Effects of Submergence on Low and Moderate Reynolds Number Free-Surface Flow Around a Matrix of Cubes

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Z. Ikram ◽  
E. J. Avital ◽  
J. J. R. Williams
Keyword(s):  
Reynolds Number ◽  
Free Surface ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Immersed Boundary ◽  
Surface Boundary ◽  
Reynolds Number Flow ◽  
Eddy Simulation ◽  
Moderate Reynolds Number ◽  
Submergence Depth

The effect of reducing submergence depth at a low and moderate Reynolds number flow is investigated using large eddy simulation (LES) around a matrix of cubes. The submerged body is modeled using an immersed boundary method, while the free-surface is accounted for using a moving mesh. Results show that for reducing the submergence depth, the forces acting on the cube reduce as the force variation increased. Variation in depth is also found to influence the level of damping and redistribution of turbulence near the free-surface boundary. Both submergence depth and Reynolds number are also found to influence the dominant free-surface signature and shedding frequencies from the cube. In the interobstacle region (IOR), the variation of Reynolds number and submergence depth is found to have little effect.

Detached Eddy Simulation of Free-Surface Flow Around a Submerged Submarine Fairwater

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Z. Ikram ◽  
E. J. Avital ◽  
J. J. R. Williams
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Significant Rise ◽  
Surface Flow ◽  
Tip Vortex ◽  
Immersed Boundary ◽  
Wake Region ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Submergence Depth

The effects of reducing submergence depth around a submerged submarine fairwater without its associated appendages is numerically studied using detached eddy simulation. The submerged body is modeled using the ghost-cell immersed boundary method, while the free-surface is accounted for by using a moving mesh. The numerical simulations are performed at a Reynolds number of 11 × 106 for a submergence ratio in the range of 0.44–0.32 and for Froude numbers <1. This paper examines the effect of depth variation on the statistical and structural behavior of the flow around a fully submerged fairwater. The results include profiles of the time averaged velocity, turbulent intensities, turbulent kinetic energy spectra and budget. These have all shown that the major part of the turbulence is confined to the near wake region of the fairwater. Vortical structures are found to show no significant rise or interaction with the free-surface, while in the wake region, the results show that vorticity is present for over 50% of the total monitored period. Reducing the submergence depth is found to influence the tip vortex shedding. Additionally, time averaged forces, force variations, and shedding frequency are also examined. In all cases, the surface waves generated by the submerged fairwater are of a Kelvin kind.

Flow of Wall Jet Near Channel Exit at Moderate Reynolds Number

2010 ◽  
Author(s):  
Md. Abul Kalam Azad ◽  
Roger E. Khayat
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Free Surface ◽  
Boundary Conditions ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Wall Jet ◽  
Channel Exit ◽  
Moderate Reynolds Number ◽  
Layer Region

The wall jet flow near channel exit at moderate Reynolds Number, emerging from a two-dimensional channel, is examined theoretically in this study. Poiseuille flow conditions are assumed to prevail far upstream from the exit. The problem is solved using the method of matched asymptotic expansions. The small parameter involved in the expansions is the inverse Reynolds number. The flow and stress fields are obtained as composite expansions by matching the flow in the boundary-layer region near the free surface, flow in the outer layer region and the flow in the core region. The fluid is assumed to be Newtonian and it is found that the jet contracts downstream from the channel exit. The influence of inertia on the shape of free surface, the velocity and stress is emphasized and the higher order boundary layer is explored. To leading order, the problem is similar to the case of the free jet (Tillett) [1] with different boundary conditions. A similarity solution can be carried out using a similarity variable problem which is then solved as an initial-value problem, where the equation is integrated subject to the boundary conditions and a guessed value of the slope at the origin. The slope is adjusted until reasonable matching is achieved between the solution and the asymptotic form at large θ. The level of contraction is essentially independent of inertia, but the contraction moves further downstream with increasing Reynolds number. The present work provides the correct conditions near exit, which are required to determine the jet structure further downstream. If the jet becomes thin far downstream, a boundary layer formulation can be used with the presently predicted boundary conditions for steady and possibly transient flows.

SPLASH Free-Surface Flow Code Methodology for Hydrodynamic Design and Analysis of IACC Yachts

1993 ◽  
Author(s):  
Bruce S. Rosen ◽  
Joseph P. Laiosa ◽  
Warren H. Davis ◽  
David Stavetski
Keyword(s):  
Free Surface ◽  
High Performance ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Surface Boundary ◽  
Induced Drag ◽  
Free Surface Boundary Condition ◽  
Surface Boundary Condition ◽  
America’S Cup ◽  
Areas Of Interest

A unique free-surface flow methodology and its application to design and analysis of IACC yachts are discussed. Numerical aspects of the inviscid panel code and details of the free-surface boundary condition are included, along with enhancements developed specifically for the '92 America's Cup defense. Extensive code validation using wind tunnel and towing tank experimental data address several areas of interest to the yacht designer. Lift and induced drag at zero Froude number are studied via a series of isolated fin/bulb/winglet appendages. An isolated surface piercing foil is used to evaluate simple lift/free­surface interactions. For complete IACC yacht models, upright wave resistance is investigated, as well as lift and induced drag at heel and yaw. The excellent correlation obtained for these cases demonstrates the value of this linear free-surface methodology for use in designing high performance sailing yachts.

