Abstract:
Experimental investigation of the mean flow characteristics in the velocity field
as well as the thermal field of thermally stratified free and trip ring excited coaxial
jets have been carried out for different flow conditions. Isothermal as well
as thermally stratified or non-isothermal co-axial jet flows are developed by
issuing two jets with different unidirectional velocities from a concentric
compound nozzle. The hot central jet comes out from a central nozzle while the
annular ambient jet is emitted through the annular space between the outer and
the central nozzle. Four outer to inner jet velocity ratios have been considered in
the experiment. The temperature of the central jet is varied to establish different
temperature gradient between the central jet and the annular jet by varying the
supply voltage to the heater placed upstream of the central nozzle. Three
different values of temperature ratios have been considered. The excitation is
made by two trip rings, one placed inside the central nozzle called inner trip ring
and the other placed outside the central nozzle called outer trip ring.
Measurements of mean velocity and mean temperature are made in the mixing
zone of these two jets with the help of a pitot static tube with embedded
thermocouple in it.
For the nozzle configurations used in the present study, mlxmg as well as
momentum exchange in co-axial jets occur more readily at lower velocity ratio
than those of the higher one. Thermal diffusion from the hot central jet is also
found to occur more rapidly at lower velocity ratio. In case of inner or outer trip
ring excited co-axial jets, a negative pressure zone is created due to the presence
of the wake. This wake facilitates better mixing between two jets. Amongst the
inner and outer trip ring excited and unexcited configurations of this experiment
inner trip ring is found the most efficient one in mixing different jets both
dynamically and thermally.
