequently collisions on the particle and wall than the two-way scheme. The reason is that the one-way scheme ignored the particle-flow interactions.
We investigated particulate flows by coupling simulations of the three-dimensional incompressible... more We investigated particulate flows by coupling simulations of the three-dimensional incompressible Navier–Stokes equation with the immersed boundary method (IBM). The results obtained from the two-way coupled simulation were compared with those of the one-way simulation, which is generally applied for clarifying the particle kinematics in industry. In the present flow simulation, the IBM was solved using a ghost–cell approach and the particles and walls were defined by a level set function. Using proposed algorithms, particle–particle and particle–wall collisions were implemented simply; the subsequent coupling simulations were conducted stably. Additionally, the wake structures of the moving, colliding and rebounding particles were comprehensively compared with previous numerical and experimental results. In simulations of 50, 100, 200 and 500 particles, particle–wall collisions were more frequent in the one–way scheme than in the two-way scheme. This difference was linked to differ...
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Papers by Kota Fukuda