Abstract:
The flow characteristics in the developing region of coaxial axisymmetric confined
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jets were studied numerically. The computer programme used for this purpose
employed finite volume discretisation of Na'vier-Stokes equations and a twoequation
(k-i;) turbulence modeL After"sUffiCiert1testing against bench-mark
experimental and analytical data, the computer programme was used for the
prediction of coaxial jet.
The present study is confined to jets of a fixed diameter ratio of 2.48. To study the
effect of boundary layer at primary jet exit, four different velocity profiles were
considered. The Reynolds number and the velocity ratio were kept unchanged for
these four cases and were taken to be 3.28 X 104 and 0.023, respectively. Then, for
the same Reynolds number, the flow development was studied for four different
velocity ratios viz., 0.05, 0.1, 0.2 and 0.5. Finally, the Reynolds number was
increased to 3.28 X 105 and for a velocity ratio of 0.5 computations were made for
two inlet profiles.
It is found that recirculation phenomena; growth rate of jet and turbulence
intensity distinctly depend on the shear layer of velocity profile at primary nozzle "
exit. However, pressure is rather insensitive to inlet profile variation. For higher
velocity ratios (>0.023) recirculation does not occur and the turbulence intensity
is found to be suppressed. It is further 's~en "that the flow assumes a self
preserving profile in the later part of the developing region.
