A Simulation Method For The Breaking WavesGenerated By A Submerged Hydrofoil (original) (raw)
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NUMERICAL STUDY OF FREE SURFACE EFFECT ON THE FLOW AROUND SHALLOWLY SUBMERGED HYDROFOIL
buet.ac.bd
The wave generation due to the presence of a body moving at steady forward speed beneath a free surface has been the subject of extensive research work in marine hydrodynamics. In this study, the free surface effect on the flow around shallowly submerged hydrofoil is numerically computed. Finite Volume Method (FVM) based on Navier-Stokes equations is used for this purpose. The standard NACA 0012 hydrofoil section is used for ease of comparison with available experimental data. The k-ε turbulence model has been implemented to simulate turbulent flow past the foil surface. To get the free surface elevation, "Volume of Fluid" (VOF) method is incorporated in numerical simulation. Grid independency is checked using four grids of different sizes. To validate the computational results, the free surface wave generated by the flow around hydrofoil at submergence depth ratio h/c = 0.91 is compared with experimental results published by Duncan. The computed results show satisfactory agreement with the experimental measurements. Finally, free surface effects on wave profile are computed for six submergence depth ratios, h/c ranging from 0.911 to 4.0 and maximum amplitude at two different Froude nos. (F n = 0.5672 and 0.70)
Numerical Investigation of 2-D Wave Making Characteristics of a Submerged Hydrofoil
Journal of ETA Maritime Science
In this study, 2-D wave making characteristics of a submerged hydrofoil has been investigated in a numerical fashion. Experimental data available for different depths of submergence and flow velocities have been compared to the results obtained by a commercial RANS CFD code and an in-house SPH code. The capabilities of the numerical approaches in terms of capturing the free surface deformation have been assessed. At high Froude numbers, the induced wave profiles have been observed to exhibit an unsteady nature by both numerical methods. The pressure contours obtained from the numerical analysis have also been compared with each other. It has been seen that the agreement between the results of the well-established RANS method and recently progressing SPH technique is encouraging for further development.
Effect of a Numerical Simulation of a Hydrofoil Near a Free Surface
Advances and Applications in Fluid Mechanics, 2017
Effect of a hydrofoil moving beneath a free surface is studied for several angles of attack for several speeds and submersion depths. In this study, NACA0012 foil is used. Finite volume method is both used for momentum and for k-ε equations where convective and diffusive terms are discretized, using QUICK and central schemes, respectively. Free surface is studied using volume-of-fluid method. Numerical results are also discussed.
A numerical method for non-linear flow about a submerged hydrofoil
Journal of Engineering Mathematics, 1985
A numerical method is presented for computing two-dimensional potential flow about a wing with a cusped trailing edge immersed beneath the free surface of a running stream of infinite depth. The full non-linear boundary conditions are retained at the free surface of the fluid, and the conditions on the hydrofoil are also stated exactly. The problem is solved numerically using integral-equation techniques combined with Newton's method. Surface profiles and the pressure distribution on the body are shown for different body geometries.
EPJ Web of Conferences, 2015
Accurate simulation of turbulent free surface flows around surface ships has a central role in the optimal design of such naval vessels. The flow problem to be simulated is rich in complexity and poses many modeling challenges because of the existence of breaking waves around the ship hull, and because of the interaction of the two-phase flow with the turbulent boundary layer. In this paper, our goal is to estimate the lift and drag coefficients for NACA 0012 of hydrofoil advancing in calm water under steady conditions with free surface and emerged NACA 0015. The commercial CFD software FLUENT version 14 is used for the computations in the present study. The calculated grid is established using the code computer GAMBIT 2.3.26.The shear stress k-ȦSST model is used for turbulence modeling and the volume of fluid technique is employed to simulate the free-surface motion. In this computation, the second order upwind scheme is used for discretizing the convection terms in the momentum transport equations, the Modified HRIC scheme for VOF discretisation. The results obtained compare well with the experimental data.
2015
Steady three-dimensional and two free surface waves generated by moving bodies are presented, the flow problem to be simulated is rich in complexity and poses many modeling challenges because of the existence of breaking waves around the ship hull, and because of the interaction of the two-phase flow with the turbulent boundary layer. The results of several simulations are reported. The first study was performed for NACA0012 of hydrofoil with different meshes, this section is analyzed at h/c= 1, 0345 for 2D. In the second simulation a mathematically defined Wigley hull form is used to investigate the application of a commercial CFD code in prediction of the total resistance and its components from tangential and normal forces on the hull wetted surface. The computed resistance and wave profiles are used to estimate the coefficient of the total resistance for Wigley hull advancing in calm water under steady conditions. The commercial CFD software FLUENT version 12 is used for the com...
Toward the LES of flow past a submerged hydrofoil
2002
The fluid flow past a body placed in a steady stream close to a free surface is the object of the current investigation. The viscous, incompressible Navier-Stokes equations, supplemented by linearized dynamic and kinematic boundary conditions at the free surface, are solved so that the water-surface elevation can be integrated into the solution and solved for, together with the velocity and pressure fields. The potential and limitations of the method will be illustrated and discussed.
Analysis of the Unsteady Flow Around a Hydrofoil at Various Incidences
Springer eBooks, 2020
The oscillating hydrofoils used in underwater propulsion devices often experience large variations of the flow incidence, which favors cavitation at large angle of attack, and therefore a severe degradation of the performance, additional flow instability, and even cavitation erosion. These various phenomena make numerical simulations of the flow around oscillating hydrofoils quite challenging, especially in cases where the laminar-turbulent transition usually occurs when the blade has a high angle of attack. In the present study, the unsteady flow around a stationary Clark-Y hydrofoil is simulated at five fix incidence angles using the Star CCM+ software. The results show that the lift coefficient increases continuously with the incidence angle up to 15°, even after a separation vortex is generated near the trailing edge. Then, as a slight stall occurs at 20°, the lift coefficients obtained with the k-ω SST and SST − transition models become significantly different, mostly because of the different prediction of laminar to turbulence transition at the hydrofoil leading edge. Under deep stall condition at 25°, the flow is much more complex and the hydrofoil performance decreases dramatically. The lift force predicted by the SST transition model is more periodic than with the SST k-ω model. Although the general vortex evolution predicted by the two turbulence models is similar, the local pressure experiences larger amplitude variations with the k-ω SST model, as can be also observed from the evolution of the lift coefficient.
Performance analysis of 3D hydrofoil under free surface
Ocean Engineering, 2007
The purpose of the present paper is to develop a potential-based panel method for determining the steady potential flow about threedimensional hydrofoil under free surface. The method uses constant-strength doublets and source density distribution over the foil body surface and thereby Dirichlet-type boundary condition is used instead of Neumann-type condition. On the undisturbed free surface source density is used to meet the free surface condition that is linearised in terms of double-body model approach and is discretised by a one-side, upstream, four-point finite difference operator. After solving the doublets on the foil and sources on the free surface, the numerical results of pressure, lift and resistance coefficients and also wave profiles can then be calculated for different Froude number and depth of submergence to demonstrate the influence of free surface and aspect ratio effects on performance of the hydrofoil. r