Investigation of the Large-Scale Flow Structures in the Cooling Jets Used in the Blown Film Manufacturing Process

The development of the flow field produced by concentric jets used in the blown-film manufacturing process was studied experimentally using hot wire anemometry. It was found that the inner jet was entrained into the outer jet before the outer jet attached to the wall. The inner shear layer of the outer jet attached to the surface 3H to 5H downstream of the jet exit, and the outside shear layer of the outer jet attaches to the surface approximately 12H downstream of the jet exit. The distribution and the spectra of the fluctuating wall pressure was measured using microphones. Measurements of two-point two-time correlation of the fluctuating pressure were used to characterize the development of the large-scale structures. It was found that the structures were convected along the surface at 0.45 to 0.7 of the outer jet velocity for different ratios between inner and outer jet velocities. It was also found that the convection velocity of the large scale structures in the region farther than 10H down stream of the jet exit was determined by the upper jet velocity.