Experimental study of swirling coaxial jets

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.