MEASUREMENTS AND CONTROL OF FLOW OSCILLATION INDUCED BY A CYLINDER PLACED IN A TWO-DIMENSIONAL TURBULENT JET

摘要

An experimental study is presented of the jet flow, effusing with a velocity profile of developed turbulent flow, and of the flow control by means of sound emission. The impinging distance, defined as the distance between the exit and the cylinder, is x_i, the slit width h is 10mm, and the cylinder diameter d is 20mm. The exit velocity of two-dimensional turbulent air jet is settled at 20 m/s. Measurements include pressures around the cylinder, and the velocity of the jet flow. An oscillation of impinging jet is induced by inserting a cylinder over a range of the impinging distance, 3 < x_i/h < 10, even when the jet effuses with a profile of developed turbulent flow. At the impinging distance of x_i/h = 8, the oscillation process of mean velocity field is shown by means of the contours of mean velocity and arranged as an animation. The sound emission with the same frequency as that of natural oscillation stabilizes the periodic motion of the original oscillation. The jet flow is controlled to oscillate at a deviated frequency in the case when the intense sound was emitted within an extent of frequency deviation from the natural frequency. The flow with two peak frequencies, observed in the spectrum at x_i/h = 10, is also controlled by emitting the sound with either of the frequencies. The free jet, effusing with a pro- file of developed turbulent flow, might be controlled by various frequencies.