Effect of pulsation on the near flow field of a submerged water jet
The current study investigates the effect of pulsation frequency on the near field characteristics of a submerged water jet using the technique of dye visualization. Flow visualization was performed in water over the range: Reynolds number 540–1540, Strouhal number 0.16–1.75, and at constant amplitude of pulsation of 18%. The results show that the mixing and entrainment process at lower Reynolds number occurs due to diffusion process owing to relatively stable shear layer for the case of a steady jet, whereas the external pulsation promotes an early instability in the shear layer where irregular structures promotes mixing between the jet and surrounding fluids. Images of streaklines show that initial mixing and entrainment processes in the potential core of the jet is due to the development of large vortical structures. While beyond the potential core, mixing and entrainment are governed by the small-scale structures. Further results show that the initiation and growth of vortices in the shear layer depends on the pulse frequency. For a given Reynolds number and amplitude, the number of vortical structures and their size changes with frequency. With an increase in the pulsation frequency, there is an increase in the spreading of the jet along with stretching of the vortical structures. An optimum pulsating frequency at which the effect of pulsation on the flow is maximum occurs at St = 0.44, independent of Reynolds number. These results should eventually lead to a better understanding of the physical phenomena responsible for enhanced mixing and entrainment processes in the presence of pulsating jets.
KeywordsSubmerged water jet pulsation frequency dye visualization entrainment mixing
- 11.Popiel C O and Trass O 1991 Visualization of a free and impinging round jet. Experimental Thermal and Fluid Science 4: 253–264Google Scholar
- 12.Han B and Goldstein R J 2003 Instantaneous energy separation in a free jet. Part I. Flow measurement and visualization. International Journal of Heat and Mass Transfer 46: 3975–3981Google Scholar
- 15.Otani Y, Norikazu N and Hitoshi E 1995 Removal of fine particles from smooth flat surfaces by consecutive pulse air jets. Aerosol Science and Technology 23: 665–673Google Scholar
- 16.Grosshans H, Szasz R-Z and Funchs L 2015 Enhanced liquid gas mixing due to pulsating injection. Computers and Fluid 107: 196–204Google Scholar
- 18.Yadav H, Srivastava A and Agrawal A 2016 Characterization of pulsating submerged jet—A particle image velocimetry study. Journal of Thermal Science and Engineering Applications 8: 011014Google Scholar