).
A first set of calculation is used to test the base-model.
The known properties (mass conservative, fast and stable dry and rewet)
were reproduced. A momentum loss due to streamline curvature is described
for the first time. In a second step, a set of test cases is created that
verifies all terms of the turbulence model with a chain of analytical solutions.
The performance of the
k-
model
in stable stratified fluids was tested by comparison with laboratory experiments.
The zero pressure gradient wall boundary layer was compared with cooled
bottom wind tunnel experiments. For the layer where the MONIN-OBUKHOV-similarity
hypothesis applies, the model results can be improved by supplementing
the turbulence model with a stability function. The standard
k-
model
is able to reproduce the turbulence collapse, when applied to the free
and plain shear layer. Free shear layers are very sensible to inflow conditions,
therefore the relevance of this comparison has to be judged carefully.
In a final step the model is applied to flow situations
that are typical for erosion and deposition in the estuary. For the erosion
process an estimate of accuracy is found by comparing calculations with
and without stability function. In combination with the erosion model an
error of 15% in the bottom friction results in a ca. 40% error in the erosional
mass flux. The flow deposits sediment when slowing down around slack water.
In the test case a transient formation of turbulence bubbles is calculated.
The frequency of this bubbling is lower than the tidal frequency. This
flow is no longer comparable with existing experiments, especially stationary
channel flows. The calculated re-ignition of turbulence starting from the
rough bottom would explain the episodic nature of deposition observed in
the Weser estuary.