user's manual for corhyd: an internal diffuser hydraulics model - IfH

A reasonably good discharge distribution along the diffuser (first bar-chart, Fig. 26) with
maximum deviations from the mean discharge of not more than 5 % of the mean discharge
(second bar-chart, Fig. 26) is obtained. Due to different pressure losses along the diffuser pipe
and the port/riser configurations (line in second bar-chart, Fig. 26) the discharge is increasing
here to the seaward end. Usually diffuser cannot be laid horizontally as assumed here, because
of the sloping bathymetries. Therefore another calculation is shown in Fig. 26 on the right
side, with a sloped diffuser with an assumed elevation difference of 3 m along the diffuser
length of 449 m (= 6.7 % 0 ). The discharge deviation in this case is almost neglectable, which
is due to a higher pressure difference between the sewage in the diffuser pipe and the heavier
ambient water especially in deeper waters at the seaward diffuser end.
The flow velocities in the diffuser pipe continuously decrease in seaward direction (fourth
bar-chart, Fig. 26). For the last 25 port locations velocities below 0.5 m/s are predicted, which
might cause sedimentation of particles in the diffuser. This number reduces for peak flows
(Q = 12 m³/s), (Fig. 27), to about 16 but still the last 75 m of the diffuser have velocities much
lower than 0.5 m/s. That means, that even for maximum discharges scouring velocities are not
obtained for the end part of the diffuser. Considering, that the present treatment is only coarse
screening, this might cause problems for the diffuser end part.
Fig. 26: Flow characteristics for design flow. Left: horizontal diffuser, right: sloped diffuser 3m/449m.
Top-down: Individual riser flow distribution along diffuser, riser flow deviation from mean,
losses in port/riser configurations (line), port and jet discharge velocities and diffuser pipe
velocities, port and diffuser diameter (lines)
Institut für Hydromechanik, Universität Karlsruhe 55