2009 Volume 4 Issue 3 Pages 578-589
Pulsating jets are very common and useful in various industrial aspects. However, they have some different basic characteristics from steady jets. In this research, the authors reveal both the frequency and the amplitude effects of pulsations on a jet, including large-amplitude cases. Experiments are conducted at a Reynolds number of 5,000, Strouhal numbers of 0.011 - 0.27 and velocity-amplitude ratios of 0.1 - 1.0. Using a hot-wire anemometry, the authors show centre velocities, radial profiles, half widths and total flow rates at several positions downward a nozzle exit. From centre velocities and radial profiles, we can see that the streamwise scale of the potential core is less than three times the diameter. From half widths and total flow rates, we can see that the pulsation enhances mixing, and confirm the frequency and the amplitude effects specifically. On the other hand, from centre velocities and radial profiles, we cannot see the both effects clearly. As a result, the authors show the combined frequency-and-amplitude effect upon total flow rate, which consists with small-amplitude results by Crow and Champagne (1971), and find the optimum frequencies.
