| dc.description.abstract | Channel flows depicting that of a river in which
effluents are released at half the river depth and in the
middle of the stream width is numerically modelled using the K-E
model. The flow modelled was such that the main free stream
velocity is 5 mls with secondary flows (V and W) of 0.5 mls and
temperature of 30 °c and zero species concentration. The jet of
fluid which is released co-axially in the main stream has a
velocity of 10 mis, temperature of 100 °c and a concentration of 5
units per volume of species at the point of release.
The velocity, temperature and mass transfer profiles showed
a good symmetry along the channel width with a sharp peak value
signifying the effect of release which reduces gradually on
moving downstream.
The momentum, heat and mass transport were found to decay
to an asymptotic value on moving down stream away from the point of
release.
The depthwise momentum, heat, and mass transport decayed in
the region around the point of release in a good agreement with
the theoretic;:alsolution of axi-symmetric plumes. Downstream away
from the point of release, it was noticed that the driving force
which is the high momentum, temperature, and mass gradients
resulting from the jet of fluid ejected at the point of
release reduces gradually. This resulted in a mixed-up region of
flow in which both the depthwise momentum, heat, and
mass-concentration decayed to asymp,totic value just
1
above the free stream values. The decay mode was found to adopt
a decreasing trend in the region around the point of release to
change to an increasing one at some distance downstream. The same
behaviour is found near the channel walls and descending
downstream but with smaller magnitude compared to the central
region since the effect of release also decreases on moving
towards the channel walls together with the effect of the wall
itself on turbulence.
The iso-velocity are found to confirm the fact that the flow
in the channel is sYmmetrical about the centre plane. The resulting
down stream velocity was found to stabilize to a value of order
1.2Uo' Uo being the free stream velocity. In the case of the
isotherms, again they were found to be symmetrical about the centre
plane with a maximum range of 1.3To' To being the free stream
temperature. Nearly a similar result to that of temperature was
found for the mass transport.· | en |
