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

Fig. 34: Flow characteristics for: Left: tapered diffuser covered or laid in a trench with additional short
risers, right: tapered diffuser on piles without risers, both for design flow Q d = 8 m³/s. Topdown:
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)
These differences especially caused by the local losses of the flow entering a riser and further
additional loss formulations would not result out of existing diffuser programs (e.g. Fischer et
al., 1979, implemented as code PLUMEHYD; and Wood et al., 1993, implemented as DIFF).
The design and the important optimization of the riser diameters, is not possible in other
programs, although influences on design parameters are huge.
a ) Tunneled diffuser - long risers
Nowadays tunneled outfalls are also affordable in some cases. Often long risers have to used
in these circumstances (Fig. 35). To achieve a more homogeneous discharge distribution the
riser diameters have to be modified: 0.35 m in the end part and 0.25 at the near-shore part of
the diffuser. Fig. 36 shows the flow characteristics for a tunneled diffuser with long risers.
The more homogeneous flow distribution causes that the total head compared to the previous
case is even a bit smaller.
Institut für Hydromechanik, Universität Karlsruhe 62