Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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Turbulent Free-Surface Flows: A Comparison Between Numerical Simulations and Experimental Measurements
Turbulent Free-Surface Flows: A Comparison Between Numerical Simulations and Experimental Measurements
Pages 249-265
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From page 249... ...
The numerical results show that turbulent roughening of the ocean surface scales according to threedimensional similarity theory. An extensive inertial range is established in the kinetic and potential energy spectral.
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From page 250... ...
The Kelvin wave disturbance is subtracted out of the measured ciata rising linear wave-cut analysis. We superimpose on top of the mean velocity field a fluctuating velocity filial that is based on the rms velocity fluctuations that are measured in the towing tank.
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From page 251... ...
2.2 E'ree-Surface Boundary Conditions The Helmhottz decomposition of the velocity field requires that an additional boundary condition be imposed on the free surface. An expedient boundary condition that can be specified is that the normal component of the rotational velocity is zero on the free surface: -U0x-V9v+w ~ (~)
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From page 252... ...
Most LES absorb the isotropic SGS stresses into the pressure-gradient term in the Navier-Stokes equations, but in free-surface flows this term is required to predict turbulent roughening of the free surface (see Dommermuth & Novikov, 1993)
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From page 253... ...
where am is the wave disturbance due to Kelvin waves, ¢~' is the wave disturbance due to turbulence, Hi is a mean disturbance due to turbulence, and vi is a fluctuating disturbance due to turbulence. We assume that the Kelvin waves do not interact strongly with the turbulent wake.
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From page 254... ...
where free-slip boundary conditions are initially imposed on the free surface and the bottom, and periodic boundary conditions are imposed in the horizontal plane. The mean velocity in the LES is calculated by definition: < U >= V x ~ , (24)
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From page 255... ...
For the grid-stirred turbulence experiments, three planes have been measured: one vertical plane in the center of the water tunnel and two horizontal planes, 3mm and 110mm beTow the free surface. The area of each image plane is about 180mm x 130mm and the leading edge is about 235mm downstream of the wire mesh.
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From page 256... ...
Power-law behavior of energy spectra. The results of other researchers seem to suggest that a free surface is capable of supporting a reverse energy cascade, which is a property of two-dimensional turbulence (see Sarpkaya's review, 1995~.
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From page 257... ...
One spectrum is based on ciata measured close to the free surface (z = -3mm) and the other is based on data measured in the bulk of the flow (z = -llOmm)
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From page 258... ...
At the next station, at time t = 3.95, the correlation coefficients for the mean axial velocity and the turbulent kinetic energy are high, whereas the coefficient for the mean axial vorticity is Tow. The tow correlation coefficient in the vorticity field is due to the breakup of a pair of bilge vortices.
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From page 259... ...
The mean turbulent kinetic energy, mean streamwise velocity, and mean axial vorticity are respectively shown in the (a)
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From page 260... ...
(1995) Vorticity, free surface, and surfactants.
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From page 261... ...
In ~ _ 0 ~ O u~ o o ~ ~ - u~ o co ~ O C~l _ ·~ ~ ~ ~ ~ — N · · `17 11 11 11 11 11 11 O O O {~~ -E ~ ~ ~ ~ -E _ _ _ C: _ _ _ _ _ _ I ~ , 0 + ~ X ~ Q o C' a)
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From page 264... ...
~n a ~a cN o o ~n aa a ~a Q X o o ~ ' 1 ., ~ r_ .~ :,' 264 0 O O O 1 _ ~: ~o a' D _ - _ _ ·_ a' ' ~ O a 5 O a)
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