1. No category

Sabina Raducan1,2
( 1Summer Placement Student at HR Wallingford, 2University of Kent, 3rd Year MPhys Student)
Introduction
The aim of this project was to validate numerical model results obtained using the sediment transport module of the CFD model REEF3D. The model output
was validated against experimental data from published papers and internal studies conducted at HR Wallingford.
REEF3D is an open-source CFD code, written in highly modular C++. The model was developed by Dr Hans Bihs from the Norwegian University of Science and
Technology, Trondheim. This code uses the continuity and the incompressible Reynolds-averaged Navier-Stokes (RANS) equations as the governing equations
for mass and momentum conservation. The flow is solved as a two phase flow problem. REEF3D is able to simulate complex motions of the air water
interface, using the level set method. Sediment transport is calculated using well known sediment concentration and bed load transport formulae.
Two dimensional simulations
In the first study, a twodimensional numerical model
was established in order to
simulate the development of
scour around an offshore
pipeline, under the influence of
unidirectional steady currents.
Different aspects of the
simulation were compared with
results from the literature.
agreement with findings from
previous studies.
Figure 1. Instantaneous streamlines of vortex
formation at t=2 s.
In the model results a vortex was
observed immediately downstream of
the pipeline. This behaviour was in
The pressure magnitude was
also investigated, being within
the range of the theoretical
value.
Under this flow regime sediment transport is expected to occur as bed load
only. Although the model predicted the qualitative behaviour of the bed
reasonably well quantitative comparisons of model results and experimental
data were poor.
Scour validation tests
Scour around contractions
The second study simulated 3D
scour and deposition patterns for
steady flow around a rectangular
abutment.
The computational domain was
set 3 m long, 1.2 m wide and 0.4
m high. The sediment used was
fine uniform sand.
The numerical results were
compared with the lab data
obtained at HR Wallingford’s
Froude Modelling Hall.
It was observed that the
simulation gave accurate
predictions of the scour
development, with only
minor differences in terms of
deposition.
Figure 2. Hydrostatic pressure when the water level is
h=0.35 m.
For the third study, a 3D
simulation was set up in
order to reproduce a series of
tests conducted at the
University of Basilicata in Italy.
Figure 3.Photograph of one of the structures used
in Test no. 3
The tests were simulating the
development of scour around
contractions in a rectangular
flume.
The computational domain
was 16 m long, 1 m wide
Figure 6.
Morphological bed
change at the end of
the simulation
and 0.35 m high.
The sediment used was coarse sand with
median a grain diameter (d50) of 1.7 mm.
After initial calibration good results were
obtained. Due to the very large domain
sizes, the running time of the simulation
was very long (about two weeks) which
represented a major problem in testing
different parameters.
Figure 4. Simulated bed profile and measured bed
profile at after t=49.3 hours, along a 2D transect
Figure 5.
3D simulation of the morphological
bed change, showing the deposition
and the scour developed around a
rectangular abutment
Figure 7. Experimental flume during
the test, at University of Basilicata
Figure 8. Bed profile after a simulated time of t=8
hours, along a 2D transect through the middle of the
domain
Conclusions
We conclude that the REEF3D code appears to be a promising tool for the simulation of sediment transport under both steady and unsteady flow conditions.
Acknowledgments
Dr Hans Bihs NTNU, Trondheim