The effects of coil insert length on mixing enhancement of a round jet.

摘要

Results of experimental investigations of the effects of distortion caused by coil inserts on a turbulent jet from a round tube are presented. The coils had constant pitch spacing and wire diameter, but different axial lengths. The ratio of the pitch spacing to the tube inside diameter, p/D, was 1.2 and the ratio of the coils wire diameter to the tube inside diameter, d/D, was 0.06. The ratios of the coil length to the tube inside diameter, L/D, were 22.5, 11.26, 5.64, 2.82, and 1.41. The experiments were carried out at six axial locations of X/D = 0.1, 1, 3, 5, 10, and 15 and various radial locations. Results showed that the coil inserts enhance the mixing process between the jet and surrounding air. For X/D > 5, based on jet half width and axial decay of maximum mean velocity, the highest mixing was obtained with the coil with L/D = 1.41. It is conjectured that the enhanced mixing is due to generation of the streamwise vortices by the coil insert.