Abstract
Measurements of the kinetic energy of turbulence under spilling waves have been analysed using orthogonal wavelets. Data have been collected using 2-D laser Doppler velocimetry for pre-breaking regular waves, generated in a wave tank. The contribution of different scale vortices is computed, and also phase resolved. It is found that micro-vortices (2 mm <l<0.10 m for the tested case) and mid-size vortices (0.10 m<l<4.0 m for the tested case) are generally dominant, carrying more than 70% of the total turbulence energy under the wave crest. The phase resolved energy spectra are computed, which allows the computation of the transverse and of the longitudinal correlations.
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Abbreviations
- ∼:
-
phase or ensemble average operator
- Λ:
-
phasic average operator
- −:
-
time average operator
- 〈...〉:
-
ensemble average
- α∼3α1 :
-
Kolgomorov constant
- γ γ jk :
-
function
- ρ :
-
mass density (kg/m3)
- ν :
-
kinematic fluid viscosity (m2/s)
- Λ:
-
integral length scale of turbulence (m)
- ΔT i :
-
time interval (s)
- λ E :
-
Taylor length micro-scale (m)
- ε :
-
turbulent energy dissipation rate (m2/s3)
- κ :
-
turbulent kinetic energy (m2/s2)
- ζ :
-
translation parameter
- τ E :
-
Eulerian time micro-scale (s)
- τ :
-
shear stress (Pa)
- η K :
-
Kolgomorov length micro-scale (m)
- A j (x):
-
approximation at level j
- a :
-
dilation parameter
- C :
-
wave celerity (m/s)
- D j (x):
-
detail at level j
- DWT:
-
discrete wavelet transform
- E 1(k 1), E 2({ik}1):
-
energy spectrum in the wave-number domain (m3/s2)
- E 1(f):
-
energy spectrum in frequency domain (m2/s)
- f :
-
frequency (Hz), function
- f acq :
-
sampling frequency (Hz)
- g :
-
gravitational acceleration (m/s2)
- h :
-
local water depth (m)
- H :
-
wave height (m)
- k, k 1 :
-
wave number (m−1)
- k min, k max :
-
minimum, maximum wave number
- k d :
-
dissipative wave number (m−1)
- k :
-
wave number (vector) (m−1)
- l :
-
length scale (m)
- LDV:
-
laser Doppler velocimetry
- N :
-
number of samples
- N:
-
number of levels in wavelet decomposition
- PIV:
-
particle image velocimetry
- R E(r):
-
normalised Eulerian space autocorrelation
- R E(τ):
-
normalised Eulerian time autocorrelation
- Re λ :
-
Reynolds number based on Taylor micro-scale
- s sj :
-
fluctuating rate of strain (s−1)
- STFT:
-
short time Fourier transform
- T :
-
wave period (s)
- T m :
-
period of time averaging (s)
- TFR:
-
time frequency representation
- t, t k, t′, τ:
-
time variable (s)
- T E :
-
time macro-scale of turbulence (s)
- ū :
-
mean velocity
- u′ ν′ :
-
fluctuating velocity (m/s)
- ~u,~v :
-
organised fluctuating velocity (m/s)
- U, V. W :
-
velocity scales, velocity components (m/s)
- u :
-
turbulence scale (m/s)
- u :
-
velocity vector (m/s)
- VITA:
-
variable interval time average
- W jk :
-
wavelet coefficients
- x, y, z, x i :
-
spatial co-ordinates (m)
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Published online: 23 November 2002
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Longo, S. Turbulence under spilling breakers using discrete wavelets. Experiments in Fluids 34, 181–191 (2003). https://doi.org/10.1007/s00348-002-0545-1
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DOI: https://doi.org/10.1007/s00348-002-0545-1