Abstract
This study investigates the suppression of the so-called hole tone produced when a jet, issued from a circular nozzle or hole in a plate, goes through a similar hole in a second plate. The mean velocity of the air jet u0 was 10 m/s. The nozzle and end plate hole both had a diameter of 51 mm, and the impingement length Lim between the nozzle and end plate was 50?90 mm. We propose a new passive control method of suppressing the tone which might disorganize the feedback loop with an axisymmetric obstacle on the end plate. We find that the effect of the obstacle is well described by the combination (W/Lim, h) where W is the distance from the edge of the end plate hole to the inner wall of the obstacle, and h is the obstacle height. The tone is suppressed when backflows from the obstacle affect the jet shear layers near the nozzle exit. We also do a direct sound computation for a typical case where the tone is successfully suppressed. Axisymmetric uniformity observed in the uncontrolled case is broken almost completely in the controlled case. The destruction is maintained by the process in which three-dimensional vortices in the jet shear layers convect downstream, interact with the obstacle and recursively disturb the inflow from the nozzle exit. We also discuss a transition of flow fields from an original state to a suppressed state when we put the obstacle on the end plate abruptly in the computation.
