Abstract:
An experimental study on swirling coaxial jets has been performed. As a pre requisite
and for the sake of comparison a study has also been carried out on their non-swirling
counterparts. The experimental procedure included a hierarchical investigation of single
non-swirling circular, annular and coaxial jets and finally swirling circular, annular and
coaxial jets. Swirl has been imparted on the outer and inner jet alternatively by
embedding spiral guide vanes on the outer or i~er surfaces of the central PVC pipes of
42-mm diameter. The outer nozzle has a diameter of 80 mm. Measurements have been
taken for two Reynolds numbers viz. 2.7x104 and 4.0IxI04
• The guide vanes used have
helix angles of inclinations of 15° and 30° corresponding to the swirl numbers of 0.27 and
0.58 respectively.
In a circular jet there exists a potential core where velocity remains constant and is equal
to the exit velocity. Similar to the potential core there exists a void core in an annular jet
where velocity remains zero; and in the experiment both of them are found to extend up
to the location ofx/d=3. In the coaxial jets the potential core is reduced to the location of
x/d=2.It is found that in case of both the non-swirling and swirling coaxial jets the two
velocity fields remain active up to the location of x/d=3 for lower velocity ratios (when
UzlU] is less than or equal to unity) and extends up to a location of x/d=5 for higher
velocity ratios (when UzlU] is greater than unity). The dispersion of jet is found to have
been enhanced with the increase of swirl angle.
