Penetration of vertical pulsed jets in crossflow at low velocity ratio

Using the visualization method, the initial rise and penetration of a circular turbulent pulsed jet into a transverse air flow are studied at the ratio of jet velocities to the transverse flow r = u j /u f = 0.67–2.33. A comparative assessment of the penetration of a pulsating jet into a transverse flow for frequencies from 0 to 20 Hz is carried out. The cases of both stationary and oscillating jet flows are analyzed. The penetration of a pulsating jet into a transverse flow is shown to be more significant than for a stationary one and depends on an increase in the ratio of velocities and frequency: it increases linearly at a fixed frequency and passes through a minimum at a fixed ratio of velocities.

Experimental Study on Physical Behavior of Fluidic Oscillator in a Confined Cavity with Sudden Expansion

In this study, two-dimensional time-resolved particle image velocimetry (2D-TR-PIV) was used to investigate the effect of the external domain on oscillating jets from double-feedback fluidic oscillators. Two different cases with different Re numbers (2680–10,730), as free external domain and fully confined were studied. Time-averaged results showed although a self-oscillating jet was attained for the free external domain, it could not be achieved for a fully confined geometry. For a fully confined geometry at Re = 2680, two symmetric vortices did not allow the jet to oscillate and at Re = 6440, the flow pattern in the external region became non-symmetric due to the Coanda vortex, subsequently, the self-oscillating jet was not observed. At Re = 10,730, the strength of the jet was inclined to cope with such vortices and tended to oscillate. However, strong vortices were created near the exit region of the fluidic oscillator, which led to an almost non-symmetric pattern. In addition, the proper orthogonal decomposition (POD) method and phase-averaged analysis were applied to obtain the unsteady behavior of flow and the most energetic dynamic structure. Interestingly, at Re = 6440, the third mode was still energetic for fully confined, but for other cases, the first two modes were the most energetic modes, which showed vigorous coherent structures.

Investigation of self-excited oscillation chamber cavitation effect with special emphasis on wall shape

Analysis of the self-excited oscillating jet nozzle makes it possible to investigate the influence of structural and geometric shapes on the effect of self-excited oscillation cavitation and energy efficiency. In this paper, a new self-excited oscillation chamber structure was obtained using a Bézier curve to reconstruct the wall transition surface, and the cavitation airbag energy concentration was maximized to efficiently utilize the pulse energy. Numerical analysis and simulation were used to study the turbulent kinetic energy, steam volume fraction, and vortex growth cycle of the outlet. The results showed that the novel chamber wall structure weakens the interior secondary vortex in the self-excited oscillation chamber and forms a large cavitation airbag area and reduces energy dissipation. In addition, using the new chamber with redesigned wall structure, the peak turbulent kinetic energy, the velocity at the jet exit, and the vapor volume fraction inside the chamber increased approximately 10.3%, 14.6%, and 9.1%, respectively.