Characteristics of granular sheet of dense granular jet oblique impact

Abstract

Dense granular impinging jets widely exist in natural flow phenomena and industrial processes, such as the rapid heating, cooling or drying, and gasification. It is important to investigate the factors influencing the flow patterns of dense granular impinging jets and reveal the evolution rules of the flow patterns. The dynamic behaviors of the dense granular impinging jets are experimentally studied by a high-speed camera and image processing software of Image J. The effects of the particle diameter, the granular jet velocity (u0) and the solid content of the granular jet (xp) on flow pattern of the granular impinging jet are investigated. Two flow regimes of the dense granular impinging jets, i.e., the liquid-like granular film and the scattering pattern, are identified. The results show that with the increase of the particle diameter and the granular jet velocity, both the solid content of the granular jet and the inter-particle collision frequency decrease, which results in the transition of granular sheet to scattering pattern. With the increase of granular jet velocity, the opening angle of the granular sheet from the side view increases, while the opening angle from the front view increases first and sharply decreases later. The results also show that with the increase of the granular jet velocity, the liquid-like granular film becomes unstable and a non-axisymmetric oscillation appears. And the amplitude and frequency of the liquid-like granular film increase with granular jet velocity increasing, and are significantly affected by particle diameter. The interesting behaviors of the liquid-like surface waves are observed on the granular sheet. The surface waves become remarkable with the increase of the granular jet velocity, and their propagating velocities normalized by the granular jet velocity vary from 0.7 to 0.9. The waves propagating on the granular sheet may emerge, which will reduce the frequencies of the surface waves and increase the surface wavelengths. The results also show that the oscillation frequency of the granular film nearly equals the pulsation frequency of the granular jet. It is indicated that the gas-solid interaction inside the nozzle increases with granular jet velocity increasing, and causes the instability of the granular jet, resulting in the non-axisymmetric oscillation on the granular sheet consequently. The results in this paper present significant knowledge of the dense granular impinging jets and also provide some principles for the applications in dense granular impinging jets in industrial processes.