Numerical Simulation Of 3D Flow Research Articles

Numerical Simulation of 3D Flow in Right-angled Confluences with Bed Elevation Discordance in Both Converging Channels

The paper studies a combined effect of bed steps (BS) in both converging channels on the 3D flow in a confluence with α = 90°. Nine combinations of bed elevation discordance ratio values in the two channels are analysed. It is shown that:1) a portion of the tributary flow is redirected upstream and that the vertical flow deflection in the lower half of water column is significantly reduced when the BS in the main river is higher than that in the tributary, 2) the shape of the recirculation zone (RZ) and the delay in its development are strongly governed by the presence of the BS in the tributary, whereas the BS in the main river only affects the size of the RZ and the dynamics of its distortion and 3) both river banks are endangered by erosion in confluences with BSs in both converging channels.

Numerical simulation of 3D flow past a real-life marine hydrokinetic turbine

We simulate three-dimensional, turbulent flow past an axial-flow marine hydrokinetic (MHK) turbine mounted on the bed of a rectangular open channel by adapting a computational framework developed for carrying out high-resolution large-eddy simulation (LES) in arbitrarily complex domains involving moving or stationary boundaries. The complex turbine geometry, including the rotor and all stationary components, is handled by employing the curvilinear immersed boundary (CURVIB) method [1,2]. Velocity boundary conditions near all solid surfaces are reconstructed using a wall model based on solving the simplified boundary layer equations [2]. To demonstrate the capabilities of the model we apply it to simulate the flow past a Gen4 axial flow MHK turbine developed by Verdant Power for the Roosevelt Island Tidal Energy (RITE) project in the East River in New York City, USA. We carry out systematic grid refinement studies, using grids with up to 185 million nodes, for only the turbine rotor placed in an infinite free stream to show that the computed torque converges to a grid insensitive value, which is in good agreement with field measurements. We also carry out LES for the complete turbine configuration, including the pylon, nacelle and rotor, mounted on the bed of a straight rectangular open channel. The computed results illustrate the complexity of the flow and show that the power output of the complete turbine is primarily dependent on the rotor geometry and tip speed ratio, and is not affected by the stationary components of the turbine and the presence of the channel bed. The complete turbine simulation also reveals that the downstream wake of the turbine consists of three main regions: (1) the outer layer with the spiral blade tip vortices rotating in the same direction as the blades; (2) the counter-rotating inner layer surrounded by the spiral tip vortices; and (3) the core layer co-rotating with respect to the tip vortices. This study is the first to report the three-dimensional wake structure of MHK turbines.

Numerical Simulation of 3D Flow in Rotation Cup of Rotor Spinning

To make design of rotation cup device more reasonable, the air-flow-field in rotation cup should be analyzed. Numerical simulation is conducted on 3D flow in rotation cup of rotor spinning with Fluent and the simulation results reveal the airflow characteristics as: the vortex is generated in rotation cup and the airflow speed decreases gradually on slip plane; the airflow in the type of V accumulation groove is more intensive and a little faster than that in the type of U accumulation groove in the same condition; there exist two strands of reverse direction airflow in accumulation groove; there exist two high pressure regions on slip plane and accumulation groove.

Numerical simulation of 3D flow around an overlapping cylinder

This paper investigates the complex interaction between turbulent flow and a deep-water marine structure (overlapping circular cylinders) using a commercial computational fluid dynamics code applying the large eddy simulation approach. A number of three-dimensional large eddy simulations of wake flow around overlapping cylinders of finite heights are carried out for incoming flow Reynolds number in the range 1·0 × 104 to 1·0 × 105. The effect of the height of a circular mud mat having a fixed diameter and its effect on the turbulent flow and pressure fields around this kind of bluff body is investigated. The numerically computed results show some features of the complex separated flow structures and wake properties behind the cylinder. The simulated flow velocity field together with the bed material data can be used to evaluate and estimate the scour around the overlapping cylinder and assess its stability.

