The distortion of a round jet by coil inserts of various lengths

Results of experimental investigations of turbulent jets with coil inserts of constant wire diameter and pitch spacing, but various lengths are presented. For the coil inserts, the ratios of pitch spacing and wire diameter to the tube inside diameter, p/D, and d/D, are 1.2 and 0.06 respectively and the ratios of the coil length to the tube inside diameter, L/D, are 1.41, 2.82, 5.64, 11.26 and 22.5. Results show that at the tube outlet, the largest mixing is obtained for the coils with L/D=11.26 and 22.5. Reducing the coil length would delay the mixing process to a further downstream location.