Numerical Simulation of Nonlinear Wave Propagation and Breaking Over Constant-Slope Bottom

2006 ◽  
Author(s):  
Aggelos S. Dimakopoulos ◽  
Athanassios A. Dimas
Keyword(s):  
Numerical Simulation ◽  
Free Surface ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Surface Boundary ◽  
Nonlinear Wave Propagation ◽  
Large Wave ◽  
Slope Bottom ◽  
Wave Heights ◽  
Constant Slope

The numerical simulation of the two-dimensional free-surface flow resulting from the propagation of nonlinear gravity waves over constant-slope bottom is presented. The simulation is based on the numerical solution of the Euler equations subject to the fully nonlinear free-surface boundary conditions and the appropriate bottom, inflow and outflow conditions using a hybrid finite-differences and spectral-method scheme. Wave breaking is accounted for by a surface roller model. The formulation includes a boundary-fitted transformation and is suitable for future extension to incorporate large-eddy and large-wave simulation terms. Results are presented for the simulation of the free-surface flow over two different bottom topographies, with constant slope values of 1:10 and 1:50, and three different inflow wave heights. Over the bottom slope, waves of small wave heights are modified according to linear theory. For nonlinear waves, wavelengths are becoming shorter, the free surface elevation deviates from its initial sinusoidal shape and wave heights increase with decreasing depth. Breaking is observed for the cases with the larger initial wave height and the smaller outflow depth.

Large-eddy simulation of the turbulent free-surface flow in an unbaffled stirred tank reactor

2010 ◽  
Vol 65 (15) ◽  
pp. 4307-4322 ◽  
Author(s):  
N. Lamarque ◽  
B. Zoppé ◽  
O. Lebaigue ◽  
Y. Dolias ◽  
M. Bertrand ◽  
...  
Keyword(s):  
Free Surface ◽  
Large Eddy Simulation ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Stirred Tank ◽  
Stirred Tank Reactor ◽  
Tank Reactor ◽  
Eddy Simulation ◽  
Large Eddy

scholarly journals Numerical investigations of the free surface flow around a surface piercing hydrofoil

2021 ◽  
Vol 44 ◽  
pp. 87-94
Author(s):  
Costel Ungureanu
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Efficiency Index ◽  
Surface Flow ◽  
Point Of View ◽  
Breaking Wave ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Boundary Layer Interaction ◽  
Wave Effects

Starting with January 2013, naval architects faces new challenges, as all ships greater than 400 tons must comply with energy efficiency index (MPEC 62, 2011). From ship hydrodynamics point of view one handy solution is using Energy Saving Devices (ESD), with the main purpose to improve the flow parameters entering the propeller. For ballast loading condition the ESD may intersect the free surface disturbing and complicating the flow due to free surface /boundary layer interaction, turbulence and breaking wave effects that coexist and which are not completely clarified so far. Therefore, a free surface flow around a NACA 0012 surface piercing hydrofoil is numerically investigated and the results are compared to experimental results obtained in the Towing Tank of the Naval Architecture Faculty, “Dunarea de Jos” University of Galati. The comparison includes drag and free surface elevation on hydrofoil surface together with numerical uncertainty.

scholarly journals Numerical Simulation of Free Surface Flow on Spillways and Channel Chutes with Wall and Step Abutments by Coupling Turbulence and Air Entrainment Models

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3036
Author(s):  
Le Thi Thu Hien ◽  
Duong Hoai Duc
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Air Entrainment ◽  
Surface Flow ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Optimal Distance ◽  
Large Eddy ◽  
Flow Through ◽  
Turbulent Models

Spillways and channel chutes are widely used in hydraulic works. Two kinds of abutment—walls and steps—are usually constructed to dissipate energy; however, they may also cause cavitation at the abutment position. In this study, we used Flow 3D with the Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) turbulent models which included air entrainment to simulate the free surface flow through the spillway, channel chute and stilling basin of the Ngan Truoi construction to optimize the configuration of walls and dams. We measured the water level, velocity and pressure to estimate the influence of grid size and the turbulent model type used. Our results highlight the need to include air entrainment in the model simulating rapid flow over a hydraulic construction. With adjustments for energy loss, this study shows that walls provide the best results and the optimal distance between two walls is 2.8 m.

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