Download Numerical Model of Sediment Transport in Free Surface Flow

Sveučilište u Zagrebu
Vizualni identitet
Priručnik grafičkih standarda za
oblikovanje vizualnih identiteta sastavnica
Znak Sveučilišta
Verzija 2
c/b pozitiv
2.2.
Crno – bijeli pozitiv znaka Sveučilišta u Zagrebu (verzija
2) standardno je reproduciran u crnoj boji Pantone
Black, odnosno njenom cmyk ekvivalentu.
Detaljne specifikacije nalaze se u poglavlju Program
boja Priručnika grafičkih standarda za oblikovanje
vizualnih identiteta sastavnica.
Validation of the model is carried out
on a 140◦ channel test cases with
movable sand bed.
-0.05
-0.05
-0.1
-0.1
-0.15
-0.2
-0.25
-0.25
-0.5
0
x [m]
0.5
-0.3
-1
1
y [m]
D x / B = 7.65
0
-0.05
-0.05
-0.1
-0.1
-0.15
-0.2
-0.25
-0.25
0
x [m]
0.5
-0.3
-1
1
0
-0.05
-0.05
-0.1
-0.1
-0.15
-0.2
-0.25
-0.25
0.5
-0.3
-1
1
Bed-load transport vector is directly coupled
with the Exner equation.
Flow and Sediment Transport in a
140◦ Channel With a Mobile Bed
-0.05
-0.05
-0.1
-0.1
-0.15
-0.2
-0.2
-0.25
-0.25
0
x [m]
0.5
-0.3
-1
1
0
-0.05
-0.05
-0.1
-0.1
-0.15
-0.2
-0.25
-0.25
0
x [m]
0.5
-0.3
-1
1
0
-0.05
-0.05
-0.1
-0.1
-0.15
1
0.5
1
0.5
1
-0.15
-0.2
-0.2
-0.25
-0.25
0
x [m]
0.5
D x / B = 21.53
0
-0.5
0
x [m]
-0.5
D x / B = 19.63
-0.3
-1
0
x [m]
-0.5
-0.15
-0.2
-0.5
1
D x / B = 18.08
0
-0.3
-1
0.5
-0.15
D x / B = 16.55
Bed elevation η is evaluated using the Exner
equation (FAM):
(2)
0
-0.5
0
x [m]
-0.5
D x / B = 14.93
0
-0.3
-1
1
-0.15
-0.2
y [m]
(1)
0.5
D x / B = 11.17
0
0
x [m]
0
x [m]
-0.5
D x / B = 10.07
-0.5
1
-0.15
-0.2
-0.5
0.5
D x / B = 8.90
0
-0.3
-1
0
x [m]
-0.5
D x / B = 13.15
where τb is the bed shear stress vector, C is
a constant (1.5 - 2.3), ∇s is a surface gradient and η is bed elevation.
1
∂η
[∇•qb + D − E]
=
∂t 1 − n
-0.15
-0.2
-0.3
-1
τb
− C|q0| · ∇sη ,
qb = q0
|τb|
y [m]
0
-0.3
-1
where c is the sediment concentration, vs is
the sediment fall velocity and νt is sediment
diffusivity.
Bed-load transport is modelled by an explicit
expression and discretised using the Finite
Area Method (FAM):
0
y [m]
The sediment module incorporates
suspended load and bed-load transport, with sand bed elevation evaluated using the Exner equation. Deformation of sand bed due to sediment deposition and scour is performed by the automatic mesh motion solver.
Suspended load transport of sediment is
modelled by the convection-diffusion equation:
g
∂c
+ ∇• U − vs
c = ∇•(νt∇c) ,
∂t
|g|
D x / B = 6.32
y [m]
The flow solver is based on the
Ghost Fluid Method finite volume
solver gfmFoam, which will be incorporated in the next release of
foam-extend package.
Mathematical Model
y [m]
A 3D numerical model for simulation
of free surface flow and sediment
transport with sand bed deformation
is presented in this study.
D x / B = 3.50
y [m]
ABSTRACT
Figure 2: Comparison of water depth levels
y [m]
Simulation of flow and sediment transport
in channels, rivers and shallow seas is a
challenging, but important problem due to
the impact of sediment erosion and deposition on river beds, sea beds and marine objects. Coupling between the fluid flow and
sediment transport is required in order to
achieve satisfying results. This includes accurate predictions of the flow and free surface waves, realistic shear stress values,
correct suspended and bed-load sediment
transport calculations with stable bed motion capabilities.
y [m]
Introduction
Vanja ŠKURIĆ
Flow and sediment transport in a 140◦ channel is simulated. The channel is covered
with a 30 cm sand layer, where suspended
transport, bed-load transport and bed deformation occur simultaneously. Bed depth
measurements performed by Olesen (1985)
are used for validation. The case is considered steady-state, since the experiment
reaches equilibrium conditions. Comparison
between the simulated and measured water depth levels at various sections of the
curved channel are shown.
y [m]
9
y [m]
University of Zagreb
Faculty of Mechanical Engineering and Naval Architecture
Department of Energy, Power Engineering and Environment
korekcija znaka za smanjenje od 14 mm
Numerical Model of Sediment Transport
in Free Surface Flow
y [m]
FSB
Radi kvalitete i preciznosti reprodukcije, znak
Sveučilišta nije dozvoljeno rekonstruirati (precrtavati,
skenirati...) Vektorizirani znak nalazi se na elektroničkom
mediju koji je sastavni dio Priručnika grafičkih
standarda za oblikovanje vizualnih identiteta sastavnica.
0.5
1
-0.3
-1
-0.5
0
x [m]
Conclusion
Figure 1: Experimental set-up of a 140◦ channel
8th Floor CFD@FSB
Zagreb, 2017
Numerical model for simulation of free surface flow and sediment transport was presented here. Results from a curved channel simulation show very good agreement
with the experimental data in most sections,
which can be further improved with a better
definition of inlet and outlet flow boundary
conditions. Further validation is required.
Supervisor: Prof. Hrvoje Jasak
www.fsb.hr/cfd
Feel free to contact us at [email protected] or take a look at our YouTube channel: 8th Floor CFD@FSB.