Environmental Engineering Reference
In-Depth Information
Fig. 7. H up / h , S up / S , L e / h and V a of experimental and simulation results at a 45 degree angle
difference in the comparison of the height of upwelling field when the inlet flow velocity is
6.7 cm/s, which may be caused by the lack of particle concentration in the experiment. The
mean error between the experiment and simulation was within 8%. In this arrangement, the
resistance to the water flow is intensified, and a large pressure gradient is generated around
the reef so that a large-scale back vortex flow is produced.
4.1.3 Brief conclusion
In this small chapter, the flow field around a single hollow cube artificial reef is analyzed
qualitatively and quantitatively by physical experiment and numerical simulation. The flow
field within and in back of the artificial reef with a 45 degree angle has a lower flow velocity
than a 90 degree angle. The scale and intensity of the upwelling field of artificial reef with a
90 degree angle are larger than a 45 degree angle. However, a biggish area of slow flow field
is obtained at a 45 degree angle. The results of numerical simulation show good agreements
with experimental measurements which provide powerful support for the next numerical
analysis with regard to the effect of reef height on the flow field of a single artificial reef and
the effect of spacing on the parallel and vertical binary combined artificial reefs.
4.2 Effect of reef height on the upwelling field and back vortex flow field
4.2.1 Distributions of the upwelling field
Fig. 8 shows that, with the same inlet velocity, the variation of reef height have nearly no
effect on the general structure of the upwelling field. The upwelling field is mainly
distributed at the top left corner of the artificial reef and has a fan shaped. The values of the
upwelling flow velocity gradually decrease from inside to outside. Generally speaking, the
height, breadth and area of the upwelling field always increase with the height of the
artificial reef, and these rules are the same as those of a solid cube artificial reef (Pan et al.,
2005).
4.2.2 The effect of the reef height on the intensity of the upwelling field
The effect of the reef height on the intensity of the upwelling field was measured by using
V max and V a . The normalized maximum and average upwelling flow velocities are defined
as the ratio of the flow velocity to the inlet current velocity, i.e., V max / U in and V a / U in .
According to Fig. 9, the normalized maximum upwelling flow velocity first increases and
then decreases with increasing reef height and peaks at 8.0~9.0, where the value of V max is
close to inlet flow velocity. The maximum upwelling flow velocity remains stable when the
reef height is less than 7.0; afterwards, it increases rapidly until 9.0. The normalized average
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