Visualization of coherent structure of acoustically forced, turbulent round jet

The coherent structures of forced and unforced turbulent round jet are investigated experimentally by flow visualization. The Strouhal number, based on the nozzle diameter and exit velocity as well as the forcing frequency, varies from 0.1 to 1.1. The Reynolds number of the flow is 9400. The forced disturbances have a significant effect on the coherent structure of round jet. There is a resonance frequency for forced round jet. Compared with the unforced jet, the maximum change of coherent structure of forced jet achieves when the forced frequency is close to this resonance frequency. The response of coherent structure is much sensitive to low forced frequency than that to high forced frequency.