Experimental study of oscillation of axisymmetric turbulent opposed jets with modulated airflow

Abstract

Oscillation behaviors of axisymmetric opposed jets with modulated airflow were experimentally studied. The oscillation frequency, the oscillation amplitude, and the movement velocity of the impingement plane at various nozzle separations, excitation frequencies, and exit turbulence intensities have been investigated by a hot-wire anemometer and flow visualization technique combined with a high-speed camera. Results show that the oscillation frequency of the impingement plane is nearly equal to the excitation frequency, whereas the oscillation amplitude decreases with the increase of the excitation frequency. The full-scale amplitude oscillation occurs at low excitation frequencies and 2 L/D 8 (where L is the nozzle separation and D is the diameter of the nozzle exit). With the increase of the exit turbulence intensity caused by a turbulence generating plate, the oscillation amplitude decreases remarkably. Flow regimes of axisymmetric opposed jets with excitations are analyzed and discussed based on the experimental results.

Experimental study on oscillation behaviors in T-jets reactor with excitation

“…The flapping oscillation amplitude of impingement plane increases with excitation amplitude both in Reactors I and II, which is consistent with the results of axial oscillation in round opposed jets (Li et al, 2013a) and horizontal oscillation in planar opposed jets with excitation (Li et al, 2013b). The flapping amplitude decreases with the increase of excitation frequencies in Reactor I, but it will reach peak value at a certain excitation frequency in Reactor II, which has not been reported in other studies.…”

“…Current results indicate that the excited oscillation is caused by the pulsed inflow and its frequency is determined by the excitation frequency, which can be explained similarly to our previous work (Li et al, 2013a). Conclusions in the study reveal that the difference of instantaneous velocities caused by pulsed inflow will result in the movement of the impingement plane, and the oscillation frequency will synchronize with the excitation frequency.…”

“…As the images were acquired at an interval of 0.001 s, the time series of locations of the impingement planes can be obtained conveniently using the image processing software. The detailed method of image processing can be found in our previous paper (Li et al, 2013a). Thomas and Ameel (2010) are different from those in current study, the Strouhal numbers are close to each other, as shown in Table 2.…”

“…Results of our previous studies show that the impingement plane of axisymmetric and unrestricted opposed jets under modulated airflow exhibits periodic oscillations, and the excitation frequency, the excitation amplitude and the jet separation have substantial effects on the amplitude of the excited oscillation (Li et al, 2013a). For planar and unrestricted opposed jets with acoustic excitation, the acoustic excitation results in a horizontal periodic oscillation at L/hr4, and the transition from the deflecting oscillation to horizontal oscillation occurs with asynchronous excitation at high amplitude and L/h4 4 (Li et al, 2013b).…”

Numerical study of particle behavior in laminar axisymmetric opposed-jet flows

“…As for the axisymmetric opposed jets, multiple steady states of impinging plane in closely spaced axisymmetric opposed jets have been found by experimental way [6,7] and numerical way [3]. Li et al [4,8,9] experimentally studied the dynamic behavior of the impinging plane and found the phenomena of axial quasi-periodic oscillation of impinging plane and stagnation point offsets when L/D varied. The complex turbulent characteristic in impinging zone has also been widely studied [10][11][12][13][14].…”