Transcript Simone Ferrari - University of Cagliari

2.3 Experiments: data elaboration
Realizations = instantaneous images with
measured concentration
Film (=55°, Fr=14.8)
0.09
1
0.08
0.09
50
50
0.9
50
0.07
40
0.8
40
0.07
40
0.7
0.06
0.06
30
30
0.5
20
Y/D
20
30
0.6
Y/D
Y/D
30
Y/D
0.08
50
40
20
0.05
0.05
20
0.04
0.04
0.4
10
10
0.3
0
0.2
0
0
0
10
10
20
20
30
30
40
X/D
40
X/D
50
50
60
60
70
70
80
80
10
10
0.03
0
0.02
0.03
0.02
0
0.1
0
Mean concentration field (non-dimensionalised
by the initial maximum concentration)
0
0
10
20
10
20
30
30
40
X/D
40
X/D
50
50
60
60
70
70
80
80
Variance of the concentration, nondimensionalised by the square of
the maximum concentration
0.01
0.01
0
0
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Cilindro investito da una corrente uniforme
Vortici oscillanti a valle di un cilindro
investito da una corrente uniforme
Scia turbolenta a valle di un cilindro investito
da una corrente uniforme Re=8000…
… e Re=20000
Scia turbolenta in una wind farm offshore
Scia turbolenta in un’automobile …
…e in una turbina
BOTTOM DENSITY CURRENTS
•
•
•
•
In case of free surface discharge, a stratified flow develops.
Anyway the discharge is done, brine sinks toward the bottom and brine
travels downslope, following bottom bathymetry, as a stratified flow.
In a stratified flow, dilution is achieved with three mechanisms: molecular
diffusion (very slow), dispersion by external forces (such as currents or
tides, not always guaranteed) and turbulent mixing.
Kelvin-Helmholtz billows
COURSE B – SECTION 10 – SLIDE 09
BOTTOM DENSITY CURRENTS
•
K-H billows develop when
FrD 
UU  U D
1
  U
g D
H

•
In a stratified flow over the bottom of the sea, the thickness of layer
mixed is
•
U D2
H
g (  D  U )
Mixing in negatively buoyant stratified flows happens if the velocity
gradient is large (that is if the bottom is enough inclined) or near to local
bottom irregularities; after this mixing, there is another stratified flow,
less dense, to be mixed.
COURSE B – SECTION 10 – SLIDE 10