Analysis of the Characteristics of Tidal Current at Kurushima Strait-Field Observations and Numerical Simulation of 3D-Flow

This study presents the results of analysis of the field observations and the numerical simulation of tidal currents in the Kurushima Strait. The field data measured tidal currents at the two points near the Strait for fifteen days and measured vertical distributions of tidal currents in the west channel of the Strait for 10 hours in one day. The numerical simulation is performed by a multi-level model of tide and tidal currents as horizontal eddy viscosity terms, described with the Smagorinsky's formulas, are incorporated. The specific peculiarities of the complex coastal line and bottom topography of the Strait are taken into account in the model. The tidal current fields are reproduced by the model. Several components of tidal currents and the location of streaks, generated in the Strait, can be predicted by the numerical simulation.

Numerical simulation of incompressible flows through granular porous media

The primitive equations of incompressible flows through isotropic granular porous media have been deduced by DuPlessis and Masliyah in the form of generalized Navier–Stokes equations. We first derive some analytical solutions of these equations in the form of generalized Hagen–Poiseuille, Couette–Poiseuille and Beltrami type flows. The respective classic flows are the limit cases of generalized solutions as porosity approaches zero. Then we develop a finite difference semi-implicit scheme, which is applied to numerical simulation of 3D flows in granular porous medium. The theoretical properties of accuracy and stability of this scheme are investigated and a method of specifying boundary conditions is suggested. The constructed scheme is applied to simulation of the obtained analytical solutions as well as to test problems of the lid-driven cavity flow.

Hydrodynamics of a floodplain recirculation zone investigated by field monitoring and numerical simulation

Abstract Results are presented from a combined field monitoring and numerical modelling study of flow dynamics within a floodplain recirculation zone. An array of four acoustic Doppler velocimeters (ADVs) was employed to monitor 3D flow velocities within a backwater site on the River Culm, Devon, UK. Patterns of measured mean velocity and turbulent kinetic energy are compared with the results of a numerical simulation of 3D flow carried out using the computational fluid dynamics software package fluent . Simulation results illustrate the presence of flow recirculation within the backwater zone, which is consistent with lateral flow convergence monitored in the field along the upstream portion of the channel-backwater interface. Both the simulation results and ADV data highlight the existence of a free-shear layer at the mixing interface between these flows, which is characterized by high levels of turbulent kinetic energy. However, simulated turbulent kinetic energy levels are significantly lower than those monitored in the field. In addition, ADV data illustrate deviations from isotropic turbulence that may not be simulated using a two-equation k -ɛ turbulence model. These results provide quantitative evidence of the hydraulic mechanisms responsible for promoting high rates of suspended sediment deposition in such backwater recirculation zones, and highlight several modelling issues that require further attention.

Numerical Simulation of 3D Flow around a Circular Cylinder. Part 2. Visualization of three dimensional flow.

Three dimensional flow field around a circular cylinder was analyzed by using a third-order upwind finite-difference method for Reynolds number-1000. Instantaneous flow fields were visualized and investigated in relation to the analysis of time and space correlation reported previously. It was found that beat frequency of drag force corresponds to the phenomena that the streamwise position of Karman vortex near wake moves back and forth. Streamwise vortex pairs around separation line deform primary vortices in the near wake and made secondary streamwise vortices. The three dimensional vortices around separation line influence the separation angle.

Numerical Simulation of 3D Flow around a Circular Cylinder. 1st Report. Analysis of Time and Space Correlation.

Three dimensional flow field around a circular cylinder was analyzed by using a third-order upwind finite-difference method for Reynolds number=1000. Lift and drag force spectrum have some peaks near main karman frequency. It was also found that streamwise velocity and pressure spectrum around separation point have some peaks with a difference mode of these peaks (beat mode). Spanwise flow structure is formed by such modes that have nearly half frequency of Karman mode (half mode) and which are created by three-dimensional vortices. In the present analysis, three dimensional vortices induce half modes and a beat mode additional to Karman mode, resulting in the observation of complex three dimensional flow field.